Trait winit::platform::pump_events::EventLoopExtPumpEvents
source · pub trait EventLoopExtPumpEvents {
type UserEvent;
// Required method
fn pump_events<F>(
&mut self,
timeout: Option<Duration>,
event_handler: F,
) -> PumpStatus
where F: FnMut(Event<Self::UserEvent>, &EventLoopWindowTarget<Self::UserEvent>);
}
Expand description
Additional methods on EventLoop
for pumping events within an external event loop
Required Associated Types§
sourcetype UserEvent
type UserEvent
A type provided by the user that can be passed through Event::UserEvent
.
Required Methods§
sourcefn pump_events<F>(
&mut self,
timeout: Option<Duration>,
event_handler: F,
) -> PumpStatus
fn pump_events<F>( &mut self, timeout: Option<Duration>, event_handler: F, ) -> PumpStatus
Pump the EventLoop
to check for and dispatch pending events.
This API is designed to enable applications to integrate Winit into an external event loop, for platforms that can support this.
The given timeout
limits how long it may block waiting for new events.
Passing a timeout
of Some(Duration::ZERO)
would ensure your external
event loop is never blocked but you would likely need to consider how
to throttle your own external loop.
Passing a timeout
of None
means that it may wait indefinitely for new
events before returning control back to the external loop.
§Example
fn main() -> std::process::ExitCode {
let mut event_loop = EventLoop::new().unwrap();
let window = WindowBuilder::new()
.with_title("A fantastic window!")
.build(&event_loop)
.unwrap();
'main: loop {
let timeout = Some(Duration::ZERO);
let status = event_loop.pump_events(timeout, |event, elwt| {
match event {
Event::WindowEvent {
event: WindowEvent::CloseRequested,
window_id,
} if window_id == window.id() => elwt.exit(),
Event::AboutToWait => {
window.request_redraw();
}
_ => (),
}
});
if let PumpStatus::Exit(exit_code) = status {
break 'main ExitCode::from(exit_code as u8);
}
// Sleep for 1/60 second to simulate application work
//
// Since `pump_events` doesn't block it will be important to
// throttle the loop in the app somehow.
println!("Update()");
sleep(Duration::from_millis(16));
}
}
Note: This is not a portable API, and its usage involves a number of caveats and trade offs that should be considered before using this API!
You almost certainly shouldn’t use this API, unless you absolutely know it’s the only practical option you have.
§Synchronous events
Some events must only be handled synchronously via the closure that is passed to Winit so that the handler will also be synchronized with the window system and operating system.
This is because some events are driven by a window system callback where the window systems expects the application to have handled the event before returning.
These events can not be buffered and handled outside of the closure passed to Winit.
As a general rule it is not recommended to ever buffer events to handle them outside of the closure passed to Winit since it’s difficult to provide guarantees about which events are safe to buffer across all operating systems.
Notable events that will certainly create portability problems if buffered and handled outside of Winit include:
-
RedrawRequested
events, used to schedule rendering.macOS for example uses a
drawRect
callback to drive rendering within applications and expects rendering to be finished before thedrawRect
callback returns.For portability it’s strongly recommended that applications should keep their rendering inside the closure provided to Winit.
-
Any lifecycle events, such as
Suspended
/Resumed
.The handling of these events needs to be synchronized with the operating system and it would never be appropriate to buffer a notification that your application has been suspended or resumed and then handled that later since there would always be a chance that other lifecycle events occur while the event is buffered.
§Supported Platforms
- Windows
- Linux
- MacOS
- Android
§Unsupported Platforms
- Web: This API is fundamentally incompatible with the event-based way in which Web browsers work because it’s not possible to have a long-running external loop that would block the browser and there is nothing that can be polled to ask for new new events. Events are delivered via callbacks based on an event loop that is internal to the browser itself.
- iOS: It’s not possible to stop and start an
NSApplication
repeatedly on iOS so there’s no way to support the same approach to polling as on MacOS.
§Platform-specific
-
Windows: The implementation will use
PeekMessage
when checking for window messages to avoid blocking your external event loop. -
MacOS: The implementation works in terms of stopping the global
NSApp
whenever the applicationRunLoop
indicates that it is preparing to block and wait for new events.This is very different to the polling APIs that are available on other platforms (the lower level polling primitives on MacOS are private implementation details for
NSApp
which aren’t accessible to application developers)It’s likely this will be less efficient than polling on other OSs and it also means the
NSApp
is stopped while outside of the Winit event loop - and that’s observable (for example to crates likerfd
) because theNSApp
is global state.If you render outside of Winit you are likely to see window resizing artifacts since MacOS expects applications to render synchronously during any
drawRect
callback.