iced/winit/src/application.rs

//! Create interactive, native cross-platform applications.
mod state;

pub use state::State;

use crate::conversion;
use crate::core;
use crate::core::mouse;
use crate::core::renderer;
use crate::core::theme;
use crate::core::time::Instant;
use crate::core::widget::operation;
use crate::core::window;
use crate::core::{Color, Event, Point, Size, Theme};
use crate::debug;
use crate::futures::futures;
use crate::futures::{Executor, Runtime, Subscription};
use crate::graphics;
use crate::graphics::compositor::{self, Compositor};
use crate::runtime::clipboard;
use crate::runtime::program::Program;
use crate::runtime::user_interface::{self, UserInterface};
use crate::runtime::Command;
use crate::{Clipboard, Error, Proxy, Settings};

use futures::channel::mpsc;
use futures::channel::oneshot;

use std::borrow::Cow;
use std::mem::ManuallyDrop;
use std::sync::Arc;

/// An interactive, native cross-platform application.
///
/// This trait is the main entrypoint of Iced. Once implemented, you can run
/// your GUI application by simply calling [`run`]. It will run in
/// its own window.
///
/// An [`Application`] can execute asynchronous actions by returning a
/// [`Command`] in some of its methods.
///
/// When using an [`Application`] with the `debug` feature enabled, a debug view
/// can be toggled by pressing `F12`.
pub trait Application: Program
where
    Self::Theme: DefaultStyle,
{
    /// The data needed to initialize your [`Application`].
    type Flags;

    /// Returns the unique name of the [`Application`].
    fn name() -> &'static str;

    /// Initializes the [`Application`] with the flags provided to
    /// [`run`] as part of the [`Settings`].
    ///
    /// Here is where you should return the initial state of your app.
    ///
    /// Additionally, you can return a [`Command`] if you need to perform some
    /// async action in the background on startup. This is useful if you want to
    /// load state from a file, perform an initial HTTP request, etc.
    fn new(flags: Self::Flags) -> (Self, Command<Self::Message>);

    /// Returns the current title of the [`Application`].
    ///
    /// This title can be dynamic! The runtime will automatically update the
    /// title of your application when necessary.
    fn title(&self) -> String;

    /// Returns the current `Theme` of the [`Application`].
    fn theme(&self) -> Self::Theme;

    /// Returns the `Style` variation of the `Theme`.
    fn style(&self, theme: &Self::Theme) -> Appearance {
        theme.default_style()
    }

    /// Returns the event `Subscription` for the current state of the
    /// application.
    ///
    /// The messages produced by the `Subscription` will be handled by
    /// [`update`](#tymethod.update).
    ///
    /// A `Subscription` will be kept alive as long as you keep returning it!
    ///
    /// By default, it returns an empty subscription.
    fn subscription(&self) -> Subscription<Self::Message> {
        Subscription::none()
    }

    /// Returns the scale factor of the [`Application`].
    ///
    /// It can be used to dynamically control the size of the UI at runtime
    /// (i.e. zooming).
    ///
    /// For instance, a scale factor of `2.0` will make widgets twice as big,
    /// while a scale factor of `0.5` will shrink them to half their size.
    ///
    /// By default, it returns `1.0`.
    fn scale_factor(&self) -> f64 {
        1.0
    }
}

/// The appearance of an application.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Appearance {
    /// The background [`Color`] of the application.
    pub background_color: Color,

    /// The default text [`Color`] of the application.
    pub text_color: Color,
}

/// The default style of an [`Application`].
pub trait DefaultStyle {
    /// Returns the default style of an [`Application`].
    fn default_style(&self) -> Appearance;

    /// Returns a [`Palette`] for the [`Application`], if possible.
    fn palette(&self) -> Option<theme::Palette> {
        None
    }
}

impl DefaultStyle for Theme {
    fn default_style(&self) -> Appearance {
        default(self)
    }

    fn palette(&self) -> Option<theme::Palette> {
        Some(self.palette())
    }
}

/// The default [`Appearance`] of an [`Application`] with the built-in [`Theme`].
pub fn default(theme: &Theme) -> Appearance {
    let palette = theme.extended_palette();

    Appearance {
        background_color: palette.background.base.color,
        text_color: palette.background.base.text,
    }
}

/// Runs an [`Application`] with an executor, compositor, and the provided
/// settings.
pub fn run<A, E, C>(
    settings: Settings<A::Flags>,
    graphics_settings: graphics::Settings,
) -> Result<(), Error>
where
    A: Application + 'static,
    E: Executor + 'static,
    C: Compositor<Renderer = A::Renderer> + 'static,
    A::Theme: DefaultStyle,
{
    use futures::task;
    use futures::Future;
    use winit::event_loop::EventLoop;

    debug::init(A::name());
    let boot_span = debug::boot();

    let event_loop = EventLoop::with_user_event()
        .build()
        .expect("Create event loop");

    let (proxy, worker) = Proxy::new(event_loop.create_proxy());

    let runtime = {
        let executor = E::new().map_err(Error::ExecutorCreationFailed)?;
        executor.spawn(worker);

        Runtime::new(executor, proxy.clone())
    };

    let (application, init_command) = {
        let flags = settings.flags;

        runtime.enter(|| A::new(flags))
    };

    let id = settings.id;
    let title = application.title();

    let (boot_sender, boot_receiver) = oneshot::channel();
    let (event_sender, event_receiver) = mpsc::unbounded();
    let (control_sender, control_receiver) = mpsc::unbounded();

    let instance = Box::pin(run_instance::<A, E, C>(
        application,
        runtime,
        proxy,
        boot_receiver,
        event_receiver,
        control_sender,
        init_command,
        settings.fonts,
        boot_span,
    ));

    let context = task::Context::from_waker(task::noop_waker_ref());

    struct Runner<Message: 'static, F, C> {
        instance: std::pin::Pin<Box<F>>,
        context: task::Context<'static>,
        boot: Option<BootConfig<C>>,
        sender: mpsc::UnboundedSender<winit::event::Event<Message>>,
        receiver: mpsc::UnboundedReceiver<winit::event_loop::ControlFlow>,
        error: Option<Error>,
        #[cfg(target_arch = "wasm32")]
        is_booted: std::rc::Rc<std::cell::RefCell<bool>>,
        #[cfg(target_arch = "wasm32")]
        queued_events: Vec<winit::event::Event<Message>>,
    }

    struct BootConfig<C> {
        sender: oneshot::Sender<Boot<C>>,
        id: Option<String>,
        title: String,
        window_settings: window::Settings,
        graphics_settings: graphics::Settings,
    }

    let runner = Runner {
        instance,
        context,
        boot: Some(BootConfig {
            sender: boot_sender,
            id,
            title,
            window_settings: settings.window,
            graphics_settings,
        }),
        sender: event_sender,
        receiver: control_receiver,
        error: None,
        #[cfg(target_arch = "wasm32")]
        is_booted: std::rc::Rc::new(std::cell::RefCell::new(false)),
        #[cfg(target_arch = "wasm32")]
        queued_events: Vec::new(),
    };

    impl<Message, F, C> winit::application::ApplicationHandler<Message>
        for Runner<Message, F, C>
    where
        F: Future<Output = ()>,
        C: Compositor + 'static,
    {
        fn resumed(&mut self, event_loop: &winit::event_loop::ActiveEventLoop) {
            let Some(BootConfig {
                sender,
                id,
                title,
                window_settings,
                graphics_settings,
            }) = self.boot.take()
            else {
                return;
            };

            let should_be_visible = window_settings.visible;
            let exit_on_close_request = window_settings.exit_on_close_request;

            #[cfg(target_arch = "wasm32")]
            let target = window_settings.platform_specific.target.clone();

            let window_attributes = conversion::window_attributes(
                window_settings,
                &title,
                event_loop.primary_monitor(),
                id,
            )
            .with_visible(false);

            log::debug!("Window attributes: {window_attributes:#?}");

            let window = match event_loop.create_window(window_attributes) {
                Ok(window) => Arc::new(window),
                Err(error) => {
                    self.error = Some(Error::WindowCreationFailed(error));
                    event_loop.exit();
                    return;
                }
            };

            let finish_boot = {
                let window = window.clone();

                async move {
                    let compositor =
                        C::new(graphics_settings, window.clone()).await?;

                    sender
                        .send(Boot {
                            window,
                            compositor,
                            should_be_visible,
                            exit_on_close_request,
                        })
                        .ok()
                        .expect("Send boot event");

                    Ok::<_, graphics::Error>(())
                }
            };

            #[cfg(not(target_arch = "wasm32"))]
            if let Err(error) = futures::executor::block_on(finish_boot) {
                self.error = Some(Error::GraphicsCreationFailed(error));
                event_loop.exit();
            }

            #[cfg(target_arch = "wasm32")]
            {
                use winit::platform::web::WindowExtWebSys;

                let canvas = window.canvas().expect("Get window canvas");
                let _ = canvas.set_attribute(
                    "style",
                    "display: block; width: 100%; height: 100%",
                );

                let window = web_sys::window().unwrap();
                let document = window.document().unwrap();
                let body = document.body().unwrap();

                let target = target.and_then(|target| {
                    body.query_selector(&format!("#{target}"))
                        .ok()
                        .unwrap_or(None)
                });

                match target {
                    Some(node) => {
                        let _ = node.replace_with_with_node_1(&canvas).expect(
                            &format!("Could not replace #{}", node.id()),
                        );
                    }
                    None => {
                        let _ = body
                            .append_child(&canvas)
                            .expect("Append canvas to HTML body");
                    }
                };

                let is_booted = self.is_booted.clone();

                wasm_bindgen_futures::spawn_local(async move {
                    finish_boot.await.expect("Finish boot!");

                    *is_booted.borrow_mut() = true;
                });
            }
        }

        fn new_events(
            &mut self,
            event_loop: &winit::event_loop::ActiveEventLoop,
            cause: winit::event::StartCause,
        ) {
            if self.boot.is_some() {
                return;
            }

            self.process_event(
                event_loop,
                winit::event::Event::NewEvents(cause),
            );
        }

        fn window_event(
            &mut self,
            event_loop: &winit::event_loop::ActiveEventLoop,
            window_id: winit::window::WindowId,
            event: winit::event::WindowEvent,
        ) {
            #[cfg(target_os = "windows")]
            let is_move_or_resize = matches!(
                event,
                winit::event::WindowEvent::Resized(_)
                    | winit::event::WindowEvent::Moved(_)
            );

            self.process_event(
                event_loop,
                winit::event::Event::WindowEvent { window_id, event },
            );

            // TODO: Remove when unnecessary
            // On Windows, we emulate an `AboutToWait` event after every `Resized` event
            // since the event loop does not resume during resize interaction.
            // More details: https://github.com/rust-windowing/winit/issues/3272
            #[cfg(target_os = "windows")]
            {
                if is_move_or_resize {
                    self.process_event(
                        event_loop,
                        winit::event::Event::AboutToWait,
                    );
                }
            }
        }

        fn user_event(
            &mut self,
            event_loop: &winit::event_loop::ActiveEventLoop,
            message: Message,
        ) {
            self.process_event(
                event_loop,
                winit::event::Event::UserEvent(message),
            );
        }

        fn about_to_wait(
            &mut self,
            event_loop: &winit::event_loop::ActiveEventLoop,
        ) {
            self.process_event(event_loop, winit::event::Event::AboutToWait);
        }
    }

    impl<Message, F, C> Runner<Message, F, C>
    where
        F: Future<Output = ()>,
    {
        fn process_event(
            &mut self,
            event_loop: &winit::event_loop::ActiveEventLoop,
            event: winit::event::Event<Message>,
        ) {
            // On Wasm, events may start being processed before the compositor
            // boots up. We simply queue them and process them once ready.
            #[cfg(target_arch = "wasm32")]
            if !*self.is_booted.borrow() {
                self.queued_events.push(event);
                return;
            } else if !self.queued_events.is_empty() {
                let queued_events = std::mem::take(&mut self.queued_events);

                // This won't infinitely recurse, since we `mem::take`
                for event in queued_events {
                    self.process_event(event_loop, event);
                }
            }

            if event_loop.exiting() {
                return;
            }

            self.sender.start_send(event).expect("Send event");

            let poll = self.instance.as_mut().poll(&mut self.context);

            match poll {
                task::Poll::Pending => {
                    if let Ok(Some(flow)) = self.receiver.try_next() {
                        event_loop.set_control_flow(flow);
                    }
                }
                task::Poll::Ready(_) => {
                    event_loop.exit();
                }
            }
        }
    }

    #[cfg(not(target_arch = "wasm32"))]
    {
        let mut runner = runner;
        let _ = event_loop.run_app(&mut runner);

        runner.error.map(Err).unwrap_or(Ok(()))
    }

    #[cfg(target_arch = "wasm32")]
    {
        use winit::platform::web::EventLoopExtWebSys;
        let _ = event_loop.spawn_app(runner);

        Ok(())
    }
}

struct Boot<C> {
    window: Arc<winit::window::Window>,
    compositor: C,
    should_be_visible: bool,
    exit_on_close_request: bool,
}

async fn run_instance<A, E, C>(
    mut application: A,
    mut runtime: Runtime<E, Proxy<A::Message>, A::Message>,
    mut proxy: Proxy<A::Message>,
    mut boot: oneshot::Receiver<Boot<C>>,
    mut event_receiver: mpsc::UnboundedReceiver<
        winit::event::Event<A::Message>,
    >,
    mut control_sender: mpsc::UnboundedSender<winit::event_loop::ControlFlow>,
    init_command: Command<A::Message>,
    fonts: Vec<Cow<'static, [u8]>>,
    boot_span: debug::Span,
) where
    A: Application + 'static,
    E: Executor + 'static,
    C: Compositor<Renderer = A::Renderer> + 'static,
    A::Theme: DefaultStyle,
{
    use futures::stream::StreamExt;
    use winit::event;
    use winit::event_loop::ControlFlow;

    let Boot {
        window,
        mut compositor,
        should_be_visible,
        exit_on_close_request,
    } = boot.try_recv().ok().flatten().expect("Receive boot");

    let mut renderer = compositor.create_renderer();

    for font in fonts {
        compositor.load_font(font);
    }

    let mut state = State::new(&application, &window);
    let mut viewport_version = state.viewport_version();
    let physical_size = state.physical_size();

    let mut clipboard = Clipboard::connect(&window);
    let mut cache = user_interface::Cache::default();
    let mut surface = compositor.create_surface(
        window.clone(),
        physical_size.width,
        physical_size.height,
    );
    let mut should_exit = false;

    if should_be_visible {
        window.set_visible(true);
    }

    run_command(
        &application,
        &mut compositor,
        &mut surface,
        &mut cache,
        &state,
        &mut renderer,
        init_command,
        &mut runtime,
        &mut clipboard,
        &mut should_exit,
        &mut proxy,
        &window,
    );

    let recipes = application.subscription().into_recipes();
    debug::subscriptions_tracked(recipes.len());
    runtime.track(recipes);

    boot_span.finish();

    let mut user_interface = ManuallyDrop::new(build_user_interface(
        &application,
        cache,
        &mut renderer,
        state.logical_size(),
    ));

    let mut mouse_interaction = mouse::Interaction::default();
    let mut events = Vec::new();
    let mut messages = Vec::new();
    let mut user_events = 0;
    let mut redraw_pending = false;

    while let Some(event) = event_receiver.next().await {
        match event {
            event::Event::NewEvents(
                event::StartCause::Init
                | event::StartCause::ResumeTimeReached { .. },
            ) if !redraw_pending => {
                window.request_redraw();
                redraw_pending = true;
            }
            event::Event::PlatformSpecific(event::PlatformSpecific::MacOS(
                event::MacOS::ReceivedUrl(url),
            )) => {
                use crate::core::event;

                events.push(Event::PlatformSpecific(
                    event::PlatformSpecific::MacOS(event::MacOS::ReceivedUrl(
                        url,
                    )),
                ));
            }
            event::Event::UserEvent(message) => {
                messages.push(message);
                user_events += 1;
            }
            event::Event::WindowEvent {
                event: event::WindowEvent::RedrawRequested { .. },
                ..
            } => {
                let physical_size = state.physical_size();

                if physical_size.width == 0 || physical_size.height == 0 {
                    continue;
                }

                let current_viewport_version = state.viewport_version();

                if viewport_version != current_viewport_version {
                    let logical_size = state.logical_size();

                    let layout_span = debug::layout(window::Id::MAIN);
                    user_interface = ManuallyDrop::new(
                        ManuallyDrop::into_inner(user_interface)
                            .relayout(logical_size, &mut renderer),
                    );
                    layout_span.finish();

                    compositor.configure_surface(
                        &mut surface,
                        physical_size.width,
                        physical_size.height,
                    );

                    viewport_version = current_viewport_version;
                }

                // TODO: Avoid redrawing all the time by forcing widgets to
                // request redraws on state changes
                //
                // Then, we can use the `interface_state` here to decide if a redraw
                // is needed right away, or simply wait until a specific time.
                let redraw_event = Event::Window(
                    window::Id::MAIN,
                    window::Event::RedrawRequested(Instant::now()),
                );

                let (interface_state, _) = user_interface.update(
                    &[redraw_event.clone()],
                    state.cursor(),
                    &mut renderer,
                    &mut clipboard,
                    &mut messages,
                );

                let _ = control_sender.start_send(match interface_state {
                    user_interface::State::Updated {
                        redraw_request: Some(redraw_request),
                    } => match redraw_request {
                        window::RedrawRequest::NextFrame => {
                            window.request_redraw();

                            ControlFlow::Wait
                        }
                        window::RedrawRequest::At(at) => {
                            ControlFlow::WaitUntil(at)
                        }
                    },
                    _ => ControlFlow::Wait,
                });

                runtime.broadcast(redraw_event, core::event::Status::Ignored);

                let draw_span = debug::draw(window::Id::MAIN);
                let new_mouse_interaction = user_interface.draw(
                    &mut renderer,
                    state.theme(),
                    &renderer::Style {
                        text_color: state.text_color(),
                    },
                    state.cursor(),
                );
                redraw_pending = false;
                draw_span.finish();

                if new_mouse_interaction != mouse_interaction {
                    window.set_cursor(conversion::mouse_interaction(
                        new_mouse_interaction,
                    ));

                    mouse_interaction = new_mouse_interaction;
                }

                let present_span = debug::present(window::Id::MAIN);
                match compositor.present(
                    &mut renderer,
                    &mut surface,
                    state.viewport(),
                    state.background_color(),
                ) {
                    Ok(()) => {
                        present_span.finish();
                    }
                    Err(error) => match error {
                        // This is an unrecoverable error.
                        compositor::SurfaceError::OutOfMemory => {
                            panic!("{error:?}");
                        }
                        _ => {
                            // Try rendering again next frame.
                            window.request_redraw();
                        }
                    },
                }
            }
            event::Event::WindowEvent {
                event: window_event,
                ..
            } => {
                if requests_exit(&window_event, state.modifiers())
                    && exit_on_close_request
                {
                    break;
                }

                #[cfg(feature = "debug")]
                if let winit::event::WindowEvent::KeyboardInput {
                    event:
                        winit::event::KeyEvent {
                            logical_key:
                                winit::keyboard::Key::Named(
                                    winit::keyboard::NamedKey::F12,
                                ),
                            state: winit::event::ElementState::Pressed,
                            repeat: false,
                            ..
                        },
                    ..
                } = &window_event
                {
                    crate::debug::toggle_comet();
                }

                state.update(&window, &window_event);

                if let Some(event) = conversion::window_event(
                    window::Id::MAIN,
                    window_event,
                    state.scale_factor(),
                    state.modifiers(),
                ) {
                    events.push(event);
                }
            }
            event::Event::AboutToWait => {
                if events.is_empty() && messages.is_empty() {
                    continue;
                }

                let interface_state = if events.is_empty() {
                    user_interface::State::Updated {
                        redraw_request: None,
                    }
                } else {
                    let interact_span = debug::interact(window::Id::MAIN);
                    let (interface_state, statuses) = user_interface.update(
                        &events,
                        state.cursor(),
                        &mut renderer,
                        &mut clipboard,
                        &mut messages,
                    );

                    for (event, status) in
                        events.drain(..).zip(statuses.into_iter())
                    {
                        runtime.broadcast(event, status);
                    }
                    interact_span.finish();

                    interface_state
                };

                if !messages.is_empty()
                    || matches!(
                        interface_state,
                        user_interface::State::Outdated
                    )
                {
                    let mut cache =
                        ManuallyDrop::into_inner(user_interface).into_cache();

                    // Update application
                    update(
                        &mut application,
                        &mut compositor,
                        &mut surface,
                        &mut cache,
                        &mut state,
                        &mut renderer,
                        &mut runtime,
                        &mut clipboard,
                        &mut should_exit,
                        &mut proxy,
                        &mut messages,
                        &window,
                    );

                    user_interface = ManuallyDrop::new(build_user_interface(
                        &application,
                        cache,
                        &mut renderer,
                        state.logical_size(),
                    ));

                    if should_exit {
                        break;
                    }

                    if user_events > 0 {
                        proxy.free_slots(user_events);
                        user_events = 0;
                    }
                }

                if !redraw_pending {
                    window.request_redraw();
                    redraw_pending = true;
                }
            }
            _ => {}
        }
    }

    // Manually drop the user interface
    drop(ManuallyDrop::into_inner(user_interface));
}

/// Returns true if the provided event should cause an [`Application`] to
/// exit.
pub fn requests_exit(
    event: &winit::event::WindowEvent,
    _modifiers: winit::keyboard::ModifiersState,
) -> bool {
    use winit::event::WindowEvent;

    match event {
        WindowEvent::CloseRequested => true,
        #[cfg(target_os = "macos")]
        WindowEvent::KeyboardInput {
            event:
                winit::event::KeyEvent {
                    logical_key: winit::keyboard::Key::Character(c),
                    state: winit::event::ElementState::Pressed,
                    ..
                },
            ..
        } if c == "q" && _modifiers.super_key() => true,
        _ => false,
    }
}

/// Builds a [`UserInterface`] for the provided [`Application`], logging
/// [`struct@Debug`] information accordingly.
pub fn build_user_interface<'a, A: Application>(
    application: &'a A,
    cache: user_interface::Cache,
    renderer: &mut A::Renderer,
    size: Size,
) -> UserInterface<'a, A::Message, A::Theme, A::Renderer>
where
    A::Theme: DefaultStyle,
{
    let view_span = debug::view(window::Id::MAIN);
    let view = application.view();
    view_span.finish();

    let layout_span = debug::layout(window::Id::MAIN);
    let user_interface = UserInterface::build(view, size, cache, renderer);
    layout_span.finish();

    user_interface
}

/// Updates an [`Application`] by feeding it the provided messages, spawning any
/// resulting [`Command`], and tracking its [`Subscription`].
pub fn update<A: Application, C, E: Executor>(
    application: &mut A,
    compositor: &mut C,
    surface: &mut C::Surface,
    cache: &mut user_interface::Cache,
    state: &mut State<A>,
    renderer: &mut A::Renderer,
    runtime: &mut Runtime<E, Proxy<A::Message>, A::Message>,
    clipboard: &mut Clipboard,
    should_exit: &mut bool,
    proxy: &mut Proxy<A::Message>,
    messages: &mut Vec<A::Message>,
    window: &winit::window::Window,
) where
    C: Compositor<Renderer = A::Renderer> + 'static,
    A::Theme: DefaultStyle,
{
    for message in messages.drain(..) {
        let update_span = debug::update(&message);
        let command = runtime.enter(|| application.update(message));

        run_command(
            application,
            compositor,
            surface,
            cache,
            state,
            renderer,
            command,
            runtime,
            clipboard,
            should_exit,
            proxy,
            window,
        );
        update_span.finish();
    }

    state.synchronize(application, window);

    let recipes = application.subscription().into_recipes();
    debug::subscriptions_tracked(recipes.len());
    runtime.track(recipes);
}

/// Runs the actions of a [`Command`].
pub fn run_command<A, C, E>(
    application: &A,
    compositor: &mut C,
    surface: &mut C::Surface,
    cache: &mut user_interface::Cache,
    state: &State<A>,
    renderer: &mut A::Renderer,
    command: Command<A::Message>,
    runtime: &mut Runtime<E, Proxy<A::Message>, A::Message>,
    clipboard: &mut Clipboard,
    should_exit: &mut bool,
    proxy: &mut Proxy<A::Message>,
    window: &winit::window::Window,
) where
    A: Application,
    E: Executor,
    C: Compositor<Renderer = A::Renderer> + 'static,
    A::Theme: DefaultStyle,
{
    use crate::runtime::command;
    use crate::runtime::system;
    use crate::runtime::window;

    let actions = command.actions();
    debug::commands_spawned(actions.len());

    for action in actions {
        match action {
            command::Action::Future(future) => {
                runtime.spawn(future);
            }
            command::Action::Stream(stream) => {
                runtime.run(stream);
            }
            command::Action::Clipboard(action) => match action {
                clipboard::Action::Read(tag, kind) => {
                    let message = tag(clipboard.read(kind));

                    proxy.send(message);
                }
                clipboard::Action::Write(contents, kind) => {
                    clipboard.write(kind, contents);
                }
            },
            command::Action::Window(action) => match action {
                window::Action::Close(_id) => {
                    *should_exit = true;
                }
                window::Action::Drag(_id) => {
                    let _res = window.drag_window();
                }
                window::Action::Spawn { .. } => {
                    log::warn!(
                        "Spawning a window is only available with \
                        multi-window applications."
                    );
                }
                window::Action::Resize(_id, size) => {
                    let _ =
                        window.request_inner_size(winit::dpi::LogicalSize {
                            width: size.width,
                            height: size.height,
                        });
                }
                window::Action::FetchSize(_id, callback) => {
                    let size =
                        window.inner_size().to_logical(window.scale_factor());

                    proxy.send(callback(Size::new(size.width, size.height)));
                }
                window::Action::FetchMaximized(_id, callback) => {
                    proxy.send(callback(window.is_maximized()));
                }
                window::Action::Maximize(_id, maximized) => {
                    window.set_maximized(maximized);
                }
                window::Action::FetchMinimized(_id, callback) => {
                    proxy.send(callback(window.is_minimized()));
                }
                window::Action::Minimize(_id, minimized) => {
                    window.set_minimized(minimized);
                }
                window::Action::FetchPosition(_id, callback) => {
                    let position = window
                        .inner_position()
                        .map(|position| {
                            let position = position
                                .to_logical::<f32>(window.scale_factor());

                            Point::new(position.x, position.y)
                        })
                        .ok();

                    proxy.send(callback(position));
                }
                window::Action::Move(_id, position) => {
                    window.set_outer_position(winit::dpi::LogicalPosition {
                        x: position.x,
                        y: position.y,
                    });
                }
                window::Action::ChangeMode(_id, mode) => {
                    window.set_visible(conversion::visible(mode));
                    window.set_fullscreen(conversion::fullscreen(
                        window.current_monitor(),
                        mode,
                    ));
                }
                window::Action::ChangeIcon(_id, icon) => {
                    window.set_window_icon(conversion::icon(icon));
                }
                window::Action::FetchMode(_id, tag) => {
                    let mode = if window.is_visible().unwrap_or(true) {
                        conversion::mode(window.fullscreen())
                    } else {
                        core::window::Mode::Hidden
                    };

                    proxy.send(tag(mode));
                }
                window::Action::ToggleMaximize(_id) => {
                    window.set_maximized(!window.is_maximized());
                }
                window::Action::ToggleDecorations(_id) => {
                    window.set_decorations(!window.is_decorated());
                }
                window::Action::RequestUserAttention(_id, user_attention) => {
                    window.request_user_attention(
                        user_attention.map(conversion::user_attention),
                    );
                }
                window::Action::GainFocus(_id) => {
                    window.focus_window();
                }
                window::Action::ChangeLevel(_id, level) => {
                    window.set_window_level(conversion::window_level(level));
                }
                window::Action::ShowSystemMenu(_id) => {
                    if let mouse::Cursor::Available(point) = state.cursor() {
                        window.show_window_menu(winit::dpi::LogicalPosition {
                            x: point.x,
                            y: point.y,
                        });
                    }
                }
                window::Action::FetchId(_id, tag) => {
                    proxy.send(tag(window.id().into()));
                }
                window::Action::RunWithHandle(_id, tag) => {
                    use window::raw_window_handle::HasWindowHandle;

                    if let Ok(handle) = window.window_handle() {
                        proxy.send(tag(handle));
                    }
                }

                window::Action::Screenshot(_id, tag) => {
                    let bytes = compositor.screenshot(
                        renderer,
                        surface,
                        state.viewport(),
                        state.background_color(),
                    );

                    proxy.send(tag(window::Screenshot::new(
                        bytes,
                        state.physical_size(),
                    )));
                }
            },
            command::Action::System(action) => match action {
                system::Action::QueryInformation(_tag) => {
                    #[cfg(feature = "system")]
                    {
                        let graphics_info = compositor.fetch_information();
                        let mut proxy = proxy.clone();

                        let _ = std::thread::spawn(move || {
                            let information =
                                crate::system::information(graphics_info);

                            let message = _tag(information);

                            proxy.send(message);
                        });
                    }
                }
            },
            command::Action::Widget(action) => {
                let mut current_cache = std::mem::take(cache);
                let mut current_operation = Some(action);

                let mut user_interface = build_user_interface(
                    application,
                    current_cache,
                    renderer,
                    state.logical_size(),
                );

                while let Some(mut operation) = current_operation.take() {
                    user_interface.operate(renderer, operation.as_mut());

                    match operation.finish() {
                        operation::Outcome::None => {}
                        operation::Outcome::Some(message) => {
                            proxy.send(message);
                        }
                        operation::Outcome::Chain(next) => {
                            current_operation = Some(next);
                        }
                    }
                }

                current_cache = user_interface.into_cache();
                *cache = current_cache;
            }
            command::Action::LoadFont { bytes, tagger } => {
                // TODO: Error handling (?)
                compositor.load_font(bytes);

                proxy.send(tagger(Ok(())));
            }
            command::Action::Custom(_) => {
                log::warn!("Unsupported custom action in `iced_winit` shell");
            }
        }
    }
}