[compiz] Question regarding window output extents

[Danny Baumann]

Hi,

in a plugin I am developing with some other people (namely: tabbed
window grouper), we want to paint a glow like effect around the windows.
This is done by adding the glow as "second decoration" around the window
decoration.
The question now is: How can we communicate the fact that there is a
second set of decoration properly to other plugins so that window
damaging and transformation are aware of the glow? 
>From my understanding, the member "output" of the CompWindow structure
is supposed to do exactly that. But its contents get overwritten by the
decoration plugin on every window state change and window
activation/deactivation, so our plugin can't use it (and the function
setWindowFrameExtents) directly because the changes aren't persistent.

Is there a function or struct member I can use to propagate this
properly? Any suggestions are highly appreciated.

Thanks!

Regards,

Danny