winit/src/platform_impl/web/cursor.rs

use super::backend::Style;
use super::event_loop::runner::{EventWrapper, WeakShared};
use super::main_thread::{MainThreadMarker, MainThreadSafe};
use super::EventLoopWindowTarget;
use crate::cursor::{BadImage, Cursor, CursorImage};
use cursor_icon::CursorIcon;
use std::ops::Deref;
use std::sync::Weak;
use std::{
    cell::RefCell,
    future,
    hash::{Hash, Hasher},
    mem,
    ops::DerefMut,
    rc::Rc,
    sync::Arc,
    task::{Poll, Waker},
};
use wasm_bindgen::{closure::Closure, JsCast};
use wasm_bindgen_futures::JsFuture;
use web_sys::{
    Blob, Document, HtmlCanvasElement, HtmlImageElement, ImageBitmap, ImageBitmapOptions,
    ImageBitmapRenderingContext, ImageData, PremultiplyAlpha, Url, Window,
};

#[derive(Debug)]
pub(crate) enum CustomCursorBuilder {
    Image(CursorImage),
    Url {
        url: String,
        hotspot_x: u16,
        hotspot_y: u16,
    },
}

impl CustomCursorBuilder {
    pub fn from_rgba(
        rgba: Vec<u8>,
        width: u16,
        height: u16,
        hotspot_x: u16,
        hotspot_y: u16,
    ) -> Result<CustomCursorBuilder, BadImage> {
        Ok(CustomCursorBuilder::Image(CursorImage::from_rgba(
            rgba, width, height, hotspot_x, hotspot_y,
        )?))
    }
}

#[derive(Clone, Debug)]
pub struct CustomCursor(Arc<MainThreadSafe<RefCell<ImageState>>>);

impl Hash for CustomCursor {
    fn hash<H: Hasher>(&self, state: &mut H) {
        Arc::as_ptr(&self.0).hash(state);
    }
}

impl PartialEq for CustomCursor {
    fn eq(&self, other: &Self) -> bool {
        Arc::ptr_eq(&self.0, &other.0)
    }
}

impl Eq for CustomCursor {}

impl CustomCursor {
    fn new(main_thread: MainThreadMarker) -> Self {
        Self(Arc::new(MainThreadSafe::new(
            main_thread,
            RefCell::new(ImageState::Loading(None)),
        )))
    }

    pub(crate) fn build<T>(
        builder: CustomCursorBuilder,
        window_target: &EventLoopWindowTarget<T>,
    ) -> Self {
        let main_thread = window_target.runner.main_thread();

        match builder {
            CustomCursorBuilder::Image(image) => ImageState::from_rgba(
                main_thread,
                window_target.runner.window(),
                window_target.runner.document().clone(),
                &image,
            ),
            CustomCursorBuilder::Url {
                url,
                hotspot_x,
                hotspot_y,
            } => ImageState::from_url(main_thread, url, hotspot_x, hotspot_y),
        }
    }
}

#[derive(Debug)]
pub struct CursorHandler {
    main_thread: MainThreadMarker,
    runner: WeakShared,
    style: Style,
    visible: bool,
    cursor: SelectedCursor,
}

impl CursorHandler {
    pub(crate) fn new(main_thread: MainThreadMarker, runner: WeakShared, style: Style) -> Self {
        Self {
            main_thread,
            runner,
            style,
            visible: true,
            cursor: SelectedCursor::default(),
        }
    }

    pub fn set_cursor(&mut self, cursor: Cursor) {
        match cursor {
            Cursor::Icon(icon) => {
                if let SelectedCursor::Icon(old_icon)
                | SelectedCursor::ImageLoading {
                    previous: Previous::Icon(old_icon),
                    ..
                } = &self.cursor
                {
                    if *old_icon == icon {
                        return;
                    }
                }

                self.cursor = SelectedCursor::Icon(icon);
                self.set_style();
            }
            Cursor::Custom(cursor) => {
                let cursor = cursor.inner;

                if let SelectedCursor::ImageLoading {
                    cursor: old_cursor, ..
                }
                | SelectedCursor::ImageReady(old_cursor) = &self.cursor
                {
                    if *old_cursor == cursor {
                        return;
                    }
                }

                let mut image = cursor.0.get(self.main_thread).borrow_mut();
                match image.deref_mut() {
                    ImageState::Loading(state) => {
                        *state = Some(self.runner.clone());
                        drop(image);
                        self.cursor = SelectedCursor::ImageLoading {
                            cursor,
                            previous: mem::take(&mut self.cursor).into(),
                        };
                    }
                    ImageState::Failed => log::error!("tried to load invalid cursor"),
                    ImageState::Ready { .. } => {
                        drop(image);
                        self.cursor = SelectedCursor::ImageReady(cursor);
                        self.set_style();
                    }
                };
            }
        }
    }

    pub fn set_cursor_visible(&mut self, visible: bool) {
        if !visible && self.visible {
            self.visible = false;
            self.style.set("cursor", "none");
        } else if visible && !self.visible {
            self.visible = true;
            self.set_style();
        }
    }

    pub fn handle_cursor_ready(&mut self, result: Result<CustomCursorHandle, CustomCursorHandle>) {
        if let SelectedCursor::ImageLoading {
            cursor: current_cursor,
            ..
        } = &self.cursor
        {
            let current_cursor = Arc::downgrade(&current_cursor.0);

            let (Ok(new_cursor) | Err(new_cursor)) = &result;

            if !new_cursor.0.ptr_eq(&current_cursor) {
                return;
            }

            let SelectedCursor::ImageLoading { cursor, previous } = mem::take(&mut self.cursor)
            else {
                unreachable!("found wrong state")
            };

            match result {
                Ok(_) => {
                    self.cursor = SelectedCursor::ImageReady(cursor);
                    self.set_style();
                }
                Err(_) => self.cursor = previous.into(),
            }
        }
    }

    fn set_style(&self) {
        if self.visible {
            match &self.cursor {
                SelectedCursor::Icon(icon)
                | SelectedCursor::ImageLoading {
                    previous: Previous::Icon(icon),
                    ..
                } => self.style.set("cursor", icon.name()),
                SelectedCursor::ImageLoading {
                    previous: Previous::Image(cursor),
                    ..
                }
                | SelectedCursor::ImageReady(cursor) => {
                    if let ImageState::Ready { style, .. } =
                        cursor.0.get(self.main_thread).borrow().deref()
                    {
                        self.style.set("cursor", style)
                    } else {
                        unreachable!("found invalid saved state")
                    }
                }
            }
        }
    }
}

#[derive(Debug)]
enum SelectedCursor {
    Icon(CursorIcon),
    ImageLoading {
        cursor: CustomCursor,
        previous: Previous,
    },
    ImageReady(CustomCursor),
}

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::ImageReady(cursor),
        }
    }
}

#[derive(Debug)]
pub enum Previous {
    Icon(CursorIcon),
    Image(CustomCursor),
}

impl From<SelectedCursor> for Previous {
    fn from(value: SelectedCursor) -> Self {
        match value {
            SelectedCursor::Icon(icon) => Self::Icon(icon),
            SelectedCursor::ImageLoading { previous, .. } => previous,
            SelectedCursor::ImageReady(image) => Self::Image(image),
        }
    }
}

#[derive(Debug)]
enum ImageState {
    Loading(Option<WeakShared>),
    Failed,
    Ready {
        style: String,
        _object_url: Option<ObjectUrl>,
        _image: HtmlImageElement,
    },
}

impl ImageState {
    fn from_rgba(
        main_thread: MainThreadMarker,
        window: &Window,
        document: Document,
        image: &CursorImage,
    ) -> CustomCursor {
        // 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.
        // 7. Notify event loop if one is registered.

        // 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::prelude::wasm_bindgen;
            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.rgba.len() as u32);
            array.copy_from(&image.rgba);
            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.rgba),
            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 mut options = ImageBitmapOptions::new();
        options.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 this = CustomCursor::new(main_thread);

        wasm_bindgen_futures::spawn_local({
            let weak = Arc::downgrade(&this.0);
            let CursorImage {
                width,
                height,
                hotspot_x,
                hotspot_y,
                ..
            } = *image;
            async move {
                // Keep checking if all references are dropped between every `await` call.
                if weak.strong_count() == 0 {
                    return;
                }

                let bitmap: ImageBitmap = bitmap
                    .await
                    .expect("found invalid state in `ImageData`")
                    .unchecked_into();

                if weak.strong_count() == 0 {
                    return;
                }

                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);

                if weak.strong_count() == 0 {
                    return;
                }

                let Some(blob) = blob else {
                    log::error!("creating object URL from custom cursor failed");
                    let Some(this) = weak.upgrade() else {
                        return;
                    };
                    let mut this = this.get(main_thread).borrow_mut();
                    let ImageState::Loading(runner) = this.deref_mut() else {
                        unreachable!("found invalid state");
                    };
                    let runner = runner.take();
                    *this = ImageState::Failed;

                    if let Some(runner) = runner.and_then(|weak| weak.upgrade()) {
                        runner.send_event(EventWrapper::CursorReady(Err(CustomCursorHandle(weak))));
                    }

                    return;
                };

                // 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));

                Self::decode(main_thread, weak, url, hotspot_x, hotspot_y).await;
            }
        });

        this
    }

    fn from_url(
        main_thread: MainThreadMarker,
        url: String,
        hotspot_x: u16,
        hotspot_y: u16,
    ) -> CustomCursor {
        let this = CustomCursor::new(main_thread);
        wasm_bindgen_futures::spawn_local(Self::decode(
            main_thread,
            Arc::downgrade(&this.0),
            UrlType::Plain(url),
            hotspot_x,
            hotspot_y,
        ));

        this
    }

    async fn decode(
        main_thread: MainThreadMarker,
        weak: Weak<MainThreadSafe<RefCell<ImageState>>>,
        url: UrlType,
        hotspot_x: u16,
        hotspot_y: u16,
    ) {
        if weak.strong_count() == 0 {
            return;
        }

        // 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;

        let Some(this) = weak.upgrade() else {
            return;
        };
        let mut this = this.get(main_thread).borrow_mut();

        let ImageState::Loading(runner) = this.deref_mut() else {
            unreachable!("found invalid state");
        };
        let runner = runner.take();

        if let Err(error) = result {
            log::error!("decoding custom cursor failed: {error:?}");
            *this = ImageState::Failed;

            if let Some(runner) = runner.and_then(|weak| weak.upgrade()) {
                runner.send_event(EventWrapper::CursorReady(Err(CustomCursorHandle(weak))));
            }

            return;
        }

        *this = ImageState::Ready {
            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,
        };

        // 7. Notify event loop if one is registered.
        if let Some(runner) = runner.and_then(|weak| weak.upgrade()) {
            runner.send_event(EventWrapper::CursorReady(Ok(CustomCursorHandle(weak))));
        }
    }
}

#[derive(Clone)]
pub struct CustomCursorHandle(Weak<MainThreadSafe<RefCell<ImageState>>>);

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()`");
    }
}