According to http://www.x.org/releases/X11R7.6/doc/libX11/specs/libX11/libX11.html#VisibilityNotify_Events "A region of a window is visible if someone looking at the screen can actually see it.". Thus it makes sense for VisibilityNotify events to be fired when the screen blanks due to DPMS. I understand VisibilityNotify events on screensaver or on window obscuration are only possible with a non-compositing window manager but some kind of event must be possible when putting the display into a DPMS mode, right?
There's some circumstancial evidence that this used to work - e.g. http://lists.kde.org/?l=kwin&m=125068441515308&w=2 - although I haven't been able to find any old fedora livecds where this works.
How to reproduce:
I used the script in http://stackoverflow.com/questions/1667525/visibility-notify-event-in-pygtk to show VisibilityNotify events. I see events when hiding the window or locking the screen with a non-compositing kwin, as expected. But I see no events with either a compositing or non-compositing kwin after 'sleep 10; xset dpms off'.
Whatever these bugs are, they are probably not libXext's fault.
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