Opening a Window on keyboard_input.just_pressed makes it trigger again

[DasLixou]

Bevy version

0.13

[Optional] Relevant system information

Windows 11

What you did

I made a system similar to the one in the keyboard_input example. But on the check whether the key A was just pressed, I then spawn a window.

fn spawn_debug_window(input: Res<ButtonInput<KeyCode>>, mut commands: Commands) {
    if input.just_pressed(KeyCode::F1) {
        info!("just pressed");
        commands.spawn(Window {
            title: "Debug".to_owned(),
            ..Default::default()
        });
    }
}

What went wrong

It spams opening new windows, the just_pressed is held for multiple frames.
I think this happens because it opens a new window, thus the focus is on the new window and the press counts as a new press?

2024-03-03T11:54:46.916247Z  INFO my_project::debug: just pressed
2024-03-03T11:54:46.930608Z  INFO bevy_winit::system: Creating new window "Debug" (25v4)
2024-03-03T11:54:46.967434Z  INFO my_project::debug: just pressed
2024-03-03T11:54:46.974474Z  INFO bevy_winit::system: Creating new window "Debug" (27v1)
2024-03-03T11:54:47.014095Z  INFO my_project::debug: just pressed
2024-03-03T11:54:47.036982Z  INFO bevy_winit::system: Creating new window "Debug" (29v1)
2024-03-03T11:54:47.078519Z  INFO my_project::debug: just pressed
2024-03-03T11:54:47.119463Z  INFO bevy_winit::system: Creating new window "Debug" (31v1)

[SpecificProtagonist]

When a new window is spawned, winit sends a key released event for to the old window and a key pressed event to the new one (tested without Bevy too).

I'm not sure if that's intentional. If not, we need to crate an issue in the winit repo; if it is, we need to work around this by ignoring key release events if in the same frame a window has been created and a key press event for the same button gets received.

Edit: These event happen when a window loses/gains focus. They have the is_synthetic flag set in that case. There's currently a discussion on whether winit should keep synthetic events: rust-windowing/winit#3543

So just_pressed and just_released are bugged. They trigger not just when the key was just pressed/released but also when focus was gained/lost with the key pressed.

We could just ignore synthetic events ourselves. The problem is that the button state can change while no Bevy window is focused. I think it might be best to wait until Bevy gains focus again to check whether to emit those events, and maybe keep the current behavior as a separate function.