Move Web backend to winit-web

winit-web/src/async/abortable.rs

@@ -0,0 +1,96 @@
+use std::error::Error;
+use std::fmt::{self, Display, Formatter};
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+use std::task::{Context, Poll};
+
+use pin_project::pin_project;
+
+use super::AtomicWaker;
+
+#[pin_project]
+pub struct Abortable<F: Future> {
+    #[pin]
+    future: F,
+    shared: Arc<Shared>,
+}
+
+impl<F: Future> Abortable<F> {
+    pub fn new(handle: AbortHandle, future: F) -> Self {
+        Self { future, shared: handle.0 }
+    }
+}
+
+impl<F: Future> Future for Abortable<F> {
+    type Output = Result<F::Output, Aborted>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        if self.shared.aborted.load(Ordering::Relaxed) {
+            return Poll::Ready(Err(Aborted));
+        }
+
+        if let Poll::Ready(value) = self.as_mut().project().future.poll(cx) {
+            return Poll::Ready(Ok(value));
+        }
+
+        self.shared.waker.register(cx.waker());
+
+        if self.shared.aborted.load(Ordering::Relaxed) {
+            return Poll::Ready(Err(Aborted));
+        }
+
+        Poll::Pending
+    }
+}
+
+#[derive(Debug)]
+struct Shared {
+    waker: AtomicWaker,
+    aborted: AtomicBool,
+}
+
+#[derive(Clone, Debug)]
+pub struct AbortHandle(Arc<Shared>);
+
+impl AbortHandle {
+    pub fn new() -> Self {
+        Self(Arc::new(Shared { waker: AtomicWaker::new(), aborted: AtomicBool::new(false) }))
+    }
+
+    pub fn abort(&self) {
+        self.0.aborted.store(true, Ordering::Relaxed);
+        self.0.waker.wake()
+    }
+}
+
+#[derive(Debug)]
+pub struct DropAbortHandle(AbortHandle);
+
+impl DropAbortHandle {
+    pub fn new(handle: AbortHandle) -> Self {
+        Self(handle)
+    }
+
+    pub fn handle(&self) -> AbortHandle {
+        self.0.clone()
+    }
+}
+
+impl Drop for DropAbortHandle {
+    fn drop(&mut self) {
+        self.0.abort()
+    }
+}
+
+#[derive(Copy, Clone, Debug, Eq, Hash, PartialEq)]
+pub struct Aborted;
+
+impl Display for Aborted {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "`Abortable` future has been aborted")
+    }
+}
+
+impl Error for Aborted {}

winit-web/src/async/atomic_waker.rs

@@ -0,0 +1,35 @@
+use std::cell::RefCell;
+use std::ops::Deref;
+use std::task::Waker;
+
+#[derive(Debug)]
+pub struct AtomicWaker(RefCell<Option<Waker>>);
+
+impl AtomicWaker {
+    pub const fn new() -> Self {
+        Self(RefCell::new(None))
+    }
+
+    pub fn register(&self, waker: &Waker) {
+        let mut this = self.0.borrow_mut();
+
+        if let Some(old_waker) = this.deref() {
+            if old_waker.will_wake(waker) {
+                return;
+            }
+        }
+
+        *this = Some(waker.clone());
+    }
+
+    pub fn wake(&self) {
+        if let Some(waker) = self.0.borrow_mut().take() {
+            waker.wake();
+        }
+    }
+}
+
+// SAFETY: Wasm without the `atomics` target feature is single-threaded.
+unsafe impl Send for AtomicWaker {}
+// SAFETY: Wasm without the `atomics` target feature is single-threaded.
+unsafe impl Sync for AtomicWaker {}

winit-web/src/async/channel.rs

@@ -0,0 +1,81 @@
+use std::future;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::mpsc::{self, RecvError, SendError, TryRecvError};
+use std::sync::Arc;
+use std::task::Poll;
+
+use super::AtomicWaker;
+
+pub fn channel<T>() -> (Sender<T>, Receiver<T>) {
+    let (sender, receiver) = mpsc::channel();
+    let shared = Arc::new(Shared { closed: AtomicBool::new(false), waker: AtomicWaker::new() });
+
+    let sender = Sender { sender, shared: Arc::clone(&shared) };
+    let receiver = Receiver { receiver, shared };
+
+    (sender, receiver)
+}
+
+pub struct Sender<T> {
+    sender: mpsc::Sender<T>,
+    shared: Arc<Shared>,
+}
+
+impl<T> Sender<T> {
+    pub fn send(&self, event: T) -> Result<(), SendError<T>> {
+        self.sender.send(event)?;
+        self.shared.waker.wake();
+
+        Ok(())
+    }
+}
+
+impl<T> Drop for Sender<T> {
+    fn drop(&mut self) {
+        self.shared.closed.store(true, Ordering::Relaxed);
+        self.shared.waker.wake();
+    }
+}
+
+pub struct Receiver<T> {
+    receiver: mpsc::Receiver<T>,
+    shared: Arc<Shared>,
+}
+
+impl<T> Receiver<T> {
+    pub async fn next(&self) -> Result<T, RecvError> {
+        future::poll_fn(|cx| match self.receiver.try_recv() {
+            Ok(event) => Poll::Ready(Ok(event)),
+            Err(TryRecvError::Empty) => {
+                self.shared.waker.register(cx.waker());
+
+                match self.receiver.try_recv() {
+                    Ok(event) => Poll::Ready(Ok(event)),
+                    Err(TryRecvError::Empty) => {
+                        if self.shared.closed.load(Ordering::Relaxed) {
+                            Poll::Ready(Err(RecvError))
+                        } else {
+                            Poll::Pending
+                        }
+                    },
+                    Err(TryRecvError::Disconnected) => Poll::Ready(Err(RecvError)),
+                }
+            },
+            Err(TryRecvError::Disconnected) => Poll::Ready(Err(RecvError)),
+        })
+        .await
+    }
+
+    pub fn try_recv(&self) -> Result<Option<T>, RecvError> {
+        match self.receiver.try_recv() {
+            Ok(value) => Ok(Some(value)),
+            Err(TryRecvError::Empty) => Ok(None),
+            Err(TryRecvError::Disconnected) => Err(RecvError),
+        }
+    }
+}
+
+struct Shared {
+    closed: AtomicBool,
+    waker: AtomicWaker,
+}

winit-web/src/async/concurrent_queue.rs

@@ -0,0 +1,52 @@
+use std::cell::{Cell, RefCell};
+
+#[derive(Debug)]
+pub struct ConcurrentQueue<T> {
+    queue: RefCell<Vec<T>>,
+    closed: Cell<bool>,
+}
+
+pub enum PushError<T> {
+    #[allow(dead_code)]
+    Full(T),
+    Closed(T),
+}
+
+pub enum PopError {
+    Empty,
+    Closed,
+}
+
+impl<T> ConcurrentQueue<T> {
+    pub fn unbounded() -> Self {
+        Self { queue: RefCell::new(Vec::new()), closed: Cell::new(false) }
+    }
+
+    pub fn push(&self, value: T) -> Result<(), PushError<T>> {
+        if self.closed.get() {
+            return Err(PushError::Closed(value));
+        }
+
+        self.queue.borrow_mut().push(value);
+        Ok(())
+    }
+
+    pub fn pop(&self) -> Result<T, PopError> {
+        self.queue.borrow_mut().pop().ok_or_else(|| {
+            if self.closed.get() {
+                PopError::Closed
+            } else {
+                PopError::Empty
+            }
+        })
+    }
+
+    pub fn close(&self) -> bool {
+        !self.closed.replace(true)
+    }
+}
+
+// SAFETY: Wasm without the `atomics` target feature is single-threaded.
+unsafe impl<T> Send for ConcurrentQueue<T> {}
+// SAFETY: Wasm without the `atomics` target feature is single-threaded.
+unsafe impl<T> Sync for ConcurrentQueue<T> {}

winit-web/src/async/dispatcher.rs

@@ -0,0 +1,149 @@
+use std::cell::Ref;
+use std::cmp::Ordering;
+use std::fmt::{self, Debug, Formatter};
+use std::hash::{Hash, Hasher};
+use std::rc::Rc;
+use std::sync::{Arc, Condvar, Mutex};
+
+use super::super::main_thread::MainThreadMarker;
+use super::{channel, Receiver, Sender, Wrapper};
+
+pub struct Dispatcher<T: 'static>(Wrapper<T, Arc<Sender<Closure<T>>>, Closure<T>>);
+
+struct Closure<T>(Box<dyn FnOnce(&T) + Send>);
+
+impl<T> Clone for Dispatcher<T> {
+    fn clone(&self) -> Self {
+        Self(self.0.clone())
+    }
+}
+
+impl<T> Debug for Dispatcher<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Dispatcher").finish_non_exhaustive()
+    }
+}
+
+impl<T> Eq for Dispatcher<T> {}
+
+impl<T> Hash for Dispatcher<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.0.hash(state);
+    }
+}
+
+impl<T> Ord for Dispatcher<T> {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.0.cmp(&other.0)
+    }
+}
+
+impl<T> PartialEq for Dispatcher<T> {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.eq(&other.0)
+    }
+}
+
+impl<T> PartialOrd for Dispatcher<T> {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl<T> Dispatcher<T> {
+    pub fn new(main_thread: MainThreadMarker, value: T) -> (Self, DispatchRunner<T>) {
+        let (sender, receiver) = channel::<Closure<T>>();
+        let sender = Arc::new(sender);
+        let receiver = Rc::new(receiver);
+
+        let wrapper = Wrapper::new(
+            main_thread,
+            value,
+            |value, Closure(closure)| {
+                // SAFETY: The given `Closure` here isn't really `'static`, so we shouldn't do
+                // anything funny with it here. See `Self::queue()`.
+                closure(value.borrow().as_ref().unwrap())
+            },
+            {
+                let receiver = Rc::clone(&receiver);
+                move |value| async move {
+                    while let Ok(Closure(closure)) = receiver.next().await {
+                        // SAFETY: The given `Closure` here isn't really `'static`, so we shouldn't
+                        // do anything funny with it here. See `Self::queue()`.
+                        closure(value.borrow().as_ref().unwrap())
+                    }
+                }
+            },
+            sender,
+            |sender, closure| {
+                // SAFETY: The given `Closure` here isn't really `'static`, so we shouldn't do
+                // anything funny with it here. See `Self::queue()`.
+                sender.send(closure).unwrap()
+            },
+        );
+        (Self(wrapper.clone()), DispatchRunner { wrapper, receiver })
+    }
+
+    pub fn value(&self, main_thread: MainThreadMarker) -> Ref<'_, T> {
+        self.0.value(main_thread)
+    }
+
+    pub fn dispatch(&self, f: impl 'static + FnOnce(&T) + Send) {
+        if let Some(main_thread) = MainThreadMarker::new() {
+            f(&self.0.value(main_thread))
+        } else {
+            self.0.send(Closure(Box::new(f)))
+        }
+    }
+
+    pub fn queue<R: Send>(&self, f: impl FnOnce(&T) -> R + Send) -> R {
+        if let Some(main_thread) = MainThreadMarker::new() {
+            f(&self.0.value(main_thread))
+        } else {
+            let pair = Arc::new((Mutex::new(None), Condvar::new()));
+            let closure = Box::new({
+                let pair = pair.clone();
+                move |value: &T| {
+                    *pair.0.lock().unwrap() = Some(f(value));
+                    pair.1.notify_one();
+                }
+            }) as Box<dyn FnOnce(&T) + Send>;
+            // SAFETY: The `transmute` is necessary because `Closure` requires `'static`. This is
+            // safe because this function won't return until `f` has finished executing. See
+            // `Self::new()`.
+            let closure = Closure(unsafe {
+                std::mem::transmute::<
+                    Box<dyn FnOnce(&T) + Send>,
+                    Box<dyn FnOnce(&T) + Send + 'static>,
+                >(closure)
+            });
+
+            self.0.send(closure);
+
+            let mut started = pair.0.lock().unwrap();
+
+            while started.is_none() {
+                started = pair.1.wait(started).unwrap();
+            }
+
+            started.take().unwrap()
+        }
+    }
+}
+
+pub struct DispatchRunner<T: 'static> {
+    wrapper: Wrapper<T, Arc<Sender<Closure<T>>>, Closure<T>>,
+    receiver: Rc<Receiver<Closure<T>>>,
+}
+
+impl<T> DispatchRunner<T> {
+    pub fn run(&self, main_thread: MainThreadMarker) {
+        while let Some(Closure(closure)) =
+            self.receiver.try_recv().expect("should only be closed when `Dispatcher` is dropped")
+        {
+            // SAFETY: The given `Closure` here isn't really `'static`, so we shouldn't do anything
+            // funny with it here. See `Self::queue()`.
+            closure(&self.wrapper.value(main_thread))
+        }
+    }
+}

winit-web/src/async/mod.rs

@@ -0,0 +1,18 @@
+mod abortable;
+#[cfg(not(target_feature = "atomics"))]
+mod atomic_waker;
+mod channel;
+#[cfg(not(target_feature = "atomics"))]
+mod concurrent_queue;
+mod dispatcher;
+mod notifier;
+mod wrapper;
+
+pub(crate) use atomic_waker::AtomicWaker;
+use concurrent_queue::{ConcurrentQueue, PushError};
+
+pub use self::abortable::{AbortHandle, Abortable, DropAbortHandle};
+pub use self::channel::{channel, Receiver, Sender};
+pub use self::dispatcher::{DispatchRunner, Dispatcher};
+pub use self::notifier::{Notified, Notifier};
+pub(crate) use self::wrapper::Wrapper;

winit-web/src/async/notifier.rs

@@ -0,0 +1,75 @@
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::{Arc, OnceLock};
+use std::task::{Context, Poll, Waker};
+
+use super::{ConcurrentQueue, PushError};
+
+#[derive(Debug)]
+pub struct Notifier<T: Clone>(Arc<Inner<T>>);
+
+impl<T: Clone> Notifier<T> {
+    pub fn new() -> Self {
+        Self(Arc::new(Inner { queue: ConcurrentQueue::unbounded(), value: OnceLock::new() }))
+    }
+
+    pub fn notify(self, value: T) {
+        if self.0.value.set(value).is_err() {
+            unreachable!("value set before")
+        }
+    }
+
+    pub fn notified(&self) -> Notified<T> {
+        Notified(Some(Arc::clone(&self.0)))
+    }
+}
+
+impl<T: Clone> Drop for Notifier<T> {
+    fn drop(&mut self) {
+        self.0.queue.close();
+
+        while let Ok(waker) = self.0.queue.pop() {
+            waker.wake()
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct Notified<T: Clone>(Option<Arc<Inner<T>>>);
+
+impl<T: Clone> Future for Notified<T> {
+    type Output = Option<T>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.0.take().expect("`Receiver` polled after completion");
+
+        if this.value.get().is_none() {
+            match this.queue.push(cx.waker().clone()) {
+                Ok(()) => {
+                    if this.value.get().is_none() {
+                        self.0 = Some(this);
+                        return Poll::Pending;
+                    }
+                },
+                Err(PushError::Closed(_)) => (),
+                Err(PushError::Full(_)) => {
+                    unreachable!("found full queue despite using unbounded queue")
+                },
+            }
+        }
+
+        match Arc::try_unwrap(this)
+            .map(|mut inner| inner.value.take())
+            .map_err(|this| this.value.get().cloned())
+        {
+            Ok(Some(value)) | Err(Some(value)) => Poll::Ready(Some(value)),
+            _ => Poll::Ready(None),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct Inner<T> {
+    queue: ConcurrentQueue<Waker>,
+    value: OnceLock<T>,
+}

winit-web/src/async/wrapper.rs

@@ -0,0 +1,113 @@
+use std::cell::{Ref, RefCell};
+use std::cmp;
+use std::future::Future;
+use std::hash::{Hash, Hasher};
+use std::marker::PhantomData;
+use std::sync::Arc;
+
+use super::super::main_thread::MainThreadMarker;
+
+// Unsafe wrapper type that allows us to use `T` when it's not `Send` from other threads.
+// `value` **must** only be accessed on the main thread.
+#[derive(Debug)]
+pub struct Wrapper<V: 'static, S: Clone + Send, E> {
+    value: Value<V>,
+    handler: fn(&RefCell<Option<V>>, E),
+    sender_data: S,
+    sender_handler: fn(&S, E),
+}
+
+#[derive(Debug)]
+struct Value<V> {
+    // SAFETY:
+    // This value must not be accessed if not on the main thread.
+    //
+    // - We wrap this in an `Arc` to allow it to be safely cloned without accessing the value.
+    // - The `RefCell` lets us mutably access in the main thread but is safe to drop in any thread
+    //   because it has no `Drop` behavior.
+    // - The `Option` lets us safely drop `T` only in the main thread.
+    value: Arc<RefCell<Option<V>>>,
+    // Prevent's `Send` or `Sync` to be automatically implemented.
+    local: PhantomData<*const ()>,
+}
+
+// SAFETY: See `Self::value`.
+unsafe impl<V> Send for Value<V> {}
+// SAFETY: See `Self::value`.
+unsafe impl<V> Sync for Value<V> {}
+
+impl<V, S: Clone + Send, E> Wrapper<V, S, E> {
+    pub fn new<R: Future<Output = ()>>(
+        _: MainThreadMarker,
+        value: V,
+        handler: fn(&RefCell<Option<V>>, E),
+        receiver: impl 'static + FnOnce(Arc<RefCell<Option<V>>>) -> R,
+        sender_data: S,
+        sender_handler: fn(&S, E),
+    ) -> Self {
+        let value = Arc::new(RefCell::new(Some(value)));
+
+        wasm_bindgen_futures::spawn_local({
+            let value = Arc::clone(&value);
+            async move {
+                receiver(Arc::clone(&value)).await;
+                drop(value.borrow_mut().take().unwrap());
+            }
+        });
+
+        Self { value: Value { value, local: PhantomData }, handler, sender_data, sender_handler }
+    }
+
+    pub fn send(&self, event: E) {
+        if MainThreadMarker::new().is_some() {
+            (self.handler)(&self.value.value, event)
+        } else {
+            (self.sender_handler)(&self.sender_data, event)
+        }
+    }
+
+    pub fn value(&self, _: MainThreadMarker) -> Ref<'_, V> {
+        Ref::map(self.value.value.borrow(), |value| value.as_ref().unwrap())
+    }
+
+    pub fn with_sender_data<T>(&self, f: impl FnOnce(&S) -> T) -> T {
+        f(&self.sender_data)
+    }
+}
+
+impl<V, S: Clone + Send, E> Clone for Wrapper<V, S, E> {
+    fn clone(&self) -> Self {
+        Self {
+            value: Value { value: self.value.value.clone(), local: PhantomData },
+            handler: self.handler,
+            sender_data: self.sender_data.clone(),
+            sender_handler: self.sender_handler,
+        }
+    }
+}
+
+impl<V, S: Clone + Send, E> Eq for Wrapper<V, S, E> {}
+
+impl<V, S: Clone + Send, E> Hash for Wrapper<V, S, E> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        Arc::as_ptr(&self.value.value).hash(state)
+    }
+}
+
+impl<V, S: Clone + Send, E> Ord for Wrapper<V, S, E> {
+    fn cmp(&self, other: &Self) -> cmp::Ordering {
+        Arc::as_ptr(&self.value.value).cmp(&Arc::as_ptr(&other.value.value))
+    }
+}
+
+impl<V, S: Clone + Send, E> PartialOrd for Wrapper<V, S, E> {
+    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl<V, S: Clone + Send, E> PartialEq for Wrapper<V, S, E> {
+    fn eq(&self, other: &Self) -> bool {
+        Arc::ptr_eq(&self.value.value, &other.value.value)
+    }
+}

winit-web/src/cursor.rs

@@ -0,0 +1,721 @@
+use std::cell::RefCell;
+use std::future::{self, Future};
+use std::hash::{Hash, Hasher};
+use std::mem;
+use std::ops::{Deref, DerefMut};
+use std::pin::Pin;
+use std::rc::Rc;
+use std::sync::Arc;
+use std::task::{ready, Context, Poll, Waker};
+use std::time::Duration;
+
+use cursor_icon::CursorIcon;
+use js_sys::{Array, Object};
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::JsCast;
+use wasm_bindgen_futures::JsFuture;
+use web_sys::{
+    Blob, Document, DomException, HtmlCanvasElement, HtmlImageElement, ImageBitmap,
+    ImageBitmapOptions, ImageBitmapRenderingContext, ImageData, PremultiplyAlpha, Url, Window,
+};
+use winit_core::cursor::{Cursor, CursorImage, CustomCursorProvider, CustomCursorSource};
+
+use crate::backend::Style;
+use crate::event_loop::ActiveEventLoop;
+use crate::main_thread::{MainThreadMarker, MainThreadSafe};
+use crate::r#async::{AbortHandle, Abortable, DropAbortHandle, Notified, Notifier};
+use crate::CustomCursorError;
+
+#[derive(Clone, Debug)]
+pub struct CustomCursor {
+    pub(crate) animation: bool,
+    state: Arc<MainThreadSafe<RefCell<ImageState>>>,
+}
+
+impl CustomCursor {
+    pub(crate) fn new(event_loop: &ActiveEventLoop, source: CustomCursorSource) -> Self {
+        match source {
+            CustomCursorSource::Image(image) => Self::build_spawn(
+                event_loop,
+                from_rgba(event_loop.runner.window(), event_loop.runner.document().clone(), &image),
+                false,
+            ),
+            CustomCursorSource::Url { url, hotspot_x, hotspot_y } => Self::build_spawn(
+                event_loop,
+                from_url(UrlType::Plain(url), hotspot_x, hotspot_y),
+                false,
+            ),
+            CustomCursorSource::Animation(animation) => {
+                let (duration, cursors) = animation.into_raw();
+                Self::build_spawn(
+                    event_loop,
+                    from_animation(event_loop.runner.main_thread(), duration, cursors.into_iter()),
+                    true,
+                )
+            },
+        }
+    }
+
+    fn build_spawn<F, S>(window_target: &ActiveEventLoop, task: F, animation: bool) -> CustomCursor
+    where
+        F: 'static + Future<Output = Result<S, CustomCursorError>>,
+        S: Into<ImageState>,
+    {
+        let handle = AbortHandle::new();
+        let this = CustomCursor {
+            animation,
+            state: Arc::new(MainThreadSafe::new(
+                window_target.runner.main_thread(),
+                RefCell::new(ImageState::Loading {
+                    notifier: Notifier::new(),
+                    _handle: DropAbortHandle::new(handle.clone()),
+                }),
+            )),
+        };
+        let weak = Arc::downgrade(&this.state);
+        let main_thread = window_target.runner.main_thread();
+
+        let task = Abortable::new(handle, {
+            async move {
+                let result = task.await;
+
+                let this = weak.upgrade().expect("`CursorHandler` invalidated without aborting");
+                let mut this = this.get(main_thread).borrow_mut();
+
+                match result {
+                    Ok(new_state) => {
+                        let ImageState::Loading { notifier, .. } =
+                            mem::replace(this.deref_mut(), new_state.into())
+                        else {
+                            unreachable!("found invalid state");
+                        };
+                        notifier.notify(Ok(()));
+                    },
+                    Err(error) => {
+                        let ImageState::Loading { notifier, .. } =
+                            mem::replace(this.deref_mut(), ImageState::Failed(error.clone()))
+                        else {
+                            unreachable!("found invalid state");
+                        };
+                        notifier.notify(Err(error));
+                    },
+                }
+            }
+        });
+
+        wasm_bindgen_futures::spawn_local(async move {
+            let _ = task.await;
+        });
+
+        this
+    }
+
+    pub(crate) fn new_async(
+        event_loop: &ActiveEventLoop,
+        source: CustomCursorSource,
+    ) -> CustomCursorFuture {
+        let CustomCursor { animation, state } = Self::new(event_loop, source);
+        let binding = state.get(event_loop.runner.main_thread()).borrow();
+        let ImageState::Loading { notifier, .. } = binding.deref() else {
+            unreachable!("found invalid state")
+        };
+        let notified = notifier.notified();
+        drop(binding);
+
+        CustomCursorFuture { notified, animation, state: Some(state) }
+    }
+}
+
+impl CustomCursorProvider for CustomCursor {
+    fn is_animated(&self) -> bool {
+        self.animation
+    }
+}
+
+impl Hash for CustomCursor {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        Arc::as_ptr(&self.state).hash(state);
+    }
+}
+
+impl PartialEq for CustomCursor {
+    fn eq(&self, other: &Self) -> bool {
+        Arc::ptr_eq(&self.state, &other.state)
+    }
+}
+
+impl Eq for CustomCursor {}
+
+#[derive(Debug)]
+pub struct CustomCursorFuture {
+    notified: Notified<Result<(), CustomCursorError>>,
+    animation: bool,
+    state: Option<Arc<MainThreadSafe<RefCell<ImageState>>>>,
+}
+
+impl Future for CustomCursorFuture {
+    type Output = Result<CustomCursor, CustomCursorError>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        if self.state.is_none() {
+            panic!("`CustomCursorFuture` polled after completion")
+        }
+
+        let result = ready!(Pin::new(&mut self.notified).poll(cx)).unwrap();
+        let state = self.state.take().expect("`CustomCursorFuture` polled after completion");
+
+        Poll::Ready(result.map(|_| CustomCursor { animation: self.animation, state }))
+    }
+}
+
+#[derive(Debug)]
+pub struct CursorHandler(Rc<RefCell<Inner>>);
+
+#[derive(Debug)]
+struct Inner {
+    main_thread: MainThreadMarker,
+    canvas: HtmlCanvasElement,
+    style: Style,
+    visible: bool,
+    cursor: SelectedCursor,
+}
+
+impl CursorHandler {
+    pub(crate) fn new(
+        main_thread: MainThreadMarker,
+        canvas: HtmlCanvasElement,
+        style: Style,
+    ) -> Self {
+        Self(Rc::new(RefCell::new(Inner {
+            main_thread,
+            canvas,
+            style,
+            visible: true,
+            cursor: SelectedCursor::default(),
+        })))
+    }
+
+    pub fn set_cursor(&self, cursor: Cursor) {
+        let mut this = self.0.borrow_mut();
+
+        match cursor {
+            Cursor::Icon(icon) => {
+                if let SelectedCursor::Icon(old_icon)
+                | SelectedCursor::Loading { previous: Previous::Icon(old_icon), .. } =
+                    &this.cursor
+                {
+                    if *old_icon == icon {
+                        return;
+                    }
+                }
+
+                this.cursor = SelectedCursor::Icon(icon);
+                this.set_style();
+            },
+            Cursor::Custom(cursor) => {
+                let cursor = match cursor.cast_ref::<CustomCursor>() {
+                    Some(cursor) => cursor,
+                    None => todo!(),
+                };
+
+                if let SelectedCursor::Loading { cursor: old_cursor, .. }
+                | SelectedCursor::Image(old_cursor)
+                | SelectedCursor::Animation { cursor: old_cursor, .. } = &this.cursor
+                {
+                    if old_cursor == cursor {
+                        return;
+                    }
+                }
+
+                let state = cursor.state.get(this.main_thread).borrow();
+
+                match state.deref() {
+                    ImageState::Loading { notifier, .. } => {
+                        let notified = notifier.notified();
+                        let handle = DropAbortHandle::new(AbortHandle::new());
+                        let task = Abortable::new(handle.handle(), {
+                            let weak = Rc::downgrade(&self.0);
+                            async move {
+                                let _ = notified.await;
+                                let handler = weak
+                                    .upgrade()
+                                    .expect("`CursorHandler` invalidated without aborting");
+                                handler.borrow_mut().notify();
+                            }
+                        });
+                        wasm_bindgen_futures::spawn_local(async move {
+                            let _ = task.await;
+                        });
+
+                        drop(state);
+                        this.cursor = SelectedCursor::Loading {
+                            cursor: cursor.clone(),
+                            previous: mem::take(&mut this.cursor).into(),
+                            _handle: handle,
+                        };
+                    },
+                    ImageState::Failed(error) => {
+                        tracing::error!(
+                            "trying to load custom cursor that has failed to load: {error}"
+                        )
+                    },
+                    ImageState::Image(_) => {
+                        drop(state);
+                        this.cursor = SelectedCursor::Image(cursor.clone());
+                        this.set_style();
+                    },
+                    ImageState::Animation(animation) => {
+                        let canvas: &CanvasAnimateExt = this.canvas.unchecked_ref();
+                        let animation = canvas.animate_with_keyframe_animation_options(
+                            Some(&animation.keyframes),
+                            &animation.options,
+                        );
+                        drop(state);
+
+                        if !this.visible {
+                            animation.cancel();
+                        }
+
+                        this.cursor = SelectedCursor::Animation {
+                            animation: AnimationDropper(animation),
+                            cursor: cursor.clone(),
+                        };
+                        this.set_style();
+                    },
+                };
+            },
+        }
+    }
+
+    pub fn set_cursor_visible(&self, visible: bool) {
+        let mut this = self.0.borrow_mut();
+
+        if !visible && this.visible {
+            this.visible = false;
+            this.style.set("cursor", "none");
+
+            if let SelectedCursor::Animation { animation, .. } = &this.cursor {
+                animation.0.cancel();
+            }
+        } else if visible && !this.visible {
+            this.visible = true;
+            this.set_style();
+        }
+    }
+}
+
+impl Inner {
+    fn set_style(&self) {
+        if self.visible {
+            match &self.cursor {
+                SelectedCursor::Icon(icon)
+                | SelectedCursor::Loading { previous: Previous::Icon(icon), .. } => {
+                    if let CursorIcon::Default = icon {
+                        self.style.remove("cursor")
+                    } else {
+                        self.style.set("cursor", icon.name())
+                    }
+                },
+                SelectedCursor::Loading { previous: Previous::Image(cursor), .. }
+                | SelectedCursor::Image(cursor) => {
+                    match cursor.state.get(self.main_thread).borrow().deref() {
+                        ImageState::Image(Image { style, .. }) => self.style.set("cursor", style),
+                        _ => unreachable!("found invalid saved state"),
+                    }
+                },
+                SelectedCursor::Loading {
+                    previous: Previous::Animation { animation, .. }, ..
+                }
+                | SelectedCursor::Animation { animation, .. } => {
+                    self.style.remove("cursor");
+                    animation.0.play()
+                },
+            }
+        }
+    }
+
+    fn notify(&mut self) {
+        let SelectedCursor::Loading { cursor, previous, .. } = mem::take(&mut self.cursor) else {
+            unreachable!("found wrong state")
+        };
+
+        let state = cursor.state.get(self.main_thread).borrow();
+        match state.deref() {
+            ImageState::Image(_) => {
+                drop(state);
+                self.cursor = SelectedCursor::Image(cursor);
+                self.set_style();
+            },
+            ImageState::Animation(animation) => {
+                let canvas: &CanvasAnimateExt = self.canvas.unchecked_ref();
+                let animation = canvas.animate_with_keyframe_animation_options(
+                    Some(&animation.keyframes),
+                    &animation.options,
+                );
+                drop(state);
+
+                if !self.visible {
+                    animation.cancel();
+                }
+
+                self.cursor =
+                    SelectedCursor::Animation { animation: AnimationDropper(animation), cursor };
+                self.set_style();
+            },
+            ImageState::Failed(error) => {
+                tracing::error!("custom cursor failed to load: {error}");
+                self.cursor = previous.into()
+            },
+            ImageState::Loading { .. } => unreachable!("notified without being ready"),
+        }
+    }
+}
+
+#[derive(Debug)]
+enum SelectedCursor {
+    Icon(CursorIcon),
+    Loading { cursor: CustomCursor, previous: Previous, _handle: DropAbortHandle },
+    Image(CustomCursor),
+    Animation { cursor: CustomCursor, animation: AnimationDropper },
+}
+
+impl Default for SelectedCursor {
+    fn default() -> Self {
+        Self::Icon(Default::default())
+    }
+}
+
+impl From<Previous> for SelectedCursor {
+    fn from(previous: Previous) -> Self {
+        match previous {
+            Previous::Icon(icon) => Self::Icon(icon),
+            Previous::Image(cursor) => Self::Image(cursor),
+            Previous::Animation { cursor, animation } => Self::Animation { cursor, animation },
+        }
+    }
+}
+
+#[derive(Debug)]
+enum Previous {
+    Icon(CursorIcon),
+    Image(CustomCursor),
+    Animation { cursor: CustomCursor, animation: AnimationDropper },
+}
+
+impl From<SelectedCursor> for Previous {
+    fn from(value: SelectedCursor) -> Self {
+        match value {
+            SelectedCursor::Icon(icon) => Self::Icon(icon),
+            SelectedCursor::Loading { previous, .. } => previous,
+            SelectedCursor::Image(image) => Self::Image(image),
+            SelectedCursor::Animation { cursor, animation } => {
+                Self::Animation { cursor, animation }
+            },
+        }
+    }
+}
+
+#[derive(Debug)]
+enum ImageState {
+    Loading { notifier: Notifier<Result<(), CustomCursorError>>, _handle: DropAbortHandle },
+    Failed(CustomCursorError),
+    Image(Image),
+    Animation(Animation),
+}
+
+#[derive(Debug)]
+struct Image {
+    style: String,
+    _object_url: Option<ObjectUrl>,
+    _image: HtmlImageElement,
+}
+
+impl From<Image> for ImageState {
+    fn from(image: Image) -> Self {
+        Self::Image(image)
+    }
+}
+
+#[derive(Debug)]
+struct Animation {
+    keyframes: Array,
+    options: KeyframeAnimationOptions,
+    _images: Vec<CustomCursor>,
+}
+
+impl From<Animation> for ImageState {
+    fn from(animation: Animation) -> Self {
+        Self::Animation(animation)
+    }
+}
+
+#[derive(Debug)]
+enum UrlType {
+    Plain(String),
+    Object(ObjectUrl),
+}
+
+impl UrlType {
+    fn url(&self) -> &str {
+        match &self {
+            UrlType::Plain(url) => url,
+            UrlType::Object(object_url) => &object_url.0,
+        }
+    }
+}
+
+#[derive(Debug)]
+struct ObjectUrl(String);
+
+impl Drop for ObjectUrl {
+    fn drop(&mut self) {
+        Url::revoke_object_url(&self.0).expect("unexpected exception in `URL.revokeObjectURL()`");
+    }
+}
+
+#[derive(Debug)]
+struct AnimationDropper(WebAnimation);
+
+impl Drop for AnimationDropper {
+    fn drop(&mut self) {
+        self.0.cancel()
+    }
+}
+
+fn from_rgba(
+    window: &Window,
+    document: Document,
+    image: &CursorImage,
+) -> impl Future<Output = Result<Image, CustomCursorError>> {
+    // 1. Create an `ImageData` from the RGBA data.
+    // 2. Create an `ImageBitmap` from the `ImageData`.
+    // 3. Draw `ImageBitmap` on an `HTMLCanvasElement`.
+    // 4. Create a `Blob` from the `HTMLCanvasElement`.
+    // 5. Create an object URL from the `Blob`.
+    // 6. Decode the image on an `HTMLImageElement` from the URL.
+
+    // 1. Create an `ImageData` from the RGBA data.
+    // Adapted from https://github.com/rust-windowing/softbuffer/blob/ab7688e2ed2e2eca51b3c4e1863a5bd7fe85800e/src/web.rs#L196-L223
+    #[cfg(target_feature = "atomics")]
+    // Can't share `SharedArrayBuffer` with `ImageData`.
+    let result = {
+        use js_sys::{Uint8Array, Uint8ClampedArray};
+        use wasm_bindgen::JsValue;
+
+        #[wasm_bindgen]
+        extern "C" {
+            #[wasm_bindgen(js_namespace = ImageData)]
+            type ImageDataExt;
+            #[wasm_bindgen(catch, constructor, js_class = ImageData)]
+            fn new(array: Uint8ClampedArray, sw: u32) -> Result<ImageDataExt, JsValue>;
+        }
+
+        let array = Uint8Array::new_with_length(image.buffer().len() as u32);
+        array.copy_from(image.buffer());
+        let array = Uint8ClampedArray::new(&array);
+        ImageDataExt::new(array, image.width() as u32)
+            .map(JsValue::from)
+            .map(ImageData::unchecked_from_js)
+    };
+    #[cfg(not(target_feature = "atomics"))]
+    let result = ImageData::new_with_u8_clamped_array(
+        wasm_bindgen::Clamped(image.buffer()),
+        image.width() as u32,
+    );
+    let image_data = result.expect("found wrong image size");
+
+    // 2. Create an `ImageBitmap` from the `ImageData`.
+    //
+    // We call `createImageBitmap()` before spawning the future,
+    // to not have to clone the image buffer.
+    let options = ImageBitmapOptions::new();
+    options.set_premultiply_alpha(PremultiplyAlpha::None);
+    let bitmap = JsFuture::from(
+        window
+            .create_image_bitmap_with_image_data_and_image_bitmap_options(&image_data, &options)
+            .expect("unexpected exception in `createImageBitmap()`"),
+    );
+
+    let width = image.width();
+    let height = image.height();
+    let hotspot_x = image.hotspot_x();
+    let hotspot_y = image.hotspot_y();
+    async move {
+        let bitmap: ImageBitmap =
+            bitmap.await.expect("found invalid state in `ImageData`").unchecked_into();
+
+        let canvas: HtmlCanvasElement =
+            document.create_element("canvas").expect("invalid tag name").unchecked_into();
+        #[allow(clippy::disallowed_methods)]
+        canvas.set_width(width as u32);
+        #[allow(clippy::disallowed_methods)]
+        canvas.set_height(height as u32);
+
+        // 3. Draw `ImageBitmap` on an `HTMLCanvasElement`.
+        let context: ImageBitmapRenderingContext = canvas
+            .get_context("bitmaprenderer")
+            .expect("unexpected exception in `HTMLCanvasElement.getContext()`")
+            .expect("`bitmaprenderer` context unsupported")
+            .unchecked_into();
+        context.transfer_from_image_bitmap(&bitmap);
+        drop(bitmap);
+        drop(context);
+
+        // 4. Create a `Blob` from the `HTMLCanvasElement`.
+        //
+        // To keep the `Closure` alive until `HTMLCanvasElement.toBlob()` is done,
+        // we do the whole `Waker` strategy. Commonly on `Drop` the callback is aborted,
+        // but it would increase complexity and isn't possible in this case.
+        // Keep in mind that `HTMLCanvasElement.toBlob()` can call the callback immediately.
+        let value = Rc::new(RefCell::new(None));
+        let waker = Rc::new(RefCell::<Option<Waker>>::new(None));
+        let callback = Closure::once({
+            let value = value.clone();
+            let waker = waker.clone();
+            move |blob: Option<Blob>| {
+                *value.borrow_mut() = Some(blob);
+                if let Some(waker) = waker.borrow_mut().take() {
+                    waker.wake();
+                }
+            }
+        });
+        canvas
+            .to_blob(callback.as_ref().unchecked_ref())
+            .expect("failed with `SecurityError` despite only source coming from memory");
+        let blob = future::poll_fn(|cx| {
+            if let Some(blob) = value.borrow_mut().take() {
+                Poll::Ready(blob)
+            } else {
+                *waker.borrow_mut() = Some(cx.waker().clone());
+                Poll::Pending
+            }
+        })
+        .await;
+        drop(canvas);
+
+        let Some(blob) = blob else {
+            return Err(CustomCursorError::Blob);
+        };
+
+        // 5. Create an object URL from the `Blob`.
+        let url = Url::create_object_url_with_blob(&blob)
+            .expect("unexpected exception in `URL.createObjectURL()`");
+        let url = UrlType::Object(ObjectUrl(url));
+
+        from_url(url, hotspot_x, hotspot_y).await
+    }
+}
+
+async fn from_url(
+    url: UrlType,
+    hotspot_x: u16,
+    hotspot_y: u16,
+) -> Result<Image, CustomCursorError> {
+    // 6. Decode the image on an `HTMLImageElement` from the URL.
+    let image = HtmlImageElement::new().expect("unexpected exception in `new HtmlImageElement`");
+    image.set_src(url.url());
+    let result = JsFuture::from(image.decode()).await;
+
+    if let Err(error) = result {
+        debug_assert!(error.has_type::<DomException>());
+        let error: DomException = error.unchecked_into();
+        debug_assert_eq!(error.name(), "EncodingError");
+        let error = error.message();
+
+        return Err(CustomCursorError::Decode(error));
+    }
+
+    Ok(Image {
+        style: format!("url({}) {hotspot_x} {hotspot_y}, auto", url.url()),
+        _object_url: match url {
+            UrlType::Plain(_) => None,
+            UrlType::Object(object_url) => Some(object_url),
+        },
+        _image: image,
+    })
+}
+
+#[allow(clippy::await_holding_refcell_ref)] // false-positive
+async fn from_animation(
+    main_thread: MainThreadMarker,
+    duration: Duration,
+    cursors: impl ExactSizeIterator<Item = winit_core::cursor::CustomCursor>,
+) -> Result<Animation, CustomCursorError> {
+    let keyframes = Array::new();
+    let mut images = Vec::with_capacity(cursors.len());
+
+    for cursor in cursors {
+        let cursor = cursor.cast_ref::<CustomCursor>().unwrap();
+        let state = cursor.state.get(main_thread).borrow();
+
+        match state.deref() {
+            ImageState::Loading { notifier, .. } => {
+                let notified = notifier.notified();
+                drop(state);
+                notified.await.unwrap()?;
+            },
+            ImageState::Failed(error) => return Err(error.clone()),
+            ImageState::Image(_) => drop(state),
+            ImageState::Animation(_) => unreachable!("check in `CustomCursorSource` failed"),
+        }
+
+        let state = cursor.state.get(main_thread).borrow();
+        let style = match state.deref() {
+            ImageState::Image(Image { style, .. }) => style,
+            _ => unreachable!("found invalid state"),
+        };
+
+        let keyframe: Keyframe = Object::new().unchecked_into();
+        keyframe.set_cursor(style);
+        keyframes.push(&keyframe);
+        drop(state);
+
+        images.push(cursor.clone());
+    }
+
+    keyframes.push(&keyframes.get(0));
+
+    let options: KeyframeAnimationOptions = Object::new().unchecked_into();
+    options.set_duration(duration.as_millis() as f64);
+    options.set_iterations(f64::INFINITY);
+
+    Ok(Animation { keyframes, options, _images: images })
+}
+
+#[wasm_bindgen]
+extern "C" {
+    type CanvasAnimateExt;
+
+    #[wasm_bindgen(method, js_name = animate)]
+    fn animate_with_keyframe_animation_options(
+        this: &CanvasAnimateExt,
+        keyframes: Option<&Object>,
+        options: &KeyframeAnimationOptions,
+    ) -> WebAnimation;
+
+    #[derive(Debug)]
+    type WebAnimation;
+
+    #[wasm_bindgen(method)]
+    fn cancel(this: &WebAnimation);
+
+    #[wasm_bindgen(method)]
+    fn play(this: &WebAnimation);
+
+    #[wasm_bindgen(extends = Object)]
+    type Keyframe;
+
+    #[wasm_bindgen(method, setter, js_name = cursor)]
+    fn set_cursor(this: &Keyframe, value: &str);
+
+    #[derive(Debug)]
+    #[wasm_bindgen(extends = Object)]
+    type KeyframeAnimationOptions;
+
+    #[wasm_bindgen(method, setter, js_name = duration)]
+    fn set_duration(this: &KeyframeAnimationOptions, value: f64);
+
+    #[wasm_bindgen(method, setter, js_name = iterations)]
+    fn set_iterations(this: &KeyframeAnimationOptions, value: f64);
+}

winit-web/src/error.rs

@@ -0,0 +1,10 @@
+use std::fmt;
+
+#[derive(Debug)]
+pub struct OsError(pub String);
+
+impl fmt::Display for OsError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}

winit-web/src/event.rs

@@ -0,0 +1,12 @@
+use winit_core::event::DeviceId;
+
+pub(crate) fn mkdid(pointer_id: i32) -> Option<DeviceId> {
+    if let Ok(pointer_id) = u32::try_from(pointer_id) {
+        Some(DeviceId::from_raw(pointer_id as i64))
+    } else if pointer_id == -1 {
+        None
+    } else {
+        tracing::error!("found unexpected negative `PointerEvent.pointerId`: {pointer_id}");
+        None
+    }
+}

winit-web/src/event_loop/mod.rs

@@ -0,0 +1,103 @@
+use std::sync::atomic::{AtomicBool, Ordering};
+
+use winit_core::application::ApplicationHandler;
+use winit_core::error::{EventLoopError, NotSupportedError};
+use winit_core::event_loop::ActiveEventLoop as RootActiveEventLoop;
+
+use crate::{
+    backend, HasMonitorPermissionFuture, MonitorPermissionFuture, PollStrategy, WaitUntilStrategy,
+};
+
+mod proxy;
+pub(crate) mod runner;
+mod state;
+mod window_target;
+
+pub(crate) use window_target::ActiveEventLoop;
+
+#[derive(Debug)]
+pub struct EventLoop {
+    elw: ActiveEventLoop,
+}
+
+#[derive(Default, Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct PlatformSpecificEventLoopAttributes {}
+
+static EVENT_LOOP_CREATED: AtomicBool = AtomicBool::new(false);
+
+impl EventLoop {
+    pub fn new(_: &PlatformSpecificEventLoopAttributes) -> Result<Self, EventLoopError> {
+        if EVENT_LOOP_CREATED.swap(true, Ordering::Relaxed) {
+            // For better cross-platformness.
+            return Err(EventLoopError::RecreationAttempt);
+        }
+
+        Ok(EventLoop { elw: ActiveEventLoop::new() })
+    }
+
+    fn allow_event_loop_recreation() {
+        EVENT_LOOP_CREATED.store(false, Ordering::Relaxed);
+    }
+
+    pub fn run_app<A: ApplicationHandler>(self, app: A) -> ! {
+        let app = Box::new(app);
+
+        // SAFETY: The `transmute` is necessary because `run()` requires `'static`. This is safe
+        // because this function will never return and all resources not cleaned up by the point we
+        // `throw` will leak, making this actually `'static`.
+        let app = unsafe {
+            std::mem::transmute::<
+                Box<dyn ApplicationHandler + '_>,
+                Box<dyn ApplicationHandler + 'static>,
+            >(app)
+        };
+
+        self.elw.run(app, false);
+
+        // Throw an exception to break out of Rust execution and use unreachable to tell the
+        // compiler this function won't return, giving it a return type of '!'
+        backend::throw(
+            "Using exceptions for control flow, don't mind me. This isn't actually an error!",
+        );
+
+        unreachable!();
+    }
+
+    pub fn spawn_app<A: ApplicationHandler + 'static>(self, app: A) {
+        self.elw.run(Box::new(app), true);
+    }
+
+    pub fn window_target(&self) -> &dyn RootActiveEventLoop {
+        &self.elw
+    }
+
+    pub fn set_poll_strategy(&self, strategy: PollStrategy) {
+        self.elw.set_poll_strategy(strategy);
+    }
+
+    pub fn poll_strategy(&self) -> PollStrategy {
+        self.elw.poll_strategy()
+    }
+
+    pub fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.elw.set_wait_until_strategy(strategy);
+    }
+
+    pub fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.elw.wait_until_strategy()
+    }
+
+    pub fn has_multiple_screens(&self) -> Result<bool, NotSupportedError> {
+        self.elw.has_multiple_screens()
+    }
+
+    pub fn request_detailed_monitor_permission(&self) -> MonitorPermissionFuture {
+        MonitorPermissionFuture(self.elw.request_detailed_monitor_permission())
+    }
+
+    pub fn has_detailed_monitor_permission(&self) -> HasMonitorPermissionFuture {
+        HasMonitorPermissionFuture(
+            self.elw.runner.monitor().has_detailed_monitor_permission_async(),
+        )
+    }
+}

winit-web/src/event_loop/proxy.rs

@@ -0,0 +1,104 @@
+use std::future;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+use std::task::Poll;
+
+use winit_core::event_loop::EventLoopProxyProvider;
+
+use super::super::main_thread::MainThreadMarker;
+use crate::event_loop::runner::WeakShared;
+use crate::r#async::{AtomicWaker, Wrapper};
+
+#[derive(Debug)]
+pub struct EventLoopProxy(Wrapper<WeakShared, Arc<State>, ()>);
+
+#[derive(Debug)]
+struct State {
+    awoken: AtomicBool,
+    waker: AtomicWaker,
+    closed: AtomicBool,
+}
+
+impl EventLoopProxy {
+    pub fn new(main_thread: MainThreadMarker, runner: WeakShared) -> Self {
+        let state = Arc::new(State {
+            awoken: AtomicBool::new(false),
+            waker: AtomicWaker::new(),
+            closed: AtomicBool::new(false),
+        });
+
+        Self(Wrapper::new(
+            main_thread,
+            runner,
+            |runner, _| {
+                let runner = runner.borrow();
+                let runner = runner.as_ref().unwrap();
+
+                if let Some(runner) = runner.upgrade() {
+                    runner.send_proxy_wake_up(true);
+                }
+            },
+            {
+                let state = Arc::clone(&state);
+
+                move |runner| async move {
+                    while future::poll_fn(|cx| {
+                        if state.awoken.swap(false, Ordering::Relaxed) {
+                            Poll::Ready(true)
+                        } else {
+                            state.waker.register(cx.waker());
+
+                            if state.awoken.swap(false, Ordering::Relaxed) {
+                                Poll::Ready(true)
+                            } else {
+                                if state.closed.load(Ordering::Relaxed) {
+                                    return Poll::Ready(false);
+                                }
+
+                                Poll::Pending
+                            }
+                        }
+                    })
+                    .await
+                    {
+                        let runner = runner.borrow();
+                        let runner = runner.as_ref().unwrap();
+
+                        if let Some(runner) = runner.upgrade() {
+                            runner.send_proxy_wake_up(false);
+                        }
+                    }
+                }
+            },
+            state,
+            |state, _| {
+                state.awoken.store(true, Ordering::Relaxed);
+                state.waker.wake();
+            },
+        ))
+    }
+
+    pub fn take(&self) -> bool {
+        debug_assert!(
+            MainThreadMarker::new().is_some(),
+            "this should only be called from the main thread"
+        );
+
+        self.0.with_sender_data(|state| state.awoken.swap(false, Ordering::Relaxed))
+    }
+}
+
+impl Drop for EventLoopProxy {
+    fn drop(&mut self) {
+        self.0.with_sender_data(|state| {
+            state.closed.store(true, Ordering::Relaxed);
+            state.waker.wake();
+        });
+    }
+}
+
+impl EventLoopProxyProvider for EventLoopProxy {
+    fn wake_up(&self) {
+        self.0.send(())
+    }
+}

winit-web/src/event_loop/runner.rs

@@ -0,0 +1,888 @@
+use std::cell::{Cell, RefCell};
+use std::collections::{HashSet, VecDeque};
+use std::ops::Deref;
+use std::rc::{Rc, Weak};
+use std::sync::Arc;
+use std::{fmt, iter};
+
+use dpi::PhysicalSize;
+use wasm_bindgen::prelude::Closure;
+use wasm_bindgen::JsCast;
+use web_sys::{Document, KeyboardEvent, Navigator, PageTransitionEvent, PointerEvent, WheelEvent};
+use web_time::{Duration, Instant};
+use winit_core::application::ApplicationHandler;
+use winit_core::event::{
+    DeviceEvent, DeviceId, ElementState, RawKeyEvent, StartCause, WindowEvent,
+};
+use winit_core::event_loop::{ControlFlow, DeviceEvents};
+use winit_core::window::WindowId;
+
+use super::proxy::EventLoopProxy;
+use super::state::State;
+use crate::backend::{EventListenerHandle, SafeAreaHandle};
+use crate::event_loop::ActiveEventLoop;
+use crate::main_thread::MainThreadMarker;
+use crate::monitor::MonitorHandler;
+use crate::r#async::DispatchRunner;
+use crate::web_sys::event::mouse_button_to_id;
+use crate::window::Inner;
+use crate::{backend, event, EventLoop, PollStrategy, WaitUntilStrategy};
+
+#[derive(Debug)]
+pub struct Shared(Rc<Execution>);
+
+impl Clone for Shared {
+    fn clone(&self) -> Self {
+        Shared(self.0.clone())
+    }
+}
+
+type OnEventHandle<T> = RefCell<Option<EventListenerHandle<dyn FnMut(T)>>>;
+
+struct Execution {
+    main_thread: MainThreadMarker,
+    event_loop_proxy: Arc<EventLoopProxy>,
+    control_flow: Cell<ControlFlow>,
+    poll_strategy: Cell<PollStrategy>,
+    wait_until_strategy: Cell<WaitUntilStrategy>,
+    exit: Cell<bool>,
+    runner: RefCell<RunnerEnum>,
+    suspended: Cell<bool>,
+    event_loop_recreation: Cell<bool>,
+    events: RefCell<VecDeque<Event>>,
+    id: Cell<usize>,
+    window: web_sys::Window,
+    navigator: Navigator,
+    document: Document,
+    #[allow(clippy::type_complexity)]
+    all_canvases: RefCell<Vec<(WindowId, Weak<backend::Canvas>, DispatchRunner<Inner>)>>,
+    redraw_pending: RefCell<HashSet<WindowId>>,
+    destroy_pending: RefCell<VecDeque<WindowId>>,
+    pub(crate) monitor: Rc<MonitorHandler>,
+    safe_area: Rc<SafeAreaHandle>,
+    page_transition_event_handle: RefCell<Option<backend::PageTransitionEventHandle>>,
+    device_events: Cell<DeviceEvents>,
+    on_mouse_move: OnEventHandle<PointerEvent>,
+    on_wheel: OnEventHandle<WheelEvent>,
+    on_mouse_press: OnEventHandle<PointerEvent>,
+    on_mouse_release: OnEventHandle<PointerEvent>,
+    on_key_press: OnEventHandle<KeyboardEvent>,
+    on_key_release: OnEventHandle<KeyboardEvent>,
+    on_visibility_change: OnEventHandle<web_sys::Event>,
+}
+
+impl fmt::Debug for Execution {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Execution").finish_non_exhaustive()
+    }
+}
+
+enum RunnerEnum {
+    /// The `EventLoop` is created but not being run.
+    Pending,
+    /// The `EventLoop` is running some async initialization and is waiting to be started.
+    Initializing(Runner),
+    /// The `EventLoop` is being run.
+    Running(Runner),
+    /// The `EventLoop` is exited after being started with `EventLoop::run_app`. Since
+    /// `EventLoop::run_app` takes ownership of the `EventLoop`, we can be certain
+    /// that this event loop will never be run again.
+    Destroyed,
+}
+
+impl RunnerEnum {
+    fn maybe_runner(&self) -> Option<&Runner> {
+        match self {
+            RunnerEnum::Running(runner) => Some(runner),
+            _ => None,
+        }
+    }
+}
+
+struct Runner {
+    state: State,
+    app: Box<dyn ApplicationHandler>,
+    event_loop: ActiveEventLoop,
+}
+
+impl fmt::Debug for Runner {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Runner")
+            .field("state", &self.state)
+            .field("app", &"<ApplicationHandler>")
+            .field("event_loop", &self.event_loop)
+            .finish()
+    }
+}
+
+impl Runner {
+    pub fn new(app: Box<dyn ApplicationHandler>, event_loop: ActiveEventLoop) -> Self {
+        Runner { state: State::Init, app, event_loop }
+    }
+
+    /// Returns the corresponding `StartCause` for the current `state`, or `None`
+    /// when in `Exit` state.
+    fn maybe_start_cause(&self) -> Option<StartCause> {
+        Some(match self.state {
+            State::Init => StartCause::Init,
+            State::Poll { .. } => StartCause::Poll,
+            State::Wait { start } => StartCause::WaitCancelled { start, requested_resume: None },
+            State::WaitUntil { start, end, .. } => {
+                StartCause::WaitCancelled { start, requested_resume: Some(end) }
+            },
+            State::Exit => return None,
+        })
+    }
+
+    fn handle_single_event(&mut self, runner: &Shared, event: Event) {
+        match event {
+            Event::NewEvents(cause) => self.app.new_events(&self.event_loop, cause),
+            Event::WindowEvent { window_id, event } => {
+                self.app.window_event(&self.event_loop, window_id, event)
+            },
+            Event::ScaleChange { canvas, size, scale } => {
+                if let Some(canvas) = canvas.upgrade() {
+                    canvas.handle_scale_change(
+                        runner,
+                        |window_id, event| {
+                            self.app.window_event(&self.event_loop, window_id, event);
+                        },
+                        size,
+                        scale,
+                    )
+                }
+            },
+            Event::DeviceEvent { device_id, event } => {
+                self.app.device_event(&self.event_loop, device_id, event)
+            },
+            Event::UserWakeUp => self.app.proxy_wake_up(&self.event_loop),
+            Event::Suspended => self.app.suspended(&self.event_loop),
+            Event::Resumed => self.app.resumed(&self.event_loop),
+            Event::CreateSurfaces => self.app.can_create_surfaces(&self.event_loop),
+            Event::AboutToWait => self.app.about_to_wait(&self.event_loop),
+        }
+    }
+}
+
+impl Shared {
+    pub fn new() -> Self {
+        let main_thread = MainThreadMarker::new().expect("only callable from inside the `Window`");
+        #[allow(clippy::disallowed_methods)]
+        let window = web_sys::window().expect("only callable from inside the `Window`");
+        #[allow(clippy::disallowed_methods)]
+        let navigator = window.navigator();
+        #[allow(clippy::disallowed_methods)]
+        let document = window.document().expect("Failed to obtain document");
+
+        Shared(Rc::<Execution>::new_cyclic(|weak| {
+            let proxy_spawner = EventLoopProxy::new(main_thread, WeakShared(weak.clone()));
+
+            let monitor = MonitorHandler::new(
+                main_thread,
+                window.clone(),
+                &navigator,
+                WeakShared(weak.clone()),
+            );
+
+            let safe_area = SafeAreaHandle::new(&window, &document);
+
+            Execution {
+                main_thread,
+                event_loop_proxy: Arc::new(proxy_spawner),
+                control_flow: Cell::new(ControlFlow::default()),
+                poll_strategy: Cell::new(PollStrategy::default()),
+                wait_until_strategy: Cell::new(WaitUntilStrategy::default()),
+                exit: Cell::new(false),
+                runner: RefCell::new(RunnerEnum::Pending),
+                suspended: Cell::new(false),
+                event_loop_recreation: Cell::new(false),
+                events: RefCell::new(VecDeque::new()),
+                window,
+                navigator,
+                document,
+                id: Cell::new(0),
+                all_canvases: RefCell::new(Vec::new()),
+                redraw_pending: RefCell::new(HashSet::new()),
+                destroy_pending: RefCell::new(VecDeque::new()),
+                monitor: Rc::new(monitor),
+                safe_area: Rc::new(safe_area),
+                page_transition_event_handle: RefCell::new(None),
+                device_events: Cell::default(),
+                on_mouse_move: RefCell::new(None),
+                on_wheel: RefCell::new(None),
+                on_mouse_press: RefCell::new(None),
+                on_mouse_release: RefCell::new(None),
+                on_key_press: RefCell::new(None),
+                on_key_release: RefCell::new(None),
+                on_visibility_change: RefCell::new(None),
+            }
+        }))
+    }
+
+    pub fn main_thread(&self) -> MainThreadMarker {
+        self.0.main_thread
+    }
+
+    pub fn window(&self) -> &web_sys::Window {
+        &self.0.window
+    }
+
+    pub fn navigator(&self) -> &Navigator {
+        &self.0.navigator
+    }
+
+    pub fn document(&self) -> &Document {
+        &self.0.document
+    }
+
+    pub fn add_canvas(
+        &self,
+        id: WindowId,
+        canvas: Weak<backend::Canvas>,
+        runner: DispatchRunner<Inner>,
+    ) {
+        self.0.all_canvases.borrow_mut().push((id, canvas, runner));
+    }
+
+    pub fn notify_destroy_window(&self, id: WindowId) {
+        self.0.destroy_pending.borrow_mut().push_back(id);
+    }
+
+    pub(crate) fn start(&self, app: Box<dyn ApplicationHandler>, event_loop: ActiveEventLoop) {
+        let mut runner = self.0.runner.borrow_mut();
+        assert!(matches!(*runner, RunnerEnum::Pending));
+        if self.0.monitor.is_initializing() {
+            *runner = RunnerEnum::Initializing(Runner::new(app, event_loop));
+        } else {
+            *runner = RunnerEnum::Running(Runner::new(app, event_loop));
+
+            drop(runner);
+
+            self.init();
+            self.set_listener();
+        }
+    }
+
+    pub(crate) fn start_delayed(&self) {
+        let event_handler = match self.0.runner.replace(RunnerEnum::Pending) {
+            RunnerEnum::Initializing(event_handler) => event_handler,
+            // The event loop wasn't started yet.
+            RunnerEnum::Pending => return,
+            _ => unreachable!("event loop already started before waiting for initialization"),
+        };
+        *self.0.runner.borrow_mut() = RunnerEnum::Running(event_handler);
+
+        self.init();
+        self.set_listener();
+    }
+
+    // Set the event callback to use for the event loop runner
+    // This the event callback is a fairly thin layer over the user-provided callback that closes
+    // over a RootActiveEventLoop reference
+    fn set_listener(&self) {
+        *self.0.page_transition_event_handle.borrow_mut() = Some(backend::on_page_transition(
+            self.window().clone(),
+            {
+                let runner = self.clone();
+                move |event: PageTransitionEvent| {
+                    if event.persisted() {
+                        runner.0.suspended.set(false);
+                        runner.send_event(Event::Resumed);
+                    }
+                }
+            },
+            {
+                let runner = self.clone();
+                move |event: PageTransitionEvent| {
+                    runner.0.suspended.set(true);
+                    if event.persisted() {
+                        runner.send_event(Event::Suspended);
+                    } else {
+                        runner.handle_unload();
+                    }
+                }
+            },
+        ));
+
+        let runner = self.clone();
+        let window = self.window().clone();
+        let navigator = self.navigator().clone();
+        *self.0.on_mouse_move.borrow_mut() = Some(EventListenerHandle::new(
+            self.window().clone(),
+            "pointermove",
+            Closure::new(move |event: PointerEvent| {
+                if !runner.device_events() {
+                    return;
+                }
+
+                // chorded button event
+                let device_id = event::mkdid(event.pointer_id());
+
+                if let Some(button) = backend::event::mouse_button(&event) {
+                    let state = if backend::event::mouse_buttons(&event).contains(button.into()) {
+                        ElementState::Pressed
+                    } else {
+                        ElementState::Released
+                    };
+
+                    runner.send_event(Event::DeviceEvent {
+                        device_id,
+                        event: DeviceEvent::Button {
+                            button: mouse_button_to_id(button).into(),
+                            state,
+                        },
+                    });
+
+                    return;
+                }
+
+                // pointer move event
+                let mut delta = backend::event::MouseDelta::init(&navigator, &event);
+                runner.send_events(backend::event::pointer_move_event(event).map(|event| {
+                    let delta = delta.delta(&event).to_physical(backend::scale_factor(&window));
+
+                    Event::DeviceEvent {
+                        device_id,
+                        event: DeviceEvent::PointerMotion { delta: (delta.x, delta.y) },
+                    }
+                }));
+            }),
+        ));
+        let runner = self.clone();
+        let window = self.window().clone();
+        *self.0.on_wheel.borrow_mut() = Some(EventListenerHandle::new(
+            self.window().clone(),
+            "wheel",
+            Closure::new(move |event: WheelEvent| {
+                if !runner.device_events() {
+                    return;
+                }
+
+                if let Some(delta) = backend::event::mouse_scroll_delta(&window, &event) {
+                    runner.send_event(Event::DeviceEvent {
+                        device_id: None,
+                        event: DeviceEvent::MouseWheel { delta },
+                    });
+                }
+            }),
+        ));
+        let runner = self.clone();
+        *self.0.on_mouse_press.borrow_mut() = Some(EventListenerHandle::new(
+            self.window().clone(),
+            "pointerdown",
+            Closure::new(move |event: PointerEvent| {
+                if !runner.device_events() {
+                    return;
+                }
+
+                let button = backend::event::mouse_button(&event).expect("no mouse button pressed");
+                runner.send_event(Event::DeviceEvent {
+                    device_id: event::mkdid(event.pointer_id()),
+                    event: DeviceEvent::Button {
+                        button: mouse_button_to_id(button).into(),
+                        state: ElementState::Pressed,
+                    },
+                });
+            }),
+        ));
+        let runner = self.clone();
+        *self.0.on_mouse_release.borrow_mut() = Some(EventListenerHandle::new(
+            self.window().clone(),
+            "pointerup",
+            Closure::new(move |event: PointerEvent| {
+                if !runner.device_events() {
+                    return;
+                }
+
+                let button = backend::event::mouse_button(&event).expect("no mouse button pressed");
+                runner.send_event(Event::DeviceEvent {
+                    device_id: event::mkdid(event.pointer_id()),
+                    event: DeviceEvent::Button {
+                        button: mouse_button_to_id(button).into(),
+                        state: ElementState::Released,
+                    },
+                });
+            }),
+        ));
+        let runner = self.clone();
+        *self.0.on_key_press.borrow_mut() = Some(EventListenerHandle::new(
+            self.window().clone(),
+            "keydown",
+            Closure::new(move |event: KeyboardEvent| {
+                if !runner.device_events() {
+                    return;
+                }
+
+                runner.send_event(Event::DeviceEvent {
+                    device_id: None,
+                    event: DeviceEvent::Key(RawKeyEvent {
+                        physical_key: backend::event::key_code(&event),
+                        state: ElementState::Pressed,
+                    }),
+                });
+            }),
+        ));
+        let runner = self.clone();
+        *self.0.on_key_release.borrow_mut() = Some(EventListenerHandle::new(
+            self.window().clone(),
+            "keyup",
+            Closure::new(move |event: KeyboardEvent| {
+                if !runner.device_events() {
+                    return;
+                }
+
+                runner.send_event(Event::DeviceEvent {
+                    device_id: None,
+                    event: DeviceEvent::Key(RawKeyEvent {
+                        physical_key: backend::event::key_code(&event),
+                        state: ElementState::Released,
+                    }),
+                });
+            }),
+        ));
+        let runner = self.clone();
+        *self.0.on_visibility_change.borrow_mut() = Some(EventListenerHandle::new(
+            // Safari <14 doesn't support the `visibilitychange` event on `Window`.
+            self.document().clone(),
+            "visibilitychange",
+            Closure::new(move |_| {
+                if !runner.0.suspended.get() {
+                    for (id, canvas, _) in &*runner.0.all_canvases.borrow() {
+                        if let Some(canvas) = canvas.upgrade() {
+                            let is_visible = backend::is_visible(runner.document());
+                            // only fire if:
+                            // - not visible and intersects
+                            // - not visible and we don't know if it intersects yet
+                            // - visible and intersects
+                            if let (false, Some(true) | None) | (true, Some(true)) =
+                                (is_visible, canvas.is_intersecting.get())
+                            {
+                                runner.send_event(Event::WindowEvent {
+                                    window_id: *id,
+                                    event: WindowEvent::Occluded(!is_visible),
+                                });
+                            }
+                        }
+                    }
+                }
+            }),
+        ));
+    }
+
+    // Generate a strictly increasing ID
+    // This is used to differentiate windows when handling events
+    pub fn generate_id(&self) -> usize {
+        let id = self.0.id.get();
+        self.0.id.set(id.checked_add(1).expect("exhausted `WindowId`"));
+
+        id
+    }
+
+    pub fn request_redraw(&self, id: WindowId) {
+        self.0.redraw_pending.borrow_mut().insert(id);
+        self.send_events([]);
+    }
+
+    fn init(&self) {
+        // NB: For consistency all platforms must call `can_create_surfaces` even though Web
+        // applications don't themselves have a formal surface destroy/create lifecycle.
+        self.run_until_cleared(
+            [Event::NewEvents(StartCause::Init), Event::CreateSurfaces].into_iter(),
+        );
+    }
+
+    // Run the polling logic for the Poll ControlFlow, which involves clearing the queue
+    pub fn poll(&self) {
+        let start_cause = Event::NewEvents(StartCause::Poll);
+        self.run_until_cleared(iter::once(start_cause));
+    }
+
+    // Run the logic for waking from a WaitUntil, which involves clearing the queue
+    // Generally there shouldn't be events built up when this is called
+    pub fn resume_time_reached(&self, start: Instant, requested_resume: Instant) {
+        let start_cause =
+            Event::NewEvents(StartCause::ResumeTimeReached { start, requested_resume });
+        self.run_until_cleared(iter::once(start_cause));
+    }
+
+    // Add an event to the event loop runner, from the user or an event handler
+    //
+    // It will determine if the event should be immediately sent to the user or buffered for later
+    pub(crate) fn send_event(&self, event: Event) {
+        self.send_events(iter::once(event));
+    }
+
+    // Add a user event to the event loop runner.
+    //
+    // This will schedule the event loop to wake up instead of waking it up immediately if its not
+    // running.
+    pub(crate) fn send_proxy_wake_up(&self, local: bool) {
+        // If the event loop is closed, it should discard any new events
+        if self.is_closed() {
+            return;
+        }
+
+        if local {
+            // If the loop is not running and triggered locally, queue on next microtick.
+            if let Ok(RunnerEnum::Running(_)) =
+                self.0.runner.try_borrow().as_ref().map(Deref::deref)
+            {
+                self.window().queue_microtask(
+                    &Closure::once_into_js({
+                        let this = Rc::downgrade(&self.0);
+                        move || {
+                            if let Some(shared) = this.upgrade() {
+                                Shared(shared).send_event(Event::UserWakeUp)
+                            }
+                        }
+                    })
+                    .unchecked_into(),
+                );
+
+                return;
+            }
+        }
+
+        self.send_event(Event::UserWakeUp);
+    }
+
+    // Add a series of events to the event loop runner
+    //
+    // It will determine if the event should be immediately sent to the user or buffered for later
+    pub(crate) fn send_events(&self, events: impl IntoIterator<Item = Event>) {
+        // If the event loop is closed, it should discard any new events
+        if self.is_closed() {
+            return;
+        }
+        // If we can run the event processing right now, or need to queue this and wait for later
+        let mut process_immediately = true;
+        match self.0.runner.try_borrow().as_ref().map(Deref::deref) {
+            // If the runner is attached but not running, we always wake it up.
+            Ok(RunnerEnum::Running(_)) => (),
+            // The runner still hasn't been attached: queue this event and wait for it to be
+            Ok(RunnerEnum::Pending | RunnerEnum::Initializing(_)) => {
+                process_immediately = false;
+            },
+            // Some other code is mutating the runner, which most likely means
+            // the event loop is running and busy. So we queue this event for
+            // it to be processed later.
+            Err(_) => {
+                process_immediately = false;
+            },
+            // This is unreachable since `self.is_closed() == true`.
+            Ok(RunnerEnum::Destroyed) => unreachable!(),
+        }
+        if !process_immediately {
+            // Queue these events to look at later
+            self.0.events.borrow_mut().extend(events);
+            return;
+        }
+        // At this point, we know this is a fresh set of events
+        // Now we determine why new events are incoming, and handle the events
+        let start_cause = match (self.0.runner.borrow().maybe_runner())
+            .unwrap_or_else(|| {
+                unreachable!("The runner cannot process events when it is not attached")
+            })
+            .maybe_start_cause()
+        {
+            Some(c) => c,
+            // If we're in the exit state, don't do event processing
+            None => return,
+        };
+        // Take the start event, then the events provided to this function, and run an iteration of
+        // the event loop
+        let start_event = Event::NewEvents(start_cause);
+        let events = iter::once(start_event).chain(events);
+        self.run_until_cleared(events);
+    }
+
+    // Process the destroy-pending windows. This should only be called from
+    // `run_until_cleared`, somewhere between emitting `NewEvents` and `AboutToWait`.
+    fn process_destroy_pending_windows(&self) {
+        while let Some(id) = self.0.destroy_pending.borrow_mut().pop_front() {
+            self.0.all_canvases.borrow_mut().retain(|&(item_id, ..)| item_id != id);
+            self.handle_event(Event::WindowEvent {
+                window_id: id,
+                event: winit_core::event::WindowEvent::Destroyed,
+            });
+            self.0.redraw_pending.borrow_mut().remove(&id);
+        }
+    }
+
+    // Given the set of new events, run the event loop until the main events and redraw events are
+    // cleared
+    //
+    // This will also process any events that have been queued or that are queued during processing
+    fn run_until_cleared(&self, events: impl Iterator<Item = Event>) {
+        for event in events {
+            self.handle_event(event);
+        }
+        self.process_destroy_pending_windows();
+
+        // Collect all of the redraw events to avoid double-locking the RefCell
+        let redraw_events: Vec<WindowId> = self.0.redraw_pending.borrow_mut().drain().collect();
+        for window_id in redraw_events {
+            self.handle_event(Event::WindowEvent {
+                window_id,
+                event: WindowEvent::RedrawRequested,
+            });
+        }
+
+        self.handle_event(Event::AboutToWait);
+
+        self.apply_control_flow();
+        // If the event loop is closed, it has been closed this iteration and now the closing
+        // event should be emitted
+        if self.is_closed() {
+            self.handle_loop_destroyed();
+        }
+    }
+
+    fn handle_unload(&self) {
+        self.exit();
+        self.apply_control_flow();
+        // We don't call `handle_loop_destroyed` here because we don't need to
+        // perform cleanup when the Web browser is going to destroy the page.
+        //
+        // We do want to run the application handler's `Drop` impl.
+        *self.0.runner.borrow_mut() = RunnerEnum::Destroyed;
+    }
+
+    // handle_event takes in events and either queues them or applies a callback
+    //
+    // It should only ever be called from `run_until_cleared`.
+    fn handle_event(&self, event: Event) {
+        if self.is_closed() {
+            self.exit();
+        }
+        match *self.0.runner.borrow_mut() {
+            RunnerEnum::Running(ref mut runner) => {
+                runner.handle_single_event(self, event);
+            },
+            // If an event is being handled without a runner somehow, add it to the event queue so
+            // it will eventually be processed
+            RunnerEnum::Pending => self.0.events.borrow_mut().push_back(event),
+            // If the Runner has been destroyed, there is nothing to do.
+            RunnerEnum::Destroyed => return,
+            // This function should never be called if we are still waiting for something.
+            RunnerEnum::Initializing(_) => unreachable!(),
+        }
+
+        let is_closed = self.exiting();
+
+        // Don't take events out of the queue if the loop is closed or the runner doesn't exist
+        // If the runner doesn't exist and this method recurses, it will recurse infinitely
+        if !is_closed && self.0.runner.borrow().maybe_runner().is_some() {
+            // Pre-fetch window commands to avoid having to wait until the next event loop cycle
+            // and potentially block other threads in the meantime.
+            for (_, window, runner) in self.0.all_canvases.borrow().iter() {
+                if let Some(window) = window.upgrade() {
+                    runner.run(self.main_thread());
+                    drop(window)
+                }
+            }
+
+            // Take an event out of the queue and handle it
+            // Make sure not to let the borrow_mut live during the next handle_event
+            let event = {
+                let mut events = self.0.events.borrow_mut();
+
+                // Pre-fetch `UserEvent`s to avoid having to wait until the next event loop cycle.
+                events.extend(self.0.event_loop_proxy.take().then_some(Event::UserWakeUp));
+
+                events.pop_front()
+            };
+            if let Some(event) = event {
+                self.handle_event(event);
+            }
+        }
+    }
+
+    // Apply the new ControlFlow that has been selected by the user
+    // Start any necessary timeouts etc
+    fn apply_control_flow(&self) {
+        let new_state = if self.exiting() {
+            State::Exit
+        } else {
+            match self.control_flow() {
+                ControlFlow::Poll => {
+                    let cloned = self.clone();
+                    State::Poll {
+                        _request: backend::Schedule::new(
+                            self.poll_strategy(),
+                            self.window(),
+                            move || cloned.poll(),
+                        ),
+                    }
+                },
+                ControlFlow::Wait => State::Wait { start: Instant::now() },
+                ControlFlow::WaitUntil(end) => {
+                    let start = Instant::now();
+
+                    let delay = if end <= start { Duration::from_millis(0) } else { end - start };
+
+                    let cloned = self.clone();
+
+                    State::WaitUntil {
+                        start,
+                        end,
+                        _timeout: backend::Schedule::new_with_duration(
+                            self.wait_until_strategy(),
+                            self.window(),
+                            move || cloned.resume_time_reached(start, end),
+                            delay,
+                        ),
+                    }
+                },
+            }
+        };
+
+        if let RunnerEnum::Running(ref mut runner) = *self.0.runner.borrow_mut() {
+            runner.state = new_state;
+        }
+    }
+
+    fn handle_loop_destroyed(&self) {
+        let all_canvases = std::mem::take(&mut *self.0.all_canvases.borrow_mut());
+        *self.0.page_transition_event_handle.borrow_mut() = None;
+        *self.0.on_mouse_move.borrow_mut() = None;
+        *self.0.on_wheel.borrow_mut() = None;
+        *self.0.on_mouse_press.borrow_mut() = None;
+        *self.0.on_mouse_release.borrow_mut() = None;
+        *self.0.on_key_press.borrow_mut() = None;
+        *self.0.on_key_release.borrow_mut() = None;
+        *self.0.on_visibility_change.borrow_mut() = None;
+        // Dropping the `Runner` drops the event handler closure, which will in
+        // turn drop all `Window`s moved into the closure.
+        *self.0.runner.borrow_mut() = RunnerEnum::Destroyed;
+        for (_, canvas, _) in all_canvases {
+            // In case any remaining `Window`s are still not dropped, we will need
+            // to explicitly remove the event handlers associated with their canvases.
+            if let Some(canvas) = canvas.upgrade() {
+                canvas.remove_listeners();
+            }
+        }
+        // At this point, the `self.0` `Rc` should only be strongly referenced
+        // by the following:
+        // * `self`, i.e. the item which triggered this event loop wakeup, which is usually a
+        //   `wasm-bindgen` `Closure`, which will be dropped after returning to the JS glue code.
+        // * The `ActiveEventLoop` leaked inside `EventLoop::run_app` due to the JS exception thrown
+        //   at the end.
+        // * For each undropped `Window`:
+        //     * The `register_redraw_request` closure.
+        //     * The `destroy_fn` closure.
+        if self.0.event_loop_recreation.get() {
+            EventLoop::allow_event_loop_recreation();
+        }
+    }
+
+    // Check if the event loop is currently closed
+    fn is_closed(&self) -> bool {
+        match self.0.runner.try_borrow().as_ref().map(Deref::deref) {
+            Ok(RunnerEnum::Running(runner)) => runner.state.exiting(),
+            // The event loop is not closed since it is not initialized.
+            Ok(RunnerEnum::Pending) => false,
+            // The event loop is closed since it has been destroyed.
+            Ok(RunnerEnum::Destroyed) => true,
+            // The event loop is not closed since its still waiting to be started.
+            Ok(RunnerEnum::Initializing(_)) => false,
+            // Some other code is mutating the runner, which most likely means
+            // the event loop is running and busy.
+            Err(_) => false,
+        }
+    }
+
+    pub fn listen_device_events(&self, allowed: DeviceEvents) {
+        self.0.device_events.set(allowed)
+    }
+
+    fn device_events(&self) -> bool {
+        match self.0.device_events.get() {
+            DeviceEvents::Always => true,
+            DeviceEvents::WhenFocused => {
+                self.0.all_canvases.borrow().iter().any(|(_, canvas, _)| {
+                    if let Some(canvas) = canvas.upgrade() {
+                        canvas.has_focus.get()
+                    } else {
+                        false
+                    }
+                })
+            },
+            DeviceEvents::Never => false,
+        }
+    }
+
+    pub fn event_loop_recreation(&self, allow: bool) {
+        self.0.event_loop_recreation.set(allow)
+    }
+
+    pub(crate) fn control_flow(&self) -> ControlFlow {
+        self.0.control_flow.get()
+    }
+
+    pub(crate) fn set_control_flow(&self, control_flow: ControlFlow) {
+        self.0.control_flow.set(control_flow)
+    }
+
+    pub(crate) fn exit(&self) {
+        self.0.exit.set(true)
+    }
+
+    pub(crate) fn exiting(&self) -> bool {
+        self.0.exit.get()
+    }
+
+    pub(crate) fn set_poll_strategy(&self, strategy: PollStrategy) {
+        self.0.poll_strategy.set(strategy)
+    }
+
+    pub(crate) fn poll_strategy(&self) -> PollStrategy {
+        self.0.poll_strategy.get()
+    }
+
+    pub(crate) fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.0.wait_until_strategy.set(strategy)
+    }
+
+    pub(crate) fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.0.wait_until_strategy.get()
+    }
+
+    pub(crate) fn event_loop_proxy(&self) -> &Arc<EventLoopProxy> {
+        &self.0.event_loop_proxy
+    }
+
+    pub(crate) fn weak(&self) -> WeakShared {
+        WeakShared(Rc::downgrade(&self.0))
+    }
+
+    pub(crate) fn monitor(&self) -> &Rc<MonitorHandler> {
+        &self.0.monitor
+    }
+
+    pub(crate) fn safe_area(&self) -> &Rc<SafeAreaHandle> {
+        &self.0.safe_area
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct WeakShared(Weak<Execution>);
+
+impl WeakShared {
+    pub fn upgrade(&self) -> Option<Shared> {
+        self.0.upgrade().map(Shared)
+    }
+}
+
+#[allow(clippy::enum_variant_names)]
+pub(crate) enum Event {
+    NewEvents(StartCause),
+    WindowEvent { window_id: WindowId, event: WindowEvent },
+    ScaleChange { canvas: Weak<backend::Canvas>, size: PhysicalSize<u32>, scale: f64 },
+    DeviceEvent { device_id: Option<DeviceId>, event: DeviceEvent },
+    Suspended,
+    CreateSurfaces,
+    Resumed,
+    AboutToWait,
+    UserWakeUp,
+}

winit-web/src/event_loop/state.rs

@@ -0,0 +1,18 @@
+use web_time::Instant;
+
+use super::backend;
+
+#[derive(Debug)]
+pub enum State {
+    Init,
+    WaitUntil { _timeout: backend::Schedule, start: Instant, end: Instant },
+    Wait { start: Instant },
+    Poll { _request: backend::Schedule },
+    Exit,
+}
+
+impl State {
+    pub fn exiting(&self) -> bool {
+        matches!(self, State::Exit)
+    }
+}

winit-web/src/event_loop/window_target.rs

@@ -0,0 +1,574 @@
+use std::cell::Cell;
+use std::clone::Clone;
+use std::iter;
+use std::rc::Rc;
+use std::sync::Arc;
+
+use web_sys::Element;
+use winit_core::application::ApplicationHandler;
+use winit_core::cursor::{CustomCursor as CoreCustomCursor, CustomCursorSource};
+use winit_core::error::{NotSupportedError, RequestError};
+use winit_core::event::{ElementState, KeyEvent, TouchPhase, WindowEvent};
+use winit_core::event_loop::{
+    ActiveEventLoop as RootActiveEventLoop, ControlFlow, DeviceEvents,
+    EventLoopProxy as RootEventLoopProxy, OwnedDisplayHandle as CoreOwnedDisplayHandle,
+};
+use winit_core::keyboard::ModifiersState;
+use winit_core::monitor::MonitorHandle as CoremMonitorHandle;
+use winit_core::window::{Theme, WindowId};
+
+use super::super::lock;
+use super::super::monitor::MonitorPermissionFuture;
+use super::runner::Event;
+use super::{backend, runner};
+use crate::cursor::CustomCursor;
+use crate::event_loop::proxy::EventLoopProxy;
+use crate::window::Window;
+use crate::{CustomCursorFuture, PollStrategy, WaitUntilStrategy};
+
+#[derive(Default, Debug)]
+struct ModifiersShared(Rc<Cell<ModifiersState>>);
+
+impl ModifiersShared {
+    fn set(&self, new: ModifiersState) {
+        self.0.set(new)
+    }
+
+    fn get(&self) -> ModifiersState {
+        self.0.get()
+    }
+}
+
+impl Clone for ModifiersShared {
+    fn clone(&self) -> Self {
+        Self(Rc::clone(&self.0))
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct ActiveEventLoop {
+    pub(crate) runner: runner::Shared,
+    modifiers: ModifiersShared,
+}
+
+impl ActiveEventLoop {
+    pub fn new() -> Self {
+        Self { runner: runner::Shared::new(), modifiers: ModifiersShared::default() }
+    }
+
+    pub(crate) fn run(&self, app: Box<dyn ApplicationHandler>, event_loop_recreation: bool) {
+        self.runner.event_loop_recreation(event_loop_recreation);
+        self.runner.start(app, self.clone());
+    }
+
+    pub fn generate_id(&self) -> WindowId {
+        WindowId::from_raw(self.runner.generate_id())
+    }
+
+    pub fn create_custom_cursor_async(&self, source: CustomCursorSource) -> CustomCursorFuture {
+        CustomCursorFuture(CustomCursor::new_async(self, source))
+    }
+
+    pub fn register(&self, canvas: &Rc<backend::Canvas>, window_id: WindowId) {
+        let canvas_clone = canvas.clone();
+
+        canvas.on_touch_start();
+
+        let runner = self.runner.clone();
+        let has_focus = canvas.has_focus.clone();
+        let modifiers = self.modifiers.clone();
+        canvas.on_blur(move || {
+            has_focus.set(false);
+
+            let clear_modifiers = (!modifiers.get().is_empty()).then(|| {
+                modifiers.set(ModifiersState::empty());
+                Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::ModifiersChanged(ModifiersState::empty().into()),
+                }
+            });
+
+            runner.send_events(clear_modifiers.into_iter().chain(iter::once(Event::WindowEvent {
+                window_id,
+                event: WindowEvent::Focused(false),
+            })));
+        });
+
+        let runner = self.runner.clone();
+        let has_focus = canvas.has_focus.clone();
+        canvas.on_focus(move || {
+            if !has_focus.replace(true) {
+                runner.send_event(Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::Focused(true),
+                });
+            }
+        });
+
+        // It is possible that at this point the canvas has
+        // been focused before the callback can be called.
+        let focused = canvas
+            .document()
+            .active_element()
+            .filter(|element| {
+                let canvas: &Element = canvas.raw();
+                element == canvas
+            })
+            .is_some();
+
+        if focused {
+            canvas.has_focus.set(true);
+            self.runner
+                .send_event(Event::WindowEvent { window_id, event: WindowEvent::Focused(true) })
+        }
+
+        let runner = self.runner.clone();
+        let modifiers = self.modifiers.clone();
+        canvas.on_keyboard_press(
+            move |physical_key, logical_key, text, location, repeat, active_modifiers| {
+                let modifiers_changed = (modifiers.get() != active_modifiers).then(|| {
+                    modifiers.set(active_modifiers);
+                    Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::ModifiersChanged(active_modifiers.into()),
+                    }
+                });
+
+                runner.send_events(
+                    iter::once(Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::KeyboardInput {
+                            device_id: None,
+                            event: KeyEvent {
+                                physical_key,
+                                logical_key: logical_key.clone(),
+                                text: text.clone(),
+                                location,
+                                state: ElementState::Pressed,
+                                repeat,
+                                text_with_all_modifiers: text,
+                                key_without_modifiers: logical_key,
+                            },
+                            is_synthetic: false,
+                        },
+                    })
+                    .chain(modifiers_changed),
+                );
+            },
+        );
+
+        let runner = self.runner.clone();
+        let modifiers = self.modifiers.clone();
+        canvas.on_keyboard_release(
+            move |physical_key, logical_key, text, location, repeat, active_modifiers| {
+                let modifiers_changed = (modifiers.get() != active_modifiers).then(|| {
+                    modifiers.set(active_modifiers);
+                    Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::ModifiersChanged(active_modifiers.into()),
+                    }
+                });
+
+                runner.send_events(
+                    iter::once(Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::KeyboardInput {
+                            device_id: None,
+                            event: KeyEvent {
+                                physical_key,
+                                logical_key: logical_key.clone(),
+                                text: text.clone(),
+                                location,
+                                state: ElementState::Released,
+                                repeat,
+                                text_with_all_modifiers: text,
+                                key_without_modifiers: logical_key,
+                            },
+                            is_synthetic: false,
+                        },
+                    })
+                    .chain(modifiers_changed),
+                )
+            },
+        );
+
+        let has_focus = canvas.has_focus.clone();
+        canvas.on_pointer_leave({
+            let runner = self.runner.clone();
+            let has_focus = has_focus.clone();
+            let modifiers = self.modifiers.clone();
+
+            move |active_modifiers, device_id, primary, position, kind| {
+                let focus = (has_focus.get() && modifiers.get() != active_modifiers).then(|| {
+                    modifiers.set(active_modifiers);
+                    Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::ModifiersChanged(active_modifiers.into()),
+                    }
+                });
+
+                runner.send_events(focus.into_iter().chain(iter::once(Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::PointerLeft {
+                        device_id,
+                        primary,
+                        position: Some(position),
+                        kind,
+                    },
+                })))
+            }
+        });
+
+        canvas.on_pointer_enter({
+            let runner = self.runner.clone();
+            let has_focus = has_focus.clone();
+            let modifiers = self.modifiers.clone();
+
+            move |active_modifiers, device_id, primary, position, kind| {
+                let focus = (has_focus.get() && modifiers.get() != active_modifiers).then(|| {
+                    modifiers.set(active_modifiers);
+                    Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::ModifiersChanged(active_modifiers.into()),
+                    }
+                });
+
+                runner.send_events(focus.into_iter().chain(iter::once(Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::PointerEntered { device_id, primary, position, kind },
+                })))
+            }
+        });
+
+        canvas.on_pointer_move(
+            {
+                let runner = self.runner.clone();
+                let has_focus = has_focus.clone();
+                let modifiers = self.modifiers.clone();
+
+                move |device_id, events| {
+                    runner.send_events(events.flat_map(
+                        |(active_modifiers, primary, position, source)| {
+                            let modifiers = (has_focus.get()
+                                && modifiers.get() != active_modifiers)
+                                .then(|| {
+                                    modifiers.set(active_modifiers);
+                                    Event::WindowEvent {
+                                        window_id,
+                                        event: WindowEvent::ModifiersChanged(
+                                            active_modifiers.into(),
+                                        ),
+                                    }
+                                });
+
+                            modifiers.into_iter().chain(iter::once(Event::WindowEvent {
+                                window_id,
+                                event: WindowEvent::PointerMoved {
+                                    device_id,
+                                    primary,
+                                    position,
+                                    source,
+                                },
+                            }))
+                        },
+                    ));
+                }
+            },
+            {
+                let runner = self.runner.clone();
+                let has_focus = has_focus.clone();
+                let modifiers = self.modifiers.clone();
+
+                move |active_modifiers, device_id, primary, position, state, button| {
+                    let modifiers =
+                        (has_focus.get() && modifiers.get() != active_modifiers).then(|| {
+                            modifiers.set(active_modifiers);
+                            Event::WindowEvent {
+                                window_id,
+                                event: WindowEvent::ModifiersChanged(active_modifiers.into()),
+                            }
+                        });
+
+                    runner.send_events(modifiers.into_iter().chain([Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::PointerButton {
+                            device_id,
+                            primary,
+                            state,
+                            position,
+                            button,
+                        },
+                    }]));
+                }
+            },
+        );
+
+        canvas.on_pointer_press({
+            let runner = self.runner.clone();
+            let modifiers = self.modifiers.clone();
+
+            move |active_modifiers, device_id, primary, position, button| {
+                let modifiers = (modifiers.get() != active_modifiers).then(|| {
+                    modifiers.set(active_modifiers);
+                    Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::ModifiersChanged(active_modifiers.into()),
+                    }
+                });
+
+                runner.send_events(modifiers.into_iter().chain(iter::once(Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::PointerButton {
+                        device_id,
+                        primary,
+                        state: ElementState::Pressed,
+                        position,
+                        button,
+                    },
+                })));
+            }
+        });
+
+        canvas.on_pointer_release({
+            let runner = self.runner.clone();
+            let has_focus = has_focus.clone();
+            let modifiers = self.modifiers.clone();
+
+            move |active_modifiers, device_id, primary, position, button| {
+                let modifiers =
+                    (has_focus.get() && modifiers.get() != active_modifiers).then(|| {
+                        modifiers.set(active_modifiers);
+                        Event::WindowEvent {
+                            window_id,
+                            event: WindowEvent::ModifiersChanged(active_modifiers.into()),
+                        }
+                    });
+
+                runner.send_events(modifiers.into_iter().chain(iter::once(Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::PointerButton {
+                        device_id,
+                        primary,
+                        state: ElementState::Released,
+                        position,
+                        button,
+                    },
+                })));
+            }
+        });
+
+        let runner = self.runner.clone();
+        let modifiers = self.modifiers.clone();
+        canvas.on_mouse_wheel(move |delta, active_modifiers| {
+            let modifiers_changed =
+                (has_focus.get() && modifiers.get() != active_modifiers).then(|| {
+                    modifiers.set(active_modifiers);
+                    Event::WindowEvent {
+                        window_id,
+                        event: WindowEvent::ModifiersChanged(active_modifiers.into()),
+                    }
+                });
+
+            runner.send_events(modifiers_changed.into_iter().chain(iter::once(
+                Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::MouseWheel {
+                        device_id: None,
+                        delta,
+                        phase: TouchPhase::Moved,
+                    },
+                },
+            )));
+        });
+
+        let runner = self.runner.clone();
+        canvas.on_dark_mode(move |is_dark_mode| {
+            let theme = if is_dark_mode { Theme::Dark } else { Theme::Light };
+            runner.send_event(Event::WindowEvent {
+                window_id,
+                event: WindowEvent::ThemeChanged(theme),
+            });
+        });
+
+        canvas.on_resize_scale(
+            {
+                let runner = self.runner.clone();
+                let canvas = canvas_clone.clone();
+
+                move |size, scale| {
+                    runner.send_event(Event::ScaleChange {
+                        canvas: Rc::downgrade(&canvas),
+                        size,
+                        scale,
+                    })
+                }
+            },
+            {
+                let runner = self.runner.clone();
+                let canvas = canvas_clone.clone();
+
+                move |new_size| {
+                    canvas.set_current_size(new_size);
+                    if canvas.old_size() != new_size {
+                        canvas.set_old_size(new_size);
+                        runner.send_event(Event::WindowEvent {
+                            window_id,
+                            event: WindowEvent::SurfaceResized(new_size),
+                        });
+                        canvas.request_animation_frame();
+                    }
+                }
+            },
+        );
+
+        let runner = self.runner.clone();
+        canvas.on_intersection(move |is_intersecting| {
+            // only fire if visible while skipping the first event if it's intersecting
+            if backend::is_visible(runner.document())
+                && !(is_intersecting && canvas_clone.is_intersecting.get().is_none())
+            {
+                runner.send_event(Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::Occluded(!is_intersecting),
+                });
+            }
+
+            canvas_clone.is_intersecting.set(Some(is_intersecting));
+        });
+
+        let runner = self.runner.clone();
+        canvas.on_animation_frame(move || runner.request_redraw(window_id));
+
+        canvas.on_context_menu();
+    }
+
+    pub(crate) fn set_poll_strategy(&self, strategy: PollStrategy) {
+        self.runner.set_poll_strategy(strategy)
+    }
+
+    pub(crate) fn poll_strategy(&self) -> PollStrategy {
+        self.runner.poll_strategy()
+    }
+
+    pub(crate) fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.runner.set_wait_until_strategy(strategy)
+    }
+
+    pub(crate) fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.runner.wait_until_strategy()
+    }
+
+    pub(crate) fn is_cursor_lock_raw(&self) -> bool {
+        lock::is_cursor_lock_raw(self.runner.navigator(), self.runner.document())
+    }
+
+    pub(crate) fn has_multiple_screens(&self) -> Result<bool, NotSupportedError> {
+        self.runner
+            .monitor()
+            .is_extended()
+            .ok_or(NotSupportedError::new("has_multiple_screens is not supported"))
+    }
+
+    pub(crate) fn request_detailed_monitor_permission(&self) -> MonitorPermissionFuture {
+        self.runner.monitor().request_detailed_monitor_permission()
+    }
+
+    pub(crate) fn has_detailed_monitor_permission(&self) -> bool {
+        self.runner.monitor().has_detailed_monitor_permission()
+    }
+
+    pub(crate) fn event_loop_proxy(&self) -> Arc<EventLoopProxy> {
+        self.runner.event_loop_proxy().clone()
+    }
+}
+
+impl RootActiveEventLoop for ActiveEventLoop {
+    fn create_proxy(&self) -> RootEventLoopProxy {
+        let event_loop_proxy = self.event_loop_proxy();
+        RootEventLoopProxy::new(event_loop_proxy)
+    }
+
+    fn create_window(
+        &self,
+        window_attributes: winit_core::window::WindowAttributes,
+    ) -> Result<Box<dyn winit_core::window::Window>, RequestError> {
+        let window = Window::new(self, window_attributes)?;
+        Ok(Box::new(window))
+    }
+
+    fn create_custom_cursor(
+        &self,
+        source: CustomCursorSource,
+    ) -> Result<CoreCustomCursor, RequestError> {
+        Ok(CoreCustomCursor(Arc::new(CustomCursor::new(self, source))))
+    }
+
+    fn available_monitors(&self) -> Box<dyn Iterator<Item = CoremMonitorHandle>> {
+        Box::new(
+            self.runner
+                .monitor()
+                .available_monitors()
+                .into_iter()
+                .map(|monitor| CoremMonitorHandle(Arc::new(monitor))),
+        )
+    }
+
+    fn primary_monitor(&self) -> Option<CoremMonitorHandle> {
+        self.runner.monitor().primary_monitor().map(|monitor| CoremMonitorHandle(Arc::new(monitor)))
+    }
+
+    fn listen_device_events(&self, allowed: DeviceEvents) {
+        self.runner.listen_device_events(allowed)
+    }
+
+    fn system_theme(&self) -> Option<Theme> {
+        backend::is_dark_mode(self.runner.window()).map(|is_dark_mode| {
+            if is_dark_mode {
+                Theme::Dark
+            } else {
+                Theme::Light
+            }
+        })
+    }
+
+    fn set_control_flow(&self, control_flow: ControlFlow) {
+        self.runner.set_control_flow(control_flow)
+    }
+
+    fn control_flow(&self) -> ControlFlow {
+        self.runner.control_flow()
+    }
+
+    fn exit(&self) {
+        self.runner.exit()
+    }
+
+    fn exiting(&self) -> bool {
+        self.runner.exiting()
+    }
+
+    fn owned_display_handle(&self) -> CoreOwnedDisplayHandle {
+        CoreOwnedDisplayHandle::new(Arc::new(OwnedDisplayHandle))
+    }
+
+    fn rwh_06_handle(&self) -> &dyn rwh_06::HasDisplayHandle {
+        self
+    }
+}
+
+impl rwh_06::HasDisplayHandle for ActiveEventLoop {
+    fn display_handle(&self) -> Result<rwh_06::DisplayHandle<'_>, rwh_06::HandleError> {
+        let raw = rwh_06::RawDisplayHandle::Web(rwh_06::WebDisplayHandle::new());
+        unsafe { Ok(rwh_06::DisplayHandle::borrow_raw(raw)) }
+    }
+}
+
+#[derive(Clone)]
+pub(crate) struct OwnedDisplayHandle;
+
+impl rwh_06::HasDisplayHandle for OwnedDisplayHandle {
+    fn display_handle(&self) -> Result<rwh_06::DisplayHandle<'_>, rwh_06::HandleError> {
+        let raw = rwh_06::RawDisplayHandle::Web(rwh_06::WebDisplayHandle::new());
+        unsafe { Ok(rwh_06::DisplayHandle::borrow_raw(raw)) }
+    }
+}

winit-web/src/keyboard.rs

@@ -0,0 +1,530 @@
+use smol_str::SmolStr;
+use winit_core::keyboard::{Key, KeyCode, NamedKey, NativeKey, NativeKeyCode, PhysicalKey};
+
+pub trait FromAttributeValue {
+    fn from_attribute_value(kav: &str) -> Self
+    where
+        Self: Sized;
+}
+
+impl FromAttributeValue for Key {
+    fn from_attribute_value(kav: &str) -> Self {
+        Key::Named(match kav {
+            "Unidentified" => return Key::Unidentified(NativeKey::Web(SmolStr::new(kav))),
+            "Dead" => return Key::Dead(None),
+            "Alt" => NamedKey::Alt,
+            "AltGraph" => NamedKey::AltGraph,
+            "CapsLock" => NamedKey::CapsLock,
+            "Control" => NamedKey::Control,
+            "Fn" => NamedKey::Fn,
+            "FnLock" => NamedKey::FnLock,
+            "NumLock" => NamedKey::NumLock,
+            "ScrollLock" => NamedKey::ScrollLock,
+            "Shift" => NamedKey::Shift,
+            "Symbol" => NamedKey::Symbol,
+            "SymbolLock" => NamedKey::SymbolLock,
+            #[allow(deprecated)]
+            "Super" => NamedKey::Super,
+            #[allow(deprecated)]
+            "Hyper" => NamedKey::Hyper,
+            "Meta" => NamedKey::Meta,
+            "Enter" => NamedKey::Enter,
+            "Tab" => NamedKey::Tab,
+            "ArrowDown" => NamedKey::ArrowDown,
+            "ArrowLeft" => NamedKey::ArrowLeft,
+            "ArrowRight" => NamedKey::ArrowRight,
+            "ArrowUp" => NamedKey::ArrowUp,
+            "End" => NamedKey::End,
+            "Home" => NamedKey::Home,
+            "PageDown" => NamedKey::PageDown,
+            "PageUp" => NamedKey::PageUp,
+            "Backspace" => NamedKey::Backspace,
+            "Clear" => NamedKey::Clear,
+            "Copy" => NamedKey::Copy,
+            "CrSel" => NamedKey::CrSel,
+            "Cut" => NamedKey::Cut,
+            "Delete" => NamedKey::Delete,
+            "EraseEof" => NamedKey::EraseEof,
+            "ExSel" => NamedKey::ExSel,
+            "Insert" => NamedKey::Insert,
+            "Paste" => NamedKey::Paste,
+            "Redo" => NamedKey::Redo,
+            "Undo" => NamedKey::Undo,
+            "Accept" => NamedKey::Accept,
+            "Again" => NamedKey::Again,
+            "Attn" => NamedKey::Attn,
+            "Cancel" => NamedKey::Cancel,
+            "ContextMenu" => NamedKey::ContextMenu,
+            "Escape" => NamedKey::Escape,
+            "Execute" => NamedKey::Execute,
+            "Find" => NamedKey::Find,
+            "Help" => NamedKey::Help,
+            "Pause" => NamedKey::Pause,
+            "Play" => NamedKey::Play,
+            "Props" => NamedKey::Props,
+            "Select" => NamedKey::Select,
+            "ZoomIn" => NamedKey::ZoomIn,
+            "ZoomOut" => NamedKey::ZoomOut,
+            "BrightnessDown" => NamedKey::BrightnessDown,
+            "BrightnessUp" => NamedKey::BrightnessUp,
+            "Eject" => NamedKey::Eject,
+            "LogOff" => NamedKey::LogOff,
+            "Power" => NamedKey::Power,
+            "PowerOff" => NamedKey::PowerOff,
+            "PrintScreen" => NamedKey::PrintScreen,
+            "Hibernate" => NamedKey::Hibernate,
+            "Standby" => NamedKey::Standby,
+            "WakeUp" => NamedKey::WakeUp,
+            "AllCandidates" => NamedKey::AllCandidates,
+            "Alphanumeric" => NamedKey::Alphanumeric,
+            "CodeInput" => NamedKey::CodeInput,
+            "Compose" => NamedKey::Compose,
+            "Convert" => NamedKey::Convert,
+            "FinalMode" => NamedKey::FinalMode,
+            "GroupFirst" => NamedKey::GroupFirst,
+            "GroupLast" => NamedKey::GroupLast,
+            "GroupNext" => NamedKey::GroupNext,
+            "GroupPrevious" => NamedKey::GroupPrevious,
+            "ModeChange" => NamedKey::ModeChange,
+            "NextCandidate" => NamedKey::NextCandidate,
+            "NonConvert" => NamedKey::NonConvert,
+            "PreviousCandidate" => NamedKey::PreviousCandidate,
+            "Process" => NamedKey::Process,
+            "SingleCandidate" => NamedKey::SingleCandidate,
+            "HangulMode" => NamedKey::HangulMode,
+            "HanjaMode" => NamedKey::HanjaMode,
+            "JunjaMode" => NamedKey::JunjaMode,
+            "Eisu" => NamedKey::Eisu,
+            "Hankaku" => NamedKey::Hankaku,
+            "Hiragana" => NamedKey::Hiragana,
+            "HiraganaKatakana" => NamedKey::HiraganaKatakana,
+            "KanaMode" => NamedKey::KanaMode,
+            "KanjiMode" => NamedKey::KanjiMode,
+            "Katakana" => NamedKey::Katakana,
+            "Romaji" => NamedKey::Romaji,
+            "Zenkaku" => NamedKey::Zenkaku,
+            "ZenkakuHankaku" => NamedKey::ZenkakuHankaku,
+            "Soft1" => NamedKey::Soft1,
+            "Soft2" => NamedKey::Soft2,
+            "Soft3" => NamedKey::Soft3,
+            "Soft4" => NamedKey::Soft4,
+            "ChannelDown" => NamedKey::ChannelDown,
+            "ChannelUp" => NamedKey::ChannelUp,
+            "Close" => NamedKey::Close,
+            "MailForward" => NamedKey::MailForward,
+            "MailReply" => NamedKey::MailReply,
+            "MailSend" => NamedKey::MailSend,
+            "MediaClose" => NamedKey::MediaClose,
+            "MediaFastForward" => NamedKey::MediaFastForward,
+            "MediaPause" => NamedKey::MediaPause,
+            "MediaPlay" => NamedKey::MediaPlay,
+            "MediaPlayPause" => NamedKey::MediaPlayPause,
+            "MediaRecord" => NamedKey::MediaRecord,
+            "MediaRewind" => NamedKey::MediaRewind,
+            "MediaStop" => NamedKey::MediaStop,
+            "MediaTrackNext" => NamedKey::MediaTrackNext,
+            "MediaTrackPrevious" => NamedKey::MediaTrackPrevious,
+            "New" => NamedKey::New,
+            "Open" => NamedKey::Open,
+            "Print" => NamedKey::Print,
+            "Save" => NamedKey::Save,
+            "SpellCheck" => NamedKey::SpellCheck,
+            "Key11" => NamedKey::Key11,
+            "Key12" => NamedKey::Key12,
+            "AudioBalanceLeft" => NamedKey::AudioBalanceLeft,
+            "AudioBalanceRight" => NamedKey::AudioBalanceRight,
+            "AudioBassBoostDown" => NamedKey::AudioBassBoostDown,
+            "AudioBassBoostToggle" => NamedKey::AudioBassBoostToggle,
+            "AudioBassBoostUp" => NamedKey::AudioBassBoostUp,
+            "AudioFaderFront" => NamedKey::AudioFaderFront,
+            "AudioFaderRear" => NamedKey::AudioFaderRear,
+            "AudioSurroundModeNext" => NamedKey::AudioSurroundModeNext,
+            "AudioTrebleDown" => NamedKey::AudioTrebleDown,
+            "AudioTrebleUp" => NamedKey::AudioTrebleUp,
+            "AudioVolumeDown" => NamedKey::AudioVolumeDown,
+            "AudioVolumeUp" => NamedKey::AudioVolumeUp,
+            "AudioVolumeMute" => NamedKey::AudioVolumeMute,
+            "MicrophoneToggle" => NamedKey::MicrophoneToggle,
+            "MicrophoneVolumeDown" => NamedKey::MicrophoneVolumeDown,
+            "MicrophoneVolumeUp" => NamedKey::MicrophoneVolumeUp,
+            "MicrophoneVolumeMute" => NamedKey::MicrophoneVolumeMute,
+            "SpeechCorrectionList" => NamedKey::SpeechCorrectionList,
+            "SpeechInputToggle" => NamedKey::SpeechInputToggle,
+            "LaunchApplication1" => NamedKey::LaunchApplication1,
+            "LaunchApplication2" => NamedKey::LaunchApplication2,
+            "LaunchCalendar" => NamedKey::LaunchCalendar,
+            "LaunchContacts" => NamedKey::LaunchContacts,
+            "LaunchMail" => NamedKey::LaunchMail,
+            "LaunchMediaPlayer" => NamedKey::LaunchMediaPlayer,
+            "LaunchMusicPlayer" => NamedKey::LaunchMusicPlayer,
+            "LaunchPhone" => NamedKey::LaunchPhone,
+            "LaunchScreenSaver" => NamedKey::LaunchScreenSaver,
+            "LaunchSpreadsheet" => NamedKey::LaunchSpreadsheet,
+            "LaunchWebBrowser" => NamedKey::LaunchWebBrowser,
+            "LaunchWebCam" => NamedKey::LaunchWebCam,
+            "LaunchWordProcessor" => NamedKey::LaunchWordProcessor,
+            "BrowserBack" => NamedKey::BrowserBack,
+            "BrowserFavorites" => NamedKey::BrowserFavorites,
+            "BrowserForward" => NamedKey::BrowserForward,
+            "BrowserHome" => NamedKey::BrowserHome,
+            "BrowserRefresh" => NamedKey::BrowserRefresh,
+            "BrowserSearch" => NamedKey::BrowserSearch,
+            "BrowserStop" => NamedKey::BrowserStop,
+            "AppSwitch" => NamedKey::AppSwitch,
+            "Call" => NamedKey::Call,
+            "Camera" => NamedKey::Camera,
+            "CameraFocus" => NamedKey::CameraFocus,
+            "EndCall" => NamedKey::EndCall,
+            "GoBack" => NamedKey::GoBack,
+            "GoHome" => NamedKey::GoHome,
+            "HeadsetHook" => NamedKey::HeadsetHook,
+            "LastNumberRedial" => NamedKey::LastNumberRedial,
+            "Notification" => NamedKey::Notification,
+            "MannerMode" => NamedKey::MannerMode,
+            "VoiceDial" => NamedKey::VoiceDial,
+            "TV" => NamedKey::TV,
+            "TV3DMode" => NamedKey::TV3DMode,
+            "TVAntennaCable" => NamedKey::TVAntennaCable,
+            "TVAudioDescription" => NamedKey::TVAudioDescription,
+            "TVAudioDescriptionMixDown" => NamedKey::TVAudioDescriptionMixDown,
+            "TVAudioDescriptionMixUp" => NamedKey::TVAudioDescriptionMixUp,
+            "TVContentsMenu" => NamedKey::TVContentsMenu,
+            "TVDataService" => NamedKey::TVDataService,
+            "TVInput" => NamedKey::TVInput,
+            "TVInputComponent1" => NamedKey::TVInputComponent1,
+            "TVInputComponent2" => NamedKey::TVInputComponent2,
+            "TVInputComposite1" => NamedKey::TVInputComposite1,
+            "TVInputComposite2" => NamedKey::TVInputComposite2,
+            "TVInputHDMI1" => NamedKey::TVInputHDMI1,
+            "TVInputHDMI2" => NamedKey::TVInputHDMI2,
+            "TVInputHDMI3" => NamedKey::TVInputHDMI3,
+            "TVInputHDMI4" => NamedKey::TVInputHDMI4,
+            "TVInputVGA1" => NamedKey::TVInputVGA1,
+            "TVMediaContext" => NamedKey::TVMediaContext,
+            "TVNetwork" => NamedKey::TVNetwork,
+            "TVNumberEntry" => NamedKey::TVNumberEntry,
+            "TVPower" => NamedKey::TVPower,
+            "TVRadioService" => NamedKey::TVRadioService,
+            "TVSatellite" => NamedKey::TVSatellite,
+            "TVSatelliteBS" => NamedKey::TVSatelliteBS,
+            "TVSatelliteCS" => NamedKey::TVSatelliteCS,
+            "TVSatelliteToggle" => NamedKey::TVSatelliteToggle,
+            "TVTerrestrialAnalog" => NamedKey::TVTerrestrialAnalog,
+            "TVTerrestrialDigital" => NamedKey::TVTerrestrialDigital,
+            "TVTimer" => NamedKey::TVTimer,
+            "AVRInput" => NamedKey::AVRInput,
+            "AVRPower" => NamedKey::AVRPower,
+            "ColorF0Red" => NamedKey::ColorF0Red,
+            "ColorF1Green" => NamedKey::ColorF1Green,
+            "ColorF2Yellow" => NamedKey::ColorF2Yellow,
+            "ColorF3Blue" => NamedKey::ColorF3Blue,
+            "ColorF4Grey" => NamedKey::ColorF4Grey,
+            "ColorF5Brown" => NamedKey::ColorF5Brown,
+            "ClosedCaptionToggle" => NamedKey::ClosedCaptionToggle,
+            "Dimmer" => NamedKey::Dimmer,
+            "DisplaySwap" => NamedKey::DisplaySwap,
+            "DVR" => NamedKey::DVR,
+            "Exit" => NamedKey::Exit,
+            "FavoriteClear0" => NamedKey::FavoriteClear0,
+            "FavoriteClear1" => NamedKey::FavoriteClear1,
+            "FavoriteClear2" => NamedKey::FavoriteClear2,
+            "FavoriteClear3" => NamedKey::FavoriteClear3,
+            "FavoriteRecall0" => NamedKey::FavoriteRecall0,
+            "FavoriteRecall1" => NamedKey::FavoriteRecall1,
+            "FavoriteRecall2" => NamedKey::FavoriteRecall2,
+            "FavoriteRecall3" => NamedKey::FavoriteRecall3,
+            "FavoriteStore0" => NamedKey::FavoriteStore0,
+            "FavoriteStore1" => NamedKey::FavoriteStore1,
+            "FavoriteStore2" => NamedKey::FavoriteStore2,
+            "FavoriteStore3" => NamedKey::FavoriteStore3,
+            "Guide" => NamedKey::Guide,
+            "GuideNextDay" => NamedKey::GuideNextDay,
+            "GuidePreviousDay" => NamedKey::GuidePreviousDay,
+            "Info" => NamedKey::Info,
+            "InstantReplay" => NamedKey::InstantReplay,
+            "Link" => NamedKey::Link,
+            "ListProgram" => NamedKey::ListProgram,
+            "LiveContent" => NamedKey::LiveContent,
+            "Lock" => NamedKey::Lock,
+            "MediaApps" => NamedKey::MediaApps,
+            "MediaAudioTrack" => NamedKey::MediaAudioTrack,
+            "MediaLast" => NamedKey::MediaLast,
+            "MediaSkipBackward" => NamedKey::MediaSkipBackward,
+            "MediaSkipForward" => NamedKey::MediaSkipForward,
+            "MediaStepBackward" => NamedKey::MediaStepBackward,
+            "MediaStepForward" => NamedKey::MediaStepForward,
+            "MediaTopMenu" => NamedKey::MediaTopMenu,
+            "NavigateIn" => NamedKey::NavigateIn,
+            "NavigateNext" => NamedKey::NavigateNext,
+            "NavigateOut" => NamedKey::NavigateOut,
+            "NavigatePrevious" => NamedKey::NavigatePrevious,
+            "NextFavoriteChannel" => NamedKey::NextFavoriteChannel,
+            "NextUserProfile" => NamedKey::NextUserProfile,
+            "OnDemand" => NamedKey::OnDemand,
+            "Pairing" => NamedKey::Pairing,
+            "PinPDown" => NamedKey::PinPDown,
+            "PinPMove" => NamedKey::PinPMove,
+            "PinPToggle" => NamedKey::PinPToggle,
+            "PinPUp" => NamedKey::PinPUp,
+            "PlaySpeedDown" => NamedKey::PlaySpeedDown,
+            "PlaySpeedReset" => NamedKey::PlaySpeedReset,
+            "PlaySpeedUp" => NamedKey::PlaySpeedUp,
+            "RandomToggle" => NamedKey::RandomToggle,
+            "RcLowBattery" => NamedKey::RcLowBattery,
+            "RecordSpeedNext" => NamedKey::RecordSpeedNext,
+            "RfBypass" => NamedKey::RfBypass,
+            "ScanChannelsToggle" => NamedKey::ScanChannelsToggle,
+            "ScreenModeNext" => NamedKey::ScreenModeNext,
+            "Settings" => NamedKey::Settings,
+            "SplitScreenToggle" => NamedKey::SplitScreenToggle,
+            "STBInput" => NamedKey::STBInput,
+            "STBPower" => NamedKey::STBPower,
+            "Subtitle" => NamedKey::Subtitle,
+            "Teletext" => NamedKey::Teletext,
+            "VideoModeNext" => NamedKey::VideoModeNext,
+            "Wink" => NamedKey::Wink,
+            "ZoomToggle" => NamedKey::ZoomToggle,
+            "F1" => NamedKey::F1,
+            "F2" => NamedKey::F2,
+            "F3" => NamedKey::F3,
+            "F4" => NamedKey::F4,
+            "F5" => NamedKey::F5,
+            "F6" => NamedKey::F6,
+            "F7" => NamedKey::F7,
+            "F8" => NamedKey::F8,
+            "F9" => NamedKey::F9,
+            "F10" => NamedKey::F10,
+            "F11" => NamedKey::F11,
+            "F12" => NamedKey::F12,
+            "F13" => NamedKey::F13,
+            "F14" => NamedKey::F14,
+            "F15" => NamedKey::F15,
+            "F16" => NamedKey::F16,
+            "F17" => NamedKey::F17,
+            "F18" => NamedKey::F18,
+            "F19" => NamedKey::F19,
+            "F20" => NamedKey::F20,
+            "F21" => NamedKey::F21,
+            "F22" => NamedKey::F22,
+            "F23" => NamedKey::F23,
+            "F24" => NamedKey::F24,
+            "F25" => NamedKey::F25,
+            "F26" => NamedKey::F26,
+            "F27" => NamedKey::F27,
+            "F28" => NamedKey::F28,
+            "F29" => NamedKey::F29,
+            "F30" => NamedKey::F30,
+            "F31" => NamedKey::F31,
+            "F32" => NamedKey::F32,
+            "F33" => NamedKey::F33,
+            "F34" => NamedKey::F34,
+            "F35" => NamedKey::F35,
+            string => return Key::Character(SmolStr::new(string)),
+        })
+    }
+}
+
+impl FromAttributeValue for PhysicalKey {
+    fn from_attribute_value(kcav: &str) -> Self {
+        PhysicalKey::Code(match kcav {
+            "Backquote" => KeyCode::Backquote,
+            "Backslash" => KeyCode::Backslash,
+            "BracketLeft" => KeyCode::BracketLeft,
+            "BracketRight" => KeyCode::BracketRight,
+            "Comma" => KeyCode::Comma,
+            "Digit0" => KeyCode::Digit0,
+            "Digit1" => KeyCode::Digit1,
+            "Digit2" => KeyCode::Digit2,
+            "Digit3" => KeyCode::Digit3,
+            "Digit4" => KeyCode::Digit4,
+            "Digit5" => KeyCode::Digit5,
+            "Digit6" => KeyCode::Digit6,
+            "Digit7" => KeyCode::Digit7,
+            "Digit8" => KeyCode::Digit8,
+            "Digit9" => KeyCode::Digit9,
+            "Equal" => KeyCode::Equal,
+            "IntlBackslash" => KeyCode::IntlBackslash,
+            "IntlRo" => KeyCode::IntlRo,
+            "IntlYen" => KeyCode::IntlYen,
+            "KeyA" => KeyCode::KeyA,
+            "KeyB" => KeyCode::KeyB,
+            "KeyC" => KeyCode::KeyC,
+            "KeyD" => KeyCode::KeyD,
+            "KeyE" => KeyCode::KeyE,
+            "KeyF" => KeyCode::KeyF,
+            "KeyG" => KeyCode::KeyG,
+            "KeyH" => KeyCode::KeyH,
+            "KeyI" => KeyCode::KeyI,
+            "KeyJ" => KeyCode::KeyJ,
+            "KeyK" => KeyCode::KeyK,
+            "KeyL" => KeyCode::KeyL,
+            "KeyM" => KeyCode::KeyM,
+            "KeyN" => KeyCode::KeyN,
+            "KeyO" => KeyCode::KeyO,
+            "KeyP" => KeyCode::KeyP,
+            "KeyQ" => KeyCode::KeyQ,
+            "KeyR" => KeyCode::KeyR,
+            "KeyS" => KeyCode::KeyS,
+            "KeyT" => KeyCode::KeyT,
+            "KeyU" => KeyCode::KeyU,
+            "KeyV" => KeyCode::KeyV,
+            "KeyW" => KeyCode::KeyW,
+            "KeyX" => KeyCode::KeyX,
+            "KeyY" => KeyCode::KeyY,
+            "KeyZ" => KeyCode::KeyZ,
+            "Minus" => KeyCode::Minus,
+            "Period" => KeyCode::Period,
+            "Quote" => KeyCode::Quote,
+            "Semicolon" => KeyCode::Semicolon,
+            "Slash" => KeyCode::Slash,
+            "AltLeft" => KeyCode::AltLeft,
+            "AltRight" => KeyCode::AltRight,
+            "Backspace" => KeyCode::Backspace,
+            "CapsLock" => KeyCode::CapsLock,
+            "ContextMenu" => KeyCode::ContextMenu,
+            "ControlLeft" => KeyCode::ControlLeft,
+            "ControlRight" => KeyCode::ControlRight,
+            "Enter" => KeyCode::Enter,
+            "MetaLeft" => KeyCode::MetaLeft,
+            "MetaRight" => KeyCode::MetaRight,
+            "ShiftLeft" => KeyCode::ShiftLeft,
+            "ShiftRight" => KeyCode::ShiftRight,
+            "Space" => KeyCode::Space,
+            "Tab" => KeyCode::Tab,
+            "Convert" => KeyCode::Convert,
+            "KanaMode" => KeyCode::KanaMode,
+            "Lang1" => KeyCode::Lang1,
+            "Lang2" => KeyCode::Lang2,
+            "Lang3" => KeyCode::Lang3,
+            "Lang4" => KeyCode::Lang4,
+            "Lang5" => KeyCode::Lang5,
+            "NonConvert" => KeyCode::NonConvert,
+            "Delete" => KeyCode::Delete,
+            "End" => KeyCode::End,
+            "Help" => KeyCode::Help,
+            "Home" => KeyCode::Home,
+            "Insert" => KeyCode::Insert,
+            "PageDown" => KeyCode::PageDown,
+            "PageUp" => KeyCode::PageUp,
+            "ArrowDown" => KeyCode::ArrowDown,
+            "ArrowLeft" => KeyCode::ArrowLeft,
+            "ArrowRight" => KeyCode::ArrowRight,
+            "ArrowUp" => KeyCode::ArrowUp,
+            "NumLock" => KeyCode::NumLock,
+            "Numpad0" => KeyCode::Numpad0,
+            "Numpad1" => KeyCode::Numpad1,
+            "Numpad2" => KeyCode::Numpad2,
+            "Numpad3" => KeyCode::Numpad3,
+            "Numpad4" => KeyCode::Numpad4,
+            "Numpad5" => KeyCode::Numpad5,
+            "Numpad6" => KeyCode::Numpad6,
+            "Numpad7" => KeyCode::Numpad7,
+            "Numpad8" => KeyCode::Numpad8,
+            "Numpad9" => KeyCode::Numpad9,
+            "NumpadAdd" => KeyCode::NumpadAdd,
+            "NumpadBackspace" => KeyCode::NumpadBackspace,
+            "NumpadClear" => KeyCode::NumpadClear,
+            "NumpadClearEntry" => KeyCode::NumpadClearEntry,
+            "NumpadComma" => KeyCode::NumpadComma,
+            "NumpadDecimal" => KeyCode::NumpadDecimal,
+            "NumpadDivide" => KeyCode::NumpadDivide,
+            "NumpadEnter" => KeyCode::NumpadEnter,
+            "NumpadEqual" => KeyCode::NumpadEqual,
+            "NumpadHash" => KeyCode::NumpadHash,
+            "NumpadMemoryAdd" => KeyCode::NumpadMemoryAdd,
+            "NumpadMemoryClear" => KeyCode::NumpadMemoryClear,
+            "NumpadMemoryRecall" => KeyCode::NumpadMemoryRecall,
+            "NumpadMemoryStore" => KeyCode::NumpadMemoryStore,
+            "NumpadMemorySubtract" => KeyCode::NumpadMemorySubtract,
+            "NumpadMultiply" => KeyCode::NumpadMultiply,
+            "NumpadParenLeft" => KeyCode::NumpadParenLeft,
+            "NumpadParenRight" => KeyCode::NumpadParenRight,
+            "NumpadStar" => KeyCode::NumpadStar,
+            "NumpadSubtract" => KeyCode::NumpadSubtract,
+            "Escape" => KeyCode::Escape,
+            "Fn" => KeyCode::Fn,
+            "FnLock" => KeyCode::FnLock,
+            "PrintScreen" => KeyCode::PrintScreen,
+            "ScrollLock" => KeyCode::ScrollLock,
+            "Pause" => KeyCode::Pause,
+            "BrowserBack" => KeyCode::BrowserBack,
+            "BrowserFavorites" => KeyCode::BrowserFavorites,
+            "BrowserForward" => KeyCode::BrowserForward,
+            "BrowserHome" => KeyCode::BrowserHome,
+            "BrowserRefresh" => KeyCode::BrowserRefresh,
+            "BrowserSearch" => KeyCode::BrowserSearch,
+            "BrowserStop" => KeyCode::BrowserStop,
+            "Eject" => KeyCode::Eject,
+            "LaunchApp1" => KeyCode::LaunchApp1,
+            "LaunchApp2" => KeyCode::LaunchApp2,
+            "LaunchMail" => KeyCode::LaunchMail,
+            "MediaPlayPause" => KeyCode::MediaPlayPause,
+            "MediaSelect" => KeyCode::MediaSelect,
+            "MediaStop" => KeyCode::MediaStop,
+            "MediaTrackNext" => KeyCode::MediaTrackNext,
+            "MediaTrackPrevious" => KeyCode::MediaTrackPrevious,
+            "Power" => KeyCode::Power,
+            "Sleep" => KeyCode::Sleep,
+            "AudioVolumeDown" => KeyCode::AudioVolumeDown,
+            "AudioVolumeMute" => KeyCode::AudioVolumeMute,
+            "AudioVolumeUp" => KeyCode::AudioVolumeUp,
+            "WakeUp" => KeyCode::WakeUp,
+            #[allow(deprecated)]
+            "Super" => KeyCode::Super,
+            #[allow(deprecated)]
+            "Hyper" => KeyCode::Hyper,
+            #[allow(deprecated)]
+            "Turbo" => KeyCode::Turbo,
+            "Abort" => KeyCode::Abort,
+            "Resume" => KeyCode::Resume,
+            "Suspend" => KeyCode::Suspend,
+            "Again" => KeyCode::Again,
+            "Copy" => KeyCode::Copy,
+            "Cut" => KeyCode::Cut,
+            "Find" => KeyCode::Find,
+            "Open" => KeyCode::Open,
+            "Paste" => KeyCode::Paste,
+            "Props" => KeyCode::Props,
+            "Select" => KeyCode::Select,
+            "Undo" => KeyCode::Undo,
+            "Hiragana" => KeyCode::Hiragana,
+            "Katakana" => KeyCode::Katakana,
+            "F1" => KeyCode::F1,
+            "F2" => KeyCode::F2,
+            "F3" => KeyCode::F3,
+            "F4" => KeyCode::F4,
+            "F5" => KeyCode::F5,
+            "F6" => KeyCode::F6,
+            "F7" => KeyCode::F7,
+            "F8" => KeyCode::F8,
+            "F9" => KeyCode::F9,
+            "F10" => KeyCode::F10,
+            "F11" => KeyCode::F11,
+            "F12" => KeyCode::F12,
+            "F13" => KeyCode::F13,
+            "F14" => KeyCode::F14,
+            "F15" => KeyCode::F15,
+            "F16" => KeyCode::F16,
+            "F17" => KeyCode::F17,
+            "F18" => KeyCode::F18,
+            "F19" => KeyCode::F19,
+            "F20" => KeyCode::F20,
+            "F21" => KeyCode::F21,
+            "F22" => KeyCode::F22,
+            "F23" => KeyCode::F23,
+            "F24" => KeyCode::F24,
+            "F25" => KeyCode::F25,
+            "F26" => KeyCode::F26,
+            "F27" => KeyCode::F27,
+            "F28" => KeyCode::F28,
+            "F29" => KeyCode::F29,
+            "F30" => KeyCode::F30,
+            "F31" => KeyCode::F31,
+            "F32" => KeyCode::F32,
+            "F33" => KeyCode::F33,
+            "F34" => KeyCode::F34,
+            "F35" => KeyCode::F35,
+            _ => return PhysicalKey::Unidentified(NativeKeyCode::Unidentified),
+        })
+    }
+}

winit-web/src/lib.rs

@@ -0,0 +1,710 @@
+//! # Web
+//!
+//! Winit supports running in Browsers by compiling to WebAssembly with
+//! [`wasm-bindgen`][wasm_bindgen]. For information on using Rust on WebAssembly, check out the
+//! [Rust and WebAssembly book].
+//!
+//! The officially supported browsers are Chrome, Firefox and Safari 13.1+, though forks of these
+//! should work fine.
+//!
+//! On the Web platform, a Winit [`Window`] is backed by a [`HTMLCanvasElement`][canvas]. Winit will
+//! create that canvas for you or you can [provide your own][with_canvas]. Then you can either let
+//! Winit [insert it into the DOM for you][insert], or [retrieve the canvas][get] and insert it
+//! yourself.
+//!
+//! [canvas]: https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement
+//! [with_canvas]: WindowAttributesWeb::with_canvas
+//! [get]: WindowExtWeb::canvas
+//! [insert]: WindowAttributesWeb::with_append
+//! [wasm_bindgen]: https://docs.rs/wasm-bindgen
+//! [Rust and WebAssembly book]: https://rustwasm.github.io/book
+//!
+//! ## CSS properties
+//!
+//! It is recommended **not** to apply certain CSS properties to the canvas:
+//! - [`transform`](https://developer.mozilla.org/en-US/docs/Web/CSS/transform)
+//! - [`border`](https://developer.mozilla.org/en-US/docs/Web/CSS/border)
+//! - [`padding`](https://developer.mozilla.org/en-US/docs/Web/CSS/padding)
+//!
+//! The following APIs can't take them into account and will therefore provide inaccurate results:
+//! - [`WindowEvent::SurfaceResized`] and [`Window::(set_)surface_size()`]
+//! - [`WindowEvent::Occluded`]
+//! - [`WindowEvent::PointerMoved`], [`WindowEvent::PointerEntered`] and
+//!   [`WindowEvent::PointerLeft`].
+//! - [`Window::set_outer_position()`]
+//!
+//! [`WindowEvent::SurfaceResized`]: crate::event::WindowEvent::SurfaceResized
+//! [`Window::(set_)surface_size()`]: crate::window::Window::surface_size
+//! [`WindowEvent::Occluded`]: crate::event::WindowEvent::Occluded
+//! [`WindowEvent::PointerMoved`]: crate::event::WindowEvent::PointerMoved
+//! [`WindowEvent::PointerEntered`]: crate::event::WindowEvent::PointerEntered
+//! [`WindowEvent::PointerLeft`]: crate::event::WindowEvent::PointerLeft
+//! [`Window::set_outer_position()`]: crate::window::Window::set_outer_position
+
+// Brief introduction to the internals of the Web backend:
+// The Web backend used to support both wasm-bindgen and stdweb as methods of binding to the
+// environment. Because they are both supporting the same underlying APIs, the actual Web bindings
+// are cordoned off into backend abstractions, which present the thinnest unifying layer possible.
+//
+// When adding support for new events or interactions with the browser, first consult trusted
+// documentation (such as MDN) to ensure it is well-standardised and supported across many browsers.
+// Once you have decided on the relevant Web APIs, add support to both backends.
+//
+// The backend is used by the rest of the module to implement Winit's business logic, which forms
+// the rest of the code. 'device', 'error', 'monitor', and 'window' define Web-specific structures
+// for winit's cross-platform structures. They are all relatively simple translations.
+//
+// The event_loop module handles listening for and processing events. 'Proxy' implements
+// EventLoopProxy and 'WindowTarget' implements ActiveEventLoop. WindowTarget also handles
+// registering the event handlers. The 'Execution' struct in the 'runner' module handles taking
+// incoming events (from the registered handlers) and ensuring they are passed to the user in a
+// compliant way.
+
+macro_rules! os_error {
+    ($error:expr) => {{
+        winit_core::error::OsError::new(line!(), file!(), $error)
+    }};
+}
+
+mod r#async;
+mod cursor;
+mod error;
+mod event;
+pub(crate) mod event_loop;
+mod keyboard;
+mod lock;
+pub(crate) mod main_thread;
+mod monitor;
+pub(crate) mod web_sys;
+pub(crate) mod window;
+
+use std::cell::Ref;
+use std::error::Error;
+use std::fmt::{self, Display, Formatter};
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{Context, Poll};
+
+use ::web_sys::HtmlCanvasElement;
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+use winit_core::application::ApplicationHandler;
+use winit_core::cursor::{CustomCursor, CustomCursorSource};
+use winit_core::error::NotSupportedError;
+use winit_core::event_loop::ActiveEventLoop;
+use winit_core::monitor::MonitorHandleProvider;
+use winit_core::window::{PlatformWindowAttributes, Window};
+
+pub use self::event_loop::{EventLoop, PlatformSpecificEventLoopAttributes};
+use self::web_sys as backend;
+use self::window::Window as WebWindow;
+use crate::cursor::CustomCursorFuture as PlatformCustomCursorFuture;
+use crate::event_loop::ActiveEventLoop as WebActiveEventLoop;
+use crate::main_thread::{MainThreadMarker, MainThreadSafe};
+use crate::monitor::{
+    HasMonitorPermissionFuture as PlatformHasMonitorPermissionFuture,
+    MonitorHandle as WebMonitorHandle, MonitorPermissionFuture as PlatformMonitorPermissionFuture,
+    OrientationLockFuture as PlatformOrientationLockFuture,
+};
+
+pub trait WindowExtWeb {
+    /// Only returns the canvas if called from inside the window context (the
+    /// main thread).
+    fn canvas(&self) -> Option<Ref<'_, HtmlCanvasElement>>;
+
+    /// Returns [`true`] if calling `event.preventDefault()` is enabled.
+    ///
+    /// See [`WindowExtWeb::set_prevent_default()`] for more details.
+    fn prevent_default(&self) -> bool;
+
+    /// Sets whether `event.preventDefault()` should be called on events on the
+    /// canvas that have side effects.
+    ///
+    /// For example, by default using the mouse wheel would cause the page to scroll, enabling this
+    /// would prevent that.
+    ///
+    /// Some events are impossible to prevent. E.g. Firefox allows to access the native browser
+    /// context menu with Shift+Rightclick.
+    fn set_prevent_default(&self, prevent_default: bool);
+
+    /// Returns whether using [`CursorGrabMode::Locked`] returns raw, un-accelerated mouse input.
+    ///
+    /// This is the same as [`ActiveEventLoopExtWeb::is_cursor_lock_raw()`], and is provided for
+    /// convenience.
+    ///
+    /// [`CursorGrabMode::Locked`]: crate::window::CursorGrabMode::Locked
+    fn is_cursor_lock_raw(&self) -> bool;
+}
+
+impl WindowExtWeb for dyn Window + '_ {
+    #[inline]
+    fn canvas(&self) -> Option<Ref<'_, HtmlCanvasElement>> {
+        self.cast_ref::<WebWindow>().expect("non Web window on Web").canvas()
+    }
+
+    fn prevent_default(&self) -> bool {
+        self.cast_ref::<WebWindow>().expect("non Web window on Web").prevent_default()
+    }
+
+    fn set_prevent_default(&self, prevent_default: bool) {
+        self.cast_ref::<WebWindow>()
+            .expect("non Web window on Web")
+            .set_prevent_default(prevent_default)
+    }
+
+    fn is_cursor_lock_raw(&self) -> bool {
+        self.cast_ref::<WebWindow>().expect("non Web window on Web").is_cursor_lock_raw()
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct WindowAttributesWeb {
+    pub(crate) canvas: Option<Arc<MainThreadSafe<backend::RawCanvasType>>>,
+    pub(crate) prevent_default: bool,
+    pub(crate) focusable: bool,
+    pub(crate) append: bool,
+}
+
+impl WindowAttributesWeb {
+    /// Pass an [`HtmlCanvasElement`] to be used for this [`Window`]. If [`None`],
+    /// the default one will be created.
+    ///
+    /// In any case, the canvas won't be automatically inserted into the Web page.
+    ///
+    /// [`None`] by default.
+    pub fn with_canvas(mut self, canvas: Option<HtmlCanvasElement>) -> Self {
+        match canvas {
+            Some(canvas) => {
+                let main_thread = MainThreadMarker::new()
+                    .expect("received a `HtmlCanvasElement` outside the window context");
+                self.canvas = Some(Arc::new(MainThreadSafe::new(main_thread, canvas)));
+            },
+            None => self.canvas = None,
+        }
+
+        self
+    }
+
+    /// Sets whether `event.preventDefault()` should be called on events on the
+    /// canvas that have side effects.
+    ///
+    /// See [`WindowExtWeb::set_prevent_default()`] for more details.
+    ///
+    /// Enabled by default.
+    pub fn with_prevent_default(mut self, prevent_default: bool) -> Self {
+        self.prevent_default = prevent_default;
+        self
+    }
+
+    /// Whether the canvas should be focusable using the tab key. This is necessary to capture
+    /// canvas keyboard events.
+    ///
+    /// Enabled by default.
+    pub fn with_focusable(mut self, focusable: bool) -> Self {
+        self.focusable = focusable;
+        self
+    }
+
+    /// On window creation, append the canvas element to the Web page if it isn't already.
+    ///
+    /// Disabled by default.
+    pub fn with_append(mut self, append: bool) -> Self {
+        self.append = append;
+        self
+    }
+}
+
+impl PlatformWindowAttributes for WindowAttributesWeb {
+    fn box_clone(&self) -> Box<dyn PlatformWindowAttributes> {
+        Box::from(self.clone())
+    }
+}
+
+impl PartialEq for WindowAttributesWeb {
+    fn eq(&self, other: &Self) -> bool {
+        (match (&self.canvas, &other.canvas) {
+            (Some(this), Some(other)) => Arc::ptr_eq(this, other),
+            (None, None) => true,
+            _ => false,
+        }) && self.prevent_default.eq(&other.prevent_default)
+            && self.focusable.eq(&other.focusable)
+            && self.append.eq(&other.append)
+    }
+}
+
+impl Default for WindowAttributesWeb {
+    fn default() -> Self {
+        Self { canvas: None, prevent_default: true, focusable: true, append: false }
+    }
+}
+
+/// Additional methods on `EventLoop` that are specific to the Web.
+pub trait EventLoopExtWeb {
+    /// Initializes the winit event loop.
+    ///
+    /// Unlike
+    #[cfg_attr(target_feature = "exception-handling", doc = "`run_app()`")]
+    #[cfg_attr(
+        not(target_feature = "exception-handling"),
+        doc = "[`run_app()`]"
+    )]
+    /// [^1], this returns immediately, and doesn't throw an exception in order to
+    /// satisfy its [`!`] return type.
+    ///
+    /// Once the event loop has been destroyed, it's possible to reinitialize another event loop
+    /// by calling this function again. This can be useful if you want to recreate the event loop
+    /// while the WebAssembly module is still loaded. For example, this can be used to recreate the
+    /// event loop when switching between tabs on a single page application.
+    #[rustfmt::skip]
+    ///
+    #[cfg_attr(
+        not(target_feature = "exception-handling"),
+        doc = "[`run_app()`]: EventLoop::run_app()"
+    )]
+    /// [^1]: `run_app()` is _not_ available on Wasm when the target supports `exception-handling`.
+    fn spawn_app<A: ApplicationHandler + 'static>(self, app: A);
+
+    /// Sets the strategy for [`ControlFlow::Poll`].
+    ///
+    /// See [`PollStrategy`].
+    ///
+    /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
+    fn set_poll_strategy(&self, strategy: PollStrategy);
+
+    /// Gets the strategy for [`ControlFlow::Poll`].
+    ///
+    /// See [`PollStrategy`].
+    ///
+    /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
+    fn poll_strategy(&self) -> PollStrategy;
+
+    /// Sets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy);
+
+    /// Gets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn wait_until_strategy(&self) -> WaitUntilStrategy;
+
+    /// Returns if the users device has multiple screens. Useful to check before prompting the user
+    /// with [`EventLoopExtWeb::request_detailed_monitor_permission()`].
+    ///
+    /// Browsers might always return [`false`] to reduce fingerprinting.
+    fn has_multiple_screens(&self) -> Result<bool, NotSupportedError>;
+
+    /// Prompts the user for permission to query detailed information about available monitors. The
+    /// returned [`MonitorPermissionFuture`] can be dropped without aborting the request.
+    ///
+    /// Check [`EventLoopExtWeb::has_multiple_screens()`] before unnecessarily prompting the user
+    /// for such permissions.
+    ///
+    /// [`MonitorHandle`]s don't automatically make use of this after permission is granted. New
+    /// [`MonitorHandle`]s have to be created instead.
+    ///
+    /// [`MonitorHandle`]: crate::monitor::MonitorHandle
+    fn request_detailed_monitor_permission(&self) -> MonitorPermissionFuture;
+
+    /// Returns whether the user has given permission to access detailed monitor information.
+    ///
+    /// [`MonitorHandle`]s don't automatically make use of detailed monitor information after
+    /// permission is granted. New [`MonitorHandle`]s have to be created instead.
+    ///
+    /// [`MonitorHandle`]: crate::monitor::MonitorHandle
+    ///
+    /// [`MonitorHandle`]: crate::monitor::MonitorHandle
+    fn has_detailed_monitor_permission(&self) -> HasMonitorPermissionFuture;
+}
+
+pub trait ActiveEventLoopExtWeb {
+    /// Sets the strategy for [`ControlFlow::Poll`].
+    ///
+    /// See [`PollStrategy`].
+    ///
+    /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
+    fn set_poll_strategy(&self, strategy: PollStrategy);
+
+    /// Gets the strategy for [`ControlFlow::Poll`].
+    ///
+    /// See [`PollStrategy`].
+    ///
+    /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
+    fn poll_strategy(&self) -> PollStrategy;
+
+    /// Sets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy);
+
+    /// Gets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn wait_until_strategy(&self) -> WaitUntilStrategy;
+
+    /// Async version of [`ActiveEventLoop::create_custom_cursor()`] which waits until the
+    /// cursor has completely finished loading.
+    fn create_custom_cursor_async(&self, source: CustomCursorSource) -> CustomCursorFuture;
+
+    /// Returns whether using [`CursorGrabMode::Locked`] returns raw, un-accelerated mouse input.
+    ///
+    /// [`CursorGrabMode::Locked`]: crate::window::CursorGrabMode::Locked
+    fn is_cursor_lock_raw(&self) -> bool;
+
+    /// Returns if the users device has multiple screens. Useful to check before prompting the user
+    /// with [`EventLoopExtWeb::request_detailed_monitor_permission()`].
+    ///
+    /// Browsers might always return [`false`] to reduce fingerprinting.
+    fn has_multiple_screens(&self) -> Result<bool, NotSupportedError>;
+
+    /// Prompts the user for permission to query detailed information about available monitors. The
+    /// returned [`MonitorPermissionFuture`] can be dropped without aborting the request.
+    ///
+    /// Check [`EventLoopExtWeb::has_multiple_screens()`] before unnecessarily prompting the user
+    /// for such permissions.
+    ///
+    /// [`MonitorHandle`]s don't automatically make use of this after permission is granted. New
+    /// [`MonitorHandle`]s have to be created instead.
+    ///
+    /// [`MonitorHandle`]: crate::monitor::MonitorHandle
+    fn request_detailed_monitor_permission(&self) -> MonitorPermissionFuture;
+
+    /// Returns whether the user has given permission to access detailed monitor information.
+    ///
+    /// [`MonitorHandle`]s don't automatically make use of detailed monitor information after
+    /// permission is granted. New [`MonitorHandle`]s have to be created instead.
+    ///
+    /// [`MonitorHandle`]: crate::monitor::MonitorHandle
+    fn has_detailed_monitor_permission(&self) -> bool;
+}
+
+impl ActiveEventLoopExtWeb for dyn ActiveEventLoop + '_ {
+    #[inline]
+    fn create_custom_cursor_async(&self, source: CustomCursorSource) -> CustomCursorFuture {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        event_loop.create_custom_cursor_async(source)
+    }
+
+    #[inline]
+    fn set_poll_strategy(&self, strategy: PollStrategy) {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        event_loop.set_poll_strategy(strategy);
+    }
+
+    #[inline]
+    fn poll_strategy(&self) -> PollStrategy {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        event_loop.poll_strategy()
+    }
+
+    #[inline]
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        event_loop.set_wait_until_strategy(strategy);
+    }
+
+    #[inline]
+    fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        event_loop.wait_until_strategy()
+    }
+
+    #[inline]
+    fn is_cursor_lock_raw(&self) -> bool {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        event_loop.is_cursor_lock_raw()
+    }
+
+    #[inline]
+    fn has_multiple_screens(&self) -> Result<bool, NotSupportedError> {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        event_loop.has_multiple_screens()
+    }
+
+    #[inline]
+    fn request_detailed_monitor_permission(&self) -> MonitorPermissionFuture {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        MonitorPermissionFuture(event_loop.request_detailed_monitor_permission())
+    }
+
+    #[inline]
+    fn has_detailed_monitor_permission(&self) -> bool {
+        let event_loop = self.cast_ref::<WebActiveEventLoop>().expect("non Web event loop on Web");
+        event_loop.has_detailed_monitor_permission()
+    }
+}
+
+/// Strategy used for [`ControlFlow::Poll`][crate::event_loop::ControlFlow::Poll].
+#[derive(Clone, Copy, Debug, Default, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum PollStrategy {
+    /// Uses [`Window.requestIdleCallback()`] to queue the next event loop. If not available
+    /// this will fallback to [`setTimeout()`].
+    ///
+    /// This strategy will wait for the browser to enter an idle period before running and might
+    /// be affected by browser throttling.
+    ///
+    /// [`Window.requestIdleCallback()`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback
+    /// [`setTimeout()`]: https://developer.mozilla.org/en-US/docs/Web/API/setTimeout
+    IdleCallback,
+    /// Uses the [Prioritized Task Scheduling API] to queue the next event loop. If not available
+    /// this will fallback to [`setTimeout()`].
+    ///
+    /// This strategy will run as fast as possible without disturbing users from interacting with
+    /// the page and is not affected by browser throttling.
+    ///
+    /// This is the default strategy.
+    ///
+    /// [Prioritized Task Scheduling API]: https://developer.mozilla.org/en-US/docs/Web/API/Prioritized_Task_Scheduling_API
+    /// [`setTimeout()`]: https://developer.mozilla.org/en-US/docs/Web/API/setTimeout
+    #[default]
+    Scheduler,
+}
+
+/// Strategy used for [`ControlFlow::WaitUntil`][crate::event_loop::ControlFlow::WaitUntil].
+#[derive(Clone, Copy, Debug, Default, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum WaitUntilStrategy {
+    /// Uses the [Prioritized Task Scheduling API] to queue the next event loop. If not available
+    /// this will fallback to [`setTimeout()`].
+    ///
+    /// This strategy is commonly not affected by browser throttling unless the window is not
+    /// focused.
+    ///
+    /// This is the default strategy.
+    ///
+    /// [Prioritized Task Scheduling API]: https://developer.mozilla.org/en-US/docs/Web/API/Prioritized_Task_Scheduling_API
+    /// [`setTimeout()`]: https://developer.mozilla.org/en-US/docs/Web/API/setTimeout
+    #[default]
+    Scheduler,
+    /// Equal to [`Scheduler`][Self::Scheduler] but wakes up the event loop from a [worker].
+    ///
+    /// This strategy is commonly not affected by browser throttling regardless of window focus.
+    ///
+    /// [worker]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API
+    Worker,
+}
+
+#[derive(Debug)]
+pub struct CustomCursorFuture(pub(crate) PlatformCustomCursorFuture);
+
+impl Future for CustomCursorFuture {
+    type Output = Result<CustomCursor, CustomCursorError>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.0).poll(cx).map_ok(|cursor| CustomCursor(Arc::new(cursor)))
+    }
+}
+
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum CustomCursorError {
+    Blob,
+    Decode(String),
+}
+
+impl Display for CustomCursorError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Blob => write!(f, "failed to create `Blob`"),
+            Self::Decode(error) => write!(f, "failed to decode image: {error}"),
+        }
+    }
+}
+
+impl Error for CustomCursorError {}
+
+/// Can be dropped without aborting the request for detailed monitor permissions.
+#[derive(Debug)]
+pub struct MonitorPermissionFuture(pub(crate) PlatformMonitorPermissionFuture);
+
+impl Future for MonitorPermissionFuture {
+    type Output = Result<(), MonitorPermissionError>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.0).poll(cx)
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub enum MonitorPermissionError {
+    /// User has explicitly denied permission to query detailed monitor information.
+    Denied,
+    /// User has not decided to give permission to query detailed monitor information.
+    Prompt,
+    /// Browser does not support detailed monitor information.
+    Unsupported,
+}
+
+impl Display for MonitorPermissionError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            MonitorPermissionError::Denied => write!(
+                f,
+                "User has explicitly denied permission to query detailed monitor information"
+            ),
+            MonitorPermissionError::Prompt => write!(
+                f,
+                "User has not decided to give permission to query detailed monitor information"
+            ),
+            MonitorPermissionError::Unsupported => {
+                write!(f, "Browser does not support detailed monitor information")
+            },
+        }
+    }
+}
+
+impl Error for MonitorPermissionError {}
+
+#[derive(Debug)]
+pub struct HasMonitorPermissionFuture(PlatformHasMonitorPermissionFuture);
+
+impl Future for HasMonitorPermissionFuture {
+    type Output = bool;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.0).poll(cx)
+    }
+}
+
+/// Additional methods on [`MonitorHandle`] that are specific to the Web.
+///
+/// [`MonitorHandle`]: crate::monitor::MonitorHandle
+pub trait MonitorHandleExtWeb {
+    /// Returns whether the screen is internal to the device or external.
+    ///
+    /// External devices are generally manufactured separately from the device they are attached to
+    /// and can be connected and disconnected as needed, whereas internal screens are part of
+    /// the device and not intended to be disconnected.
+    fn is_internal(&self) -> Option<bool>;
+
+    /// Returns screen orientation data for this monitor.
+    fn orientation(&self) -> OrientationData;
+
+    /// Lock the screen orientation. The returned [`OrientationLockFuture`] can be dropped without
+    /// aborting the request.
+    ///
+    /// Will fail if another locking call is in progress.
+    fn request_lock(&self, orientation: OrientationLock) -> OrientationLockFuture;
+
+    /// Unlock the screen orientation.
+    ///
+    /// Will fail if a locking call is in progress.
+    fn unlock(&self) -> Result<(), OrientationLockError>;
+
+    /// Returns whether this [`MonitorHandle`] was created using detailed monitor permissions. If
+    /// [`false`] will always represent the current monitor the browser window is in instead of a
+    /// specific monitor.
+    ///
+    /// See [`ActiveEventLoopExtWeb::request_detailed_monitor_permission()`].
+    ///
+    /// [`MonitorHandle`]: crate::monitor::MonitorHandle
+    fn is_detailed(&self) -> bool;
+}
+
+impl MonitorHandleExtWeb for dyn MonitorHandleProvider + '_ {
+    fn is_internal(&self) -> Option<bool> {
+        self.cast_ref::<WebMonitorHandle>().unwrap().is_internal()
+    }
+
+    fn orientation(&self) -> OrientationData {
+        self.cast_ref::<WebMonitorHandle>().unwrap().orientation()
+    }
+
+    fn request_lock(&self, orientation_lock: OrientationLock) -> OrientationLockFuture {
+        let future = self.cast_ref::<WebMonitorHandle>().unwrap().request_lock(orientation_lock);
+        OrientationLockFuture(future)
+    }
+
+    fn unlock(&self) -> Result<(), OrientationLockError> {
+        self.cast_ref::<WebMonitorHandle>().unwrap().unlock()
+    }
+
+    fn is_detailed(&self) -> bool {
+        self.cast_ref::<WebMonitorHandle>().unwrap().is_detailed()
+    }
+}
+
+/// Screen orientation data.
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub struct OrientationData {
+    /// The orientation.
+    pub orientation: Orientation,
+    /// [`true`] if the [`orientation`](Self::orientation) is flipped upside down.
+    pub flipped: bool,
+    /// The most natural orientation for the screen. Computer monitors are commonly naturally
+    /// landscape mode, while mobile phones are commonly naturally portrait mode.
+    pub natural: Orientation,
+}
+
+/// Screen orientation.
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub enum Orientation {
+    /// The screen's aspect ratio has a width greater than the height.
+    Landscape,
+    /// The screen's aspect ratio has a height greater than the width.
+    Portrait,
+}
+
+/// Screen orientation lock options. Represents which orientations a user can use.
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub enum OrientationLock {
+    /// User is free to use any orientation.
+    Any,
+    /// User is locked to the most upright natural orientation for the screen. Computer monitors
+    /// are commonly naturally landscape mode, while mobile phones are commonly
+    /// naturally portrait mode.
+    Natural,
+    /// User is locked to landscape mode.
+    Landscape {
+        /// - [`None`]: User is locked to both upright or upside down landscape mode.
+        /// - [`true`]: User is locked to upright landscape mode.
+        /// - [`false`]: User is locked to upside down landscape mode.
+        flipped: Option<bool>,
+    },
+    /// User is locked to portrait mode.
+    Portrait {
+        /// - [`None`]: User is locked to both upright or upside down portrait mode.
+        /// - [`true`]: User is locked to upright portrait mode.
+        /// - [`false`]: User is locked to upside down portrait mode.
+        flipped: Option<bool>,
+    },
+}
+
+/// Can be dropped without aborting the request to lock the screen.
+#[derive(Debug)]
+pub struct OrientationLockFuture(PlatformOrientationLockFuture);
+
+impl Future for OrientationLockFuture {
+    type Output = Result<(), OrientationLockError>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.0).poll(cx)
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub enum OrientationLockError {
+    Unsupported,
+    Busy,
+}
+
+impl Display for OrientationLockError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Unsupported => write!(f, "Locking the screen orientation is not supported"),
+            Self::Busy => write!(f, "Another locking call is in progress"),
+        }
+    }
+}
+
+impl Error for OrientationLockError {}

winit-web/src/lock.rs

@@ -0,0 +1,82 @@
+use std::cell::OnceCell;
+
+use js_sys::{Object, Promise};
+use tracing::error;
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::{JsCast, JsValue};
+use web_sys::{console, Document, DomException, Element, Navigator};
+
+pub(crate) fn is_cursor_lock_raw(navigator: &Navigator, document: &Document) -> bool {
+    thread_local! {
+        static IS_CURSOR_LOCK_RAW: OnceCell<bool> = const { OnceCell::new() };
+    }
+
+    IS_CURSOR_LOCK_RAW.with(|cell| {
+        *cell.get_or_init(|| {
+            // TODO: Remove when Chrome can better advertise that they don't support unaccelerated
+            // movement on Linux.
+            // See <https://issues.chromium.org/issues/40833850>.
+            if super::web_sys::chrome_linux(navigator) {
+                return false;
+            }
+
+            let element: ElementExt = document.create_element("div").unwrap().unchecked_into();
+            let promise = element.request_pointer_lock();
+
+            if promise.is_undefined() {
+                false
+            } else {
+                thread_local! {
+                    static REJECT_HANDLER: Closure<dyn FnMut(JsValue)> = Closure::new(|_| ());
+                }
+
+                let promise: Promise = promise.unchecked_into();
+                let _ = REJECT_HANDLER.with(|handler| promise.catch(handler));
+                true
+            }
+        })
+    })
+}
+
+pub(crate) fn request_pointer_lock(navigator: &Navigator, document: &Document, element: &Element) {
+    if is_cursor_lock_raw(navigator, document) {
+        thread_local! {
+            static REJECT_HANDLER: Closure<dyn FnMut(JsValue)> = Closure::new(|error: JsValue| {
+                if let Some(error) = error.dyn_ref::<DomException>() {
+                        error!("Failed to lock pointer. {}: {}", error.name(), error.message());
+                } else {
+                    console::error_1(&error);
+                    error!("Failed to lock pointer");
+                }
+            });
+        }
+
+        let element: &ElementExt = element.unchecked_ref();
+        let options: PointerLockOptions = Object::new().unchecked_into();
+        options.set_unadjusted_movement(true);
+        let _ = REJECT_HANDLER
+            .with(|handler| element.request_pointer_lock_with_options(&options).catch(handler));
+    } else {
+        element.request_pointer_lock();
+    }
+}
+
+#[wasm_bindgen]
+extern "C" {
+    type ElementExt;
+
+    #[wasm_bindgen(method, js_name = requestPointerLock)]
+    fn request_pointer_lock(this: &ElementExt) -> JsValue;
+
+    #[wasm_bindgen(method, js_name = requestPointerLock)]
+    fn request_pointer_lock_with_options(
+        this: &ElementExt,
+        options: &PointerLockOptions,
+    ) -> Promise;
+
+    type PointerLockOptions;
+
+    #[wasm_bindgen(method, setter, js_name = unadjustedMovement)]
+    fn set_unadjusted_movement(this: &PointerLockOptions, value: bool);
+}

winit-web/src/main_thread.rs

@@ -0,0 +1,96 @@
+use std::fmt::{self, Debug, Formatter};
+use std::marker::PhantomData;
+use std::mem;
+use std::sync::OnceLock;
+
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::{JsCast, JsValue};
+
+use super::r#async::{self, Sender};
+
+thread_local! {
+    static MAIN_THREAD: bool = {
+        #[wasm_bindgen]
+        extern "C" {
+            #[derive(Clone)]
+            type Global;
+
+            #[wasm_bindgen(method, getter, js_name = Window)]
+            fn window(this: &Global) -> JsValue;
+        }
+
+        let global: Global = js_sys::global().unchecked_into();
+        !global.window().is_undefined()
+    };
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct MainThreadMarker(PhantomData<*const ()>);
+
+impl MainThreadMarker {
+    pub fn new() -> Option<Self> {
+        MAIN_THREAD.with(|is| is.then_some(Self(PhantomData)))
+    }
+}
+
+pub struct MainThreadSafe<T: 'static>(Option<T>);
+
+impl<T> MainThreadSafe<T> {
+    pub fn new(_: MainThreadMarker, value: T) -> Self {
+        DROP_HANDLER.get_or_init(|| {
+            let (sender, receiver) = r#async::channel();
+            wasm_bindgen_futures::spawn_local(
+                async move { while receiver.next().await.is_ok() {} },
+            );
+
+            sender
+        });
+
+        Self(Some(value))
+    }
+
+    pub fn into_inner(mut self, _: MainThreadMarker) -> T {
+        self.0.take().expect("already taken or dropped")
+    }
+
+    pub fn get(&self, _: MainThreadMarker) -> &T {
+        self.0.as_ref().expect("already taken or dropped")
+    }
+}
+
+impl<T: Debug> Debug for MainThreadSafe<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        if MainThreadMarker::new().is_some() {
+            f.debug_tuple("MainThreadSafe").field(&self.0).finish()
+        } else {
+            f.debug_struct("MainThreadSafe").finish_non_exhaustive()
+        }
+    }
+}
+
+impl<T> Drop for MainThreadSafe<T> {
+    fn drop(&mut self) {
+        if let Some(value) = self.0.take() {
+            if mem::needs_drop::<T>() && MainThreadMarker::new().is_none() {
+                DROP_HANDLER
+                    .get()
+                    .expect("drop handler not initialized when setting canvas")
+                    .send(DropBox(Box::new(value)))
+                    .expect("sender dropped in main thread")
+            }
+        }
+    }
+}
+
+unsafe impl<T> Send for MainThreadSafe<T> {}
+unsafe impl<T> Sync for MainThreadSafe<T> {}
+
+static DROP_HANDLER: OnceLock<Sender<DropBox>> = OnceLock::new();
+
+struct DropBox(#[allow(dead_code)] Box<dyn Any>);
+
+unsafe impl Send for DropBox {}
+unsafe impl Sync for DropBox {}
+
+trait Any {}
+impl<T> Any for T {}

winit-web/src/monitor.rs

@@ -0,0 +1,938 @@
+use std::cell::{OnceCell, Ref, RefCell};
+use std::cmp::Ordering;
+use std::fmt::{self, Debug, Formatter};
+use std::future::Future;
+use std::hash::{Hash, Hasher};
+use std::mem;
+use std::num::NonZeroU16;
+use std::ops::{Deref, DerefMut};
+use std::pin::Pin;
+use std::rc::{Rc, Weak};
+use std::sync::{Arc, OnceLock};
+use std::task::{ready, Context, Poll};
+
+use dpi::{LogicalSize, PhysicalPosition, PhysicalSize};
+use js_sys::{Object, Promise};
+use tracing::error;
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::{JsCast, JsValue};
+use wasm_bindgen_futures::JsFuture;
+use web_sys::{
+    console, DomException, Navigator, OrientationLockType, OrientationType, PermissionState,
+    PermissionStatus, ScreenOrientation, Window,
+};
+use winit_core::monitor::{MonitorHandle as CoreMonitorHandle, MonitorHandleProvider, VideoMode};
+
+use super::event_loop::runner::WeakShared;
+use super::main_thread::MainThreadMarker;
+use super::r#async::{Dispatcher, Notified, Notifier};
+use super::web_sys::{Engine, EventListenerHandle};
+use crate::{
+    MonitorPermissionError, Orientation, OrientationData, OrientationLock, OrientationLockError,
+};
+
+#[derive(Clone, Eq)]
+pub struct MonitorHandle {
+    /// [`None`] means [`web_sys::Screen`], which is always the same.
+    id: Option<u64>,
+    inner: Dispatcher<Inner>,
+}
+
+impl MonitorHandle {
+    fn new(main_thread: MainThreadMarker, inner: Inner) -> Self {
+        let id = if let Screen::Detailed { id, .. } = inner.screen { Some(id) } else { None };
+        Self { id, inner: Dispatcher::new(main_thread, inner).0 }
+    }
+
+    pub fn orientation(&self) -> OrientationData {
+        self.inner.queue(|inner| inner.orientation())
+    }
+
+    pub fn request_lock(&self, orientation_lock: OrientationLock) -> OrientationLockFuture {
+        // Short-circuit without blocking.
+        if let Some(support) = has_previous_lock_support() {
+            if !support {
+                return OrientationLockFuture::Ready(Some(Err(OrientationLockError::Unsupported)));
+            }
+        }
+
+        self.inner.queue(|inner| {
+            if !inner.has_lock_support() {
+                return OrientationLockFuture::Ready(Some(Err(OrientationLockError::Unsupported)));
+            }
+
+            let future =
+                JsFuture::from(inner.orientation_raw().lock(orientation_lock.to_js()).unwrap());
+            let notifier = Notifier::new();
+            let notified = notifier.notified();
+
+            wasm_bindgen_futures::spawn_local(async move {
+                notifier.notify(future.await.map(|_| ()).map_err(OrientationLockError::from_js));
+            });
+
+            OrientationLockFuture::Future(notified)
+        })
+    }
+
+    pub fn unlock(&self) -> Result<(), OrientationLockError> {
+        // Short-circuit without blocking.
+        if let Some(support) = has_previous_lock_support() {
+            if !support {
+                return Err(OrientationLockError::Unsupported);
+            }
+        }
+
+        self.inner.queue(|inner| {
+            if !inner.has_lock_support() {
+                return Err(OrientationLockError::Unsupported);
+            }
+
+            inner.orientation_raw().unlock().map_err(OrientationLockError::from_js)
+        })
+    }
+
+    pub fn is_internal(&self) -> Option<bool> {
+        self.inner.queue(|inner| inner.is_internal())
+    }
+
+    pub fn is_detailed(&self) -> bool {
+        self.inner.queue(|inner| inner.is_detailed())
+    }
+
+    pub(crate) fn detailed(
+        &self,
+        main_thread: MainThreadMarker,
+    ) -> Option<Ref<'_, ScreenDetailed>> {
+        let inner = self.inner.value(main_thread);
+        match &inner.screen {
+            Screen::Screen(_) => None,
+            Screen::Detailed { .. } => Some(Ref::map(inner, |inner| {
+                if let Screen::Detailed { screen, .. } = &inner.screen {
+                    screen.deref()
+                } else {
+                    unreachable!()
+                }
+            })),
+        }
+    }
+}
+
+impl MonitorHandleProvider for MonitorHandle {
+    fn id(&self) -> u128 {
+        self.native_id() as _
+    }
+
+    fn native_id(&self) -> u64 {
+        self.id.unwrap_or_default()
+    }
+
+    fn scale_factor(&self) -> f64 {
+        self.inner.queue(|inner| inner.scale_factor())
+    }
+
+    fn position(&self) -> Option<PhysicalPosition<i32>> {
+        self.inner.queue(|inner| inner.position())
+    }
+
+    fn name(&self) -> Option<std::borrow::Cow<'_, str>> {
+        self.inner.queue(|inner| inner.name().map(Into::into))
+    }
+
+    fn current_video_mode(&self) -> Option<VideoMode> {
+        Some(VideoMode::new(
+            self.inner.queue(|inner| inner.size()),
+            self.inner.queue(|inner| inner.bit_depth()),
+            None,
+        ))
+    }
+
+    fn video_modes(&self) -> Box<dyn Iterator<Item = VideoMode>> {
+        Box::new(self.current_video_mode().into_iter())
+    }
+}
+
+impl Debug for MonitorHandle {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        let (name, position, scale_factor, orientation, is_internal, is_detailed) =
+            self.inner.queue(|this| {
+                (
+                    this.name(),
+                    this.position(),
+                    this.scale_factor(),
+                    this.orientation(),
+                    this.is_internal(),
+                    this.is_detailed(),
+                )
+            });
+
+        f.debug_struct("MonitorHandle")
+            .field("name", &name)
+            .field("position", &position)
+            .field("scale_factor", &scale_factor)
+            .field("orientation", &orientation)
+            .field("is_internal", &is_internal)
+            .field("is_detailed", &is_detailed)
+            .finish()
+    }
+}
+
+impl Hash for MonitorHandle {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.id.hash(state)
+    }
+}
+
+impl Ord for MonitorHandle {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.id.cmp(&other.id)
+    }
+}
+
+impl PartialEq for MonitorHandle {
+    fn eq(&self, other: &Self) -> bool {
+        self.id.eq(&other.id)
+    }
+}
+
+impl PartialOrd for MonitorHandle {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl From<MonitorHandle> for CoreMonitorHandle {
+    fn from(monitor: MonitorHandle) -> Self {
+        CoreMonitorHandle(Arc::new(monitor))
+    }
+}
+
+#[derive(Debug)]
+pub enum OrientationLockFuture {
+    Future(Notified<Result<(), OrientationLockError>>),
+    Ready(Option<Result<(), OrientationLockError>>),
+}
+
+impl Future for OrientationLockFuture {
+    type Output = Result<(), OrientationLockError>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.get_mut() {
+            Self::Future(notified) => Pin::new(notified).poll(cx).map(Option::unwrap),
+            Self::Ready(result) => {
+                Poll::Ready(result.take().expect("`OrientationLockFuture` polled after completion"))
+            },
+        }
+    }
+}
+
+impl OrientationLock {
+    fn to_js(self) -> OrientationLockType {
+        match self {
+            OrientationLock::Any => OrientationLockType::Any,
+            OrientationLock::Natural => OrientationLockType::Natural,
+            OrientationLock::Landscape { flipped: None } => OrientationLockType::Landscape,
+            OrientationLock::Landscape { flipped: Some(flipped) } => {
+                if flipped {
+                    OrientationLockType::LandscapeSecondary
+                } else {
+                    OrientationLockType::LandscapePrimary
+                }
+            },
+            OrientationLock::Portrait { flipped: None } => OrientationLockType::Portrait,
+            OrientationLock::Portrait { flipped: Some(flipped) } => {
+                if flipped {
+                    OrientationLockType::PortraitSecondary
+                } else {
+                    OrientationLockType::PortraitPrimary
+                }
+            },
+        }
+    }
+}
+
+impl OrientationLockError {
+    fn from_js(error: JsValue) -> Self {
+        debug_assert!(error.has_type::<DomException>());
+        let error: DomException = error.unchecked_into();
+
+        if let DomException::ABORT_ERR = error.code() {
+            OrientationLockError::Busy
+        } else {
+            OrientationLockError::Unsupported
+        }
+    }
+}
+
+struct Inner {
+    window: WindowExt,
+    engine: Option<Engine>,
+    screen: Screen,
+    orientation: OnceCell<ScreenOrientationExt>,
+}
+
+impl Inner {
+    fn new(window: WindowExt, engine: Option<Engine>, screen: Screen) -> Self {
+        Self { window, engine, screen, orientation: OnceCell::new() }
+    }
+
+    fn scale_factor(&self) -> f64 {
+        match &self.screen {
+            Screen::Screen(_) => 0.,
+            Screen::Detailed { screen, .. } => screen.device_pixel_ratio(),
+        }
+    }
+
+    fn position(&self) -> Option<PhysicalPosition<i32>> {
+        if let Screen::Detailed { screen, .. } = &self.screen {
+            Some(PhysicalPosition::new(screen.left(), screen.top()))
+        } else {
+            None
+        }
+    }
+
+    fn name(&self) -> Option<String> {
+        if let Screen::Detailed { screen, .. } = &self.screen {
+            Some(screen.label())
+        } else {
+            None
+        }
+    }
+
+    fn orientation_raw(&self) -> &ScreenOrientationExt {
+        self.orientation.get_or_init(|| self.screen.orientation().unchecked_into())
+    }
+
+    fn orientation(&self) -> OrientationData {
+        let orientation = self.orientation_raw();
+
+        let angle = orientation.angle().unwrap();
+
+        match orientation.type_().unwrap() {
+            OrientationType::LandscapePrimary => OrientationData {
+                orientation: Orientation::Landscape,
+                flipped: false,
+                natural: if angle == 0 { Orientation::Landscape } else { Orientation::Portrait },
+            },
+            OrientationType::LandscapeSecondary => OrientationData {
+                orientation: Orientation::Landscape,
+                flipped: true,
+                natural: if angle == 180 { Orientation::Landscape } else { Orientation::Portrait },
+            },
+            OrientationType::PortraitPrimary => OrientationData {
+                orientation: Orientation::Portrait,
+                flipped: false,
+                natural: if angle == 0 { Orientation::Portrait } else { Orientation::Landscape },
+            },
+            OrientationType::PortraitSecondary => OrientationData {
+                orientation: Orientation::Portrait,
+                flipped: true,
+                natural: if angle == 180 { Orientation::Portrait } else { Orientation::Landscape },
+            },
+            _ => {
+                unreachable!("found unrecognized orientation: {}", orientation.type_string())
+            },
+        }
+    }
+
+    fn is_internal(&self) -> Option<bool> {
+        if let Screen::Detailed { screen, .. } = &self.screen {
+            Some(screen.is_internal())
+        } else {
+            None
+        }
+    }
+
+    fn is_detailed(&self) -> bool {
+        matches!(self.screen, Screen::Detailed { .. })
+    }
+
+    fn size(&self) -> PhysicalSize<u32> {
+        let width = self.screen.width().unwrap();
+        let height = self.screen.height().unwrap();
+
+        if let Some(Engine::Chromium) = self.engine {
+            PhysicalSize::new(width, height).cast()
+        } else {
+            LogicalSize::new(width, height).to_physical(super::web_sys::scale_factor(&self.window))
+        }
+    }
+
+    fn bit_depth(&self) -> Option<NonZeroU16> {
+        NonZeroU16::new(self.screen.color_depth().unwrap().try_into().unwrap())
+    }
+
+    fn has_lock_support(&self) -> bool {
+        *HAS_LOCK_SUPPORT.get_or_init(|| !self.orientation_raw().has_lock().is_undefined())
+    }
+}
+
+impl Drop for Inner {
+    fn drop(&mut self) {
+        if let Screen::Detailed { runner, id, screen } = &self.screen {
+            // If this is the last screen with its ID, clean it up in the `MonitorHandler`.
+            if Rc::strong_count(screen) == 1 {
+                if let Some(runner) = runner.upgrade() {
+                    let mut state = runner.monitor().state.borrow_mut();
+                    let State::Detailed(detailed) = state.deref_mut() else {
+                        unreachable!("found a `ScreenDetailed` without being in `State::Detailed`")
+                    };
+
+                    detailed.screens.retain(|(id_internal, _)| *id_internal != *id)
+                }
+            }
+        }
+    }
+}
+
+enum Screen {
+    Screen(ScreenExt),
+    Detailed { runner: WeakShared, id: u64, screen: Rc<ScreenDetailed> },
+}
+
+impl Deref for Screen {
+    type Target = ScreenExt;
+
+    fn deref(&self) -> &Self::Target {
+        match self {
+            Screen::Screen(screen) => screen,
+            Screen::Detailed { screen, .. } => screen,
+        }
+    }
+}
+
+pub struct MonitorHandler {
+    runner: WeakShared,
+    state: RefCell<State>,
+    main_thread: MainThreadMarker,
+    window: WindowExt,
+    engine: Option<Engine>,
+    screen: ScreenExt,
+}
+
+enum State {
+    Unsupported,
+    Initialize(Notified<Result<(), MonitorPermissionError>>),
+    Permission { permission: PermissionStatusExt, _handle: EventListenerHandle<dyn Fn()> },
+    Upgrade(Notified<Result<(), MonitorPermissionError>>),
+    Detailed(Detailed),
+}
+
+struct Detailed {
+    details: ScreenDetails,
+    id_counter: u64,
+    screens: Vec<(u64, Weak<ScreenDetailed>)>,
+}
+
+impl Detailed {
+    fn handle(
+        &mut self,
+        main_thread: MainThreadMarker,
+        runner: WeakShared,
+        window: WindowExt,
+        engine: Option<Engine>,
+        screen: ScreenDetailed,
+    ) -> MonitorHandle {
+        // Before creating a new entry, see if we have an ID for this screen already.
+        let found_screen = self.screens.iter().find_map(|(id, internal_screen)| {
+            let internal_screen =
+                internal_screen.upgrade().expect("dropped `MonitorHandle` without cleaning up");
+
+            if *internal_screen == screen {
+                Some((*id, internal_screen))
+            } else {
+                None
+            }
+        });
+        let (id, screen) = if let Some((id, screen)) = found_screen {
+            (id, screen)
+        } else {
+            let id = self.id_counter;
+            self.id_counter += 1;
+            let screen = Rc::new(screen);
+
+            self.screens.push((id, Rc::downgrade(&screen)));
+
+            (id, screen)
+        };
+
+        MonitorHandle::new(
+            main_thread,
+            Inner::new(window, engine, Screen::Detailed { runner, id, screen }),
+        )
+    }
+}
+
+impl MonitorHandler {
+    /// When the [`MonitorHandler`] is created, it first checks if permission has already been
+    /// granted by the user for this page, in which case it retrieves [`ScreenDetails`].
+    ///
+    /// If not, it will listen to external changes in the permission and automatically elevate
+    /// [`MonitorHandler`].
+    pub fn new(
+        main_thread: MainThreadMarker,
+        window: Window,
+        navigator: &Navigator,
+        runner: WeakShared,
+    ) -> Self {
+        let window: WindowExt = window.unchecked_into();
+        let engine = super::web_sys::engine(navigator);
+        let screen: ScreenExt = window.screen().unwrap().unchecked_into();
+
+        let state = if has_screen_details_support(&window) {
+            // First try and get permissions.
+            let permissions = navigator.permissions().expect(
+                "expected the Permissions API to be implemented if the Window Management API is \
+                 as well",
+            );
+            let descriptor: PermissionDescriptor = Object::new().unchecked_into();
+            descriptor.set_name("window-management");
+            let future = JsFuture::from(permissions.query(&descriptor).unwrap());
+
+            let runner = runner.clone();
+            let window = window.clone();
+            let notifier = Notifier::new();
+            let notified = notifier.notified();
+            wasm_bindgen_futures::spawn_local(async move {
+                let permission: PermissionStatusExt = match future.await {
+                    Ok(permission) => permission.unchecked_into(),
+                    Err(error) => unreachable_error(
+                        &error,
+                        "retrieving permission for Window Management API failed even though its \
+                         implemented",
+                    ),
+                };
+
+                let details = match permission.state() {
+                    // If we have permission, go ahead and get `ScreenDetails`.
+                    PermissionState::Granted => {
+                        let details = match JsFuture::from(window.screen_details()).await {
+                            Ok(details) => details.unchecked_into(),
+                            Err(error) => unreachable_error(
+                                &error,
+                                "getting screen details failed even though permission was granted",
+                            ),
+                        };
+                        notifier.notify(Ok(()));
+                        Some(details)
+                    },
+                    PermissionState::Denied => {
+                        notifier.notify(Err(MonitorPermissionError::Denied));
+                        None
+                    },
+                    PermissionState::Prompt => {
+                        notifier.notify(Err(MonitorPermissionError::Prompt));
+                        None
+                    },
+                    _ => {
+                        error!(
+                            "encountered unknown permission state: {}",
+                            permission.state_string()
+                        );
+                        notifier.notify(Err(MonitorPermissionError::Denied));
+                        None
+                    },
+                };
+
+                // Notifying `Future`s is not dependant on the lifetime of the runner,
+                // because they can outlive it.
+                if let Some(runner) = runner.upgrade() {
+                    if let Some(details) = details {
+                        runner.monitor().upgrade(details);
+                    } else {
+                        // If permission is denied we listen for changes so we can catch external
+                        // permission granting.
+                        let handle =
+                            Self::setup_listener(runner.weak(), window, permission.clone());
+                        *runner.monitor().state.borrow_mut() =
+                            State::Permission { permission, _handle: handle };
+                    };
+
+                    runner.start_delayed();
+                }
+            });
+
+            State::Initialize(notified)
+        } else {
+            State::Unsupported
+        };
+
+        Self { runner, state: RefCell::new(state), main_thread, window, engine, screen }
+    }
+
+    /// Listens to external permission changes and elevates [`MonitorHandle`] automatically.
+    fn setup_listener(
+        runner: WeakShared,
+        window: WindowExt,
+        permission: PermissionStatus,
+    ) -> EventListenerHandle<dyn Fn()> {
+        EventListenerHandle::new(
+            permission.clone(),
+            "change",
+            Closure::new(move || {
+                if let PermissionState::Granted = permission.state() {
+                    let future = JsFuture::from(window.screen_details());
+
+                    let runner = runner.clone();
+                    wasm_bindgen_futures::spawn_local(async move {
+                        let details = match future.await {
+                            Ok(details) => details.unchecked_into(),
+                            Err(error) => unreachable_error(
+                                &error,
+                                "getting screen details failed even though permission was granted",
+                            ),
+                        };
+
+                        if let Some(runner) = runner.upgrade() {
+                            // We drop the event listener handle here, which
+                            // doesn't drop it during its execution, because
+                            // we are in a `spawn_local()` context.
+                            runner.monitor().upgrade(details);
+                        }
+                    });
+                }
+            }),
+        )
+    }
+
+    /// Elevate [`MonitorHandler`] to [`ScreenDetails`].
+    fn upgrade(&self, details: ScreenDetails) {
+        *self.state.borrow_mut() =
+            State::Detailed(Detailed { details, id_counter: 0, screens: Vec::new() });
+    }
+
+    pub fn is_extended(&self) -> Option<bool> {
+        self.screen.is_extended()
+    }
+
+    pub fn is_initializing(&self) -> bool {
+        matches!(self.state.borrow().deref(), State::Initialize(_))
+    }
+
+    fn handle(&self, detailed: &mut Detailed, screen: ScreenDetailed) -> MonitorHandle {
+        detailed.handle(
+            self.main_thread,
+            self.runner.clone(),
+            self.window.clone(),
+            self.engine,
+            screen,
+        )
+    }
+
+    pub fn current_monitor(&self) -> MonitorHandle {
+        if let State::Detailed(detailed) = self.state.borrow_mut().deref_mut() {
+            self.handle(detailed, detailed.details.current_screen())
+        } else {
+            MonitorHandle::new(
+                self.main_thread,
+                Inner::new(self.window.clone(), self.engine, Screen::Screen(self.screen.clone())),
+            )
+        }
+    }
+
+    // Note: We have to return a `Vec` here because the iterator is otherwise not `Send` + `Sync`.
+    pub fn available_monitors(&self) -> Vec<MonitorHandle> {
+        let mut state = self.state.borrow_mut();
+        if let State::Detailed(detailed) = state.deref_mut() {
+            detailed
+                .details
+                .screens()
+                .into_iter()
+                .map(move |screen| self.handle(detailed, screen))
+                .collect()
+        } else {
+            drop(state);
+            vec![self.current_monitor()]
+        }
+    }
+
+    pub fn primary_monitor(&self) -> Option<MonitorHandle> {
+        if let State::Detailed(detailed) = self.state.borrow_mut().deref_mut() {
+            detailed
+                .details
+                .screens()
+                .into_iter()
+                .find_map(|screen| screen.is_primary().then(|| self.handle(detailed, screen)))
+        } else {
+            None
+        }
+    }
+
+    pub(crate) fn request_detailed_monitor_permission(&self) -> MonitorPermissionFuture {
+        let state = self.state.borrow();
+        let permission = match state.deref() {
+            State::Unsupported => {
+                return MonitorPermissionFuture::Ready(Some(Err(
+                    MonitorPermissionError::Unsupported,
+                )))
+            },
+            // If we are currently initializing, wait for initialization to finish before we do our
+            // thing.
+            State::Initialize(notified) => {
+                return MonitorPermissionFuture::Initialize {
+                    runner: Dispatcher::new(
+                        self.main_thread,
+                        (self.runner.clone(), self.window.clone()),
+                    )
+                    .0,
+                    notified: notified.clone(),
+                }
+            },
+            // If we finished initialization we at least possess `PermissionStatus`.
+            State::Permission { permission, .. } => permission,
+            // A request is already in progress. Use that!
+            State::Upgrade(notified) => return MonitorPermissionFuture::Upgrade(notified.clone()),
+            State::Detailed { .. } => return MonitorPermissionFuture::Ready(Some(Ok(()))),
+        };
+
+        match permission.state() {
+            PermissionState::Granted | PermissionState::Prompt => (),
+            PermissionState::Denied => {
+                return MonitorPermissionFuture::Ready(Some(Err(MonitorPermissionError::Denied)))
+            },
+            _ => {
+                error!("encountered unknown permission state: {}", permission.state_string());
+
+                return MonitorPermissionFuture::Ready(Some(Err(MonitorPermissionError::Denied)));
+            },
+        }
+
+        drop(state);
+
+        // We are ready to explicitly ask the user for permission, lets go!
+
+        let notifier = Notifier::new();
+        let notified = notifier.notified();
+        *self.state.borrow_mut() = State::Upgrade(notified.clone());
+
+        MonitorPermissionFuture::upgrade_internal(self.runner.clone(), &self.window, notifier);
+
+        MonitorPermissionFuture::Upgrade(notified)
+    }
+
+    pub fn has_detailed_monitor_permission_async(&self) -> HasMonitorPermissionFuture {
+        match self.state.borrow().deref() {
+            State::Unsupported | State::Permission { .. } | State::Upgrade(_) => {
+                HasMonitorPermissionFuture::Ready(Some(false))
+            },
+            State::Initialize(notified) => HasMonitorPermissionFuture::Future(notified.clone()),
+            State::Detailed { .. } => HasMonitorPermissionFuture::Ready(Some(true)),
+        }
+    }
+
+    pub fn has_detailed_monitor_permission(&self) -> bool {
+        match self.state.borrow().deref() {
+            State::Unsupported | State::Permission { .. } | State::Upgrade(_) => false,
+            State::Initialize(_) => {
+                unreachable!("called `has_detailed_monitor_permission()` while initializing")
+            },
+            State::Detailed { .. } => true,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub(crate) enum MonitorPermissionFuture {
+    Initialize {
+        runner: Dispatcher<(WeakShared, WindowExt)>,
+        notified: Notified<Result<(), MonitorPermissionError>>,
+    },
+    Upgrade(Notified<Result<(), MonitorPermissionError>>),
+    Ready(Option<Result<(), MonitorPermissionError>>),
+}
+
+impl MonitorPermissionFuture {
+    fn upgrade(&mut self) {
+        let notifier = Notifier::new();
+        let notified = notifier.notified();
+        let Self::Initialize { runner, .. } = mem::replace(self, Self::Upgrade(notified.clone()))
+        else {
+            unreachable!()
+        };
+
+        runner.dispatch(|(runner, window)| {
+            if let Some(runner) = runner.upgrade() {
+                *runner.monitor().state.borrow_mut() = State::Upgrade(notified);
+            }
+
+            Self::upgrade_internal(runner.clone(), window, notifier);
+        });
+    }
+
+    fn upgrade_internal(
+        runner: WeakShared,
+        window: &WindowExt,
+        notifier: Notifier<Result<(), MonitorPermissionError>>,
+    ) {
+        let future = JsFuture::from(window.screen_details());
+
+        wasm_bindgen_futures::spawn_local(async move {
+            match future.await {
+                Ok(details) => {
+                    // Notifying `Future`s is not dependant on the lifetime of the runner, because
+                    // they can outlive it.
+                    notifier.notify(Ok(()));
+
+                    if let Some(runner) = runner.upgrade() {
+                        runner.monitor().upgrade(details.unchecked_into());
+                    }
+                },
+                Err(error) => unreachable_error(
+                    &error,
+                    "getting screen details failed even though permission was granted",
+                ),
+            }
+        });
+    }
+}
+
+impl Future for MonitorPermissionFuture {
+    type Output = Result<(), MonitorPermissionError>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.get_mut();
+
+        match this {
+            Self::Initialize { notified, .. } => {
+                if let Err(error) = ready!(Pin::new(notified).poll(cx).map(Option::unwrap)) {
+                    match error {
+                        MonitorPermissionError::Denied | MonitorPermissionError::Unsupported => {
+                            Poll::Ready(Err(error))
+                        },
+                        MonitorPermissionError::Prompt => {
+                            this.upgrade();
+                            Poll::Pending
+                        },
+                    }
+                } else {
+                    Poll::Ready(Ok(()))
+                }
+            },
+            Self::Upgrade(notified) => Pin::new(notified).poll(cx).map(Option::unwrap),
+            Self::Ready(result) => Poll::Ready(
+                result.take().expect("`MonitorPermissionFuture` polled after completion"),
+            ),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum HasMonitorPermissionFuture {
+    Future(Notified<Result<(), MonitorPermissionError>>),
+    Ready(Option<bool>),
+}
+
+impl Future for HasMonitorPermissionFuture {
+    type Output = bool;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match self.get_mut() {
+            Self::Future(notified) => {
+                Pin::new(notified).poll(cx).map(Option::unwrap).map(|result| result.is_ok())
+            },
+            Self::Ready(result) => Poll::Ready(
+                result.take().expect("`MonitorPermissionFuture` polled after completion"),
+            ),
+        }
+    }
+}
+
+#[track_caller]
+fn unreachable_error(error: &JsValue, message: &str) -> ! {
+    if let Some(error) = error.dyn_ref::<DomException>() {
+        unreachable!("{message}. {}: {}", error.name(), error.message());
+    } else {
+        console::error_1(error);
+        unreachable!("{message}");
+    }
+}
+
+static HAS_LOCK_SUPPORT: OnceLock<bool> = OnceLock::new();
+
+fn has_previous_lock_support() -> Option<bool> {
+    HAS_LOCK_SUPPORT.get().cloned()
+}
+
+pub fn has_screen_details_support(window: &Window) -> bool {
+    thread_local! {
+        static HAS_SCREEN_DETAILS: OnceCell<bool> = const { OnceCell::new() };
+    }
+
+    HAS_SCREEN_DETAILS.with(|support| {
+        *support.get_or_init(|| {
+            let window: &WindowExt = window.unchecked_ref();
+            !window.has_screen_details().is_undefined()
+        })
+    })
+}
+
+#[wasm_bindgen]
+extern "C" {
+    #[derive(Clone)]
+    #[wasm_bindgen(extends = Window)]
+    pub(crate) type WindowExt;
+
+    #[wasm_bindgen(method, getter, js_name = getScreenDetails)]
+    fn has_screen_details(this: &WindowExt) -> JsValue;
+
+    #[wasm_bindgen(method, js_name = getScreenDetails)]
+    fn screen_details(this: &WindowExt) -> Promise;
+
+    type ScreenDetails;
+
+    #[wasm_bindgen(method, getter, js_name = currentScreen)]
+    fn current_screen(this: &ScreenDetails) -> ScreenDetailed;
+
+    #[wasm_bindgen(method, getter)]
+    fn screens(this: &ScreenDetails) -> Vec<ScreenDetailed>;
+
+    #[derive(Clone, PartialEq)]
+    #[wasm_bindgen(extends = web_sys::Screen)]
+    pub(crate) type ScreenExt;
+
+    #[wasm_bindgen(method, getter, js_name = isExtended)]
+    fn is_extended(this: &ScreenExt) -> Option<bool>;
+
+    #[wasm_bindgen(extends = ScreenOrientation)]
+    type ScreenOrientationExt;
+
+    #[wasm_bindgen(method, getter, js_name = type)]
+    fn type_string(this: &ScreenOrientationExt) -> String;
+
+    #[wasm_bindgen(method, getter, js_name = lock)]
+    fn has_lock(this: &ScreenOrientationExt) -> JsValue;
+
+    #[derive(PartialEq)]
+    #[wasm_bindgen(extends = ScreenExt)]
+    pub(crate) type ScreenDetailed;
+
+    #[wasm_bindgen(method, getter, js_name = devicePixelRatio)]
+    fn device_pixel_ratio(this: &ScreenDetailed) -> f64;
+
+    #[wasm_bindgen(method, getter, js_name = isInternal)]
+    fn is_internal(this: &ScreenDetailed) -> bool;
+
+    #[wasm_bindgen(method, getter, js_name = isPrimary)]
+    fn is_primary(this: &ScreenDetailed) -> bool;
+
+    #[wasm_bindgen(method, getter)]
+    fn label(this: &ScreenDetailed) -> String;
+
+    #[wasm_bindgen(method, getter)]
+    fn left(this: &ScreenDetailed) -> i32;
+
+    #[wasm_bindgen(method, getter)]
+    fn top(this: &ScreenDetailed) -> i32;
+
+    #[wasm_bindgen(extends = Object)]
+    type PermissionDescriptor;
+
+    #[wasm_bindgen(method, setter, js_name = name)]
+    fn set_name(this: &PermissionDescriptor, name: &str);
+
+    #[wasm_bindgen(extends = PermissionStatus)]
+    type PermissionStatusExt;
+
+    #[wasm_bindgen(method, getter, js_name = state)]
+    fn state_string(this: &PermissionStatusExt) -> String;
+}

winit-web/src/script/.swcrc

@@ -0,0 +1,19 @@
+{
+	"module": {
+		"type": "es6"
+	},
+	"isModule": true,
+	"minify": true,
+	"jsc": {
+		"parser": {
+			"syntax": "typescript"
+		},
+		"target": "es2022",
+		"minify": {
+			"compress": {
+				"unused": true
+			},
+			"mangle": true
+		}
+	}
+}

winit-web/src/script/eslint.config.mjs

@@ -0,0 +1,32 @@
+import eslint from '@eslint/js'
+import tseslint from 'typescript-eslint'
+import globals from 'globals'
+
+export default tseslint.config(
+	{
+		ignores: ['**/*.min.js', 'eslint.config.mjs'],
+	},
+	eslint.configs.recommended,
+	...tseslint.configs.strictTypeChecked,
+	...tseslint.configs.stylisticTypeChecked,
+	{
+		languageOptions: {
+			parserOptions: {
+				ecmaVersion: 'latest',
+				project: ['tsconfig.json'],
+				sourceType: 'module',
+			},
+			globals: {
+				...globals.browser,
+			},
+		},
+		rules: {
+			'@typescript-eslint/no-confusing-void-expression': [
+				'error',
+				{
+					ignoreArrowShorthand: true,
+				},
+			],
+		},
+	}
+)

winit-web/src/script/package.json

@@ -0,0 +1,8 @@
+{
+	"devDependencies": {
+		"@eslint/js": "^9",
+		"eslint": "^9",
+		"typescript": "^5",
+		"typescript-eslint": "^8"
+	}
+}

winit-web/src/script/scheduler.d.ts

@@ -0,0 +1,12 @@
+declare global {
+	// eslint-disable-next-line no-var
+	var scheduler: Scheduler
+}
+
+export interface Scheduler {
+	postTask<T>(callback: () => T | PromiseLike<T>, options?: SchedulerPostTaskOptions): Promise<T>
+}
+
+export interface SchedulerPostTaskOptions {
+	delay?: number
+}

winit-web/src/script/tsconfig.json

@@ -0,0 +1,14 @@
+{
+	"compilerOptions": {
+		"target": "ESNext",
+		"allowUnreachableCode": false,
+		"allowUnusedLabels": false,
+		"exactOptionalPropertyTypes": true,
+		"noImplicitOverride": true,
+		"noPropertyAccessFromIndexSignature": true,
+		"noUncheckedIndexedAccess": true,
+		"noUnusedLocals": true,
+		"noUnusedParameters": true,
+		"strict": true,
+	}
+}

winit-web/src/script/worker.min.js

@@ -0,0 +1 @@
+onmessage=e=>{let[s,a]=e.data,l=()=>s.postMessage(void 0);"scheduler"in globalThis?globalThis.scheduler.postTask(l,{delay:a}):setTimeout(l,a)};

winit-web/src/script/worker.ts

@@ -0,0 +1,10 @@
+onmessage = (event) => {
+	const [port, timeout] = event.data as [MessagePort, number]
+	const f = () => port.postMessage(undefined)
+
+	if ('scheduler' in globalThis) {
+		void globalThis.scheduler.postTask(f, { delay: timeout })
+	} else {
+		setTimeout(f, timeout)
+	}
+}

winit-web/src/web_sys/animation_frame.rs

@@ -0,0 +1,61 @@
+use std::cell::Cell;
+use std::rc::Rc;
+
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::JsCast;
+
+pub struct AnimationFrameHandler {
+    window: web_sys::Window,
+    closure: Closure<dyn FnMut()>,
+    handle: Rc<Cell<Option<i32>>>,
+}
+
+impl AnimationFrameHandler {
+    pub fn new(window: web_sys::Window) -> Self {
+        let handle = Rc::new(Cell::new(None));
+        let closure = Closure::new({
+            let handle = handle.clone();
+            move || handle.set(None)
+        });
+
+        Self { window, closure, handle }
+    }
+
+    pub fn on_animation_frame<F>(&mut self, mut f: F)
+    where
+        F: 'static + FnMut(),
+    {
+        let handle = self.handle.clone();
+        self.closure = Closure::new(move || {
+            handle.set(None);
+            f();
+        })
+    }
+
+    pub fn request(&self) {
+        if let Some(handle) = self.handle.take() {
+            self.window.cancel_animation_frame(handle).expect("Failed to cancel animation frame");
+        }
+
+        let handle = self
+            .window
+            .request_animation_frame(self.closure.as_ref().unchecked_ref())
+            .expect("Failed to request animation frame");
+
+        self.handle.set(Some(handle));
+    }
+
+    pub fn cancel(&mut self) {
+        if let Some(handle) = self.handle.take() {
+            self.window.cancel_animation_frame(handle).expect("Failed to cancel animation frame");
+        }
+    }
+}
+
+impl Drop for AnimationFrameHandler {
+    fn drop(&mut self) {
+        if let Some(handle) = self.handle.take() {
+            self.window.cancel_animation_frame(handle).expect("Failed to cancel animation frame");
+        }
+    }
+}

winit-web/src/web_sys/canvas.rs

@@ -0,0 +1,594 @@
+use std::cell::{Cell, RefCell};
+use std::ops::Deref;
+use std::rc::Rc;
+use std::sync::{Arc, Mutex};
+
+use dpi::{LogicalPosition, PhysicalPosition, PhysicalSize};
+use smol_str::SmolStr;
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::JsCast;
+use web_sys::{
+    CssStyleDeclaration, Document, Event, FocusEvent, HtmlCanvasElement, KeyboardEvent, Navigator,
+    PointerEvent, WheelEvent,
+};
+use winit_core::error::RequestError;
+use winit_core::event::{
+    ButtonSource, DeviceId, ElementState, MouseScrollDelta, PointerKind, PointerSource,
+    SurfaceSizeWriter, WindowEvent,
+};
+use winit_core::keyboard::{Key, KeyLocation, ModifiersState, PhysicalKey};
+use winit_core::monitor::Fullscreen;
+use winit_core::window::{WindowAttributes, WindowId};
+
+use super::super::cursor::CursorHandler;
+use super::super::event_loop::runner;
+use super::super::main_thread::MainThreadMarker;
+use super::animation_frame::AnimationFrameHandler;
+use super::event_handle::EventListenerHandle;
+use super::intersection_handle::IntersectionObserverHandle;
+use super::media_query_handle::MediaQueryListHandle;
+use super::pointer::PointerHandler;
+use super::{event, fullscreen, ResizeScaleHandle};
+use crate::WindowAttributesWeb;
+
+#[allow(dead_code)]
+pub struct Canvas {
+    main_thread: MainThreadMarker,
+    common: Common,
+    id: WindowId,
+    pub has_focus: Rc<Cell<bool>>,
+    pub prevent_default: Rc<Cell<bool>>,
+    pub is_intersecting: Cell<Option<bool>>,
+    pub cursor: CursorHandler,
+    handlers: RefCell<Handlers>,
+}
+
+struct Handlers {
+    animation_frame_handler: AnimationFrameHandler,
+    on_touch_start: Option<EventListenerHandle<dyn FnMut(Event)>>,
+    on_focus: Option<EventListenerHandle<dyn FnMut(FocusEvent)>>,
+    on_blur: Option<EventListenerHandle<dyn FnMut(FocusEvent)>>,
+    on_keyboard_release: Option<EventListenerHandle<dyn FnMut(KeyboardEvent)>>,
+    on_keyboard_press: Option<EventListenerHandle<dyn FnMut(KeyboardEvent)>>,
+    on_mouse_wheel: Option<EventListenerHandle<dyn FnMut(WheelEvent)>>,
+    on_dark_mode: Option<MediaQueryListHandle>,
+    pointer_handler: PointerHandler,
+    on_resize_scale: Option<ResizeScaleHandle>,
+    on_intersect: Option<IntersectionObserverHandle>,
+    on_touch_end: Option<EventListenerHandle<dyn FnMut(Event)>>,
+    on_context_menu: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,
+}
+
+pub struct Common {
+    pub window: web_sys::Window,
+    navigator: Navigator,
+    pub document: Document,
+    /// Note: resizing the HTMLCanvasElement should go through `backend::set_canvas_size` to ensure
+    /// the DPI factor is maintained. Note: this is read-only because we use a pointer to this
+    /// for [`WindowHandle`][rwh_06::WindowHandle].
+    raw: Rc<HtmlCanvasElement>,
+    style: Style,
+    old_size: Rc<Cell<PhysicalSize<u32>>>,
+    current_size: Rc<Cell<PhysicalSize<u32>>>,
+}
+
+#[derive(Clone, Debug)]
+pub struct Style {
+    pub(super) read: CssStyleDeclaration,
+    pub(super) write: CssStyleDeclaration,
+}
+
+impl Canvas {
+    pub(crate) fn create(
+        main_thread: MainThreadMarker,
+        id: WindowId,
+        window: web_sys::Window,
+        navigator: Navigator,
+        document: Document,
+        mut attr: WindowAttributes,
+    ) -> Result<Self, RequestError> {
+        let web_attributes = attr
+            .platform
+            .take()
+            .and_then(|attrs| attrs.cast::<WindowAttributesWeb>().ok())
+            .unwrap_or_default();
+
+        let canvas = match web_attributes.canvas.map(Arc::try_unwrap) {
+            Some(Ok(canvas)) => canvas.into_inner(main_thread),
+            Some(Err(canvas)) => canvas.get(main_thread).clone(),
+            None => document
+                .create_element("canvas")
+                .map_err(|_| os_error!("Failed to create canvas element"))?
+                .unchecked_into(),
+        };
+
+        if web_attributes.append && !document.contains(Some(&canvas)) {
+            document
+                .body()
+                .expect("Failed to get body from document")
+                .append_child(&canvas)
+                .expect("Failed to append canvas to body");
+        }
+
+        // A tabindex is needed in order to capture local keyboard events.
+        // A "0" value means that the element should be focusable in
+        // sequential keyboard navigation, but its order is defined by the
+        // document's source order.
+        // https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/tabindex
+        if web_attributes.focusable {
+            canvas
+                .set_attribute("tabindex", "0")
+                .map_err(|_| os_error!("Failed to set a tabindex"))?;
+        }
+
+        let style = Style::new(&window, &canvas);
+
+        let cursor = CursorHandler::new(main_thread, canvas.clone(), style.clone());
+
+        let common = Common {
+            window: window.clone(),
+            document: document.clone(),
+            navigator,
+            raw: Rc::new(canvas.clone()),
+            style,
+            old_size: Rc::default(),
+            current_size: Rc::default(),
+        };
+
+        if let Some(size) = attr.surface_size {
+            let size = size.to_logical(super::scale_factor(&common.window));
+            super::set_canvas_size(&common.document, &common.raw, &common.style, size);
+        }
+
+        if let Some(size) = attr.min_surface_size {
+            let size = size.to_logical(super::scale_factor(&common.window));
+            super::set_canvas_min_size(&common.document, &common.raw, &common.style, Some(size));
+        }
+
+        if let Some(size) = attr.max_surface_size {
+            let size = size.to_logical(super::scale_factor(&common.window));
+            super::set_canvas_max_size(&common.document, &common.raw, &common.style, Some(size));
+        }
+
+        if let Some(position) = attr.position {
+            let position = position.to_logical(super::scale_factor(&common.window));
+            super::set_canvas_position(&common.document, &common.raw, &common.style, position);
+        }
+
+        if let Some(fullscreen) = attr.fullscreen {
+            fullscreen::request_fullscreen(main_thread, &window, &document, &canvas, fullscreen);
+        }
+
+        if attr.active {
+            let _ = common.raw.focus();
+        }
+
+        Ok(Canvas {
+            main_thread,
+            common,
+            id,
+            has_focus: Rc::new(Cell::new(false)),
+            prevent_default: Rc::new(Cell::new(web_attributes.prevent_default)),
+            is_intersecting: Cell::new(None),
+            cursor,
+            handlers: RefCell::new(Handlers {
+                animation_frame_handler: AnimationFrameHandler::new(window),
+                on_touch_start: None,
+                on_blur: None,
+                on_focus: None,
+                on_keyboard_release: None,
+                on_keyboard_press: None,
+                on_mouse_wheel: None,
+                on_dark_mode: None,
+                pointer_handler: PointerHandler::new(),
+                on_resize_scale: None,
+                on_intersect: None,
+                on_touch_end: None,
+                on_context_menu: None,
+            }),
+        })
+    }
+
+    pub fn set_attribute(&self, attribute: &str, value: &str) {
+        self.common
+            .raw
+            .set_attribute(attribute, value)
+            .unwrap_or_else(|err| panic!("error: {err:?}\nSet attribute: {attribute}"))
+    }
+
+    pub fn position(&self) -> LogicalPosition<f64> {
+        let bounds = self.common.raw.get_bounding_client_rect();
+        let mut position = LogicalPosition { x: bounds.x(), y: bounds.y() };
+
+        if self.document().contains(Some(self.raw())) && self.style().get("display") != "none" {
+            position.x += super::style_size_property(self.style(), "border-left-width")
+                + super::style_size_property(self.style(), "padding-left");
+            position.y += super::style_size_property(self.style(), "border-top-width")
+                + super::style_size_property(self.style(), "padding-top");
+        }
+
+        position
+    }
+
+    #[inline]
+    pub fn old_size(&self) -> PhysicalSize<u32> {
+        self.common.old_size.get()
+    }
+
+    #[inline]
+    pub fn surface_size(&self) -> PhysicalSize<u32> {
+        self.common.current_size.get()
+    }
+
+    #[inline]
+    pub fn set_old_size(&self, size: PhysicalSize<u32>) {
+        self.common.old_size.set(size)
+    }
+
+    #[inline]
+    pub fn set_current_size(&self, size: PhysicalSize<u32>) {
+        self.common.current_size.set(size)
+    }
+
+    #[inline]
+    pub fn window(&self) -> &web_sys::Window {
+        &self.common.window
+    }
+
+    #[inline]
+    pub fn navigator(&self) -> &Navigator {
+        &self.common.navigator
+    }
+
+    #[inline]
+    pub fn document(&self) -> &Document {
+        &self.common.document
+    }
+
+    #[inline]
+    pub fn raw(&self) -> &HtmlCanvasElement {
+        &self.common.raw
+    }
+
+    #[inline]
+    pub fn style(&self) -> &Style {
+        &self.common.style
+    }
+
+    pub fn on_touch_start(&self) {
+        let prevent_default = Rc::clone(&self.prevent_default);
+        self.handlers.borrow_mut().on_touch_start =
+            Some(self.common.add_event("touchstart", move |event: Event| {
+                if prevent_default.get() {
+                    event.prevent_default();
+                }
+            }));
+    }
+
+    pub fn on_blur<F>(&self, mut handler: F)
+    where
+        F: 'static + FnMut(),
+    {
+        self.handlers.borrow_mut().on_blur =
+            Some(self.common.add_event("blur", move |_: FocusEvent| {
+                handler();
+            }));
+    }
+
+    pub fn on_focus<F>(&self, mut handler: F)
+    where
+        F: 'static + FnMut(),
+    {
+        self.handlers.borrow_mut().on_focus =
+            Some(self.common.add_event("focus", move |_: FocusEvent| {
+                handler();
+            }));
+    }
+
+    pub fn on_keyboard_release<F>(&self, mut handler: F)
+    where
+        F: 'static + FnMut(PhysicalKey, Key, Option<SmolStr>, KeyLocation, bool, ModifiersState),
+    {
+        let prevent_default = Rc::clone(&self.prevent_default);
+        self.handlers.borrow_mut().on_keyboard_release =
+            Some(self.common.add_event("keyup", move |event: KeyboardEvent| {
+                if prevent_default.get() {
+                    event.prevent_default();
+                }
+                let key = event::key(&event);
+                let modifiers = event::keyboard_modifiers(&event);
+                handler(
+                    event::key_code(&event),
+                    key,
+                    event::key_text(&event),
+                    event::key_location(&event),
+                    event.repeat(),
+                    modifiers,
+                );
+            }));
+    }
+
+    pub fn on_keyboard_press<F>(&self, mut handler: F)
+    where
+        F: 'static + FnMut(PhysicalKey, Key, Option<SmolStr>, KeyLocation, bool, ModifiersState),
+    {
+        let prevent_default = Rc::clone(&self.prevent_default);
+        self.handlers.borrow_mut().on_keyboard_press =
+            Some(self.common.add_event("keydown", move |event: KeyboardEvent| {
+                if prevent_default.get() {
+                    event.prevent_default();
+                }
+                let key = event::key(&event);
+                let modifiers = event::keyboard_modifiers(&event);
+                handler(
+                    event::key_code(&event),
+                    key,
+                    event::key_text(&event),
+                    event::key_location(&event),
+                    event.repeat(),
+                    modifiers,
+                );
+            }));
+    }
+
+    pub fn on_pointer_leave<F>(&self, handler: F)
+    where
+        F: 'static
+            + FnMut(ModifiersState, Option<DeviceId>, bool, PhysicalPosition<f64>, PointerKind),
+    {
+        self.handlers.borrow_mut().pointer_handler.on_pointer_leave(&self.common, handler)
+    }
+
+    pub fn on_pointer_enter<F>(&self, handler: F)
+    where
+        F: 'static
+            + FnMut(ModifiersState, Option<DeviceId>, bool, PhysicalPosition<f64>, PointerKind),
+    {
+        self.handlers.borrow_mut().pointer_handler.on_pointer_enter(&self.common, handler)
+    }
+
+    pub fn on_pointer_release<C>(&self, handler: C)
+    where
+        C: 'static
+            + FnMut(ModifiersState, Option<DeviceId>, bool, PhysicalPosition<f64>, ButtonSource),
+    {
+        self.handlers.borrow_mut().pointer_handler.on_pointer_release(&self.common, handler)
+    }
+
+    pub fn on_pointer_press<C>(&self, handler: C)
+    where
+        C: 'static
+            + FnMut(ModifiersState, Option<DeviceId>, bool, PhysicalPosition<f64>, ButtonSource),
+    {
+        self.handlers.borrow_mut().pointer_handler.on_pointer_press(
+            &self.common,
+            handler,
+            Rc::clone(&self.prevent_default),
+        )
+    }
+
+    pub fn on_pointer_move<C, B>(&self, cursor_handler: C, button_handler: B)
+    where
+        C: 'static
+            + FnMut(
+                Option<DeviceId>,
+                &mut dyn Iterator<
+                    Item = (ModifiersState, bool, PhysicalPosition<f64>, PointerSource),
+                >,
+            ),
+        B: 'static
+            + FnMut(
+                ModifiersState,
+                Option<DeviceId>,
+                bool,
+                PhysicalPosition<f64>,
+                ElementState,
+                ButtonSource,
+            ),
+    {
+        self.handlers.borrow_mut().pointer_handler.on_pointer_move(
+            &self.common,
+            cursor_handler,
+            button_handler,
+            Rc::clone(&self.prevent_default),
+        )
+    }
+
+    pub fn on_mouse_wheel<F>(&self, mut handler: F)
+    where
+        F: 'static + FnMut(MouseScrollDelta, ModifiersState),
+    {
+        let window = self.common.window.clone();
+        let prevent_default = Rc::clone(&self.prevent_default);
+        self.handlers.borrow_mut().on_mouse_wheel =
+            Some(self.common.add_event("wheel", move |event: WheelEvent| {
+                if prevent_default.get() {
+                    event.prevent_default();
+                }
+
+                if let Some(delta) = event::mouse_scroll_delta(&window, &event) {
+                    let modifiers = event::mouse_modifiers(&event);
+                    handler(delta, modifiers);
+                }
+            }));
+    }
+
+    pub fn on_dark_mode<F>(&self, mut handler: F)
+    where
+        F: 'static + FnMut(bool),
+    {
+        self.handlers.borrow_mut().on_dark_mode = Some(MediaQueryListHandle::new(
+            &self.common.window,
+            "(prefers-color-scheme: dark)",
+            move |mql| handler(mql.matches()),
+        ));
+    }
+
+    pub(crate) fn on_resize_scale<S, R>(&self, scale_handler: S, size_handler: R)
+    where
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
+    {
+        self.handlers.borrow_mut().on_resize_scale = Some(ResizeScaleHandle::new(
+            self.window().clone(),
+            self.document().clone(),
+            self.raw().clone(),
+            self.style().clone(),
+            scale_handler,
+            size_handler,
+        ));
+    }
+
+    pub(crate) fn on_intersection<F>(&self, handler: F)
+    where
+        F: 'static + FnMut(bool),
+    {
+        self.handlers.borrow_mut().on_intersect =
+            Some(IntersectionObserverHandle::new(self.raw(), handler));
+    }
+
+    pub(crate) fn on_animation_frame<F>(&self, f: F)
+    where
+        F: 'static + FnMut(),
+    {
+        self.handlers.borrow_mut().animation_frame_handler.on_animation_frame(f)
+    }
+
+    pub(crate) fn on_context_menu(&self) {
+        let prevent_default = Rc::clone(&self.prevent_default);
+        self.handlers.borrow_mut().on_context_menu =
+            Some(self.common.add_event("contextmenu", move |event: PointerEvent| {
+                if prevent_default.get() {
+                    event.prevent_default();
+                }
+            }));
+    }
+
+    pub(crate) fn request_fullscreen(&self, fullscreen: Fullscreen) {
+        fullscreen::request_fullscreen(
+            self.main_thread,
+            self.window(),
+            self.document(),
+            self.raw(),
+            fullscreen,
+        );
+    }
+
+    pub fn exit_fullscreen(&self) {
+        fullscreen::exit_fullscreen(self.document(), self.raw());
+    }
+
+    pub fn is_fullscreen(&self) -> bool {
+        fullscreen::is_fullscreen(self.document(), self.raw())
+    }
+
+    pub fn request_animation_frame(&self) {
+        self.handlers.borrow().animation_frame_handler.request();
+    }
+
+    pub(crate) fn handle_scale_change(
+        &self,
+        runner: &super::super::event_loop::runner::Shared,
+        event_handler: impl FnOnce(WindowId, WindowEvent),
+        current_size: PhysicalSize<u32>,
+        scale: f64,
+    ) {
+        // First, we send the `ScaleFactorChanged` event:
+        self.set_current_size(current_size);
+        let new_size = {
+            let new_size = Arc::new(Mutex::new(current_size));
+            event_handler(self.id, WindowEvent::ScaleFactorChanged {
+                scale_factor: scale,
+                surface_size_writer: SurfaceSizeWriter::new(Arc::downgrade(&new_size)),
+            });
+
+            let new_size = *new_size.lock().unwrap();
+            new_size
+        };
+
+        if current_size != new_size {
+            // Then we resize the canvas to the new size, a new `SurfaceResized` event will be sent
+            // by the `ResizeObserver`:
+            let new_size = new_size.to_logical(scale);
+            super::set_canvas_size(self.document(), self.raw(), self.style(), new_size);
+
+            // Set the size might not trigger the event because the calculation is inaccurate.
+            self.handlers
+                .borrow()
+                .on_resize_scale
+                .as_ref()
+                .expect("expected Window to still be active")
+                .notify_resize();
+        } else if self.old_size() != new_size {
+            // Then we at least send a resized event.
+            self.set_old_size(new_size);
+            runner.send_event(runner::Event::WindowEvent {
+                window_id: self.id,
+                event: WindowEvent::SurfaceResized(new_size),
+            })
+        }
+    }
+
+    pub fn remove_listeners(&self) {
+        let mut handlers = self.handlers.borrow_mut();
+        handlers.on_touch_start.take();
+        handlers.on_focus.take();
+        handlers.on_blur.take();
+        handlers.on_keyboard_release.take();
+        handlers.on_keyboard_press.take();
+        handlers.on_mouse_wheel.take();
+        handlers.on_dark_mode.take();
+        handlers.pointer_handler.remove_listeners();
+        handlers.on_resize_scale = None;
+        handlers.on_intersect = None;
+        handlers.animation_frame_handler.cancel();
+        handlers.on_touch_end = None;
+        handlers.on_context_menu = None;
+    }
+}
+
+impl Common {
+    pub fn add_event<E, F>(
+        &self,
+        event_name: &'static str,
+        handler: F,
+    ) -> EventListenerHandle<dyn FnMut(E)>
+    where
+        E: 'static + AsRef<web_sys::Event> + wasm_bindgen::convert::FromWasmAbi,
+        F: 'static + FnMut(E),
+    {
+        EventListenerHandle::new(self.raw.deref().clone(), event_name, Closure::new(handler))
+    }
+
+    pub fn raw(&self) -> &HtmlCanvasElement {
+        &self.raw
+    }
+}
+
+impl Style {
+    fn new(window: &web_sys::Window, canvas: &HtmlCanvasElement) -> Self {
+        #[allow(clippy::disallowed_methods)]
+        let read = window
+            .get_computed_style(canvas)
+            .expect("Failed to obtain computed style")
+            // this can't fail: we aren't using a pseudo-element
+            .expect("Invalid pseudo-element");
+
+        #[allow(clippy::disallowed_methods)]
+        let write = canvas.style();
+
+        Self { read, write }
+    }
+
+    pub(crate) fn get(&self, property: &str) -> String {
+        self.read.get_property_value(property).expect("Invalid property")
+    }
+
+    pub(crate) fn remove(&self, property: &str) {
+        self.write.remove_property(property).expect("Property is read only");
+    }
+
+    pub(crate) fn set(&self, property: &str, value: &str) {
+        self.write.set_property(property, value).expect("Property is read only");
+    }
+}

winit-web/src/web_sys/event.rs

@@ -0,0 +1,276 @@
+use std::cell::OnceCell;
+
+use dpi::{LogicalPosition, PhysicalPosition, Position};
+use smol_str::SmolStr;
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::{JsCast, JsValue};
+use web_sys::{KeyboardEvent, MouseEvent, Navigator, PointerEvent, WheelEvent};
+use winit_core::event::{FingerId, MouseButton, MouseScrollDelta, PointerKind};
+use winit_core::keyboard::{Key, KeyLocation, ModifiersState, NamedKey, PhysicalKey};
+
+use super::Engine;
+use crate::keyboard::FromAttributeValue;
+
+bitflags::bitflags! {
+    // https://www.w3.org/TR/pointerevents3/#the-buttons-property
+    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    pub struct ButtonsState: u16 {
+        const LEFT    = 0b00001;
+        const RIGHT   = 0b00010;
+        const MIDDLE  = 0b00100;
+        const BACK    = 0b01000;
+        const FORWARD = 0b10000;
+    }
+}
+
+impl From<ButtonsState> for MouseButton {
+    fn from(value: ButtonsState) -> Self {
+        match value {
+            ButtonsState::LEFT => MouseButton::Left,
+            ButtonsState::RIGHT => MouseButton::Right,
+            ButtonsState::MIDDLE => MouseButton::Middle,
+            ButtonsState::BACK => MouseButton::Back,
+            ButtonsState::FORWARD => MouseButton::Forward,
+            _ => MouseButton::Other(value.bits()),
+        }
+    }
+}
+
+impl From<MouseButton> for ButtonsState {
+    fn from(value: MouseButton) -> Self {
+        match value {
+            MouseButton::Left => ButtonsState::LEFT,
+            MouseButton::Right => ButtonsState::RIGHT,
+            MouseButton::Middle => ButtonsState::MIDDLE,
+            MouseButton::Back => ButtonsState::BACK,
+            MouseButton::Forward => ButtonsState::FORWARD,
+            MouseButton::Other(value) => ButtonsState::from_bits_retain(value),
+        }
+    }
+}
+
+pub fn mouse_buttons(event: &MouseEvent) -> ButtonsState {
+    ButtonsState::from_bits_retain(event.buttons())
+}
+
+pub fn mouse_button(event: &MouseEvent) -> Option<MouseButton> {
+    // https://www.w3.org/TR/pointerevents3/#the-button-property
+    match event.button() {
+        -1 => None,
+        0 => Some(MouseButton::Left),
+        1 => Some(MouseButton::Middle),
+        2 => Some(MouseButton::Right),
+        3 => Some(MouseButton::Back),
+        4 => Some(MouseButton::Forward),
+        i => {
+            Some(MouseButton::Other(i.try_into().expect("unexpected negative mouse button value")))
+        },
+    }
+}
+
+pub fn mouse_button_to_id(button: MouseButton) -> u16 {
+    match button {
+        MouseButton::Left => 0,
+        MouseButton::Right => 1,
+        MouseButton::Middle => 2,
+        MouseButton::Back => 3,
+        MouseButton::Forward => 4,
+        MouseButton::Other(value) => value,
+    }
+}
+
+pub fn mouse_position(event: &MouseEvent) -> LogicalPosition<f64> {
+    #[wasm_bindgen]
+    extern "C" {
+        type MouseEventExt;
+
+        #[wasm_bindgen(method, getter, js_name = offsetX)]
+        fn offset_x(this: &MouseEventExt) -> f64;
+
+        #[wasm_bindgen(method, getter, js_name = offsetY)]
+        fn offset_y(this: &MouseEventExt) -> f64;
+    }
+
+    let event: &MouseEventExt = event.unchecked_ref();
+
+    LogicalPosition { x: event.offset_x(), y: event.offset_y() }
+}
+
+// TODO: Remove this when Firefox supports correct movement values in coalesced events and browsers
+// have agreed on what coordinate space `movementX/Y` is using.
+// See <https://bugzilla.mozilla.org/show_bug.cgi?id=1753724>.
+// See <https://github.com/w3c/pointerlock/issues/42>.
+pub enum MouseDelta {
+    Chromium,
+    Gecko { old_position: LogicalPosition<f64>, old_delta: LogicalPosition<f64> },
+    Other,
+}
+
+impl MouseDelta {
+    pub fn init(navigator: &Navigator, event: &PointerEvent) -> Self {
+        match super::engine(navigator) {
+            Some(Engine::Chromium) => Self::Chromium,
+            // Firefox has wrong movement values in coalesced events.
+            Some(Engine::Gecko) if has_coalesced_events_support(event) => Self::Gecko {
+                old_position: mouse_position(event),
+                old_delta: LogicalPosition::new(
+                    event.movement_x() as f64,
+                    event.movement_y() as f64,
+                ),
+            },
+            _ => Self::Other,
+        }
+    }
+
+    pub fn delta(&mut self, event: &MouseEvent) -> Position {
+        match self {
+            MouseDelta::Chromium => {
+                PhysicalPosition::new(event.movement_x(), event.movement_y()).into()
+            },
+            MouseDelta::Gecko { old_position, old_delta } => {
+                let new_position = mouse_position(event);
+                let x = new_position.x - old_position.x + old_delta.x;
+                let y = new_position.y - old_position.y + old_delta.y;
+                *old_position = new_position;
+                *old_delta = LogicalPosition::new(0., 0.);
+                LogicalPosition::new(x, y).into()
+            },
+            MouseDelta::Other => {
+                LogicalPosition::new(event.movement_x(), event.movement_y()).into()
+            },
+        }
+    }
+}
+
+pub fn mouse_scroll_delta(
+    window: &web_sys::Window,
+    event: &WheelEvent,
+) -> Option<MouseScrollDelta> {
+    let x = -event.delta_x();
+    let y = -event.delta_y();
+
+    match event.delta_mode() {
+        WheelEvent::DOM_DELTA_LINE => Some(MouseScrollDelta::LineDelta(x as f32, y as f32)),
+        WheelEvent::DOM_DELTA_PIXEL => {
+            let delta = LogicalPosition::new(x, y).to_physical(super::scale_factor(window));
+            Some(MouseScrollDelta::PixelDelta(delta))
+        },
+        _ => None,
+    }
+}
+
+pub fn pointer_type(event: &PointerEvent, pointer_id: i32) -> PointerKind {
+    match event.pointer_type().as_str() {
+        "mouse" => PointerKind::Mouse,
+        "touch" => PointerKind::Touch(FingerId::from_raw(pointer_id as usize)),
+        _ => PointerKind::Unknown,
+    }
+}
+
+pub fn key_code(event: &KeyboardEvent) -> PhysicalKey {
+    let code = event.code();
+    PhysicalKey::from_attribute_value(&code)
+}
+
+pub fn key(event: &KeyboardEvent) -> Key {
+    Key::from_attribute_value(&event.key())
+}
+
+pub fn key_text(event: &KeyboardEvent) -> Option<SmolStr> {
+    let key = event.key();
+    let key = Key::from_attribute_value(&key);
+    match &key {
+        Key::Character(text) => Some(text.clone()),
+        Key::Named(NamedKey::Tab) => Some(SmolStr::new("\t")),
+        Key::Named(NamedKey::Enter) => Some(SmolStr::new("\r")),
+        _ => None,
+    }
+    .map(SmolStr::new)
+}
+
+pub fn key_location(event: &KeyboardEvent) -> KeyLocation {
+    match event.location() {
+        KeyboardEvent::DOM_KEY_LOCATION_LEFT => KeyLocation::Left,
+        KeyboardEvent::DOM_KEY_LOCATION_RIGHT => KeyLocation::Right,
+        KeyboardEvent::DOM_KEY_LOCATION_NUMPAD => KeyLocation::Numpad,
+        KeyboardEvent::DOM_KEY_LOCATION_STANDARD => KeyLocation::Standard,
+        location => {
+            tracing::warn!("Unexpected key location: {location}");
+            KeyLocation::Standard
+        },
+    }
+}
+
+pub fn keyboard_modifiers(event: &KeyboardEvent) -> ModifiersState {
+    let mut state = ModifiersState::empty();
+
+    if event.shift_key() {
+        state |= ModifiersState::SHIFT;
+    }
+    if event.ctrl_key() {
+        state |= ModifiersState::CONTROL;
+    }
+    if event.alt_key() {
+        state |= ModifiersState::ALT;
+    }
+    if event.meta_key() {
+        state |= ModifiersState::META;
+    }
+
+    state
+}
+
+pub fn mouse_modifiers(event: &MouseEvent) -> ModifiersState {
+    let mut state = ModifiersState::empty();
+
+    if event.shift_key() {
+        state |= ModifiersState::SHIFT;
+    }
+    if event.ctrl_key() {
+        state |= ModifiersState::CONTROL;
+    }
+    if event.alt_key() {
+        state |= ModifiersState::ALT;
+    }
+    if event.meta_key() {
+        state |= ModifiersState::META;
+    }
+
+    state
+}
+
+pub fn pointer_move_event(event: PointerEvent) -> impl Iterator<Item = PointerEvent> {
+    // make a single iterator depending on the availability of coalesced events
+    if has_coalesced_events_support(&event) {
+        None.into_iter().chain(
+            Some(event.get_coalesced_events().into_iter().map(PointerEvent::unchecked_from_js))
+                .into_iter()
+                .flatten(),
+        )
+    } else {
+        Some(event).into_iter().chain(None.into_iter().flatten())
+    }
+}
+
+// TODO: Remove when Safari supports `getCoalescedEvents`.
+// See <https://bugs.webkit.org/show_bug.cgi?id=210454>.
+pub fn has_coalesced_events_support(event: &PointerEvent) -> bool {
+    thread_local! {
+        static COALESCED_EVENTS_SUPPORT: OnceCell<bool> = const { OnceCell::new() };
+    }
+
+    COALESCED_EVENTS_SUPPORT.with(|support| {
+        *support.get_or_init(|| {
+            #[wasm_bindgen]
+            extern "C" {
+                type PointerCoalescedEventsSupport;
+
+                #[wasm_bindgen(method, getter, js_name = getCoalescedEvents)]
+                fn has_get_coalesced_events(this: &PointerCoalescedEventsSupport) -> JsValue;
+            }
+
+            let support: &PointerCoalescedEventsSupport = event.unchecked_ref();
+            !support.has_get_coalesced_events().is_undefined()
+        })
+    })
+}

winit-web/src/web_sys/event_handle.rs

@@ -0,0 +1,38 @@
+use wasm_bindgen::prelude::Closure;
+use wasm_bindgen::JsCast;
+use web_sys::EventTarget;
+
+pub struct EventListenerHandle<T: ?Sized> {
+    target: EventTarget,
+    event_type: &'static str,
+    listener: Closure<T>,
+}
+
+impl<T: ?Sized> EventListenerHandle<T> {
+    pub fn new<U>(target: U, event_type: &'static str, listener: Closure<T>) -> Self
+    where
+        U: Into<EventTarget>,
+    {
+        let target = target.into();
+        target
+            .add_event_listener_with_callback(event_type, listener.as_ref().unchecked_ref())
+            .expect("Failed to add event listener");
+        EventListenerHandle { target, event_type, listener }
+    }
+}
+
+impl<T: ?Sized> Drop for EventListenerHandle<T> {
+    fn drop(&mut self) {
+        self.target
+            .remove_event_listener_with_callback(
+                self.event_type,
+                self.listener.as_ref().unchecked_ref(),
+            )
+            .unwrap_or_else(|e| {
+                web_sys::console::error_2(
+                    &format!("Error removing event listener {}", self.event_type).into(),
+                    &e,
+                )
+            });
+    }
+}

winit-web/src/web_sys/fullscreen.rs

@@ -0,0 +1,157 @@
+use std::cell::OnceCell;
+
+use js_sys::{Object, Promise};
+use tracing::error;
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::{JsCast, JsValue};
+use web_sys::{console, Document, Element, HtmlCanvasElement, Window};
+use winit_core::monitor::Fullscreen;
+
+use crate::main_thread::MainThreadMarker;
+use crate::monitor::{self, MonitorHandle, ScreenDetailed};
+
+pub(crate) fn request_fullscreen(
+    main_thread: MainThreadMarker,
+    window: &Window,
+    document: &Document,
+    canvas: &HtmlCanvasElement,
+    fullscreen: Fullscreen,
+) {
+    #[wasm_bindgen]
+    extern "C" {
+        #[wasm_bindgen(extends = HtmlCanvasElement)]
+        type RequestFullscreen;
+
+        #[wasm_bindgen(method, js_name = requestFullscreen)]
+        fn request_fullscreen(this: &RequestFullscreen) -> Promise;
+
+        #[wasm_bindgen(method, js_name = requestFullscreen)]
+        fn request_fullscreen_with_options(
+            this: &RequestFullscreen,
+            options: &FullscreenOptions,
+        ) -> Promise;
+
+        #[wasm_bindgen(method, js_name = webkitRequestFullscreen)]
+        fn webkit_request_fullscreen(this: &RequestFullscreen);
+
+        type FullscreenOptions;
+
+        #[wasm_bindgen(method, setter, js_name = screen)]
+        fn set_screen(this: &FullscreenOptions, screen: &ScreenDetailed);
+    }
+
+    thread_local! {
+        static REJECT_HANDLER: Closure<dyn FnMut(JsValue)> = Closure::new(|error| {
+            console::error_1(&error);
+            error!("Failed to transition to full screen mode")
+        });
+    }
+
+    if is_fullscreen(document, canvas) {
+        return;
+    }
+
+    let canvas: &RequestFullscreen = canvas.unchecked_ref();
+
+    match fullscreen {
+        Fullscreen::Exclusive(..) => error!("Exclusive full screen mode is not supported"),
+        Fullscreen::Borderless(Some(monitor)) => {
+            if !monitor::has_screen_details_support(window) {
+                error!(
+                    "Fullscreen mode selecting a specific screen is not supported by this browser"
+                );
+                return;
+            }
+
+            let monitor = monitor.cast_ref::<MonitorHandle>().unwrap();
+
+            if let Some(monitor) = monitor.detailed(main_thread) {
+                let options: FullscreenOptions = Object::new().unchecked_into();
+                options.set_screen(&monitor);
+                REJECT_HANDLER.with(|handler| {
+                    let _ = canvas.request_fullscreen_with_options(&options).catch(handler);
+                });
+            } else {
+                error!(
+                    "Selecting a specific screen for fullscreen mode requires a detailed screen. \
+                     See `MonitorHandleExtWeb::is_detailed()`."
+                )
+            }
+        },
+        Fullscreen::Borderless(None) => {
+            if has_fullscreen_api_support(canvas) {
+                REJECT_HANDLER.with(|handler| {
+                    let _ = canvas.request_fullscreen().catch(handler);
+                });
+            } else {
+                canvas.webkit_request_fullscreen();
+            }
+        },
+    }
+}
+
+pub fn is_fullscreen(document: &Document, canvas: &HtmlCanvasElement) -> bool {
+    #[wasm_bindgen]
+    extern "C" {
+        type FullscreenElement;
+
+        #[wasm_bindgen(method, getter, js_name = webkitFullscreenElement)]
+        fn webkit_fullscreen_element(this: &FullscreenElement) -> Option<Element>;
+    }
+
+    let element = if has_fullscreen_api_support(canvas) {
+        #[allow(clippy::disallowed_methods)]
+        document.fullscreen_element()
+    } else {
+        let document: &FullscreenElement = document.unchecked_ref();
+        document.webkit_fullscreen_element()
+    };
+
+    match element {
+        Some(element) => {
+            let canvas: &Element = canvas;
+            canvas == &element
+        },
+        None => false,
+    }
+}
+
+pub fn exit_fullscreen(document: &Document, canvas: &HtmlCanvasElement) {
+    #[wasm_bindgen]
+    extern "C" {
+        type ExitFullscreen;
+
+        #[wasm_bindgen(method, js_name = webkitExitFullscreen)]
+        fn webkit_exit_fullscreen(this: &ExitFullscreen);
+    }
+
+    if has_fullscreen_api_support(canvas) {
+        #[allow(clippy::disallowed_methods)]
+        document.exit_fullscreen()
+    } else {
+        let document: &ExitFullscreen = document.unchecked_ref();
+        document.webkit_exit_fullscreen()
+    }
+}
+
+fn has_fullscreen_api_support(canvas: &HtmlCanvasElement) -> bool {
+    thread_local! {
+        static FULLSCREEN_API_SUPPORT: OnceCell<bool> = const { OnceCell::new() };
+    }
+
+    FULLSCREEN_API_SUPPORT.with(|support| {
+        *support.get_or_init(|| {
+            #[wasm_bindgen]
+            extern "C" {
+                type CanvasFullScreenApiSupport;
+
+                #[wasm_bindgen(method, getter, js_name = requestFullscreen)]
+                fn has_request_fullscreen(this: &CanvasFullScreenApiSupport) -> JsValue;
+            }
+
+            let support: &CanvasFullScreenApiSupport = canvas.unchecked_ref();
+            !support.has_request_fullscreen().is_undefined()
+        })
+    })
+}

winit-web/src/web_sys/intersection_handle.rs

@@ -0,0 +1,33 @@
+use js_sys::Array;
+use wasm_bindgen::prelude::Closure;
+use wasm_bindgen::JsCast;
+use web_sys::{Element, IntersectionObserver, IntersectionObserverEntry};
+
+pub(super) struct IntersectionObserverHandle {
+    observer: IntersectionObserver,
+    _closure: Closure<dyn FnMut(Array)>,
+}
+
+impl IntersectionObserverHandle {
+    pub fn new<F>(element: &Element, mut callback: F) -> Self
+    where
+        F: 'static + FnMut(bool),
+    {
+        let closure = Closure::new(move |entries: Array| {
+            let entry: IntersectionObserverEntry = entries.get(0).unchecked_into();
+            callback(entry.is_intersecting());
+        });
+        let observer = IntersectionObserver::new(closure.as_ref().unchecked_ref())
+            // we don't provide any `options`
+            .expect("Invalid `options`");
+        observer.observe(element);
+
+        Self { observer, _closure: closure }
+    }
+}
+
+impl Drop for IntersectionObserverHandle {
+    fn drop(&mut self) {
+        self.observer.disconnect()
+    }
+}

winit-web/src/web_sys/media_query_handle.rs

@@ -0,0 +1,48 @@
+use wasm_bindgen::prelude::Closure;
+use wasm_bindgen::JsCast;
+use web_sys::MediaQueryList;
+
+pub(super) struct MediaQueryListHandle {
+    mql: MediaQueryList,
+    closure: Closure<dyn FnMut()>,
+}
+
+impl MediaQueryListHandle {
+    pub fn new<F>(window: &web_sys::Window, media_query: &str, mut listener: F) -> Self
+    where
+        F: 'static + FnMut(&MediaQueryList),
+    {
+        let mql = window
+            .match_media(media_query)
+            .expect("Failed to parse media query")
+            .expect("Found empty media query");
+
+        let closure = Closure::new({
+            let mql = mql.clone();
+            move || listener(&mql)
+        });
+        // TODO: Replace obsolete `addListener()` with `addEventListener()` and use
+        // `MediaQueryListEvent` instead of cloning the `MediaQueryList`.
+        // Requires Safari v14.
+        mql.add_listener_with_opt_callback(Some(closure.as_ref().unchecked_ref()))
+            .expect("Invalid listener");
+
+        Self { mql, closure }
+    }
+
+    pub fn mql(&self) -> &MediaQueryList {
+        &self.mql
+    }
+}
+
+impl Drop for MediaQueryListHandle {
+    fn drop(&mut self) {
+        remove_listener(&self.mql, &self.closure);
+    }
+}
+
+fn remove_listener(mql: &MediaQueryList, listener: &Closure<dyn FnMut()>) {
+    mql.remove_listener_with_opt_callback(Some(listener.as_ref().unchecked_ref())).unwrap_or_else(
+        |e| web_sys::console::error_2(&"Error removing media query listener".into(), &e),
+    );
+}

winit-web/src/web_sys/mod.rs

@@ -0,0 +1,262 @@
+mod animation_frame;
+mod canvas;
+pub mod event;
+mod event_handle;
+mod fullscreen;
+mod intersection_handle;
+mod media_query_handle;
+mod pointer;
+mod resize_scaling;
+mod safe_area;
+mod schedule;
+
+use std::cell::OnceCell;
+
+use dpi::{LogicalPosition, LogicalSize};
+use js_sys::Array;
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::JsCast;
+use web_sys::{Document, HtmlCanvasElement, Navigator, PageTransitionEvent, VisibilityState};
+
+pub use self::canvas::{Canvas, Style};
+pub use self::event_handle::EventListenerHandle;
+pub use self::resize_scaling::ResizeScaleHandle;
+pub use self::safe_area::SafeAreaHandle;
+pub use self::schedule::Schedule;
+
+pub fn throw(msg: &str) {
+    wasm_bindgen::throw_str(msg);
+}
+
+pub struct PageTransitionEventHandle {
+    _show_listener: event_handle::EventListenerHandle<dyn FnMut(PageTransitionEvent)>,
+    _hide_listener: event_handle::EventListenerHandle<dyn FnMut(PageTransitionEvent)>,
+}
+
+pub fn on_page_transition(
+    window: web_sys::Window,
+    show_handler: impl FnMut(PageTransitionEvent) + 'static,
+    hide_handler: impl FnMut(PageTransitionEvent) + 'static,
+) -> PageTransitionEventHandle {
+    let show_closure = Closure::new(show_handler);
+    let hide_closure = Closure::new(hide_handler);
+
+    let show_listener =
+        event_handle::EventListenerHandle::new(window.clone(), "pageshow", show_closure);
+    let hide_listener = event_handle::EventListenerHandle::new(window, "pagehide", hide_closure);
+    PageTransitionEventHandle { _show_listener: show_listener, _hide_listener: hide_listener }
+}
+
+pub fn scale_factor(window: &web_sys::Window) -> f64 {
+    window.device_pixel_ratio()
+}
+
+fn fix_canvas_size(style: &Style, mut size: LogicalSize<f64>) -> LogicalSize<f64> {
+    if style.get("box-sizing") == "border-box" {
+        size.width += style_size_property(style, "border-left-width")
+            + style_size_property(style, "border-right-width")
+            + style_size_property(style, "padding-left")
+            + style_size_property(style, "padding-right");
+        size.height += style_size_property(style, "border-top-width")
+            + style_size_property(style, "border-bottom-width")
+            + style_size_property(style, "padding-top")
+            + style_size_property(style, "padding-bottom");
+    }
+
+    size
+}
+
+pub fn set_canvas_size(
+    document: &Document,
+    raw: &HtmlCanvasElement,
+    style: &Style,
+    new_size: LogicalSize<f64>,
+) {
+    if !document.contains(Some(raw)) || style.get("display") == "none" {
+        return;
+    }
+
+    let new_size = fix_canvas_size(style, new_size);
+
+    style.set("width", &format!("{}px", new_size.width));
+    style.set("height", &format!("{}px", new_size.height));
+}
+
+pub fn set_canvas_min_size(
+    document: &Document,
+    raw: &HtmlCanvasElement,
+    style: &Style,
+    dimensions: Option<LogicalSize<f64>>,
+) {
+    if let Some(dimensions) = dimensions {
+        if !document.contains(Some(raw)) || style.get("display") == "none" {
+            return;
+        }
+
+        let new_size = fix_canvas_size(style, dimensions);
+
+        style.set("min-width", &format!("{}px", new_size.width));
+        style.set("min-height", &format!("{}px", new_size.height));
+    } else {
+        style.remove("min-width");
+        style.remove("min-height");
+    }
+}
+
+pub fn set_canvas_max_size(
+    document: &Document,
+    raw: &HtmlCanvasElement,
+    style: &Style,
+    dimensions: Option<LogicalSize<f64>>,
+) {
+    if let Some(dimensions) = dimensions {
+        if !document.contains(Some(raw)) || style.get("display") == "none" {
+            return;
+        }
+
+        let new_size = fix_canvas_size(style, dimensions);
+
+        style.set("max-width", &format!("{}px", new_size.width));
+        style.set("max-height", &format!("{}px", new_size.height));
+    } else {
+        style.remove("max-width");
+        style.remove("max-height");
+    }
+}
+
+pub fn set_canvas_position(
+    document: &Document,
+    raw: &HtmlCanvasElement,
+    style: &Style,
+    mut position: LogicalPosition<f64>,
+) {
+    if document.contains(Some(raw)) && style.get("display") != "none" {
+        position.x -= style_size_property(style, "margin-left")
+            + style_size_property(style, "border-left-width")
+            + style_size_property(style, "padding-left");
+        position.y -= style_size_property(style, "margin-top")
+            + style_size_property(style, "border-top-width")
+            + style_size_property(style, "padding-top");
+    }
+
+    style.set("position", "fixed");
+    style.set("left", &format!("{}px", position.x));
+    style.set("top", &format!("{}px", position.y));
+}
+
+/// This function will panic if the element is not inserted in the DOM
+/// or is not a CSS property that represents a size in pixel.
+pub fn style_size_property(style: &Style, property: &str) -> f64 {
+    let prop = style.get(property);
+    prop.strip_suffix("px")
+        .expect("Element was not inserted into the DOM or is not a size in pixel")
+        .parse()
+        .expect("CSS property is not a size in pixel")
+}
+
+pub fn is_dark_mode(window: &web_sys::Window) -> Option<bool> {
+    window.match_media("(prefers-color-scheme: dark)").ok().flatten().map(|media| media.matches())
+}
+
+pub fn is_visible(document: &Document) -> bool {
+    document.visibility_state() == VisibilityState::Visible
+}
+
+pub type RawCanvasType = HtmlCanvasElement;
+
+#[derive(Clone, Copy)]
+pub enum Engine {
+    Chromium,
+    Gecko,
+    WebKit,
+}
+
+struct UserAgentData {
+    engine: Option<Engine>,
+    chrome_linux: bool,
+}
+
+thread_local! {
+    static USER_AGENT_DATA: OnceCell<UserAgentData> = const { OnceCell::new() };
+}
+
+pub fn chrome_linux(navigator: &Navigator) -> bool {
+    USER_AGENT_DATA.with(|data| data.get_or_init(|| user_agent(navigator)).chrome_linux)
+}
+
+pub fn engine(navigator: &Navigator) -> Option<Engine> {
+    USER_AGENT_DATA.with(|data| data.get_or_init(|| user_agent(navigator)).engine)
+}
+
+fn user_agent(navigator: &Navigator) -> UserAgentData {
+    #[wasm_bindgen]
+    extern "C" {
+        #[wasm_bindgen(extends = Navigator)]
+        type NavigatorExt;
+
+        #[wasm_bindgen(method, getter, js_name = userAgentData)]
+        fn user_agent_data(this: &NavigatorExt) -> Option<NavigatorUaData>;
+
+        type NavigatorUaData;
+
+        #[wasm_bindgen(method, getter)]
+        fn brands(this: &NavigatorUaData) -> Array;
+
+        #[wasm_bindgen(method, getter)]
+        fn platform(this: &NavigatorUaData) -> String;
+
+        type NavigatorUaBrandVersion;
+
+        #[wasm_bindgen(method, getter)]
+        fn brand(this: &NavigatorUaBrandVersion) -> String;
+    }
+
+    let navigator: &NavigatorExt = navigator.unchecked_ref();
+
+    if let Some(data) = navigator.user_agent_data() {
+        let engine = 'engine: {
+            for brand in data
+                .brands()
+                .iter()
+                .map(NavigatorUaBrandVersion::unchecked_from_js)
+                .map(|brand| brand.brand())
+            {
+                match brand.as_str() {
+                    "Chromium" => break 'engine Some(Engine::Chromium),
+                    // TODO: verify when Firefox actually implements it.
+                    "Gecko" => break 'engine Some(Engine::Gecko),
+                    // TODO: verify when Safari actually implements it.
+                    "WebKit" => break 'engine Some(Engine::WebKit),
+                    _ => (),
+                }
+            }
+
+            None
+        };
+
+        let chrome_linux = matches!(engine, Some(Engine::Chromium))
+            .then(|| data.platform() == "Linux")
+            .unwrap_or(false);
+
+        UserAgentData { engine, chrome_linux }
+    } else {
+        let engine = 'engine: {
+            let Ok(data) = navigator.user_agent() else {
+                break 'engine None;
+            };
+
+            if data.contains("Chrome/") {
+                Some(Engine::Chromium)
+            } else if data.contains("Gecko/") {
+                Some(Engine::Gecko)
+            } else if data.contains("AppleWebKit/") {
+                Some(Engine::WebKit)
+            } else {
+                None
+            }
+        };
+
+        UserAgentData { engine, chrome_linux: false }
+    }
+}

winit-web/src/web_sys/pointer.rs

@@ -0,0 +1,268 @@
+use std::cell::Cell;
+use std::rc::Rc;
+
+use dpi::PhysicalPosition;
+use web_sys::PointerEvent;
+use winit_core::event::{ButtonSource, DeviceId, ElementState, Force, PointerKind, PointerSource};
+use winit_core::keyboard::ModifiersState;
+
+use super::canvas::Common;
+use super::event;
+use super::event_handle::EventListenerHandle;
+use crate::event::mkdid;
+use crate::web_sys::event::mouse_button_to_id;
+
+#[allow(dead_code)]
+pub(super) struct PointerHandler {
+    on_cursor_leave: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,
+    on_cursor_enter: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,
+    on_cursor_move: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,
+    on_pointer_press: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,
+    on_pointer_release: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,
+    on_touch_cancel: Option<EventListenerHandle<dyn FnMut(PointerEvent)>>,
+}
+
+impl PointerHandler {
+    pub fn new() -> Self {
+        Self {
+            on_cursor_leave: None,
+            on_cursor_enter: None,
+            on_cursor_move: None,
+            on_pointer_press: None,
+            on_pointer_release: None,
+            on_touch_cancel: None,
+        }
+    }
+
+    pub fn on_pointer_leave<F>(&mut self, canvas_common: &Common, mut handler: F)
+    where
+        F: 'static
+            + FnMut(ModifiersState, Option<DeviceId>, bool, PhysicalPosition<f64>, PointerKind),
+    {
+        let window = canvas_common.window.clone();
+        self.on_cursor_leave =
+            Some(canvas_common.add_event("pointerout", move |event: PointerEvent| {
+                let modifiers = event::mouse_modifiers(&event);
+                let pointer_id = event.pointer_id();
+                let device_id = mkdid(pointer_id);
+                let position =
+                    event::mouse_position(&event).to_physical(super::scale_factor(&window));
+                let kind = event::pointer_type(&event, pointer_id);
+                handler(modifiers, device_id, event.is_primary(), position, kind);
+            }));
+    }
+
+    pub fn on_pointer_enter<F>(&mut self, canvas_common: &Common, mut handler: F)
+    where
+        F: 'static
+            + FnMut(ModifiersState, Option<DeviceId>, bool, PhysicalPosition<f64>, PointerKind),
+    {
+        let window = canvas_common.window.clone();
+        self.on_cursor_enter =
+            Some(canvas_common.add_event("pointerover", move |event: PointerEvent| {
+                let modifiers = event::mouse_modifiers(&event);
+                let pointer_id = event.pointer_id();
+                let device_id = mkdid(pointer_id);
+                let position =
+                    event::mouse_position(&event).to_physical(super::scale_factor(&window));
+                let kind = event::pointer_type(&event, pointer_id);
+                handler(modifiers, device_id, event.is_primary(), position, kind);
+            }));
+    }
+
+    pub fn on_pointer_release<C>(&mut self, canvas_common: &Common, mut handler: C)
+    where
+        C: 'static
+            + FnMut(ModifiersState, Option<DeviceId>, bool, PhysicalPosition<f64>, ButtonSource),
+    {
+        let window = canvas_common.window.clone();
+        self.on_pointer_release =
+            Some(canvas_common.add_event("pointerup", move |event: PointerEvent| {
+                let modifiers = event::mouse_modifiers(&event);
+                let pointer_id = event.pointer_id();
+                let kind = event::pointer_type(&event, pointer_id);
+
+                let button = event::mouse_button(&event).expect("no mouse button pressed");
+
+                let source = match kind {
+                    PointerKind::Mouse => ButtonSource::Mouse(button),
+                    PointerKind::Touch(finger_id) => ButtonSource::Touch {
+                        finger_id,
+                        force: Some(Force::Normalized(event.pressure().into())),
+                    },
+                    PointerKind::Unknown => ButtonSource::Unknown(mouse_button_to_id(button)),
+                };
+
+                handler(
+                    modifiers,
+                    mkdid(pointer_id),
+                    event.is_primary(),
+                    event::mouse_position(&event).to_physical(super::scale_factor(&window)),
+                    source,
+                )
+            }));
+    }
+
+    pub fn on_pointer_press<C>(
+        &mut self,
+        canvas_common: &Common,
+        mut handler: C,
+        prevent_default: Rc<Cell<bool>>,
+    ) where
+        C: 'static
+            + FnMut(ModifiersState, Option<DeviceId>, bool, PhysicalPosition<f64>, ButtonSource),
+    {
+        let window = canvas_common.window.clone();
+        let canvas = canvas_common.raw().clone();
+        self.on_pointer_press =
+            Some(canvas_common.add_event("pointerdown", move |event: PointerEvent| {
+                if prevent_default.get() {
+                    // prevent text selection
+                    event.prevent_default();
+                    // but still focus element
+                    let _ = canvas.focus();
+                }
+
+                let modifiers = event::mouse_modifiers(&event);
+                let pointer_id = event.pointer_id();
+                let kind = event::pointer_type(&event, pointer_id);
+                let button = event::mouse_button(&event).expect("no mouse button pressed");
+
+                let source = match kind {
+                    PointerKind::Mouse => {
+                        // Error is swallowed here since the error would occur every time the
+                        // mouse is clicked when the cursor is
+                        // grabbed, and there is probably not a
+                        // situation where this could fail, that we
+                        // care if it fails.
+                        let _e = canvas.set_pointer_capture(pointer_id);
+
+                        ButtonSource::Mouse(button)
+                    },
+                    PointerKind::Touch(finger_id) => ButtonSource::Touch {
+                        finger_id,
+                        force: Some(Force::Normalized(event.pressure().into())),
+                    },
+                    PointerKind::Unknown => ButtonSource::Unknown(mouse_button_to_id(button)),
+                };
+
+                handler(
+                    modifiers,
+                    mkdid(pointer_id),
+                    event.is_primary(),
+                    event::mouse_position(&event).to_physical(super::scale_factor(&window)),
+                    source,
+                )
+            }));
+    }
+
+    pub fn on_pointer_move<C, B>(
+        &mut self,
+        canvas_common: &Common,
+        mut cursor_handler: C,
+        mut button_handler: B,
+        prevent_default: Rc<Cell<bool>>,
+    ) where
+        C: 'static
+            + FnMut(
+                Option<DeviceId>,
+                &mut dyn Iterator<
+                    Item = (ModifiersState, bool, PhysicalPosition<f64>, PointerSource),
+                >,
+            ),
+        B: 'static
+            + FnMut(
+                ModifiersState,
+                Option<DeviceId>,
+                bool,
+                PhysicalPosition<f64>,
+                ElementState,
+                ButtonSource,
+            ),
+    {
+        let window = canvas_common.window.clone();
+        let canvas = canvas_common.raw().clone();
+        self.on_cursor_move =
+            Some(canvas_common.add_event("pointermove", move |event: PointerEvent| {
+                let pointer_id = event.pointer_id();
+                let device_id = mkdid(pointer_id);
+                let kind = event::pointer_type(&event, pointer_id);
+                let primary = event.is_primary();
+
+                // chorded button event
+                if let Some(button) = event::mouse_button(&event) {
+                    if prevent_default.get() {
+                        // prevent text selection
+                        event.prevent_default();
+                        // but still focus element
+                        let _ = canvas.focus();
+                    }
+
+                    let state = if event::mouse_buttons(&event).contains(button.into()) {
+                        ElementState::Pressed
+                    } else {
+                        ElementState::Released
+                    };
+
+                    let button = match kind {
+                        PointerKind::Mouse => ButtonSource::Mouse(button),
+                        PointerKind::Touch(finger_id) => {
+                            let button_id = mouse_button_to_id(button);
+
+                            if button_id != 1 {
+                                tracing::error!("unexpected touch button id: {button_id}");
+                            }
+
+                            ButtonSource::Touch {
+                                finger_id,
+                                force: Some(Force::Normalized(event.pressure().into())),
+                            }
+                        },
+                        PointerKind::Unknown => todo!(),
+                    };
+
+                    button_handler(
+                        event::mouse_modifiers(&event),
+                        device_id,
+                        primary,
+                        event::mouse_position(&event).to_physical(super::scale_factor(&window)),
+                        state,
+                        button,
+                    );
+
+                    return;
+                }
+
+                // pointer move event
+                let scale = super::scale_factor(&window);
+
+                cursor_handler(
+                    device_id,
+                    &mut event::pointer_move_event(event).map(|event| {
+                        (
+                            event::mouse_modifiers(&event),
+                            event.is_primary(),
+                            event::mouse_position(&event).to_physical(scale),
+                            match kind {
+                                PointerKind::Mouse => PointerSource::Mouse,
+                                PointerKind::Touch(finger_id) => PointerSource::Touch {
+                                    finger_id,
+                                    force: Some(Force::Normalized(event.pressure().into())),
+                                },
+                                PointerKind::Unknown => PointerSource::Unknown,
+                            },
+                        )
+                    }),
+                );
+            }));
+    }
+
+    pub fn remove_listeners(&mut self) {
+        self.on_cursor_leave = None;
+        self.on_cursor_enter = None;
+        self.on_cursor_move = None;
+        self.on_pointer_press = None;
+        self.on_pointer_release = None;
+        self.on_touch_cancel = None;
+    }
+}

winit-web/src/web_sys/resize_scaling.rs

@@ -0,0 +1,301 @@
+use std::cell::{Cell, RefCell};
+use std::rc::Rc;
+
+use dpi::{LogicalSize, PhysicalSize};
+use js_sys::{Array, Object};
+use tracing::warn;
+use wasm_bindgen::prelude::{wasm_bindgen, Closure};
+use wasm_bindgen::{JsCast, JsValue};
+use web_sys::{
+    Document, HtmlCanvasElement, MediaQueryList, ResizeObserver, ResizeObserverBoxOptions,
+    ResizeObserverEntry, ResizeObserverOptions, ResizeObserverSize, Window,
+};
+
+use super::super::backend;
+use super::canvas::Style;
+use super::media_query_handle::MediaQueryListHandle;
+
+pub struct ResizeScaleHandle(Rc<ResizeScaleInternal>);
+
+impl ResizeScaleHandle {
+    pub(crate) fn new<S, R>(
+        window: Window,
+        document: Document,
+        canvas: HtmlCanvasElement,
+        style: Style,
+        scale_handler: S,
+        resize_handler: R,
+    ) -> Self
+    where
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
+    {
+        Self(ResizeScaleInternal::new(
+            window,
+            document,
+            canvas,
+            style,
+            scale_handler,
+            resize_handler,
+        ))
+    }
+
+    pub(crate) fn notify_resize(&self) {
+        self.0.notify()
+    }
+}
+
+/// This is a helper type to help manage the `MediaQueryList` used for detecting
+/// changes of the `devicePixelRatio`.
+struct ResizeScaleInternal {
+    window: Window,
+    document: Document,
+    canvas: HtmlCanvasElement,
+    style: Style,
+    mql: RefCell<MediaQueryListHandle>,
+    observer: ResizeObserver,
+    _observer_closure: Closure<dyn FnMut(Array, ResizeObserver)>,
+    scale_handler: Box<dyn Fn(PhysicalSize<u32>, f64)>,
+    resize_handler: Box<dyn Fn(PhysicalSize<u32>)>,
+    notify_scale: Cell<bool>,
+}
+
+impl ResizeScaleInternal {
+    fn new<S, R>(
+        window: Window,
+        document: Document,
+        canvas: HtmlCanvasElement,
+        style: Style,
+        scale_handler: S,
+        resize_handler: R,
+    ) -> Rc<Self>
+    where
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
+    {
+        Rc::<ResizeScaleInternal>::new_cyclic(|weak_self| {
+            let mql = Self::create_mql(&window, {
+                let weak_self = weak_self.clone();
+                move |mql| {
+                    if let Some(rc_self) = weak_self.upgrade() {
+                        Self::handle_scale(rc_self, mql);
+                    }
+                }
+            });
+
+            let weak_self = weak_self.clone();
+            let observer_closure = Closure::new(move |entries: Array, _| {
+                if let Some(this) = weak_self.upgrade() {
+                    let size = this.process_entry(entries);
+
+                    if this.notify_scale.replace(false) {
+                        let scale = backend::scale_factor(&this.window);
+                        (this.scale_handler)(size, scale)
+                    } else {
+                        (this.resize_handler)(size)
+                    }
+                }
+            });
+            let observer = Self::create_observer(&canvas, observer_closure.as_ref());
+
+            Self {
+                window,
+                document,
+                canvas,
+                style,
+                mql: RefCell::new(mql),
+                observer,
+                _observer_closure: observer_closure,
+                scale_handler: Box::new(scale_handler),
+                resize_handler: Box::new(resize_handler),
+                notify_scale: Cell::new(false),
+            }
+        })
+    }
+
+    fn create_mql<F>(window: &Window, closure: F) -> MediaQueryListHandle
+    where
+        F: 'static + FnMut(&MediaQueryList),
+    {
+        let current_scale = super::scale_factor(window);
+        // TODO: Remove `-webkit-device-pixel-ratio`. Requires Safari v16.
+        let media_query = format!(
+            "(resolution: {current_scale}dppx),
+             (-webkit-device-pixel-ratio: {current_scale})",
+        );
+        let mql = MediaQueryListHandle::new(window, &media_query, closure);
+        debug_assert!(
+            mql.mql().matches(),
+            "created media query doesn't match, {current_scale} != {}",
+            super::scale_factor(window)
+        );
+        mql
+    }
+
+    fn create_observer(canvas: &HtmlCanvasElement, closure: &JsValue) -> ResizeObserver {
+        let observer = ResizeObserver::new(closure.as_ref().unchecked_ref())
+            .expect("Failed to create `ResizeObserver`");
+
+        // Safari doesn't support `devicePixelContentBoxSize`
+        if has_device_pixel_support() {
+            let options = ResizeObserverOptions::new();
+            options.set_box(ResizeObserverBoxOptions::DevicePixelContentBox);
+            observer.observe_with_options(canvas, &options);
+        } else {
+            observer.observe(canvas);
+        }
+
+        observer
+    }
+
+    fn notify(&self) {
+        if !self.document.contains(Some(&self.canvas)) || self.style.get("display") == "none" {
+            let size = PhysicalSize::new(0, 0);
+
+            if self.notify_scale.replace(false) {
+                let scale = backend::scale_factor(&self.window);
+                (self.scale_handler)(size, scale)
+            } else {
+                (self.resize_handler)(size)
+            }
+
+            return;
+        }
+
+        // Safari doesn't support `devicePixelContentBoxSize`
+        if has_device_pixel_support() {
+            self.observer.unobserve(&self.canvas);
+            self.observer.observe(&self.canvas);
+
+            return;
+        }
+
+        let mut size = LogicalSize::new(
+            backend::style_size_property(&self.style, "width"),
+            backend::style_size_property(&self.style, "height"),
+        );
+
+        if self.style.get("box-sizing") == "border-box" {
+            size.width -= backend::style_size_property(&self.style, "border-left-width")
+                + backend::style_size_property(&self.style, "border-right-width")
+                + backend::style_size_property(&self.style, "padding-left")
+                + backend::style_size_property(&self.style, "padding-right");
+            size.height -= backend::style_size_property(&self.style, "border-top-width")
+                + backend::style_size_property(&self.style, "border-bottom-width")
+                + backend::style_size_property(&self.style, "padding-top")
+                + backend::style_size_property(&self.style, "padding-bottom");
+        }
+
+        let size = size.to_physical(backend::scale_factor(&self.window));
+
+        if self.notify_scale.replace(false) {
+            let scale = backend::scale_factor(&self.window);
+            (self.scale_handler)(size, scale)
+        } else {
+            (self.resize_handler)(size)
+        }
+    }
+
+    fn handle_scale(self: Rc<Self>, mql: &MediaQueryList) {
+        let weak_self = Rc::downgrade(&self);
+        let scale = super::scale_factor(&self.window);
+
+        // TODO: confirm/reproduce this problem, see:
+        // <https://github.com/rust-windowing/winit/issues/2597>.
+        // This should never happen, but if it does then apparently the scale factor didn't change.
+        if mql.matches() {
+            warn!(
+                "media query tracking scale factor was triggered without a change:\nMedia Query: \
+                 {}\nCurrent Scale: {scale}",
+                mql.media(),
+            );
+            return;
+        }
+
+        let new_mql = Self::create_mql(&self.window, move |mql| {
+            if let Some(rc_self) = weak_self.upgrade() {
+                Self::handle_scale(rc_self, mql);
+            }
+        });
+        self.mql.replace(new_mql);
+
+        self.notify_scale.set(true);
+        self.notify();
+    }
+
+    fn process_entry(&self, entries: Array) -> PhysicalSize<u32> {
+        let entry: ResizeObserverEntry = entries.get(0).unchecked_into();
+
+        // Safari doesn't support `devicePixelContentBoxSize`
+        if !has_device_pixel_support() {
+            let rect = entry.content_rect();
+
+            return LogicalSize::new(rect.width(), rect.height())
+                .to_physical(backend::scale_factor(&self.window));
+        }
+
+        let entry: ResizeObserverSize =
+            entry.device_pixel_content_box_size().get(0).unchecked_into();
+
+        let writing_mode = self.style.get("writing-mode");
+
+        // means the canvas is not inserted into the DOM
+        if writing_mode.is_empty() {
+            debug_assert_eq!(entry.inline_size(), 0.);
+            debug_assert_eq!(entry.block_size(), 0.);
+
+            return PhysicalSize::new(0, 0);
+        }
+
+        let horizontal = match writing_mode.as_str() {
+            _ if writing_mode.starts_with("horizontal") => true,
+            _ if writing_mode.starts_with("vertical") | writing_mode.starts_with("sideways") => {
+                false
+            },
+            // deprecated values
+            "lr" | "lr-tb" | "rl" => true,
+            "tb" | "tb-lr" | "tb-rl" => false,
+            _ => {
+                warn!("unrecognized `writing-mode`, assuming horizontal");
+                true
+            },
+        };
+
+        if horizontal {
+            PhysicalSize::new(entry.inline_size() as u32, entry.block_size() as u32)
+        } else {
+            PhysicalSize::new(entry.block_size() as u32, entry.inline_size() as u32)
+        }
+    }
+}
+
+impl Drop for ResizeScaleInternal {
+    fn drop(&mut self) {
+        self.observer.disconnect();
+    }
+}
+
+// TODO: Remove when Safari supports `devicePixelContentBoxSize`.
+// See <https://bugs.webkit.org/show_bug.cgi?id=219005>.
+pub fn has_device_pixel_support() -> bool {
+    thread_local! {
+        static DEVICE_PIXEL_SUPPORT: bool = {
+            #[wasm_bindgen]
+            extern "C" {
+                type ResizeObserverEntryExt;
+
+                #[wasm_bindgen(js_class = ResizeObserverEntry, static_method_of = ResizeObserverEntryExt, getter)]
+                fn prototype() -> Object;
+            }
+
+            let prototype = ResizeObserverEntryExt::prototype();
+            let descriptor = Object::get_own_property_descriptor(
+                &prototype,
+                &JsValue::from_str("devicePixelContentBoxSize"),
+            );
+            !descriptor.is_undefined()
+        };
+    }
+
+    DEVICE_PIXEL_SUPPORT.with(|support| *support)
+}

winit-web/src/web_sys/safe_area.rs

@@ -0,0 +1,56 @@
+use dpi::{LogicalPosition, LogicalSize};
+use wasm_bindgen::JsCast;
+use web_sys::{Document, HtmlHtmlElement, Window};
+
+use super::Style;
+
+pub struct SafeAreaHandle {
+    style: Style,
+}
+
+impl SafeAreaHandle {
+    pub fn new(window: &Window, document: &Document) -> Self {
+        let document: HtmlHtmlElement = document.document_element().unwrap().unchecked_into();
+        #[allow(clippy::disallowed_methods)]
+        let write = document.style();
+        write
+            .set_property(
+                "--__winit_safe_area",
+                "env(safe-area-inset-top) env(safe-area-inset-right) env(safe-area-inset-bottom) \
+                 env(safe-area-inset-left)",
+            )
+            .expect("unexpected read-only declaration block");
+        #[allow(clippy::disallowed_methods)]
+        let read = window
+            .get_computed_style(&document)
+            .expect("failed to obtain computed style")
+            // this can't fail: we aren't using a pseudo-element
+            .expect("invalid pseudo-element");
+
+        SafeAreaHandle { style: Style { read, write } }
+    }
+
+    pub fn get(&self) -> (LogicalPosition<f64>, LogicalSize<f64>) {
+        let value = self.style.get("--__winit_safe_area");
+
+        let mut values = value
+            .split(' ')
+            .map(|value| value.strip_suffix("px").expect("unexpected unit other then `px` found"));
+        let top: f64 = values.next().unwrap().parse().unwrap();
+        let right: f64 = values.next().unwrap().parse().unwrap();
+        let bottom: f64 = values.next().unwrap().parse().unwrap();
+        let left: f64 = values.next().unwrap().parse().unwrap();
+        assert_eq!(values.next(), None, "unexpected fifth value");
+
+        let width = super::style_size_property(&self.style, "width") - left - right;
+        let height = super::style_size_property(&self.style, "height") - top - bottom;
+
+        (LogicalPosition::new(left, top), LogicalSize::new(width, height))
+    }
+}
+
+impl Drop for SafeAreaHandle {
+    fn drop(&mut self) {
+        self.style.remove("--__winit_safe_area");
+    }
+}

winit-web/src/web_sys/schedule.rs

@@ -0,0 +1,319 @@
+use std::cell::OnceCell;
+use std::time::Duration;
+
+use js_sys::{Array, Function, Object, Promise};
+use wasm_bindgen::closure::Closure;
+use wasm_bindgen::prelude::wasm_bindgen;
+use wasm_bindgen::{JsCast, JsValue};
+use web_sys::{
+    AbortController, AbortSignal, Blob, BlobPropertyBag, MessageChannel, MessagePort, Url, Worker,
+};
+
+use crate::{PollStrategy, WaitUntilStrategy};
+
+#[derive(Debug)]
+pub struct Schedule {
+    _closure: Closure<dyn FnMut()>,
+    inner: Inner,
+}
+
+#[derive(Debug)]
+enum Inner {
+    Scheduler {
+        controller: AbortController,
+    },
+    IdleCallback {
+        window: web_sys::Window,
+        handle: u32,
+    },
+    Timeout {
+        window: web_sys::Window,
+        handle: i32,
+        port: MessagePort,
+        _timeout_closure: Closure<dyn FnMut()>,
+    },
+    Worker(MessagePort),
+}
+
+impl Schedule {
+    pub fn new<F>(strategy: PollStrategy, window: &web_sys::Window, f: F) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        if strategy == PollStrategy::Scheduler && has_scheduler_support(window) {
+            Self::new_scheduler(window, f, None)
+        } else if strategy == PollStrategy::IdleCallback && has_idle_callback_support(window) {
+            Self::new_idle_callback(window.clone(), f)
+        } else {
+            Self::new_timeout(window.clone(), f, None)
+        }
+    }
+
+    pub fn new_with_duration<F>(
+        strategy: WaitUntilStrategy,
+        window: &web_sys::Window,
+        f: F,
+        duration: Duration,
+    ) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        match strategy {
+            WaitUntilStrategy::Scheduler => {
+                if has_scheduler_support(window) {
+                    Self::new_scheduler(window, f, Some(duration))
+                } else {
+                    Self::new_timeout(window.clone(), f, Some(duration))
+                }
+            },
+            WaitUntilStrategy::Worker => Self::new_worker(f, duration),
+        }
+    }
+
+    fn new_scheduler<F>(window: &web_sys::Window, f: F, duration: Option<Duration>) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        let window: &WindowSupportExt = window.unchecked_ref();
+        let scheduler = window.scheduler();
+
+        let closure = Closure::new(f);
+        let options: SchedulerPostTaskOptions = Object::new().unchecked_into();
+        let controller = AbortController::new().expect("Failed to create `AbortController`");
+        options.set_signal(&controller.signal());
+
+        if let Some(duration) = duration {
+            // `Duration::as_millis()` always rounds down (because of truncation), we want to round
+            // up instead. This makes sure that the we never wake up **before** the given time.
+            let duration = duration
+                .as_secs()
+                .checked_mul(1000)
+                .and_then(|secs| secs.checked_add(duration.subsec_micros().div_ceil(1000).into()))
+                .unwrap_or(u64::MAX);
+
+            options.set_delay(duration as f64);
+        }
+
+        thread_local! {
+            static REJECT_HANDLER: Closure<dyn FnMut(JsValue)> = Closure::new(|_| ());
+        }
+        REJECT_HANDLER.with(|handler| {
+            let _ = scheduler
+                .post_task_with_options(closure.as_ref().unchecked_ref(), &options)
+                .catch(handler);
+        });
+
+        Schedule { _closure: closure, inner: Inner::Scheduler { controller } }
+    }
+
+    fn new_idle_callback<F>(window: web_sys::Window, f: F) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        let closure = Closure::new(f);
+        let handle = window
+            .request_idle_callback(closure.as_ref().unchecked_ref())
+            .expect("Failed to request idle callback");
+
+        Schedule { _closure: closure, inner: Inner::IdleCallback { window, handle } }
+    }
+
+    fn new_timeout<F>(window: web_sys::Window, f: F, duration: Option<Duration>) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        let channel = MessageChannel::new().unwrap();
+        let closure = Closure::new(f);
+        let port_1 = channel.port1();
+        port_1.set_onmessage(Some(closure.as_ref().unchecked_ref()));
+        port_1.start();
+
+        let port_2 = channel.port2();
+        let timeout_closure = Closure::new(move || {
+            port_2.post_message(&JsValue::UNDEFINED).expect("Failed to send message")
+        });
+        let handle = if let Some(duration) = duration {
+            // `Duration::as_millis()` always rounds down (because of truncation), we want to round
+            // up instead. This makes sure that the we never wake up **before** the given time.
+            let duration = duration
+                .as_secs()
+                .try_into()
+                .ok()
+                .and_then(|secs: i32| secs.checked_mul(1000))
+                .and_then(|secs: i32| {
+                    let millis: i32 = duration
+                        .subsec_micros()
+                        .div_ceil(1000)
+                        .try_into()
+                        .expect("millis are somehow bigger then 1K");
+                    secs.checked_add(millis)
+                })
+                .unwrap_or(i32::MAX);
+
+            window.set_timeout_with_callback_and_timeout_and_arguments_0(
+                timeout_closure.as_ref().unchecked_ref(),
+                duration,
+            )
+        } else {
+            window.set_timeout_with_callback(timeout_closure.as_ref().unchecked_ref())
+        }
+        .expect("Failed to set timeout");
+
+        Schedule {
+            _closure: closure,
+            inner: Inner::Timeout {
+                window,
+                handle,
+                port: port_1,
+                _timeout_closure: timeout_closure,
+            },
+        }
+    }
+
+    fn new_worker<F>(f: F, duration: Duration) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        thread_local! {
+            static URL: ScriptUrl = ScriptUrl::new(include_str!("../script/worker.min.js"));
+            static WORKER: Worker = URL.with(|url| Worker::new(&url.0)).expect("`new Worker()` is not expected to fail with a local script");
+        }
+
+        let channel = MessageChannel::new().unwrap();
+        let closure = Closure::new(f);
+        let port_1 = channel.port1();
+        port_1.set_onmessage(Some(closure.as_ref().unchecked_ref()));
+        port_1.start();
+
+        // `Duration::as_millis()` always rounds down (because of truncation), we want to round
+        // up instead. This makes sure that the we never wake up **before** the given time.
+        let duration = duration
+            .as_secs()
+            .try_into()
+            .ok()
+            .and_then(|secs: u32| secs.checked_mul(1000))
+            .and_then(|secs| secs.checked_add(duration.subsec_micros().div_ceil(1000)))
+            .unwrap_or(u32::MAX);
+
+        WORKER
+            .with(|worker| {
+                let port_2 = channel.port2();
+                worker.post_message_with_transfer(
+                    &Array::of2(&port_2, &duration.into()),
+                    &Array::of1(&port_2).into(),
+                )
+            })
+            .expect("`Worker.postMessage()` is not expected to fail");
+
+        Schedule { _closure: closure, inner: Inner::Worker(port_1) }
+    }
+}
+
+impl Drop for Schedule {
+    fn drop(&mut self) {
+        match &self.inner {
+            Inner::Scheduler { controller, .. } => controller.abort(),
+            Inner::IdleCallback { window, handle, .. } => window.cancel_idle_callback(*handle),
+            Inner::Timeout { window, handle, port, .. } => {
+                window.clear_timeout_with_handle(*handle);
+                port.close();
+                port.set_onmessage(None);
+            },
+            Inner::Worker(port) => {
+                port.close();
+                port.set_onmessage(None);
+            },
+        }
+    }
+}
+
+fn has_scheduler_support(window: &web_sys::Window) -> bool {
+    thread_local! {
+        static SCHEDULER_SUPPORT: OnceCell<bool> = const { OnceCell::new() };
+    }
+
+    SCHEDULER_SUPPORT.with(|support| {
+        *support.get_or_init(|| {
+            #[wasm_bindgen]
+            extern "C" {
+                type SchedulerSupport;
+
+                #[wasm_bindgen(method, getter, js_name = scheduler)]
+                fn has_scheduler(this: &SchedulerSupport) -> JsValue;
+            }
+
+            let support: &SchedulerSupport = window.unchecked_ref();
+
+            !support.has_scheduler().is_undefined()
+        })
+    })
+}
+
+fn has_idle_callback_support(window: &web_sys::Window) -> bool {
+    thread_local! {
+        static IDLE_CALLBACK_SUPPORT: OnceCell<bool> = const { OnceCell::new() };
+    }
+
+    IDLE_CALLBACK_SUPPORT.with(|support| {
+        *support.get_or_init(|| {
+            #[wasm_bindgen]
+            extern "C" {
+                type IdleCallbackSupport;
+
+                #[wasm_bindgen(method, getter, js_name = requestIdleCallback)]
+                fn has_request_idle_callback(this: &IdleCallbackSupport) -> JsValue;
+            }
+
+            let support: &IdleCallbackSupport = window.unchecked_ref();
+            !support.has_request_idle_callback().is_undefined()
+        })
+    })
+}
+
+struct ScriptUrl(String);
+
+impl ScriptUrl {
+    fn new(script: &str) -> Self {
+        let sequence = Array::of1(&script.into());
+        let property = BlobPropertyBag::new();
+        property.set_type("text/javascript");
+        let blob = Blob::new_with_str_sequence_and_options(&sequence, &property)
+            .expect("`new Blob()` should never throw");
+
+        let url = Url::create_object_url_with_blob(&blob)
+            .expect("`URL.createObjectURL()` should never throw");
+
+        Self(url)
+    }
+}
+
+impl Drop for ScriptUrl {
+    fn drop(&mut self) {
+        Url::revoke_object_url(&self.0).expect("`URL.revokeObjectURL()` should never throw");
+    }
+}
+
+#[wasm_bindgen]
+extern "C" {
+    type WindowSupportExt;
+
+    #[wasm_bindgen(method, getter)]
+    fn scheduler(this: &WindowSupportExt) -> Scheduler;
+
+    type Scheduler;
+
+    #[wasm_bindgen(method, js_name = postTask)]
+    fn post_task_with_options(
+        this: &Scheduler,
+        callback: &Function,
+        options: &SchedulerPostTaskOptions,
+    ) -> Promise;
+
+    type SchedulerPostTaskOptions;
+
+    #[wasm_bindgen(method, setter, js_name = delay)]
+    fn set_delay(this: &SchedulerPostTaskOptions, value: f64);
+
+    #[wasm_bindgen(method, setter, js_name = signal)]
+    fn set_signal(this: &SchedulerPostTaskOptions, value: &AbortSignal);
+}

winit-web/src/window.rs

@@ -0,0 +1,467 @@
+use std::cell::Ref;
+use std::fmt;
+use std::rc::Rc;
+
+use dpi::{
+    LogicalInsets, LogicalPosition, LogicalSize, PhysicalInsets, PhysicalPosition, PhysicalSize,
+    Position, Size,
+};
+use web_sys::HtmlCanvasElement;
+use winit_core::cursor::Cursor;
+use winit_core::error::{NotSupportedError, RequestError};
+use winit_core::icon::Icon;
+use winit_core::monitor::{Fullscreen, MonitorHandle as CoremMonitorHandle};
+use winit_core::window::{
+    CursorGrabMode, ImePurpose, ResizeDirection, Theme, UserAttentionType, Window as RootWindow,
+    WindowAttributes, WindowButtons, WindowId, WindowLevel,
+};
+
+use crate::event_loop::ActiveEventLoop;
+use crate::main_thread::MainThreadMarker;
+use crate::monitor::MonitorHandler;
+use crate::r#async::Dispatcher;
+use crate::{backend, lock};
+
+pub struct Window {
+    inner: Dispatcher<Inner>,
+}
+
+impl fmt::Debug for Window {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Window").finish_non_exhaustive()
+    }
+}
+
+pub struct Inner {
+    id: WindowId,
+    pub window: web_sys::Window,
+    monitor: Rc<MonitorHandler>,
+    safe_area: Rc<backend::SafeAreaHandle>,
+    canvas: Rc<backend::Canvas>,
+    destroy_fn: Option<Box<dyn FnOnce()>>,
+}
+
+impl Window {
+    pub(crate) fn new(
+        target: &ActiveEventLoop,
+        attr: WindowAttributes,
+    ) -> Result<Self, RequestError> {
+        let id = target.generate_id();
+
+        let window = target.runner.window();
+        let navigator = target.runner.navigator();
+        let document = target.runner.document();
+        let canvas = backend::Canvas::create(
+            target.runner.main_thread(),
+            id,
+            window.clone(),
+            navigator.clone(),
+            document.clone(),
+            attr,
+        )?;
+        let canvas = Rc::new(canvas);
+
+        target.register(&canvas, id);
+
+        let runner = target.runner.clone();
+        let destroy_fn = Box::new(move || runner.notify_destroy_window(id));
+
+        let inner = Inner {
+            id,
+            window: window.clone(),
+            monitor: Rc::clone(target.runner.monitor()),
+            safe_area: Rc::clone(target.runner.safe_area()),
+            canvas,
+            destroy_fn: Some(destroy_fn),
+        };
+
+        let canvas = Rc::downgrade(&inner.canvas);
+        let (dispatcher, runner) = Dispatcher::new(target.runner.main_thread(), inner);
+        target.runner.add_canvas(id, canvas, runner);
+
+        Ok(Window { inner: dispatcher })
+    }
+
+    pub fn canvas(&self) -> Option<Ref<'_, HtmlCanvasElement>> {
+        MainThreadMarker::new()
+            .map(|main_thread| Ref::map(self.inner.value(main_thread), |inner| inner.canvas.raw()))
+    }
+
+    pub(crate) fn prevent_default(&self) -> bool {
+        self.inner.queue(|inner| inner.canvas.prevent_default.get())
+    }
+
+    pub(crate) fn set_prevent_default(&self, prevent_default: bool) {
+        self.inner.dispatch(move |inner| inner.canvas.prevent_default.set(prevent_default))
+    }
+
+    pub(crate) fn is_cursor_lock_raw(&self) -> bool {
+        self.inner.queue(move |inner| {
+            lock::is_cursor_lock_raw(inner.canvas.navigator(), inner.canvas.document())
+        })
+    }
+}
+
+impl RootWindow for Window {
+    fn id(&self) -> WindowId {
+        self.inner.queue(|inner| inner.id)
+    }
+
+    fn scale_factor(&self) -> f64 {
+        self.inner.queue(Inner::scale_factor)
+    }
+
+    fn request_redraw(&self) {
+        self.inner.dispatch(|inner| inner.canvas.request_animation_frame())
+    }
+
+    fn pre_present_notify(&self) {}
+
+    fn reset_dead_keys(&self) {
+        // Not supported
+    }
+
+    fn surface_position(&self) -> PhysicalPosition<i32> {
+        // Note: the canvas element has no window decorations.
+        (0, 0).into()
+    }
+
+    fn outer_position(&self) -> Result<PhysicalPosition<i32>, RequestError> {
+        Ok(self.inner.queue(|inner| inner.canvas.position().to_physical(inner.scale_factor())))
+    }
+
+    fn set_outer_position(&self, position: Position) {
+        self.inner.dispatch(move |inner| {
+            let position = position.to_logical::<f64>(inner.scale_factor());
+            backend::set_canvas_position(
+                inner.canvas.document(),
+                inner.canvas.raw(),
+                inner.canvas.style(),
+                position,
+            )
+        })
+    }
+
+    fn surface_size(&self) -> PhysicalSize<u32> {
+        self.inner.queue(|inner| inner.canvas.surface_size())
+    }
+
+    fn request_surface_size(&self, size: Size) -> Option<PhysicalSize<u32>> {
+        self.inner.queue(|inner| {
+            let size = size.to_logical(self.scale_factor());
+            backend::set_canvas_size(
+                inner.canvas.document(),
+                inner.canvas.raw(),
+                inner.canvas.style(),
+                size,
+            );
+            None
+        })
+    }
+
+    fn outer_size(&self) -> PhysicalSize<u32> {
+        // Note: the canvas element has no window decorations, so this is equal to `surface_size`.
+        self.surface_size()
+    }
+
+    fn safe_area(&self) -> PhysicalInsets<u32> {
+        self.inner.queue(|inner| {
+            let (safe_start_pos, safe_size) = inner.safe_area.get();
+            let safe_end_pos = LogicalPosition::new(
+                safe_start_pos.x + safe_size.width,
+                safe_start_pos.y + safe_size.height,
+            );
+
+            let surface_start_pos = inner.canvas.position();
+            let surface_size = LogicalSize::new(
+                backend::style_size_property(inner.canvas.style(), "width"),
+                backend::style_size_property(inner.canvas.style(), "height"),
+            );
+            let surface_end_pos = LogicalPosition::new(
+                surface_start_pos.x + surface_size.width,
+                surface_start_pos.y + surface_size.height,
+            );
+
+            let top = f64::max(safe_start_pos.y - surface_start_pos.y, 0.);
+            let left = f64::max(safe_start_pos.x - surface_start_pos.x, 0.);
+            let bottom = f64::max(surface_end_pos.y - safe_end_pos.y, 0.);
+            let right = f64::max(surface_end_pos.x - safe_end_pos.x, 0.);
+
+            let insets = LogicalInsets::new(top, left, bottom, right);
+            insets.to_physical(inner.scale_factor())
+        })
+    }
+
+    fn set_min_surface_size(&self, min_size: Option<Size>) {
+        self.inner.dispatch(move |inner| {
+            let dimensions = min_size.map(|min_size| min_size.to_logical(inner.scale_factor()));
+            backend::set_canvas_min_size(
+                inner.canvas.document(),
+                inner.canvas.raw(),
+                inner.canvas.style(),
+                dimensions,
+            )
+        })
+    }
+
+    fn set_max_surface_size(&self, max_size: Option<Size>) {
+        self.inner.dispatch(move |inner| {
+            let dimensions = max_size.map(|dimensions| dimensions.to_logical(inner.scale_factor()));
+            backend::set_canvas_max_size(
+                inner.canvas.document(),
+                inner.canvas.raw(),
+                inner.canvas.style(),
+                dimensions,
+            )
+        })
+    }
+
+    fn surface_resize_increments(&self) -> Option<PhysicalSize<u32>> {
+        None
+    }
+
+    fn set_surface_resize_increments(&self, _: Option<Size>) {
+        // Intentionally a no-op: users can't resize canvas elements
+    }
+
+    fn set_title(&self, title: &str) {
+        self.inner.queue(|inner| inner.canvas.set_attribute("alt", title))
+    }
+
+    fn set_transparent(&self, _: bool) {}
+
+    fn set_blur(&self, _: bool) {}
+
+    fn set_visible(&self, _: bool) {
+        // Intentionally a no-op
+    }
+
+    fn is_visible(&self) -> Option<bool> {
+        None
+    }
+
+    fn set_resizable(&self, _: bool) {
+        // Intentionally a no-op: users can't resize canvas elements
+    }
+
+    fn is_resizable(&self) -> bool {
+        true
+    }
+
+    fn set_enabled_buttons(&self, _: WindowButtons) {}
+
+    fn enabled_buttons(&self) -> WindowButtons {
+        WindowButtons::all()
+    }
+
+    fn set_minimized(&self, _: bool) {
+        // Intentionally a no-op, as canvases cannot be 'minimized'
+    }
+
+    fn is_minimized(&self) -> Option<bool> {
+        // Canvas cannot be 'minimized'
+        Some(false)
+    }
+
+    fn set_maximized(&self, _: bool) {
+        // Intentionally a no-op, as canvases cannot be 'maximized'
+    }
+
+    fn is_maximized(&self) -> bool {
+        // Canvas cannot be 'maximized'
+        false
+    }
+
+    fn set_fullscreen(&self, fullscreen: Option<Fullscreen>) {
+        self.inner.dispatch(move |inner| {
+            if let Some(fullscreen) = fullscreen {
+                inner.canvas.request_fullscreen(fullscreen);
+            } else {
+                inner.canvas.exit_fullscreen()
+            }
+        })
+    }
+
+    fn fullscreen(&self) -> Option<Fullscreen> {
+        self.inner.queue(|inner| {
+            if inner.canvas.is_fullscreen() {
+                Some(Fullscreen::Borderless(None))
+            } else {
+                None
+            }
+        })
+    }
+
+    fn set_decorations(&self, _: bool) {
+        // Intentionally a no-op, no canvas decorations
+    }
+
+    fn is_decorated(&self) -> bool {
+        true
+    }
+
+    fn set_window_level(&self, _: WindowLevel) {
+        // Intentionally a no-op, no window ordering
+    }
+
+    fn set_window_icon(&self, _: Option<Icon>) {
+        // Currently an intentional no-op
+    }
+
+    fn set_ime_cursor_area(&self, _: Position, _: Size) {
+        // Currently not implemented
+    }
+
+    fn set_ime_allowed(&self, _: bool) {
+        // Currently not implemented
+    }
+
+    fn set_ime_purpose(&self, _: ImePurpose) {
+        // Currently not implemented
+    }
+
+    fn focus_window(&self) {
+        self.inner.dispatch(|inner| {
+            let _ = inner.canvas.raw().focus();
+        })
+    }
+
+    fn has_focus(&self) -> bool {
+        self.inner.queue(|inner| inner.canvas.has_focus.get())
+    }
+
+    fn request_user_attention(&self, _: Option<UserAttentionType>) {
+        // Currently an intentional no-op
+    }
+
+    fn set_theme(&self, _: Option<Theme>) {}
+
+    fn theme(&self) -> Option<Theme> {
+        self.inner.queue(|inner| {
+            backend::is_dark_mode(&inner.window).map(|is_dark_mode| {
+                if is_dark_mode {
+                    Theme::Dark
+                } else {
+                    Theme::Light
+                }
+            })
+        })
+    }
+
+    fn set_content_protected(&self, _: bool) {}
+
+    fn title(&self) -> String {
+        String::new()
+    }
+
+    fn set_cursor(&self, cursor: Cursor) {
+        self.inner.dispatch(move |inner| inner.canvas.cursor.set_cursor(cursor))
+    }
+
+    fn set_cursor_position(&self, _: Position) -> Result<(), RequestError> {
+        Err(NotSupportedError::new("set_cursor_position is not supported").into())
+    }
+
+    fn set_cursor_grab(&self, mode: CursorGrabMode) -> Result<(), RequestError> {
+        Ok(self.inner.queue(|inner| {
+            match mode {
+                CursorGrabMode::None => inner.canvas.document().exit_pointer_lock(),
+                CursorGrabMode::Locked => lock::request_pointer_lock(
+                    inner.canvas.navigator(),
+                    inner.canvas.document(),
+                    inner.canvas.raw(),
+                ),
+                CursorGrabMode::Confined => {
+                    return Err(NotSupportedError::new("confined cursor mode is not supported"))
+                },
+            }
+
+            Ok(())
+        })?)
+    }
+
+    fn set_cursor_visible(&self, visible: bool) {
+        self.inner.dispatch(move |inner| inner.canvas.cursor.set_cursor_visible(visible))
+    }
+
+    fn drag_window(&self) -> Result<(), RequestError> {
+        Err(NotSupportedError::new("drag_window is not supported").into())
+    }
+
+    fn drag_resize_window(&self, _: ResizeDirection) -> Result<(), RequestError> {
+        Err(NotSupportedError::new("drag_resize_window is not supported").into())
+    }
+
+    fn show_window_menu(&self, _: Position) {}
+
+    fn set_cursor_hittest(&self, _: bool) -> Result<(), RequestError> {
+        Err(NotSupportedError::new("set_cursor_hittest is not supported").into())
+    }
+
+    fn current_monitor(&self) -> Option<CoremMonitorHandle> {
+        Some(self.inner.queue(|inner| inner.monitor.current_monitor()).into())
+    }
+
+    fn available_monitors(&self) -> Box<dyn Iterator<Item = CoremMonitorHandle>> {
+        Box::new(
+            self.inner
+                .queue(|inner| inner.monitor.available_monitors())
+                .into_iter()
+                .map(CoremMonitorHandle::from),
+        )
+    }
+
+    fn primary_monitor(&self) -> Option<CoremMonitorHandle> {
+        self.inner.queue(|inner| inner.monitor.primary_monitor()).map(CoremMonitorHandle::from)
+    }
+
+    fn rwh_06_display_handle(&self) -> &dyn rwh_06::HasDisplayHandle {
+        self
+    }
+
+    fn rwh_06_window_handle(&self) -> &dyn rwh_06::HasWindowHandle {
+        self
+    }
+}
+
+impl rwh_06::HasWindowHandle for Window {
+    fn window_handle(&self) -> Result<rwh_06::WindowHandle<'_>, rwh_06::HandleError> {
+        MainThreadMarker::new()
+            .map(|main_thread| {
+                let inner = self.inner.value(main_thread);
+                // SAFETY: This will only work if the reference to `HtmlCanvasElement` stays valid.
+                let canvas: &wasm_bindgen::JsValue = inner.canvas.raw();
+                let window_handle =
+                    rwh_06::WebCanvasWindowHandle::new(std::ptr::NonNull::from(canvas).cast());
+                // SAFETY: The pointer won't be invalidated as long as `Window` lives, which the
+                // lifetime is bound to.
+                unsafe {
+                    rwh_06::WindowHandle::borrow_raw(rwh_06::RawWindowHandle::WebCanvas(
+                        window_handle,
+                    ))
+                }
+            })
+            .ok_or(rwh_06::HandleError::Unavailable)
+    }
+}
+
+impl rwh_06::HasDisplayHandle for Window {
+    fn display_handle(&self) -> Result<rwh_06::DisplayHandle<'_>, rwh_06::HandleError> {
+        Ok(rwh_06::DisplayHandle::web())
+    }
+}
+
+impl Inner {
+    #[inline]
+    pub fn scale_factor(&self) -> f64 {
+        super::backend::scale_factor(&self.window)
+    }
+}
+
+impl Drop for Inner {
+    fn drop(&mut self) {
+        if let Some(destroy_fn) = self.destroy_fn.take() {
+            destroy_fn();
+        }
+    }
+}