compiz - May 2008 - X11 clients relying on Xdamage events with compiz?

Taking this here as per delfick's suggestion on the forum....

I'm working on this application that relies on Xdamage events for
notification about screen changes.

It seems compiz (and beryl, and prolly any other compositing window
mgr.) breaks the contract that (1) getting the event, (2) subtracting
the damage, and (3) XSync'ing the display ensures the change will
actually have been painted on screen. The change may appear on screen at
some later time (depending on animation) and may also occur in areas
well outside the damaged rectangle.

While I'm wondering whether it's good to break that contract, is there
any other way for an application external to compiz to retrieve the
information about areas on-screen which have changed and have those
changes already painted?

TIA,

Karl.