winit/src/platform/web.rs

#![cfg(target_arch = "wasm32")]

//! The web target does not automatically insert the canvas element object into the web page, to
//! allow end users to determine how the page should be laid out. Use the [`WindowExtWebSys`] trait
//! to retrieve the canvas from the Window. Alternatively, use the [`WindowBuilderExtWebSys`] trait
//! to provide your own canvas.

use crate::event::Event;
use crate::event_loop::ControlFlow;
use crate::event_loop::EventLoop;
use crate::event_loop::EventLoopWindowTarget;
use crate::window::WindowBuilder;

use web_sys::HtmlCanvasElement;

pub trait WindowExtWebSys {
    fn canvas(&self) -> HtmlCanvasElement;

    /// Whether the browser reports the preferred color scheme to be "dark".
    fn is_dark_mode(&self) -> bool;
}

pub trait WindowBuilderExtWebSys {
    fn with_canvas(self, canvas: Option<HtmlCanvasElement>) -> Self;
}

impl WindowBuilderExtWebSys for WindowBuilder {
    fn with_canvas(mut self, canvas: Option<HtmlCanvasElement>) -> Self {
        self.platform_specific.canvas = canvas;

        self
    }
}

/// Additional methods on `EventLoop` that are specific to the web.
pub trait EventLoopExtWebSys {
    /// A type provided by the user that can be passed through `Event::UserEvent`.
    type UserEvent;

    /// Initializes the winit event loop.
    ///
    /// Unlike `run`, this returns immediately, and doesn't throw an exception in order to
    /// satisfy its `!` return type.
    fn spawn<F>(self, event_handler: F)
    where
        F: 'static
            + FnMut(
                Event<'_, Self::UserEvent>,
                &EventLoopWindowTarget<Self::UserEvent>,
                &mut ControlFlow,
            );
}

impl<T> EventLoopExtWebSys for EventLoop<T> {
    type UserEvent = T;

    fn spawn<F>(self, event_handler: F)
    where
        F: 'static
            + FnMut(
                Event<'_, Self::UserEvent>,
                &EventLoopWindowTarget<Self::UserEvent>,
                &mut ControlFlow,
            ),
    {
        self.event_loop.spawn(event_handler)
    }
}