This patch adds root window drawing in rootless mode. Root window drawing is used by several window managers for window outlines during move or resize.
The big transparent window used to show root drawing obliterates Classic windows. This patch keeps track of the drawing on the root, and hides the transparent window when nothing is drawn so Classic is visible.
Tested with twm, windowmaker, and enlightenment with xeyes and xsnow and the window outlines. Tested on Mac OS X 10.0.4 but *not* 10.1. Not tested with multiple screens.
This patch is risky. It may significantly decrease performance. It may crash because of bugs in the dirty region handling. It may break shape support on 10.1 or some 10.0.4 systems.