winit/application.rs
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//! End user application handling.
use crate::event::{DeviceEvent, DeviceId, StartCause, WindowEvent};
use crate::event_loop::ActiveEventLoop;
use crate::window::WindowId;
/// The handler of the application events.
pub trait ApplicationHandler {
/// Emitted when new events arrive from the OS to be processed.
///
/// This is a useful place to put code that should be done before you start processing
/// events, such as updating frame timing information for benchmarking or checking the
/// [`StartCause`] to see if a timer set by
/// [`ControlFlow::WaitUntil`][crate::event_loop::ControlFlow::WaitUntil] has elapsed.
fn new_events(&mut self, event_loop: &dyn ActiveEventLoop, cause: StartCause) {
let _ = (event_loop, cause);
}
/// Emitted when the application has been resumed.
///
/// See [`suspended()`][Self::suspended].
///
/// ## Platform-specific
///
/// ### iOS
///
/// On iOS, the [`resumed()`] method is called in response to an [`applicationDidBecomeActive`]
/// callback which means the application is about to transition from the inactive to active
/// state (according to the [iOS application lifecycle]).
///
/// [`applicationDidBecomeActive`]: https://developer.apple.com/documentation/uikit/uiapplicationdelegate/1622956-applicationdidbecomeactive
/// [iOS application lifecycle]: https://developer.apple.com/documentation/uikit/app_and_environment/managing_your_app_s_life_cycle
///
/// ### Web
///
/// On Web, the [`resumed()`] method is called in response to a [`pageshow`] event if the
/// page is being restored from the [`bfcache`] (back/forward cache) - an in-memory cache
/// that stores a complete snapshot of a page (including the JavaScript heap) as the user is
/// navigating away.
///
/// [`pageshow`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/pageshow_event
/// [`bfcache`]: https://web.dev/bfcache/
///
/// ### Others
///
/// **Android / macOS / Orbital / Wayland / Windows / X11:** Unsupported.
///
/// [`resumed()`]: Self::resumed
fn resumed(&mut self, event_loop: &dyn ActiveEventLoop) {
let _ = event_loop;
}
/// Emitted from the point onwards the application should create render surfaces.
///
/// See [`destroy_surfaces()`].
///
/// ## Portability
///
/// It's recommended that applications should only initialize their render surfaces after the
/// [`can_create_surfaces()`] method is called. Some systems (specifically Android) won't allow
/// applications to create a render surface until that point.
///
/// For consistency, all platforms call this method even if they don't themselves have a formal
/// surface destroy/create lifecycle. For systems without a surface destroy/create lifecycle the
/// [`can_create_surfaces()`] event is always emitted after the [`StartCause::Init`] event.
///
/// Applications should be able to gracefully handle back-to-back [`can_create_surfaces()`] and
/// [`destroy_surfaces()`] calls.
///
/// ## Platform-specific
///
/// ### Android
///
/// On Android, the [`can_create_surfaces()`] method is called when a new [`SurfaceView`] has
/// been created. This is expected to closely correlate with the [`onResume`] lifecycle
/// event but there may technically be a discrepancy.
///
/// [`onResume`]: https://developer.android.com/reference/android/app/Activity#onResume()
///
/// Applications that need to run on Android must wait until they have been "resumed" before
/// they will be able to create a render surface (such as an `EGLSurface`, [`VkSurfaceKHR`]
/// or [`wgpu::Surface`]) which depend on having a [`SurfaceView`]. Applications must also
/// assume that if they are [suspended], then their render surfaces are invalid and should
/// be dropped.
///
/// [suspended]: Self::destroy_surfaces
/// [`SurfaceView`]: https://developer.android.com/reference/android/view/SurfaceView
/// [Activity lifecycle]: https://developer.android.com/guide/components/activities/activity-lifecycle
/// [`VkSurfaceKHR`]: https://www.khronos.org/registry/vulkan/specs/1.3-extensions/man/html/VkSurfaceKHR.html
/// [`wgpu::Surface`]: https://docs.rs/wgpu/latest/wgpu/struct.Surface.html
///
/// [`can_create_surfaces()`]: Self::can_create_surfaces
/// [`destroy_surfaces()`]: Self::destroy_surfaces
fn can_create_surfaces(&mut self, event_loop: &dyn ActiveEventLoop);
/// Called after a wake up is requested using [`EventLoopProxy::wake_up()`].
///
/// Multiple calls to the aforementioned method will be merged, and will only wake the event
/// loop once; however, due to the nature of multi-threading some wake ups may appear
/// spuriously. For these reasons, you should not rely on the number of times that this was
/// called.
///
/// The order in which this is emitted in relation to other events is not guaranteed. The time
/// at which this will be emitted is not guaranteed, only that it will happen "soon". That is,
/// there may be several executions of the event loop, including multiple redraws to windows,
/// between [`EventLoopProxy::wake_up()`] being called and the event being delivered.
///
/// [`EventLoopProxy::wake_up()`]: crate::event_loop::EventLoopProxy::wake_up
///
/// # Example
///
/// Use a [`std::sync::mpsc`] channel to handle events from a different thread.
///
/// ```no_run
/// use std::sync::mpsc;
/// use std::thread;
/// use std::time::Duration;
///
/// use winit::application::ApplicationHandler;
/// use winit::event_loop::{ActiveEventLoop, EventLoop};
///
/// struct MyApp {
/// receiver: mpsc::Receiver<u64>,
/// }
///
/// impl ApplicationHandler for MyApp {
/// # fn window_event(
/// # &mut self,
/// # _event_loop: &dyn ActiveEventLoop,
/// # _window_id: winit::window::WindowId,
/// # _event: winit::event::WindowEvent,
/// # ) {
/// # }
/// #
/// # fn can_create_surfaces(&mut self, _event_loop: &dyn ActiveEventLoop) {}
/// #
/// fn proxy_wake_up(&mut self, _event_loop: &dyn ActiveEventLoop) {
/// // Iterate current events, since wake-ups may have been merged.
/// //
/// // Note: We take care not to use `recv` or `iter` here, as those are blocking,
/// // and that would be bad for performance and might lead to a deadlock.
/// for i in self.receiver.try_iter() {
/// println!("received: {i}");
/// }
/// }
///
/// // Rest of `ApplicationHandler`
/// }
///
/// fn main() -> Result<(), Box<dyn std::error::Error>> {
/// let event_loop = EventLoop::new()?;
///
/// let (sender, receiver) = mpsc::channel();
///
/// let mut app = MyApp { receiver };
///
/// // Send an event in a loop
/// let proxy = event_loop.create_proxy();
/// let background_thread = thread::spawn(move || {
/// let mut i = 0;
/// loop {
/// println!("sending: {i}");
/// if sender.send(i).is_err() {
/// // Stop sending once `MyApp` is dropped
/// break;
/// }
/// // Trigger the wake-up _after_ we placed the event in the channel.
/// // Otherwise, `proxy_wake_up` might be triggered prematurely.
/// proxy.wake_up();
/// i += 1;
/// thread::sleep(Duration::from_secs(1));
/// }
/// });
///
/// event_loop.run_app(&mut app)?;
///
/// drop(app);
/// background_thread.join().unwrap();
///
/// Ok(())
/// }
/// ```
fn proxy_wake_up(&mut self, event_loop: &dyn ActiveEventLoop) {
let _ = event_loop;
}
/// Emitted when the OS sends an event to a winit window.
fn window_event(
&mut self,
event_loop: &dyn ActiveEventLoop,
window_id: WindowId,
event: WindowEvent,
);
/// Emitted when the OS sends an event to a device.
fn device_event(
&mut self,
event_loop: &dyn ActiveEventLoop,
device_id: DeviceId,
event: DeviceEvent,
) {
let _ = (event_loop, device_id, event);
}
/// Emitted when the event loop is about to block and wait for new events.
///
/// Most applications shouldn't need to hook into this event since there is no real relationship
/// between how often the event loop needs to wake up and the dispatching of any specific
/// events.
///
/// High frequency event sources, such as input devices could potentially lead to lots of wake
/// ups and also lots of corresponding `AboutToWait` events.
///
/// This is not an ideal event to drive application rendering from and instead applications
/// should render in response to [`WindowEvent::RedrawRequested`] events.
fn about_to_wait(&mut self, event_loop: &dyn ActiveEventLoop) {
let _ = event_loop;
}
/// Emitted when the application has been suspended.
///
/// See [`resumed()`][Self::resumed].
///
/// ## Platform-specific
///
/// ### iOS
///
/// On iOS, the [`suspended()`] method is called in response to an
/// [`applicationWillResignActive`] callback which means that the application is about to
/// transition from the active to inactive state (according to the [iOS application lifecycle]).
///
/// [`applicationWillResignActive`]: https://developer.apple.com/documentation/uikit/uiapplicationdelegate/1622950-applicationwillresignactive
/// [iOS application lifecycle]: https://developer.apple.com/documentation/uikit/app_and_environment/managing_your_app_s_life_cycle
///
/// ### Web
///
/// On Web, the [`suspended()`] method is called in response to a [`pagehide`] event if the
/// page is being restored from the [`bfcache`] (back/forward cache) - an in-memory cache that
/// stores a complete snapshot of a page (including the JavaScript heap) as the user is
/// navigating away.
///
/// [`pagehide`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/pagehide_event
/// [`bfcache`]: https://web.dev/bfcache/
///
/// ### Others
///
/// **Android / macOS / Orbital / Wayland / Windows / X11:** Unsupported.
///
/// [`suspended()`]: Self::suspended
fn suspended(&mut self, event_loop: &dyn ActiveEventLoop) {
let _ = event_loop;
}
/// Emitted when the application must destroy its render surfaces.
///
/// See [`can_create_surfaces()`] for more details.
///
/// ## Platform-specific
///
/// ### Android
///
/// On Android, the [`destroy_surfaces()`] method is called when the application's associated
/// [`SurfaceView`] is destroyed. This is expected to closely correlate with the [`onPause`]
/// lifecycle event but there may technically be a discrepancy.
///
/// [`onPause`]: https://developer.android.com/reference/android/app/Activity#onPause()
///
/// Applications that need to run on Android should assume their [`SurfaceView`] has been
/// destroyed, which indirectly invalidates any existing render surfaces that may have been
/// created outside of Winit (such as an `EGLSurface`, [`VkSurfaceKHR`] or [`wgpu::Surface`]).
///
/// After being [suspended] on Android applications must drop all render surfaces before
/// the event callback completes, which may be re-created when the application is next
/// [resumed].
///
/// [suspended]: Self::destroy_surfaces
/// [resumed]: Self::can_create_surfaces
/// [`SurfaceView`]: https://developer.android.com/reference/android/view/SurfaceView
/// [Activity lifecycle]: https://developer.android.com/guide/components/activities/activity-lifecycle
/// [`VkSurfaceKHR`]: https://www.khronos.org/registry/vulkan/specs/1.3-extensions/man/html/VkSurfaceKHR.html
/// [`wgpu::Surface`]: https://docs.rs/wgpu/latest/wgpu/struct.Surface.html
///
/// ### Others
///
/// - **iOS / macOS / Orbital / Wayland / Web / Windows / X11:** Unsupported.
///
/// [`can_create_surfaces()`]: Self::can_create_surfaces
/// [`destroy_surfaces()`]: Self::destroy_surfaces
fn destroy_surfaces(&mut self, event_loop: &dyn ActiveEventLoop) {
let _ = event_loop;
}
/// Emitted when the event loop is being shut down.
///
/// This is irreversible - if this method is called, it is guaranteed that the event loop
/// will exit right after.
fn exiting(&mut self, event_loop: &dyn ActiveEventLoop) {
let _ = event_loop;
}
/// Emitted when the application has received a memory warning.
///
/// ## Platform-specific
///
/// ### Android
///
/// On Android, the `MemoryWarning` event is sent when [`onLowMemory`] was called. The
/// application must [release memory] or risk being killed.
///
/// [`onLowMemory`]: https://developer.android.com/reference/android/app/Application.html#onLowMemory()
/// [release memory]: https://developer.android.com/topic/performance/memory#release
///
/// ### iOS
///
/// On iOS, the `MemoryWarning` event is emitted in response to an
/// [`applicationDidReceiveMemoryWarning`] callback. The application must free as much
/// memory as possible or risk being terminated, see [how to respond to memory warnings].
///
/// [`applicationDidReceiveMemoryWarning`]: https://developer.apple.com/documentation/uikit/uiapplicationdelegate/1623063-applicationdidreceivememorywarni
/// [how to respond to memory warnings]: https://developer.apple.com/documentation/uikit/app_and_environment/managing_your_app_s_life_cycle/responding_to_memory_warnings
///
/// ### Others
///
/// - **macOS / Orbital / Wayland / Web / Windows:** Unsupported.
fn memory_warning(&mut self, event_loop: &dyn ActiveEventLoop) {
let _ = event_loop;
}
}
#[deny(clippy::missing_trait_methods)]
impl<A: ?Sized + ApplicationHandler> ApplicationHandler for &mut A {
#[inline]
fn new_events(&mut self, event_loop: &dyn ActiveEventLoop, cause: StartCause) {
(**self).new_events(event_loop, cause);
}
#[inline]
fn resumed(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).resumed(event_loop);
}
#[inline]
fn can_create_surfaces(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).can_create_surfaces(event_loop);
}
#[inline]
fn proxy_wake_up(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).proxy_wake_up(event_loop);
}
#[inline]
fn window_event(
&mut self,
event_loop: &dyn ActiveEventLoop,
window_id: WindowId,
event: WindowEvent,
) {
(**self).window_event(event_loop, window_id, event);
}
#[inline]
fn device_event(
&mut self,
event_loop: &dyn ActiveEventLoop,
device_id: DeviceId,
event: DeviceEvent,
) {
(**self).device_event(event_loop, device_id, event);
}
#[inline]
fn about_to_wait(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).about_to_wait(event_loop);
}
#[inline]
fn suspended(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).suspended(event_loop);
}
#[inline]
fn destroy_surfaces(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).destroy_surfaces(event_loop);
}
#[inline]
fn exiting(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).exiting(event_loop);
}
#[inline]
fn memory_warning(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).memory_warning(event_loop);
}
}
#[deny(clippy::missing_trait_methods)]
impl<A: ?Sized + ApplicationHandler> ApplicationHandler for Box<A> {
#[inline]
fn new_events(&mut self, event_loop: &dyn ActiveEventLoop, cause: StartCause) {
(**self).new_events(event_loop, cause);
}
#[inline]
fn resumed(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).resumed(event_loop);
}
#[inline]
fn can_create_surfaces(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).can_create_surfaces(event_loop);
}
#[inline]
fn proxy_wake_up(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).proxy_wake_up(event_loop);
}
#[inline]
fn window_event(
&mut self,
event_loop: &dyn ActiveEventLoop,
window_id: WindowId,
event: WindowEvent,
) {
(**self).window_event(event_loop, window_id, event);
}
#[inline]
fn device_event(
&mut self,
event_loop: &dyn ActiveEventLoop,
device_id: DeviceId,
event: DeviceEvent,
) {
(**self).device_event(event_loop, device_id, event);
}
#[inline]
fn about_to_wait(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).about_to_wait(event_loop);
}
#[inline]
fn suspended(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).suspended(event_loop);
}
#[inline]
fn destroy_surfaces(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).destroy_surfaces(event_loop);
}
#[inline]
fn exiting(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).exiting(event_loop);
}
#[inline]
fn memory_warning(&mut self, event_loop: &dyn ActiveEventLoop) {
(**self).memory_warning(event_loop);
}
}