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From: rws@EXPO.LCS.MIT.EDU (Bob Scheifler)
Newsgroups: comp.windows.x
Subject: Re: Exposures, a couple of questions.
Message-ID: <8904051207.AA12395@EXPIRE.LCS.MIT.EDU>
Date: 5 Apr 89 12:07:34 GMT
References: <8904051022.AA02635@westhawk.uucp>
Sender: daemon@bloom-beacon.MIT.EDU
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    How can the widget tell if it is partially obscured, and
    thus know to use the more expensive drawing strategy?

You can track VisibilityNotify events, but this isn't the right solution.

    Alternatively is there a better way of tackling the problem?

You can use GraphicsExpose/NoExpose events (generated by the XCopyArea)
to tell when this does/doesn't happen.