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ui/cocoa: Comment about modifier key input quirks

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Based-on: <20210310042348.21931-1-akihiko.odaki@gmail.com>
Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Message-Id: <20210312133212.3131-1-akihiko.odaki@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
Akihiko Odaki 2021-03-12 22:32:12 +09:00 committed by Gerd Hoffmann
parent eb69442a06
commit ad7f2f8ee9
1 changed files with 37 additions and 1 deletions
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38
ui/cocoa.m
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@ -690,7 +690,43 @@ QemuCocoaView *cocoaView;
NSPoint p = [self screenLocationOfEvent:event];
NSUInteger modifiers = [event modifierFlags];
// emulate caps lock keydown and keyup
/*
* Check -[NSEvent modifierFlags] here.
*
* There is a NSEventType for an event notifying the change of
* -[NSEvent modifierFlags], NSEventTypeFlagsChanged but these operations
* are performed for any events because a modifier state may change while
* the application is inactive (i.e. no events fire) and we don't want to
* wait for another modifier state change to detect such a change.
*
* NSEventModifierFlagCapsLock requires a special treatment. The other flags
* are handled in similar manners.
*
* NSEventModifierFlagCapsLock
* ---------------------------
*
* If CapsLock state is changed, "up" and "down" events will be fired in
* sequence, effectively updates CapsLock state on the guest.
*
* The other flags
* ---------------
*
* If a flag is not set, fire "up" events for all keys which correspond to
* the flag. Note that "down" events are not fired here because the flags
* checked here do not tell what exact keys are down.
*
* If one of the keys corresponding to a flag is down, we rely on
* -[NSEvent keyCode] of an event whose -[NSEvent type] is
* NSEventTypeFlagsChanged to know the exact key which is down, which has
* the following two downsides:
* - It does not work when the application is inactive as described above.
* - It malfactions *after* the modifier state is changed while the
* application is inactive. It is because -[NSEvent keyCode] does not tell
* if the key is up or down, and requires to infer the current state from
* the previous state. It is still possible to fix such a malfanction by
* completely leaving your hands from the keyboard, which hopefully makes
* this implementation usable enough.
*/
if (!!(modifiers & NSEventModifierFlagCapsLock) !=
qkbd_state_modifier_get(kbd, QKBD_MOD_CAPSLOCK)) {
qkbd_state_key_event(kbd, Q_KEY_CODE_CAPS_LOCK, true);