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From: epstein@trwacs.UUCP (Jeremy Epstein)
Newsgroups: comp.windows.x
Subject: Window visibility question
Message-ID: <206@trwacs.UUCP>
Date: 2 May 90 14:19:41 GMT
Organization: TRW Systems Division, Fairfax VA
Lines: 42

I'm looking for a way to calculate which portions of a window are
visible and which are obscured.  I know that expose events will
tell me what I need to redraw, but I need to know when the window
becomes obscured, *not* when it is exposed.

Is there any mechanism in X11R4 to do this?  I've come up with some
hacky solutions (see below), as well as some ideas for extensions
to the protocol, but nothing simple or elegant.




Some ideas I've come up with (perhaps there's a refinement that would
make one of these reasonable?):

(1)	Visibility events provide some assistance, however they only record
	state changes between three states (totally visible, partially visible,
	and totally obscured), plus they don't report what areas are obscured.
	One possible solution is to extend visibility events so they report
	all partial obscuring, and add the (x,y,width,height) values of what
	was obscured.  Then using visibility events with expose events would
	be sufficient.

(2)	Another possibility is to periodically do XQueryTree() operations,
	and examine the placement and geometry of all windows higher in the
	stacking order.  This makes it fairly easy to figure out what areas
	are obscured.  The converse (what areas are visible) is somewhat
	more difficult, but still possible.  However, it still doesn't solve
	the problem of when to do the XQueryTree() operations, since there's
	no notification of new window creation.

(3)	By setting up for CreateWindow and MapWindow events I could be
	notified of all windows which are created, and then use the
	XQueryTree method as described above.  Of course, I'd probably also
	need to track resizing, window destruction, configuration, etc.

Any better solutions, please????
-- 
Jeremy Epstein
epstein@trwacs.uu.net
TRW Systems Division
703-876-8776