Wrong virtual keycode in WindowEvent from Alt key while holding Shift on X11

[Bakutomo]

Platform:

X11 on Linux

Steps to reproduce:

1. cargo run --example window | grep KeyboardInput
2. hold either shift key down
3. press or release the alt key

Expected result:

A WindowEvent with virtual_keycode: Some(LAlt)

Actual result:

A WindowEvent with virtual_keycode: None

The below output is from the input sequence:
press LShift, press LAlt, release LShift, release LAlt

DeviceEvent { device_id: DeviceId(X(DeviceId(12))), event: Key(KeyboardInput { scancode: 42, state: Pressed, virtual_keycode: Some(LShift), modifiers: (empty) }) }
WindowEvent { window_id: WindowId(X(WindowId(117440513))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 42, state: Pressed, virtual_keycode: Some(LShift), modifiers: SHIFT }, is_synthetic: false } }

DeviceEvent { device_id: DeviceId(X(DeviceId(12))), event: Key(KeyboardInput { scancode: 56, state: Pressed, virtual_keycode: Some(LAlt), modifiers: SHIFT }) }
WindowEvent { window_id: WindowId(X(WindowId(117440513))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 56, state: Pressed, virtual_keycode: None, modifiers: SHIFT | ALT }, is_synthetic: false } }

DeviceEvent { device_id: DeviceId(X(DeviceId(12))), event: Key(KeyboardInput { scancode: 42, state: Released, virtual_keycode: Some(LShift), modifiers: SHIFT | ALT }) }
WindowEvent { window_id: WindowId(X(WindowId(117440513))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 42, state: Released, virtual_keycode: Some(LShift), modifiers: ALT }, is_synthetic: false } }

DeviceEvent { device_id: DeviceId(X(DeviceId(12))), event: Key(KeyboardInput { scancode: 56, state: Released, virtual_keycode: Some(LAlt), modifiers: ALT }) }
WindowEvent { window_id: WindowId(X(WindowId(117440513))), event: KeyboardInput { device_id: DeviceId(X(DeviceId(3))), input: KeyboardInput { scancode: 56, state: Released, virtual_keycode: Some(LAlt), modifiers: (empty) }, is_synthetic: false } }

Note that the virtual_keycode in DeviceEvent is correct. Only WindowEvent is affected. The same problem also happens if I hold RShift instead of LShift.

[murarth]

The root cause of the problem is simple: On X11, winit uses an X KeySym value to determine which VirtualKeyCode to assign. X tells winit that the Alt key has a different keysym value when the Shift modifier is set. (Modifier state is not taken into account for DeviceEvent keysym lookup, which is why the virtual keycode is accurate for device events.)

Unfortunately, the solution is not so simple. winit could translate Shift+Alt keysyms to LAlt and RAlt, but I'm not sure whether that would be accurate for every possible environment. (These keysyms correspond to XK_Meta_L and XK_Meta_R on my system.)

Alternatively, winit could ignore modifier state altogether when assigning a key event's virtual keycode, but this has wider implications. There was some discussion on #812 about changing how winit determines virtual keycode, but it seems that no conclusions were reached.

[alice-i-cecile]

Reproduced in Leafwing-Studios/Emergence#342.

[kchibisov]

not an issue anymore iirc.