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From: swick@ATHENA.MIT.EDU (Ralph R. Swick)
Newsgroups: comp.windows.x
Subject: Re: setting a clip region in a shared GC
Message-ID: <8909081751.AA01781@LYRE.MIT.EDU>
Date: 8 Sep 89 17:51:21 GMT
References: <9050@zodiac.ADS.COM>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: DEC/MIT Project Athena
Lines: 20

> Which (if any) of the following statements is
> correct?
>
> 1. A widget may alter the clip region in a shared GC.

not without additional constraints.

> 2. A widget may briefly alter a shared GC, but must undo any changes
> it makes immediately after using them.

This works just fine as long as you're single-threaded and is
an acceptable approach.  "Immediately after using them" should
be interpreted as "before returning from the procedure which
made the modification".  [If you've gotten things to work in
a multi-threaded environment, let us know! :-)]

> 3. A widget may never alter a shared GC.

Has the combinatorial problem that you point out, so the
"leave-it-as-you-found-it" rule is generally to be preferred.