Implement WindowEvent ModifiersChanged for X11 and Wayland

[murarth]

• Tested on all platforms changed
• Compilation warnings were addressed
• cargo fmt has been run on this branch
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

[elinorbgr]

LGTM for the wayland part, cannot tell for the x11 one.

[goddessfreya]

ModifiersState seams to be functional on X11, but I don't think I ever saw the ModifierChanged event. but ModifierChanged didn't seam to be consistently showing up. but ModifierChanged didn't update when you moved your mouse off the window, so you couldn't know that the keys were released/held.

$ cargo run --example window | grep "EventsCleared\|NewEvents\|Keyboard\|Modifier"
<SNIP>
NewEvents(WaitCancelled { start: Instant { tv_sec: 167749, tv_nsec: 641587350 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 42, state: Pressed, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }) }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 42, state: Pressed, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } } }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: ModifiersChanged { device_id: DeviceId(X(DeviceId(3))), modifiers: ModifiersState { shift: true, ctrl: false, alt: false, logo: true } } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 167749, tv_nsec: 817716417 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 42, state: Released, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }) }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 42, state: Released, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: true, ctrl: false, alt: false, logo: true } } } }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: ModifiersChanged { device_id: DeviceId(X(DeviceId(3))), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 167750, tv_nsec: 737497331 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 125, state: Pressed, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }) }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 125, state: Pressed, virtual_keycode: None, modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 167750, tv_nsec: 969649256 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 42, state: Pressed, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }) }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 42, state: Pressed, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } } }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: ModifiersChanged { device_id: DeviceId(X(DeviceId(3))), modifiers: ModifiersState { shift: true, ctrl: false, alt: false, logo: true } } }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 167754, tv_nsec: 873709305 }, requested_resume: None })
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 16, state: Pressed, virtual_keycode: Some(Q), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }) }
EventsCleared
NewEvents(WaitCancelled { start: Instant { tv_sec: 167754, tv_nsec: 876675192 }, requested_resume: None })
EventsCleared

Moving your mouse onto the window, pressing the keys, moving it off, removing the keys made ModifiersState permanently loose sync.

$ cargo run --example window | grep -v "Cursor" | grep "Keyboard\|Modifier\|ModifiersChanged"
<SNIP>
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 42, state: Pressed, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }) }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 42, state: Pressed, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } } }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: ModifiersChanged { device_id: DeviceId(X(DeviceId(3))), modifiers: ModifiersState { shift: true, ctrl: false, alt: false, logo: true } } }
DeviceEvent { device_id: DeviceId(X(DeviceId(10))), event: Key(KeyboardInput { scancode: 42, state: Released, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: false } }) }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 42, state: Released, virtual_keycode: Some(LShift), modifiers: ModifiersState { shift: true, ctrl: false, alt: false, logo: true } } } }
WindowEvent { window_id: WindowId(X(WindowId(58720257))), event: ModifiersChanged { device_id: DeviceId(X(DeviceId(3))), modifiers: ModifiersState { shift: false, ctrl: false, alt: false, logo: true } } }

---

Also, shouldn't we distinguish between Left and Right shift/alt? Seams a shame we don't track them separately.

[murarth]

I've addressed the issue with modifier desync when switching windows in what I believe is the most reasonable way: When a window goes out of focus, a ModifiersChanged event is reported to the window indicating that all modifier keys are released. When a window comes into focus, a ModifiersChanged event is reported indicating any modifiers currently held. (Of course, in each of these cases, if there are no modifiers set, no event is reported.)

While this may not reflect the "true" modifier state for the user's window manager environment, it simplifies the logic required by winit to keep modifier state correct. A more "accurate" solution would require tracking last known modifier state for each open window -- increasing complexity and the potential for bugs. The most "accurate" solution would even require updating out-of-focus windows for every DeviceEvent, which would be far more complex and would create the potential of a panic due to internal RefCell borrowing.

I think the solution I've implemented will be sufficient for most applications.

[murarth]

Fixed the CI errors by running cargo fmt. Is there anything else holding this back?

[goddessfreya]

When ControlFlow is Wait, keyboard events are only reported when the mouse is moved, which leaves ModifiersChanged desynced until the mouse goes back onto the window. This keyboard delay was also reproduced on master, however, so it is not caused by this PR. LGTM.

[goddessfreya]

The keyboard delay was being "caused" by stdout being buffered... What a false positive. (Took a good half hour to figure out...)