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From: rws@EXPO.LCS.MIT.EDU
Newsgroups: comp.windows.x
Subject: Re: How to erase lines and rectangles?
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Date: 17 Jul 89 15:21:41 GMT
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If your application is only using two colors, you can use the function
GXxor or GXinvert to "undo" graphics.  If you are using more, it's harder.
Try reading sections 7.4.1 through 7.4.3 in the O'Reilly books, Volume 1
(also found in the R3 distribution in doc/tutorials/color.tbl.ms).