how to detect composit manager

[Pat Suwalski]

Dan Winship wrote:
> Yes. The latest CVS version of the EWMH defines a manager selection
> _NET_WM_CM_S0 (for screen 0, _S1 for screen 1, etc). If you're using gtk
> 2.10, you can use gdk_screen_is_composited() to test it. (If not, you
> can look at that code to see how to test it.)

Question: despite what the documentation says, does that function return 
true only when there is a compositing manager running, or just when the 
composite extension is there?

--Pat