Key repeat event has very high input lag on Windows

[arialpew]

With Winit v0.29.3 and Windows 11 24H2 build 26100.2605, the key repeat event is slow to be dispatched.

While running a game at 60 FPS, I can see between 20 and 30 frames lag between the keypress event and the keydown event (a keydown event is a pressed event with repeat = true).

A simple reproduction would be :

• Create a Rust program with Winit v0.29.3.
• Create an event loop.
• Inside the callback of EventLoop::run_on_demand, match against key event and print a message. Set control flow to ControlFlow::Pool with EventLoopWindow::set_control_flow, to immediately begin new iteration.
• Run the program and press a key but don't release it. You'll see how laggy it is for the second event to pop-in (state = Pressed, repeat = true), while the first event is near instant (state = Pressed, repeat = false). Releasing the key (state = Release, repeat = false) is also instant.

Event::WindowEvent {
    event:
        WindowEvent::KeyboardInput {
            event:
                KeyEvent {
                    state,
                    logical_key,
                    repeat,
                    ..
                },
            ..
        },
    ..
} => {
  println!("Event !");
}

The expected behavior is to get near instant feedback for all of theses events.

Edit : Also, some events are lost while the key is still being hold. To see this in practice, you buffer all the inputs and print the whole buffer inside Event::WindowEvent { event: WindowEvent::RedrawRequested, .. }, and then clear the buffer. Don't forget to add a redraw request inside Event::AboutToWait.

You'll see that some frame have empty input buffer even when the key is hold. I would expect the buffer to be refill between each RedrawRequested since the key is hold, but maybe I'm misunderstandingsome how it should be scheduled.

My setup involve Vulkan, FIFO/MAILBOX and triple buffering. I hope this isn't related because it's not that easy to debug tbh.

I don't know if v0.30 fix this, I'll test later.

Note : probably related, hard to say. The issue surface on both FIFO/MAILBOX on my app - #2127