drawing on the X11 root window with Qt5

[René J. V. Bertin]

Kai Uwe Broulik wrote:

> Note that KWIN doesn't render the X11 root window when compositing is enabled
> so this would be of little use. ‎

Who says this is for use when KWin is active too? :) Even with KWin 5.9.3 
running applications like xscreensaver somehow manage to make the root window 
(and anything drawn thereupon) visible.

R.