event_loop.rs

// Copyright © SixtyFPS GmbH <info@slint-ui.com>
// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial

#![warn(missing_docs)]
/*!
    This module contains the event loop implementation using winit, as well as the
    [WindowAdapter] trait used by the generated code and the run-time to change
    aspects of windows on the screen.
*/
use copypasta::ClipboardProvider;
use corelib::items::PointerEventButton;
use corelib::lengths::LogicalPoint;
use corelib::SharedString;
use i_slint_core as corelib;

use corelib::api::EventLoopError;
use corelib::graphics::euclid;
use corelib::input::{KeyEventType, KeyInputEvent, MouseEvent};
use corelib::window::*;
use std::cell::{RefCell, RefMut};
use std::rc::{Rc, Weak};

use crate::winitwindowadapter::WinitWindowAdapter;

use winit::event::WindowEvent;
#[cfg(not(target_arch = "wasm32"))]
use winit::platform::run_return::EventLoopExtRunReturn;

use crate::SlintUserEvent;

pub(crate) static QUIT_ON_LAST_WINDOW_CLOSED: std::sync::atomic::AtomicBool =
    std::sync::atomic::AtomicBool::new(true);

/// The Default, and the selection clippoard
type ClipboardPair = (Box<dyn ClipboardProvider>, Box<dyn ClipboardProvider>);

struct NotRunningEventLoop {
    clipboard: RefCell<ClipboardPair>,
    instance: winit::event_loop::EventLoop<SlintUserEvent>,
    event_loop_proxy: winit::event_loop::EventLoopProxy<SlintUserEvent>,
}

impl NotRunningEventLoop {
    fn new() -> Self {
        let mut builder = winit::event_loop::EventLoopBuilder::with_user_event();

        #[cfg(all(unix, not(target_os = "macos")))]
        {
            #[cfg(feature = "wayland")]
            {
                use winit::platform::wayland::EventLoopBuilderExtWayland;
                builder.with_any_thread(true);
            }
            #[cfg(feature = "x11")]
            {
                use winit::platform::x11::EventLoopBuilderExtX11;
                builder.with_any_thread(true);
            }
        }
        #[cfg(target_family = "windows")]
        {
            use winit::platform::windows::EventLoopBuilderExtWindows;
            builder.with_any_thread(true);
        }

        let instance = builder.build();
        let event_loop_proxy = instance.create_proxy();
        let clipboard = RefCell::new(create_clipboard(&instance));
        Self { clipboard, instance, event_loop_proxy }
    }
}

struct RunningEventLoop<'a> {
    event_loop_target: &'a winit::event_loop::EventLoopWindowTarget<SlintUserEvent>,
    event_loop_proxy: &'a winit::event_loop::EventLoopProxy<SlintUserEvent>,
    clipboard: &'a RefCell<ClipboardPair>,
}

pub(crate) trait EventLoopInterface {
    fn event_loop_target(&self) -> &winit::event_loop::EventLoopWindowTarget<SlintUserEvent>;
    fn event_loop_proxy(&self) -> &winit::event_loop::EventLoopProxy<SlintUserEvent>;
    fn clipboard(
        &self,
        _: i_slint_core::platform::Clipboard,
    ) -> Option<RefMut<'_, dyn ClipboardProvider>>;
}

impl EventLoopInterface for NotRunningEventLoop {
    fn event_loop_target(&self) -> &winit::event_loop::EventLoopWindowTarget<SlintUserEvent> {
        &*self.instance
    }

    fn event_loop_proxy(&self) -> &winit::event_loop::EventLoopProxy<SlintUserEvent> {
        &self.event_loop_proxy
    }

    fn clipboard(
        &self,
        clipboard: i_slint_core::platform::Clipboard,
    ) -> Option<RefMut<'_, dyn ClipboardProvider>> {
        match clipboard {
            corelib::platform::Clipboard::DefaultClipboard => {
                Some(RefMut::map(self.clipboard.borrow_mut(), |p| p.0.as_mut()))
            }
            corelib::platform::Clipboard::SelectionClipboard => {
                Some(RefMut::map(self.clipboard.borrow_mut(), |p| p.1.as_mut()))
            }
            _ => None,
        }
    }
}

impl<'a> EventLoopInterface for RunningEventLoop<'a> {
    fn event_loop_target(&self) -> &winit::event_loop::EventLoopWindowTarget<SlintUserEvent> {
        self.event_loop_target
    }

    fn event_loop_proxy(&self) -> &winit::event_loop::EventLoopProxy<SlintUserEvent> {
        self.event_loop_proxy
    }

    fn clipboard(
        &self,
        clipboard: i_slint_core::platform::Clipboard,
    ) -> Option<RefMut<'_, dyn ClipboardProvider>> {
        match clipboard {
            corelib::platform::Clipboard::DefaultClipboard => {
                Some(RefMut::map(self.clipboard.borrow_mut(), |p| p.0.as_mut()))
            }
            corelib::platform::Clipboard::SelectionClipboard => {
                Some(RefMut::map(self.clipboard.borrow_mut(), |p| p.1.as_mut()))
            }
            _ => None,
        }
    }
}

thread_local! {
    static ALL_WINDOWS: RefCell<std::collections::HashMap<winit::window::WindowId, Weak<WinitWindowAdapter>>> = RefCell::new(std::collections::HashMap::new());
    static MAYBE_LOOP_INSTANCE: RefCell<Option<NotRunningEventLoop>> = RefCell::new(Some(NotRunningEventLoop::new()));
}

scoped_tls_hkt::scoped_thread_local!(static CURRENT_WINDOW_TARGET : for<'a> &'a RunningEventLoop<'a>);

pub(crate) enum GlobalEventLoopProxyOrEventQueue {
    Proxy(winit::event_loop::EventLoopProxy<SlintUserEvent>),
    Queue(Vec<SlintUserEvent>),
}

impl GlobalEventLoopProxyOrEventQueue {
    pub(crate) fn send_event(&mut self, event: SlintUserEvent) -> Result<(), EventLoopError> {
        match self {
            GlobalEventLoopProxyOrEventQueue::Proxy(proxy) => {
                proxy.send_event(event).map_err(|_| EventLoopError::EventLoopTerminated)
            }
            GlobalEventLoopProxyOrEventQueue::Queue(queue) => {
                queue.push(event);
                Ok(())
            }
        }
    }

    fn set_proxy(&mut self, proxy: winit::event_loop::EventLoopProxy<SlintUserEvent>) {
        match self {
            GlobalEventLoopProxyOrEventQueue::Proxy(_) => {}
            GlobalEventLoopProxyOrEventQueue::Queue(queue) => {
                std::mem::take(queue)
                    .into_iter()
                    .for_each(|event| proxy.send_event(event).ok().unwrap());
                *self = GlobalEventLoopProxyOrEventQueue::Proxy(proxy);
            }
        }
    }
}

impl Default for GlobalEventLoopProxyOrEventQueue {
    fn default() -> Self {
        Self::Queue(Vec::new())
    }
}

#[cfg(not(target_arch = "wasm32"))]
pub(crate) static GLOBAL_PROXY: once_cell::sync::OnceCell<
    std::sync::Mutex<GlobalEventLoopProxyOrEventQueue>,
> = once_cell::sync::OnceCell::new();

#[cfg(target_arch = "wasm32")]
thread_local! {
    pub(crate) static GLOBAL_PROXY: RefCell<Option<GlobalEventLoopProxyOrEventQueue>> = RefCell::new(None)
}

pub(crate) fn with_window_target<T>(callback: impl FnOnce(&dyn EventLoopInterface) -> T) -> T {
    if CURRENT_WINDOW_TARGET.is_set() {
        CURRENT_WINDOW_TARGET.with(|current_target| callback(current_target))
    } else {
        MAYBE_LOOP_INSTANCE.with(|loop_instance| {
            if loop_instance.borrow().is_none() {
                *loop_instance.borrow_mut() = Some(NotRunningEventLoop::new());
            }
            callback(loop_instance.borrow().as_ref().unwrap())
        })
    }
}

pub fn register_window(id: winit::window::WindowId, window: Rc<WinitWindowAdapter>) {
    ALL_WINDOWS.with(|windows| {
        windows.borrow_mut().insert(id, Rc::downgrade(&window));
    })
}

pub fn unregister_window(id: winit::window::WindowId) {
    let _ = ALL_WINDOWS.try_with(|windows| {
        windows.borrow_mut().remove(&id);
    });
}

fn window_by_id(id: winit::window::WindowId) -> Option<Rc<WinitWindowAdapter>> {
    ALL_WINDOWS.with(|windows| windows.borrow().get(&id).and_then(|weakref| weakref.upgrade()))
}

/// This enum captures run-time specific events that can be dispatched to the event loop in
/// addition to the winit events.
pub enum CustomEvent {
    /// On wasm request_redraw doesn't wake the event loop, so we need to manually send an event
    /// so that the event loop can run
    #[cfg(target_arch = "wasm32")]
    WakeEventLoopWorkaround,
    /// Slint internal: Invoke the
    UserEvent(Box<dyn FnOnce() + Send>),
    /// Sent from `WinitWindowAdapter::hide` so that we can check if we should quit the event loop
    WindowHidden,
    Exit,
}

impl std::fmt::Debug for CustomEvent {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            #[cfg(target_arch = "wasm32")]
            Self::WakeEventLoopWorkaround => write!(f, "WakeEventLoopWorkaround"),
            Self::UserEvent(_) => write!(f, "UserEvent"),
            Self::WindowHidden => write!(f, "WindowHidden"),
            Self::Exit => write!(f, "Exit"),
        }
    }
}

mod key_codes {
    macro_rules! winit_key_to_char_fn {
        ($($char:literal # $name:ident # $($_qt:ident)|* # $($winit:ident)|* ;)*) => {
            pub fn winit_key_to_char(virtual_keycode: winit::event::VirtualKeyCode) -> Option<char> {
                let char = match(virtual_keycode) {
                    $($(winit::event::VirtualKeyCode::$winit => $char,)*)*
                    _ => return None,
                };
                Some(char)
            }
        };
    }
    i_slint_common::for_each_special_keys!(winit_key_to_char_fn);
}

fn process_window_event(
    window: Rc<WinitWindowAdapter>,
    event: WindowEvent,
    cursor_pos: &mut LogicalPoint,
    pressed: &mut bool,
) -> Result<(), i_slint_core::platform::PlatformError> {
    let runtime_window = WindowInner::from_pub(window.window());
    match event {
        WindowEvent::Resized(size) => {
            window.resize_event(size)?;
        }
        WindowEvent::CloseRequested => {
            if runtime_window.request_close() {
                window.hide()?;
            }
        }
        WindowEvent::ReceivedCharacter(ch) => {
            // On Windows, X11 and Wayland sequences like Ctrl+C will send a ReceivedCharacter after the pressed keyboard input event,
            // with a control character. We choose not to forward those but try to use the current key code instead.
            //
            // We do not want to change the text to the value of the key press when that was a
            // control key itself: We already sent that event when handling the KeyboardInput.
            let text: SharedString = if ch.is_control() {
                if let Some(ch) = window
                    .currently_pressed_key_code()
                    .take()
                    .and_then(winit_key_code_to_string)
                    .filter(|ch| !ch.is_control())
                {
                    ch
                } else {
                    return Ok(());
                }
            } else {
                ch
            }
            .into();

            window
                .window()
                .dispatch_event(corelib::platform::WindowEvent::KeyPressed { text: text.clone() });
            window.window().dispatch_event(corelib::platform::WindowEvent::KeyReleased { text });
        }
        WindowEvent::Focused(have_focus) => {
            let have_focus = have_focus || window.input_method_focused();
            // We don't render popups as separate windows yet, so treat
            // focus to be the same as being active.
            if have_focus != runtime_window.active() {
                runtime_window.set_active(have_focus);
                runtime_window.set_focus(have_focus);
            }
        }
        WindowEvent::KeyboardInput { ref input, .. } => {
            // For now: Match Qt's behavior of mapping command to control and control to meta (LWin/RWin).
            let key_code = input.virtual_keycode.map(|key_code| match key_code {
                #[cfg(target_os = "macos")]
                winit::event::VirtualKeyCode::LControl => winit::event::VirtualKeyCode::LWin,
                #[cfg(target_os = "macos")]
                winit::event::VirtualKeyCode::RControl => winit::event::VirtualKeyCode::RWin,
                #[cfg(target_os = "macos")]
                winit::event::VirtualKeyCode::LWin => winit::event::VirtualKeyCode::LControl,
                #[cfg(target_os = "macos")]
                winit::event::VirtualKeyCode::RWin => winit::event::VirtualKeyCode::RControl,
                code @ _ => code,
            });
            window.currently_pressed_key_code().set(match input.state {
                winit::event::ElementState::Pressed => key_code,
                _ => None,
            });
            if let Some(text) = key_code.and_then(key_codes::winit_key_to_char).map(|ch| ch.into())
            {
                window.window().dispatch_event(match input.state {
                    winit::event::ElementState::Pressed => {
                        corelib::platform::WindowEvent::KeyPressed { text }
                    }
                    winit::event::ElementState::Released => {
                        corelib::platform::WindowEvent::KeyReleased { text }
                    }
                });
            };
        }
        WindowEvent::Ime(winit::event::Ime::Preedit(string, preedit_selection)) => {
            let preedit_selection = preedit_selection.unwrap_or((0, 0));
            let event = KeyInputEvent {
                event_type: KeyEventType::UpdateComposition,
                text: string.into(),
                preedit_selection_start: preedit_selection.0,
                preedit_selection_end: preedit_selection.1,
                ..Default::default()
            };
            runtime_window.process_key_input(event);
        }
        WindowEvent::Ime(winit::event::Ime::Commit(string)) => {
            let event = KeyInputEvent {
                event_type: KeyEventType::CommitComposition,
                text: string.into(),
                ..Default::default()
            };
            runtime_window.process_key_input(event);
        }
        WindowEvent::CursorMoved { position, .. } => {
            let position = position.to_logical(runtime_window.scale_factor() as f64);
            *cursor_pos = euclid::point2(position.x, position.y);
            runtime_window.process_mouse_input(MouseEvent::Moved { position: *cursor_pos });
        }
        WindowEvent::CursorLeft { .. } => {
            // On the html canvas, we don't get the mouse move or release event when outside the canvas. So we have no choice but canceling the event
            if cfg!(target_arch = "wasm32") || !*pressed {
                *pressed = false;
                runtime_window.process_mouse_input(MouseEvent::Exit);
            }
        }
        WindowEvent::MouseWheel { delta, .. } => {
            let (delta_x, delta_y) = match delta {
                winit::event::MouseScrollDelta::LineDelta(lx, ly) => (lx * 60., ly * 60.),
                winit::event::MouseScrollDelta::PixelDelta(d) => {
                    let d = d.to_logical(runtime_window.scale_factor() as f64);
                    (d.x, d.y)
                }
            };
            runtime_window.process_mouse_input(MouseEvent::Wheel {
                position: *cursor_pos,
                delta_x,
                delta_y,
            });
        }
        WindowEvent::MouseInput { state, button, .. } => {
            let button = match button {
                winit::event::MouseButton::Left => PointerEventButton::Left,
                winit::event::MouseButton::Right => PointerEventButton::Right,
                winit::event::MouseButton::Middle => PointerEventButton::Middle,
                winit::event::MouseButton::Other(_) => PointerEventButton::Other,
            };
            let ev = match state {
                winit::event::ElementState::Pressed => {
                    *pressed = true;
                    MouseEvent::Pressed { position: *cursor_pos, button, click_count: 0 }
                }
                winit::event::ElementState::Released => {
                    *pressed = false;
                    MouseEvent::Released { position: *cursor_pos, button, click_count: 0 }
                }
            };
            runtime_window.process_mouse_input(ev);
        }
        WindowEvent::Touch(touch) => {
            let location = touch.location;
            // https://github.com/slint-ui/slint/issues/2424: Work around winit reporting absolute coordinates for touch - until https://github.com/rust-windowing/winit/pull/2704 is merged & released.
            #[cfg(target_family = "wasm")]
            let location = {
                let window_pos = window.winit_window().inner_position().unwrap_or_default();
                winit::dpi::PhysicalPosition::new(
                    location.x - window_pos.x as f64,
                    location.y - window_pos.y as f64,
                )
            };
            let location = location.to_logical(runtime_window.scale_factor() as f64);
            let position = euclid::point2(location.x, location.y);
            let ev = match touch.phase {
                winit::event::TouchPhase::Started => {
                    *pressed = true;
                    MouseEvent::Pressed {
                        position,
                        button: PointerEventButton::Left,
                        click_count: 0,
                    }
                }
                winit::event::TouchPhase::Ended | winit::event::TouchPhase::Cancelled => {
                    *pressed = false;
                    MouseEvent::Released {
                        position,
                        button: PointerEventButton::Left,
                        click_count: 0,
                    }
                }
                winit::event::TouchPhase::Moved => MouseEvent::Moved { position },
            };
            runtime_window.process_mouse_input(ev);
        }
        WindowEvent::ScaleFactorChanged { scale_factor, new_inner_size } => {
            if std::env::var("SLINT_SCALE_FACTOR").is_err() {
                window.window().dispatch_event(
                    corelib::platform::WindowEvent::ScaleFactorChanged {
                        scale_factor: scale_factor as f32,
                    },
                );
                // Resize the underlying graphics surface
                window.resize_event(*new_inner_size)?;
            }
        }
        WindowEvent::ThemeChanged(theme) => {
            window.set_dark_color_scheme(theme == winit::window::Theme::Dark)
        }
        _ => {}
    }
    Ok(())
}

/// Runs the event loop and renders the items in the provided `component` in its
/// own window.
#[allow(unused_mut)] // mut need changes for wasm
pub fn run() -> Result<(), corelib::platform::PlatformError> {
    use winit::event::Event;
    use winit::event_loop::{ControlFlow, EventLoopWindowTarget};

    let not_running_loop_instance = MAYBE_LOOP_INSTANCE.with(|loop_instance| {
        loop_instance.borrow_mut().take().unwrap_or_else(NotRunningEventLoop::new)
    });

    let event_loop_proxy = not_running_loop_instance.event_loop_proxy;
    #[cfg(not(target_arch = "wasm32"))]
    GLOBAL_PROXY.get_or_init(Default::default).lock().unwrap().set_proxy(event_loop_proxy.clone());
    #[cfg(target_arch = "wasm32")]
    GLOBAL_PROXY.with(|global_proxy| {
        global_proxy
            .borrow_mut()
            .get_or_insert_with(Default::default)
            .set_proxy(event_loop_proxy.clone())
    });

    let mut winit_loop = not_running_loop_instance.instance;
    let clipboard = not_running_loop_instance.clipboard;

    // With winit on Windows and with wasm, calling winit::Window::request_redraw() will not always deliver an
    // Event::RedrawRequested (for example when the mouse cursor is outside of the window). So when we get woken
    // up by the event loop to process new events from the operating system (NewEvents), we take note of all windows
    // that called request_redraw() since the last iteration and we will call draw() ourselves, unless they received
    // an Event::RedrawRequested in this new iteration. This vector collects the window ids of windows with pending
    // redraw requests in the beginning of the loop iteration, removes ids that are covered by a windowing system
    // supplied Event::RedrawRequested, and drains them for drawing at RedrawEventsCleared.
    let mut windows_with_pending_redraw_requests = Vec::new();

    // last seen cursor position
    let mut cursor_pos = LogicalPoint::default();
    let mut pressed = false;

    let outer_event_loop_error = Rc::new(RefCell::new(None));
    let inner_event_loop_error = outer_event_loop_error.clone();

    let mut run_fn = move |event: Event<SlintUserEvent>, control_flow: &mut ControlFlow| {
        match event {
            Event::WindowEvent { event, window_id } => {
                if let Some(window) = window_by_id(window_id) {
                    #[cfg(not(enable_accesskit))]
                    let process_event = true;
                    #[cfg(enable_accesskit)]
                    let process_event =
                        window.accesskit_adapter.on_event(&window.winit_window(), &event);

                    if process_event {
                        *inner_event_loop_error.borrow_mut() =
                            process_window_event(window, event, &mut cursor_pos, &mut pressed)
                                .err();
                    }
                };
            }

            Event::RedrawRequested(id) => {
                if let Some(window) = window_by_id(id) {
                    if let Ok(pos) = windows_with_pending_redraw_requests.binary_search(&id) {
                        windows_with_pending_redraw_requests.remove(pos);
                    }
                    match window.draw() {
                        Ok(redraw_requested_during_draw) => {
                            if redraw_requested_during_draw {
                                // If during rendering a new redraw_request() was issued (for example in a rendering notifier callback), then
                                // pretend that an animation is running, so that we return Poll from the event loop to ensure a repaint as
                                // soon as possible.
                                *control_flow = ControlFlow::Poll;
                            }
                        }
                        Err(rendering_error) => {
                            *inner_event_loop_error.borrow_mut() = Some(rendering_error)
                        }
                    };
                }
            }

            Event::UserEvent(SlintUserEvent::CustomEvent { event: CustomEvent::WindowHidden }) => {
                if QUIT_ON_LAST_WINDOW_CLOSED.load(std::sync::atomic::Ordering::Relaxed) {
                    let window_count = ALL_WINDOWS.with(|windows| {
                        windows
                            .borrow()
                            .values()
                            .filter(|window| window.upgrade().map_or(false, |w| w.is_shown()))
                            .count()
                    });
                    if window_count == 0 {
                        *control_flow = ControlFlow::Exit;
                    }
                }
            }

            Event::UserEvent(SlintUserEvent::CustomEvent { event: CustomEvent::Exit }) => {
                *control_flow = ControlFlow::Exit;
            }

            Event::UserEvent(SlintUserEvent::CustomEvent {
                event: CustomEvent::UserEvent(user),
            }) => {
                user();
            }

            #[cfg(target_arch = "wasm32")]
            Event::UserEvent(SlintUserEvent::CustomEvent {
                event: CustomEvent::WakeEventLoopWorkaround,
            }) => {
                *control_flow = ControlFlow::Poll;
            }

            Event::NewEvents(_) => {
                *control_flow = ControlFlow::Wait;

                windows_with_pending_redraw_requests.clear();
                ALL_WINDOWS.with(|windows| {
                    for (window_id, window_weak) in windows.borrow().iter() {
                        if window_weak.upgrade().map_or(false, |window| {
                            window.is_shown() && window.take_pending_redraw()
                        }) {
                            if let Err(insert_pos) =
                                windows_with_pending_redraw_requests.binary_search(window_id)
                            {
                                windows_with_pending_redraw_requests.insert(insert_pos, *window_id);
                            }
                        }
                    }
                });

                corelib::platform::update_timers_and_animations();
            }

            Event::RedrawEventsCleared => {
                if *control_flow != ControlFlow::Exit
                    && ALL_WINDOWS.with(|windows| {
                        windows.borrow().iter().any(|(_, w)| {
                            w.upgrade()
                                .and_then(|w| {
                                    w.window().has_active_animations().then(|| {
                                        w.request_redraw();
                                        true
                                    })
                                })
                                .unwrap_or_default()
                        })
                    })
                {
                    *control_flow = ControlFlow::Poll;
                }

                for window in
                    windows_with_pending_redraw_requests.drain(..).filter_map(window_by_id)
                {
                    match window.draw() {
                        Ok(redraw_requested_during_draw) => {
                            if redraw_requested_during_draw {
                                // If during rendering a new redraw_request() was issued (for example in a rendering notifier callback), then
                                // pretend that an animation is running, so that we return Poll from the event loop to ensure a repaint as
                                // soon as possible.
                                *control_flow = ControlFlow::Poll;
                            }
                        }
                        Err(rendering_error) => {
                            *inner_event_loop_error.borrow_mut() = Some(rendering_error);
                        }
                    }
                }

                if *control_flow == ControlFlow::Wait {
                    if let Some(next_timer) = corelib::platform::duration_until_next_timer_update()
                    {
                        *control_flow =
                            ControlFlow::WaitUntil(instant::Instant::now() + next_timer);
                    }
                }
            }

            _ => (),
        };

        if inner_event_loop_error.borrow().is_some() {
            *control_flow = ControlFlow::Exit;
        }
    };

    #[cfg(not(target_arch = "wasm32"))]
    {
        winit_loop.run_return(
            |event: Event<SlintUserEvent>,
             event_loop_target: &EventLoopWindowTarget<SlintUserEvent>,
             control_flow: &mut ControlFlow| {
                let running_instance = RunningEventLoop {
                    event_loop_target,
                    event_loop_proxy: &event_loop_proxy,
                    clipboard: &clipboard,
                };
                CURRENT_WINDOW_TARGET.set(&running_instance, || run_fn(event, control_flow))
            },
        );

        *GLOBAL_PROXY.get_or_init(Default::default).lock().unwrap() = Default::default();

        // Keep the EventLoop instance alive and re-use it in future invocations of run_event_loop().
        // Winit does not support creating multiple instances of the event loop.
        let nre = NotRunningEventLoop { clipboard, instance: winit_loop, event_loop_proxy };
        MAYBE_LOOP_INSTANCE.with(|loop_instance| *loop_instance.borrow_mut() = Some(nre));

        if let Some(error) = outer_event_loop_error.borrow_mut().take() {
            return Err(error);
        }
        Ok(())
    }

    #[cfg(target_arch = "wasm32")]
    {
        winit_loop.run(
            move |event: Event<SlintUserEvent>,
                  event_loop_target: &EventLoopWindowTarget<SlintUserEvent>,
                  control_flow: &mut ControlFlow| {
                let running_instance = RunningEventLoop {
                    event_loop_target,
                    event_loop_proxy: &event_loop_proxy,
                    clipboard: &clipboard,
                };
                CURRENT_WINDOW_TARGET.set(&running_instance, || run_fn(event, control_flow))
            },
        )
    }
}

// This function is called when we receive a control character via WindowEvent::ReceivedCharacter and
// instead want to use the last virtual key code. That happens when for example pressing Ctrl+some_key
// on Windows/X11/Wayland. This function may be missing mappings, it's trying to cover what we may be
// getting when we're getting control character sequences.
fn winit_key_code_to_string(virtual_keycode: winit::event::VirtualKeyCode) -> Option<char> {
    use winit::event::VirtualKeyCode;
    Some(match virtual_keycode {
        VirtualKeyCode::Key1 => '1',
        VirtualKeyCode::Key2 => '2',
        VirtualKeyCode::Key3 => '3',
        VirtualKeyCode::Key4 => '4',
        VirtualKeyCode::Key5 => '5',
        VirtualKeyCode::Key6 => '6',
        VirtualKeyCode::Key7 => '7',
        VirtualKeyCode::Key8 => '8',
        VirtualKeyCode::Key9 => '9',
        VirtualKeyCode::Key0 => '0',
        VirtualKeyCode::A => 'a',
        VirtualKeyCode::B => 'b',
        VirtualKeyCode::C => 'c',
        VirtualKeyCode::D => 'd',
        VirtualKeyCode::E => 'e',
        VirtualKeyCode::F => 'f',
        VirtualKeyCode::G => 'g',
        VirtualKeyCode::H => 'h',
        VirtualKeyCode::I => 'i',
        VirtualKeyCode::J => 'j',
        VirtualKeyCode::K => 'k',
        VirtualKeyCode::L => 'l',
        VirtualKeyCode::M => 'm',
        VirtualKeyCode::N => 'n',
        VirtualKeyCode::O => 'o',
        VirtualKeyCode::P => 'p',
        VirtualKeyCode::Q => 'q',
        VirtualKeyCode::R => 'r',
        VirtualKeyCode::S => 's',
        VirtualKeyCode::T => 't',
        VirtualKeyCode::U => 'u',
        VirtualKeyCode::V => 'v',
        VirtualKeyCode::W => 'w',
        VirtualKeyCode::X => 'x',
        VirtualKeyCode::Y => 'y',
        VirtualKeyCode::Z => 'z',
        VirtualKeyCode::Space => ' ',
        VirtualKeyCode::Caret => '^',
        VirtualKeyCode::Apostrophe => '\'',
        VirtualKeyCode::Asterisk => '*',
        VirtualKeyCode::Backslash => '\\',
        VirtualKeyCode::Colon => ':',
        VirtualKeyCode::Comma => ',',
        VirtualKeyCode::Equals => '=',
        VirtualKeyCode::Grave => '`',
        VirtualKeyCode::Minus => '-',
        VirtualKeyCode::Period => '.',
        VirtualKeyCode::Plus => '+',
        VirtualKeyCode::Semicolon => ';',
        VirtualKeyCode::Slash => '/',
        VirtualKeyCode::Tab => '\t',
        _ => return None,
    })
}

fn create_clipboard<T>(_event_loop: &winit::event_loop::EventLoopWindowTarget<T>) -> ClipboardPair {
    // Provide a truly silent no-op clipboard context, as copypasta's NoopClipboard spams stdout with
    // println.
    struct SilentClipboardContext;
    impl copypasta::ClipboardProvider for SilentClipboardContext {
        fn get_contents(
            &mut self,
        ) -> Result<String, Box<dyn std::error::Error + Send + Sync + 'static>> {
            Ok(Default::default())
        }

        fn set_contents(
            &mut self,
            _: String,
        ) -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
            Ok(())
        }
    }

    cfg_if::cfg_if! {
        if #[cfg(all(
            unix,
            not(any(
                target_os = "macos",
                target_os = "android",
                target_os = "ios",
                target_os = "emscripten"
            ))
        ))]
        {
            #[cfg(feature = "wayland")]
            if let Some(wayland_display) =
                winit::platform::wayland::EventLoopWindowTargetExtWayland::wayland_display(_event_loop)
            {
                let clipboard = unsafe {
                    copypasta::wayland_clipboard::create_clipboards_from_external(wayland_display)
                };
                return (Box::new(clipboard.1), Box::new(clipboard.0));
            };
            #[cfg(feature = "x11")]
            {
                use copypasta::x11_clipboard::{X11ClipboardContext, Primary, Clipboard};
                let prim = X11ClipboardContext::<Primary>::new()
                    .map_or(
                        Box::new(SilentClipboardContext) as Box<dyn ClipboardProvider>,
                        |x| Box::new(x) as Box<dyn ClipboardProvider>,
                    );
                let sec = X11ClipboardContext::<Clipboard>::new()
                    .map_or(
                        Box::new(SilentClipboardContext) as Box<dyn ClipboardProvider>,
                        |x| Box::new(x) as Box<dyn ClipboardProvider>,
                    );
                (sec, prim)
            }
            #[cfg(not(feature = "x11"))]
            (Box::new(SilentClipboardContext), Box::new(SilentClipboardContext))
        } else {
            (
                copypasta::ClipboardContext::new().map_or(
                    Box::new(SilentClipboardContext) as Box<dyn ClipboardProvider>,
                    |x| Box::new(x) as Box<dyn ClipboardProvider>,
                ),
                Box::new(SilentClipboardContext),
            )
        }
    }
}