I can't see any bug in your test program right now. But I also can't explain it.
If the root window was constantly getting damaged though, Show Repaint would be flashing the whole screen and Compiz' CPU would be higher.
I see two possible explanations:
1. A bug in your program (which I can't see)
2. Compiz is choosing to ignore damage to the root window (which I doubt, because it does smoothly respond to root window redraws)
Both seem quite unlikely. Maybe there's a third explanation... ?
I can't see any bug in your test program right now. But I also can't explain it.
If the root window was constantly getting damaged though, Show Repaint would be flashing the whole screen and Compiz' CPU would be higher.
I see two possible explanations:
1. A bug in your program (which I can't see)
2. Compiz is choosing to ignore damage to the root window (which I doubt, because it does smoothly respond to root window redraws)
Both seem quite unlikely. Maybe there's a third explanation... ?