winit/src/platform_impl/android/mod.rs

#![cfg(android_platform)]

use std::{
    collections::VecDeque,
    hash::Hash,
    sync::{
        atomic::{AtomicBool, Ordering},
        mpsc, Arc, Mutex, RwLock,
    },
    time::{Duration, Instant},
};

use android_activity::input::{InputEvent, KeyAction, Keycode, MotionAction};
use android_activity::{
    AndroidApp, AndroidAppWaker, ConfigurationRef, InputStatus, MainEvent, Rect,
};
use once_cell::sync::Lazy;
use raw_window_handle::{
    AndroidDisplayHandle, HasRawWindowHandle, RawDisplayHandle, RawWindowHandle,
};

use crate::{
    dpi::{PhysicalPosition, PhysicalSize, Position, Size},
    error,
    event::{self, InnerSizeWriter, StartCause},
    event_loop::{self, ControlFlow, EventLoopWindowTarget as RootELW},
    platform::pump_events::PumpStatus,
    window::{
        self, CursorGrabMode, ImePurpose, ResizeDirection, Theme, WindowButtons, WindowLevel,
    },
};
use crate::{error::EventLoopError, platform_impl::Fullscreen};

mod keycodes;

static HAS_FOCUS: Lazy<RwLock<bool>> = Lazy::new(|| RwLock::new(true));

/// Returns the minimum `Option<Duration>`, taking into account that `None`
/// equates to an infinite timeout, not a zero timeout (so can't just use
/// `Option::min`)
fn min_timeout(a: Option<Duration>, b: Option<Duration>) -> Option<Duration> {
    a.map_or(b, |a_timeout| {
        b.map_or(Some(a_timeout), |b_timeout| Some(a_timeout.min(b_timeout)))
    })
}

struct PeekableReceiver<T> {
    recv: mpsc::Receiver<T>,
    first: Option<T>,
}

impl<T> PeekableReceiver<T> {
    pub fn from_recv(recv: mpsc::Receiver<T>) -> Self {
        Self { recv, first: None }
    }
    pub fn has_incoming(&mut self) -> bool {
        if self.first.is_some() {
            return true;
        }
        match self.recv.try_recv() {
            Ok(v) => {
                self.first = Some(v);
                true
            }
            Err(mpsc::TryRecvError::Empty) => false,
            Err(mpsc::TryRecvError::Disconnected) => {
                warn!("Channel was disconnected when checking incoming");
                false
            }
        }
    }
    pub fn try_recv(&mut self) -> Result<T, mpsc::TryRecvError> {
        if let Some(first) = self.first.take() {
            return Ok(first);
        }
        self.recv.try_recv()
    }
}

#[derive(Clone)]
struct SharedFlagSetter {
    flag: Arc<AtomicBool>,
}
impl SharedFlagSetter {
    pub fn set(&self) -> bool {
        self.flag
            .compare_exchange(false, true, Ordering::AcqRel, Ordering::Relaxed)
            .is_ok()
    }
}

struct SharedFlag {
    flag: Arc<AtomicBool>,
}

// Used for queuing redraws from arbitrary threads. We don't care how many
// times a redraw is requested (so don't actually need to queue any data,
// we just need to know at the start of a main loop iteration if a redraw
// was queued and be able to read and clear the state atomically)
impl SharedFlag {
    pub fn new() -> Self {
        Self {
            flag: Arc::new(AtomicBool::new(false)),
        }
    }
    pub fn setter(&self) -> SharedFlagSetter {
        SharedFlagSetter {
            flag: self.flag.clone(),
        }
    }
    pub fn get_and_reset(&self) -> bool {
        self.flag.swap(false, std::sync::atomic::Ordering::AcqRel)
    }
}

#[derive(Clone)]
pub struct RedrawRequester {
    flag: SharedFlagSetter,
    waker: AndroidAppWaker,
}

impl RedrawRequester {
    fn new(flag: &SharedFlag, waker: AndroidAppWaker) -> Self {
        RedrawRequester {
            flag: flag.setter(),
            waker,
        }
    }
    pub fn request_redraw(&self) {
        if self.flag.set() {
            // Only explicitly try to wake up the main loop when the flag
            // value changes
            self.waker.wake();
        }
    }
}

#[derive(Debug, Clone, Eq, PartialEq, Hash)]
pub struct KeyEventExtra {}

pub struct EventLoop<T: 'static> {
    android_app: AndroidApp,
    window_target: event_loop::EventLoopWindowTarget<T>,
    redraw_flag: SharedFlag,
    user_events_sender: mpsc::Sender<T>,
    user_events_receiver: PeekableReceiver<T>, //must wake looper whenever something gets sent
    loop_running: bool,                        // Dispatched `NewEvents<Init>`
    running: bool,
    pending_redraw: bool,
    control_flow: ControlFlow,
    cause: StartCause,
    ignore_volume_keys: bool,
    combining_accent: Option<char>,
}

#[derive(Debug, Clone, PartialEq)]
pub(crate) struct PlatformSpecificEventLoopAttributes {
    pub(crate) android_app: Option<AndroidApp>,
    pub(crate) ignore_volume_keys: bool,
}

impl Default for PlatformSpecificEventLoopAttributes {
    fn default() -> Self {
        Self {
            android_app: Default::default(),
            ignore_volume_keys: true,
        }
    }
}

fn sticky_exit_callback<T, F>(
    evt: event::Event<T>,
    target: &RootELW<T>,
    control_flow: &mut ControlFlow,
    callback: &mut F,
) where
    F: FnMut(event::Event<T>, &RootELW<T>, &mut ControlFlow),
{
    // make ControlFlow::ExitWithCode sticky by providing a dummy
    // control flow reference if it is already ExitWithCode.
    if let ControlFlow::ExitWithCode(code) = *control_flow {
        callback(evt, target, &mut ControlFlow::ExitWithCode(code))
    } else {
        callback(evt, target, control_flow)
    }
}

impl<T: 'static> EventLoop<T> {
    pub(crate) fn new(
        attributes: &PlatformSpecificEventLoopAttributes,
    ) -> Result<Self, EventLoopError> {
        let (user_events_sender, user_events_receiver) = mpsc::channel();

        let android_app = attributes.android_app.as_ref().expect("An `AndroidApp` as passed to android_main() is required to create an `EventLoop` on Android");
        let redraw_flag = SharedFlag::new();

        Ok(Self {
            android_app: android_app.clone(),
            window_target: event_loop::EventLoopWindowTarget {
                p: EventLoopWindowTarget {
                    app: android_app.clone(),
                    redraw_requester: RedrawRequester::new(
                        &redraw_flag,
                        android_app.create_waker(),
                    ),
                    _marker: std::marker::PhantomData,
                },
                _marker: std::marker::PhantomData,
            },
            redraw_flag,
            user_events_sender,
            user_events_receiver: PeekableReceiver::from_recv(user_events_receiver),
            loop_running: false,
            running: false,
            pending_redraw: false,
            control_flow: Default::default(),
            cause: StartCause::Init,
            ignore_volume_keys: attributes.ignore_volume_keys,
            combining_accent: None,
        })
    }

    fn single_iteration<F>(&mut self, main_event: Option<MainEvent<'_>>, callback: &mut F)
    where
        F: FnMut(event::Event<T>, &RootELW<T>, &mut ControlFlow),
    {
        trace!("Mainloop iteration");

        let cause = self.cause;
        let mut control_flow = self.control_flow;
        let mut pending_redraw = self.pending_redraw;
        let mut resized = false;

        sticky_exit_callback(
            event::Event::NewEvents(cause),
            self.window_target(),
            &mut control_flow,
            callback,
        );

        if let Some(event) = main_event {
            trace!("Handling main event {:?}", event);

            match event {
                MainEvent::InitWindow { .. } => {
                    sticky_exit_callback(
                        event::Event::Resumed,
                        self.window_target(),
                        &mut control_flow,
                        callback,
                    );
                }
                MainEvent::TerminateWindow { .. } => {
                    sticky_exit_callback(
                        event::Event::Suspended,
                        self.window_target(),
                        &mut control_flow,
                        callback,
                    );
                }
                MainEvent::WindowResized { .. } => resized = true,
                MainEvent::RedrawNeeded { .. } => pending_redraw = true,
                MainEvent::ContentRectChanged { .. } => {
                    warn!("TODO: find a way to notify application of content rect change");
                }
                MainEvent::GainedFocus => {
                    *HAS_FOCUS.write().unwrap() = true;
                    sticky_exit_callback(
                        event::Event::WindowEvent {
                            window_id: window::WindowId(WindowId),
                            event: event::WindowEvent::Focused(true),
                        },
                        self.window_target(),
                        &mut control_flow,
                        callback,
                    );
                }
                MainEvent::LostFocus => {
                    *HAS_FOCUS.write().unwrap() = false;
                    sticky_exit_callback(
                        event::Event::WindowEvent {
                            window_id: window::WindowId(WindowId),
                            event: event::WindowEvent::Focused(false),
                        },
                        self.window_target(),
                        &mut control_flow,
                        callback,
                    );
                }
                MainEvent::ConfigChanged { .. } => {
                    let monitor = MonitorHandle::new(self.android_app.clone());
                    let old_scale_factor = monitor.scale_factor();
                    let scale_factor = monitor.scale_factor();
                    if (scale_factor - old_scale_factor).abs() < f64::EPSILON {
                        let new_inner_size = Arc::new(Mutex::new(
                            MonitorHandle::new(self.android_app.clone()).size(),
                        ));
                        let event = event::Event::WindowEvent {
                            window_id: window::WindowId(WindowId),
                            event: event::WindowEvent::ScaleFactorChanged {
                                inner_size_writer: InnerSizeWriter::new(Arc::downgrade(
                                    &new_inner_size,
                                )),
                                scale_factor,
                            },
                        };
                        sticky_exit_callback(
                            event,
                            self.window_target(),
                            &mut control_flow,
                            callback,
                        );
                    }
                }
                MainEvent::LowMemory => {
                    // XXX: how to forward this state to applications?
                    // It seems like ideally winit should support lifecycle and
                    // low-memory events, especially for mobile platforms.
                    warn!("TODO: handle Android LowMemory notification");
                }
                MainEvent::Start => {
                    // XXX: how to forward this state to applications?
                    warn!("TODO: forward onStart notification to application");
                }
                MainEvent::Resume { .. } => {
                    debug!("App Resumed - is running");
                    self.running = true;
                }
                MainEvent::SaveState { .. } => {
                    // XXX: how to forward this state to applications?
                    // XXX: also how do we expose state restoration to apps?
                    warn!("TODO: forward saveState notification to application");
                }
                MainEvent::Pause => {
                    debug!("App Paused - stopped running");
                    self.running = false;
                }
                MainEvent::Stop => {
                    // XXX: how to forward this state to applications?
                    warn!("TODO: forward onStop notification to application");
                }
                MainEvent::Destroy => {
                    // XXX: maybe exit mainloop to drop things before being
                    // killed by the OS?
                    warn!("TODO: forward onDestroy notification to application");
                }
                MainEvent::InsetsChanged { .. } => {
                    // XXX: how to forward this state to applications?
                    warn!("TODO: handle Android InsetsChanged notification");
                }
                unknown => {
                    trace!("Unknown MainEvent {unknown:?} (ignored)");
                }
            }
        } else {
            trace!("No main event to handle");
        }

        // temporarily decouple `android_app` from `self` so we aren't holding
        // a borrow of `self` while iterating
        let android_app = self.android_app.clone();

        // Process input events
        match android_app.input_events_iter() {
            Ok(mut input_iter) => loop {
                let read_event = input_iter.next(|event| {
                    self.handle_input_event(&android_app, event, &mut control_flow, callback)
                });

                if !read_event {
                    break;
                }
            },
            Err(err) => {
                log::warn!("Failed to get input events iterator: {err:?}");
            }
        }

        // Empty the user event buffer
        {
            while let Ok(event) = self.user_events_receiver.try_recv() {
                sticky_exit_callback(
                    crate::event::Event::UserEvent(event),
                    self.window_target(),
                    &mut control_flow,
                    callback,
                );
            }
        }

        if self.running {
            if resized {
                let size = if let Some(native_window) = self.android_app.native_window().as_ref() {
                    let width = native_window.width() as _;
                    let height = native_window.height() as _;
                    PhysicalSize::new(width, height)
                } else {
                    PhysicalSize::new(0, 0)
                };
                let event = event::Event::WindowEvent {
                    window_id: window::WindowId(WindowId),
                    event: event::WindowEvent::Resized(size),
                };
                sticky_exit_callback(event, self.window_target(), &mut control_flow, callback);
            }

            pending_redraw |= self.redraw_flag.get_and_reset();
            if pending_redraw {
                pending_redraw = false;
                let event = event::Event::RedrawRequested(window::WindowId(WindowId));
                sticky_exit_callback(event, self.window_target(), &mut control_flow, callback);
            }
        }

        // This is always the last event we dispatch before poll again
        sticky_exit_callback(
            event::Event::AboutToWait,
            self.window_target(),
            &mut control_flow,
            callback,
        );

        self.control_flow = control_flow;
        self.pending_redraw = pending_redraw;
    }

    fn handle_input_event<F>(
        &mut self,
        android_app: &AndroidApp,
        event: &InputEvent<'_>,
        control_flow: &mut ControlFlow,
        callback: &mut F,
    ) -> InputStatus
    where
        F: FnMut(event::Event<T>, &RootELW<T>, &mut ControlFlow),
    {
        let mut input_status = InputStatus::Handled;
        match event {
            InputEvent::MotionEvent(motion_event) => {
                let window_id = window::WindowId(WindowId);
                let device_id = event::DeviceId(DeviceId);

                let phase = match motion_event.action() {
                    MotionAction::Down | MotionAction::PointerDown => {
                        Some(event::TouchPhase::Started)
                    }
                    MotionAction::Up | MotionAction::PointerUp => Some(event::TouchPhase::Ended),
                    MotionAction::Move => Some(event::TouchPhase::Moved),
                    MotionAction::Cancel => Some(event::TouchPhase::Cancelled),
                    _ => {
                        None // TODO mouse events
                    }
                };
                if let Some(phase) = phase {
                    let pointers: Box<dyn Iterator<Item = android_activity::input::Pointer<'_>>> =
                        match phase {
                            event::TouchPhase::Started | event::TouchPhase::Ended => {
                                Box::new(std::iter::once(
                                    motion_event.pointer_at_index(motion_event.pointer_index()),
                                ))
                            }
                            event::TouchPhase::Moved | event::TouchPhase::Cancelled => {
                                Box::new(motion_event.pointers())
                            }
                        };

                    for pointer in pointers {
                        let location = PhysicalPosition {
                            x: pointer.x() as _,
                            y: pointer.y() as _,
                        };
                        trace!("Input event {device_id:?}, {phase:?}, loc={location:?}, pointer={pointer:?}");
                        let event = event::Event::WindowEvent {
                            window_id,
                            event: event::WindowEvent::Touch(event::Touch {
                                device_id,
                                phase,
                                location,
                                id: pointer.pointer_id() as u64,
                                force: None,
                            }),
                        };
                        sticky_exit_callback(event, self.window_target(), control_flow, callback);
                    }
                }
            }
            InputEvent::KeyEvent(key) => {
                match key.key_code() {
                    // Flag keys related to volume as unhandled. While winit does not have a way for applications
                    // to configure what keys to flag as handled, this appears to be a good default until winit
                    // can be configured.
                    Keycode::VolumeUp | Keycode::VolumeDown | Keycode::VolumeMute => {
                        if self.ignore_volume_keys {
                            input_status = InputStatus::Unhandled
                        }
                    }
                    keycode => {
                        let state = match key.action() {
                            KeyAction::Down => event::ElementState::Pressed,
                            KeyAction::Up => event::ElementState::Released,
                            _ => event::ElementState::Released,
                        };

                        let key_char = keycodes::character_map_and_combine_key(
                            android_app,
                            key,
                            &mut self.combining_accent,
                        );

                        let event = event::Event::WindowEvent {
                            window_id: window::WindowId(WindowId),
                            event: event::WindowEvent::KeyboardInput {
                                device_id: event::DeviceId(DeviceId),
                                event: event::KeyEvent {
                                    state,
                                    physical_key: keycodes::to_physical_keycode(keycode),
                                    logical_key: keycodes::to_logical(key_char, keycode),
                                    location: keycodes::to_location(keycode),
                                    repeat: key.repeat_count() > 0,
                                    text: None,
                                    platform_specific: KeyEventExtra {},
                                },
                                is_synthetic: false,
                            },
                        };
                        sticky_exit_callback(event, self.window_target(), control_flow, callback);
                    }
                }
            }
            _ => {
                warn!("Unknown android_activity input event {event:?}")
            }
        }

        input_status
    }

    pub fn run<F>(mut self, event_handler: F) -> Result<(), EventLoopError>
    where
        F: FnMut(event::Event<T>, &event_loop::EventLoopWindowTarget<T>, &mut ControlFlow),
    {
        self.run_ondemand(event_handler)
    }

    pub fn run_ondemand<F>(&mut self, mut event_handler: F) -> Result<(), EventLoopError>
    where
        F: FnMut(event::Event<T>, &event_loop::EventLoopWindowTarget<T>, &mut ControlFlow),
    {
        if self.loop_running {
            return Err(EventLoopError::AlreadyRunning);
        }

        loop {
            match self.pump_events(None, &mut event_handler) {
                PumpStatus::Exit(0) => {
                    break Ok(());
                }
                PumpStatus::Exit(code) => {
                    break Err(EventLoopError::ExitFailure(code));
                }
                _ => {
                    continue;
                }
            }
        }
    }

    pub fn pump_events<F>(&mut self, timeout: Option<Duration>, mut callback: F) -> PumpStatus
    where
        F: FnMut(event::Event<T>, &RootELW<T>, &mut ControlFlow),
    {
        if !self.loop_running {
            self.loop_running = true;

            // Reset the internal state for the loop as we start running to
            // ensure consistent behaviour in case the loop runs and exits more
            // than once
            self.pending_redraw = false;
            self.cause = StartCause::Init;
            self.control_flow = ControlFlow::Poll;

            // run the initial loop iteration
            self.single_iteration(None, &mut callback);
        }

        // Consider the possibility that the `StartCause::Init` iteration could
        // request to Exit
        if !matches!(self.control_flow, ControlFlow::ExitWithCode(_)) {
            self.poll_events_with_timeout(timeout, &mut callback);
        }
        if let ControlFlow::ExitWithCode(code) = self.control_flow {
            self.loop_running = false;

            let mut dummy = self.control_flow;
            sticky_exit_callback(
                event::Event::LoopExiting,
                self.window_target(),
                &mut dummy,
                &mut callback,
            );

            PumpStatus::Exit(code)
        } else {
            PumpStatus::Continue
        }
    }

    fn poll_events_with_timeout<F>(&mut self, mut timeout: Option<Duration>, mut callback: F)
    where
        F: FnMut(event::Event<T>, &RootELW<T>, &mut ControlFlow),
    {
        let start = Instant::now();

        self.pending_redraw |= self.redraw_flag.get_and_reset();

        timeout =
            if self.running && (self.pending_redraw || self.user_events_receiver.has_incoming()) {
                // If we already have work to do then we don't want to block on the next poll
                Some(Duration::ZERO)
            } else {
                let control_flow_timeout = match self.control_flow {
                    ControlFlow::Wait => None,
                    ControlFlow::Poll => Some(Duration::ZERO),
                    ControlFlow::WaitUntil(wait_deadline) => {
                        Some(wait_deadline.saturating_duration_since(start))
                    }
                    // `ExitWithCode()` will be reset to `Poll` before polling
                    ControlFlow::ExitWithCode(_code) => unreachable!(),
                };

                min_timeout(control_flow_timeout, timeout)
            };

        let app = self.android_app.clone(); // Don't borrow self as part of poll expression
        app.poll_events(timeout, |poll_event| {
            let mut main_event = None;

            match poll_event {
                android_activity::PollEvent::Wake => {
                    // In the X11 backend it's noted that too many false-positive wake ups
                    // would cause the event loop to run continuously. They handle this by re-checking
                    // for pending events (assuming they cover all valid reasons for a wake up).
                    //
                    // For now, user_events and redraw_requests are the only reasons to expect
                    // a wake up here so we can ignore the wake up if there are no events/requests.
                    // We also ignore wake ups while suspended.
                    self.pending_redraw |= self.redraw_flag.get_and_reset();
                    if !self.running
                        || (!self.pending_redraw && !self.user_events_receiver.has_incoming())
                    {
                        return;
                    }
                }
                android_activity::PollEvent::Timeout => {}
                android_activity::PollEvent::Main(event) => {
                    main_event = Some(event);
                }
                unknown_event => {
                    warn!("Unknown poll event {unknown_event:?} (ignored)");
                }
            }

            self.cause = match self.control_flow {
                ControlFlow::Poll => StartCause::Poll,
                ControlFlow::Wait => StartCause::WaitCancelled {
                    start,
                    requested_resume: None,
                },
                ControlFlow::WaitUntil(deadline) => {
                    if Instant::now() < deadline {
                        StartCause::WaitCancelled {
                            start,
                            requested_resume: Some(deadline),
                        }
                    } else {
                        StartCause::ResumeTimeReached {
                            start,
                            requested_resume: deadline,
                        }
                    }
                }
                // `ExitWithCode()` will be reset to `Poll` before polling
                ControlFlow::ExitWithCode(_code) => unreachable!(),
            };

            self.single_iteration(main_event, &mut callback);
        });
    }

    pub fn window_target(&self) -> &event_loop::EventLoopWindowTarget<T> {
        &self.window_target
    }

    pub fn create_proxy(&self) -> EventLoopProxy<T> {
        EventLoopProxy {
            user_events_sender: self.user_events_sender.clone(),
            waker: self.android_app.create_waker(),
        }
    }
}

pub struct EventLoopProxy<T: 'static> {
    user_events_sender: mpsc::Sender<T>,
    waker: AndroidAppWaker,
}

impl<T: 'static> Clone for EventLoopProxy<T> {
    fn clone(&self) -> Self {
        EventLoopProxy {
            user_events_sender: self.user_events_sender.clone(),
            waker: self.waker.clone(),
        }
    }
}

impl<T> EventLoopProxy<T> {
    pub fn send_event(&self, event: T) -> Result<(), event_loop::EventLoopClosed<T>> {
        self.user_events_sender
            .send(event)
            .map_err(|err| event_loop::EventLoopClosed(err.0))?;
        self.waker.wake();
        Ok(())
    }
}

pub struct EventLoopWindowTarget<T: 'static> {
    app: AndroidApp,
    redraw_requester: RedrawRequester,
    _marker: std::marker::PhantomData<T>,
}

impl<T: 'static> EventLoopWindowTarget<T> {
    pub fn primary_monitor(&self) -> Option<MonitorHandle> {
        Some(MonitorHandle::new(self.app.clone()))
    }

    pub fn available_monitors(&self) -> VecDeque<MonitorHandle> {
        let mut v = VecDeque::with_capacity(1);
        v.push_back(MonitorHandle::new(self.app.clone()));
        v
    }

    pub fn raw_display_handle(&self) -> RawDisplayHandle {
        RawDisplayHandle::Android(AndroidDisplayHandle::empty())
    }
}

#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub(crate) struct WindowId;

impl WindowId {
    pub const fn dummy() -> Self {
        WindowId
    }
}

impl From<WindowId> for u64 {
    fn from(_: WindowId) -> Self {
        0
    }
}

impl From<u64> for WindowId {
    fn from(_: u64) -> Self {
        Self
    }
}

#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct DeviceId;

impl DeviceId {
    pub const fn dummy() -> Self {
        DeviceId
    }
}

#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub struct PlatformSpecificWindowBuilderAttributes;

pub(crate) struct Window {
    app: AndroidApp,
    redraw_requester: RedrawRequester,
}

impl Window {
    pub(crate) fn new<T: 'static>(
        el: &EventLoopWindowTarget<T>,
        _window_attrs: window::WindowAttributes,
        _: PlatformSpecificWindowBuilderAttributes,
    ) -> Result<Self, error::OsError> {
        // FIXME this ignores requested window attributes

        Ok(Self {
            app: el.app.clone(),
            redraw_requester: el.redraw_requester.clone(),
        })
    }

    pub(crate) fn maybe_queue_on_main(&self, f: impl FnOnce(&Self) + Send + 'static) {
        f(self)
    }

    pub(crate) fn maybe_wait_on_main<R: Send>(&self, f: impl FnOnce(&Self) -> R + Send) -> R {
        f(self)
    }

    pub fn id(&self) -> WindowId {
        WindowId
    }

    pub fn primary_monitor(&self) -> Option<MonitorHandle> {
        Some(MonitorHandle::new(self.app.clone()))
    }

    pub fn available_monitors(&self) -> VecDeque<MonitorHandle> {
        let mut v = VecDeque::with_capacity(1);
        v.push_back(MonitorHandle::new(self.app.clone()));
        v
    }

    pub fn current_monitor(&self) -> Option<MonitorHandle> {
        Some(MonitorHandle::new(self.app.clone()))
    }

    pub fn scale_factor(&self) -> f64 {
        MonitorHandle::new(self.app.clone()).scale_factor()
    }

    pub fn request_redraw(&self) {
        self.redraw_requester.request_redraw()
    }

    pub fn pre_present_notify(&self) {}

    pub fn inner_position(&self) -> Result<PhysicalPosition<i32>, error::NotSupportedError> {
        Err(error::NotSupportedError::new())
    }

    pub fn outer_position(&self) -> Result<PhysicalPosition<i32>, error::NotSupportedError> {
        Err(error::NotSupportedError::new())
    }

    pub fn set_outer_position(&self, _position: Position) {
        // no effect
    }

    pub fn inner_size(&self) -> PhysicalSize<u32> {
        self.outer_size()
    }

    pub fn request_inner_size(&self, _size: Size) -> Option<PhysicalSize<u32>> {
        Some(self.inner_size())
    }

    pub fn outer_size(&self) -> PhysicalSize<u32> {
        MonitorHandle::new(self.app.clone()).size()
    }

    pub fn set_min_inner_size(&self, _: Option<Size>) {}

    pub fn set_max_inner_size(&self, _: Option<Size>) {}

    pub fn resize_increments(&self) -> Option<PhysicalSize<u32>> {
        None
    }

    pub fn set_resize_increments(&self, _increments: Option<Size>) {}

    pub fn set_title(&self, _title: &str) {}

    pub fn set_transparent(&self, _transparent: bool) {}

    pub fn set_visible(&self, _visibility: bool) {}

    pub fn is_visible(&self) -> Option<bool> {
        None
    }

    pub fn set_resizable(&self, _resizeable: bool) {}

    pub fn is_resizable(&self) -> bool {
        false
    }

    pub fn set_enabled_buttons(&self, _buttons: WindowButtons) {}

    pub fn enabled_buttons(&self) -> WindowButtons {
        WindowButtons::all()
    }

    pub fn set_minimized(&self, _minimized: bool) {}

    pub fn is_minimized(&self) -> Option<bool> {
        None
    }

    pub fn set_maximized(&self, _maximized: bool) {}

    pub fn is_maximized(&self) -> bool {
        false
    }

    pub fn set_fullscreen(&self, _monitor: Option<Fullscreen>) {
        warn!("Cannot set fullscreen on Android");
    }

    pub fn fullscreen(&self) -> Option<Fullscreen> {
        None
    }

    pub fn set_decorations(&self, _decorations: bool) {}

    pub fn is_decorated(&self) -> bool {
        true
    }

    pub fn set_window_level(&self, _level: WindowLevel) {}

    pub fn set_window_icon(&self, _window_icon: Option<crate::icon::Icon>) {}

    pub fn set_ime_cursor_area(&self, _position: Position, _size: Size) {}

    pub fn set_ime_allowed(&self, _allowed: bool) {}

    pub fn set_ime_purpose(&self, _purpose: ImePurpose) {}

    pub fn focus_window(&self) {}

    pub fn request_user_attention(&self, _request_type: Option<window::UserAttentionType>) {}

    pub fn set_cursor_icon(&self, _: window::CursorIcon) {}

    pub fn set_cursor_position(&self, _: Position) -> Result<(), error::ExternalError> {
        Err(error::ExternalError::NotSupported(
            error::NotSupportedError::new(),
        ))
    }

    pub fn set_cursor_grab(&self, _: CursorGrabMode) -> Result<(), error::ExternalError> {
        Err(error::ExternalError::NotSupported(
            error::NotSupportedError::new(),
        ))
    }

    pub fn set_cursor_visible(&self, _: bool) {}

    pub fn drag_window(&self) -> Result<(), error::ExternalError> {
        Err(error::ExternalError::NotSupported(
            error::NotSupportedError::new(),
        ))
    }

    pub fn drag_resize_window(
        &self,
        _direction: ResizeDirection,
    ) -> Result<(), error::ExternalError> {
        Err(error::ExternalError::NotSupported(
            error::NotSupportedError::new(),
        ))
    }

    pub fn set_cursor_hittest(&self, _hittest: bool) -> Result<(), error::ExternalError> {
        Err(error::ExternalError::NotSupported(
            error::NotSupportedError::new(),
        ))
    }

    pub fn raw_window_handle(&self) -> RawWindowHandle {
        if let Some(native_window) = self.app.native_window().as_ref() {
            native_window.raw_window_handle()
        } else {
            panic!("Cannot get the native window, it's null and will always be null before Event::Resumed and after Event::Suspended. Make sure you only call this function between those events.");
        }
    }

    pub fn raw_display_handle(&self) -> RawDisplayHandle {
        RawDisplayHandle::Android(AndroidDisplayHandle::empty())
    }

    pub fn config(&self) -> ConfigurationRef {
        self.app.config()
    }

    pub fn content_rect(&self) -> Rect {
        self.app.content_rect()
    }

    pub fn set_theme(&self, _theme: Option<Theme>) {}

    pub fn theme(&self) -> Option<Theme> {
        None
    }

    pub fn has_focus(&self) -> bool {
        *HAS_FOCUS.read().unwrap()
    }

    pub fn title(&self) -> String {
        String::new()
    }

    pub fn reset_dead_keys(&self) {}
}

#[derive(Default, Clone, Debug)]
pub struct OsError;

use std::fmt::{self, Display, Formatter};
impl Display for OsError {
    fn fmt(&self, fmt: &mut Formatter<'_>) -> Result<(), fmt::Error> {
        write!(fmt, "Android OS Error")
    }
}

pub(crate) use crate::icon::NoIcon as PlatformIcon;

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct MonitorHandle {
    app: AndroidApp,
}
impl PartialOrd for MonitorHandle {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}
impl Ord for MonitorHandle {
    fn cmp(&self, _other: &Self) -> std::cmp::Ordering {
        std::cmp::Ordering::Equal
    }
}

impl MonitorHandle {
    pub(crate) fn new(app: AndroidApp) -> Self {
        Self { app }
    }

    pub fn name(&self) -> Option<String> {
        Some("Android Device".to_owned())
    }

    pub fn size(&self) -> PhysicalSize<u32> {
        if let Some(native_window) = self.app.native_window() {
            PhysicalSize::new(native_window.width() as _, native_window.height() as _)
        } else {
            PhysicalSize::new(0, 0)
        }
    }

    pub fn position(&self) -> PhysicalPosition<i32> {
        (0, 0).into()
    }

    pub fn scale_factor(&self) -> f64 {
        self.app
            .config()
            .density()
            .map(|dpi| dpi as f64 / 160.0)
            .unwrap_or(1.0)
    }

    pub fn refresh_rate_millihertz(&self) -> Option<u32> {
        // FIXME no way to get real refresh rate for now.
        None
    }

    pub fn video_modes(&self) -> impl Iterator<Item = VideoMode> {
        let size = self.size().into();
        // FIXME this is not the real refresh rate
        // (it is guaranteed to support 32 bit color though)
        std::iter::once(VideoMode {
            size,
            bit_depth: 32,
            refresh_rate_millihertz: 60000,
            monitor: self.clone(),
        })
    }
}

#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub struct VideoMode {
    size: (u32, u32),
    bit_depth: u16,
    refresh_rate_millihertz: u32,
    monitor: MonitorHandle,
}

impl VideoMode {
    pub fn size(&self) -> PhysicalSize<u32> {
        self.size.into()
    }

    pub fn bit_depth(&self) -> u16 {
        self.bit_depth
    }

    pub fn refresh_rate_millihertz(&self) -> u32 {
        self.refresh_rate_millihertz
    }

    pub fn monitor(&self) -> MonitorHandle {
        self.monitor.clone()
    }
}