X11: how to implement a global hotkey without focusloss - c++

Question

I have a Qt app which grabs a key with XGrabKey. I want my app to show and hide, if I press the hotkey. Additionally it has to hide if it loses focus. This works well with one drawback: The XGrabKeyboard which is used by XGrabKey, generates a FocusIn ans FocusOut event. This implies that, if I press the hotkey when the app is visible, the app receives the FocusOut event, hides and immendiately after that receives the hotkeyevent and shows again.
Can I somehow avoid the X server to generate these focus events?

Answer 1

Diggin deeper for about a few hours I tinkered a solution that feels nice. It uses Qt QWidget::nativeEvent and libxcb. libxcb seems to be the next gen libX11 wrapper. But it is horribly undocumented. Uncool that Qt does not provide the mode of a QFocusEvent. But I guess thats the bane in everything wanting to be platform agnostic.
Note: This is Qt5, Qt4 had stuff like QWidget::x11info()
.h
class Class : public QWidget
{
Q_OBJECT
public:
Class(QWidget *parent = 0);
~Class();
protected:
virtual bool nativeEvent(const QByteArray &eventType, void *message, long *) override;
};
.cpp
/**************************************************************************//**
* #brief Class::nativeEvent
* This special event handler can be reimplemented in a subclass to receive
* native platform events identified by eventType which are passed in the
* message parameter. In your reimplementation of this function, if you want to
* stop the event being handled by Qt, return true and set result. If you
* return false, this native event is passed back to Qt, which translates the
* event into a Qt event and sends it to the widget.
*
* This method is called for every native event. On X11, eventType is set to
* "xcb_generic_event_t", and the message can be casted to a
* xcb_generic_event_t pointer.
*
* #param eventType
* #param message
* #return Indicator if this event shall be stoped being handled further.
*/
bool Class::nativeEvent(const QByteArray &eventType, void *message, long *)
{
if (eventType == "xcb_generic_event_t")
{
xcb_generic_event_t* event = static_cast<xcb_generic_event_t *>(message);
switch (event->response_type & ~0x80)
{
case XCB_FOCUS_IN: {
xcb_focus_in_event_t *fe = (xcb_focus_in_event_t *)event;
if (fe->mode & (XCB_NOTIFY_MODE_GRAB|XCB_NOTIFY_MODE_UNGRAB)){
return true; // Ignore this events
}
break;
}
case XCB_FOCUS_OUT: {
xcb_focus_out_event_t *fe = (xcb_focus_out_event_t *)event;
if (fe->mode & (XCB_NOTIFY_MODE_GRAB|XCB_NOTIFY_MODE_UNGRAB)){
return true; // Ignore this events
}
break;
}
}
}
return false;
}

Answer 2

I don't think so, but you can check the "mode" field in the XFocusChangeEvent. It can be NotifyNormal, NotifyWhileGrabbed, NotifyGrab, or NotifyUngrab. Grabbing keys should generate events with the last two modes, and so you may choose to ignore events with these modes, though I'm not sure how you would do that with Qt.