Fix: Handle AltGr on Windows

[hunger]

AltGr on windos sends a left control pressed followed by AltGr pressed on both winit and Qt. On AltGr release it sends left control released followed by AltGr released.

So unset left control on windows once AltGr is pressed to avoid treating special characters entered via AltGr key combos to be treated as control sequences -- leading to the input being ignored!

Fixes: #2933

[ogoffart]

I searched a bit on the internet why this would happen.
Is it true that on windows (in other apps than slint) doing Ctrl+alt+something is the same as Altgr+something? And Altgr just maps to ctrl+alt. If that's the case, we also should support the ctrl+alt =Altgr

[hunger]

Yes, I originally read that, too, but the information seems outdated by now.

In Window::dispatch_event(...) I get the following values on Windows 11, both with winit and Qt:

Key	value	comment
Ctrl (left)	\u{11}
Win	\u{17}
Alt	\u{12}
AltGr	\u{11} + \u{13}	That's via two separate key press/release events.
Ctrl (right)	\u{16}

Ignoring that "stray" \u{11} seems like an acceptable solution, even thought that theoretically breaks Ctrl-AltGr-X key combos.

[ogoffart]

So in a native Windows application, if you press "Ctrl + (left) Alt + Q", you don't get a "@" on your German keyboard ?

[hunger]

Oh! Ctrl-Alt-q indeed prints @, just as AltGr-q does. What a strange OS this is! No wonder Ctrl-Alt shortcuts are rarely used ;-)

[hunger]

New and improved! Now treats Alt-Ctrl as AltGr (by disabling the relevant flags in the modifier state).

[ogoffart]

assuming you tested that it works as expected with all combination

[hunger]

I did test Alt-CtrlL and AltGr. I did not test Alt-CtrlR :-( What kind of platform would even start to treat all those key combos the same?!

I am now wondering whether there are keyboards with a right Alt key.

[ogoffart]

I am now wondering whether there are keyboards with a right Alt key.

I think there are, but its probably usually mapped to altgr

[hunger]

OK, this is what I tested this time round (using a german keyboard layout):

key combo	windows terminal	Slint Gallery Text Edit
CtrlL-q	^Q
CtrlR-q	^Q
AltR-q	q	q
AltR-Shift-q	Q	Q
AltGr-q	@	@
CtrlL-AltL-q	@	@
CtrlL-AltL-Shift-q	^Q
CtrlR-AltL-q	@	@
CtrlL-CtrlR-AltL-q	@	@
CtrlL-CtrlR-AltL-AltGr-q	@	@
CtrlR-AltGr	@	@
CtrlL-AltGr	@	@

I think that should cover the option space... AltGr is AltR according to Wikipedia, so we should not need to cover that in Windows -- and we do anyway by using alt().