Fullscreen windows - weird behaviour

[Russell Shaw]

Andreas Falkenhahn wrote:
> Hi,
> 
> I have the following setup:
> 
> 1) An entirely black shielding window whose size is always set to the
> dimensions of the current screen. _NET_WM_STATE is set to
> _NET_WM_STATE_FULLSCREEN for this window. This window is used to cover the
> standard parts of the desktop like the task bar at the bottom and possibly
> a menu bar at the top.
> 
> 2) On top of this shielding window is my main window which is usually a
> little bit smaller than the shielding window. The main window is centered
> above the shielding window. To make sure that the shielding window never
> gets in front of my main window, I'm also setting the transient for hint
> like this:
> 
> XSetTransientForHint(display, main_window, shielding_window);
> 
> This is all working fine except in one case: When I change the screen mode
> using XF86VidModeSwitchToMode(). In that case, the taskbar suddenly pops
> up when clicking a little bit at the bottom area of the shielding window.
> This is very weird because the area is clearly occupied by my shielding
> window and mouse clicks shouldn't be passed through to the any other
> window!? How does it come that the task bar suddenly gets notified
> although I'm clearly clicking on the shielding window?
> 
> Is there any way to change this behaviour? I also tried to do an
> XGrabPointer() on my main window but this still doesn't prevent the task
> bar from popping up when clicking in the bottom area of the shielding
> window! Why is that? And why is it only when I change the screen mode
> using XF86VidModeSwitchToMode()? If I don't change the screen mode, there
> is no way to bring up the task bar by clicking on the shielding window.
> But as soon as I change the screen mode, the task bar can be accessed by
> clicking several times on the bottom of the shielding window! Anybody got
> a clue what's going on there?

You could add test code that uses XQueryTree() to find out why.

http://tronche.com/gui/x/xlib/window-information/XQueryTree.html