Path: utzoo!attcan!uunet!ficc!peter
From: peter@ficc.uu.net (Peter da Silva)
Newsgroups: comp.windows.x
Subject: Re: Fast, infinitely undoable graphics.
Message-ID: <4243@ficc.uu.net>
Date: 19 May 89 15:03:11 GMT
References: <2483@rice-chex.ai.mit.edu>
Organization: Xenix Support
Lines: 13

[keep a count of the number of times the bit has been set]

This doesn't work if you ever draw anything with color 0 (i.e., erase).

Let's say you draw a black square, and then erase a letter 'A' in the
middle of it. What do you do with the bits you cleared? Either you leave
the count alone (and have no record of the 'A'), or you decrement it (and
have an inaccurate record of the resulting square).
-- 
Peter da Silva, Xenix Support, Ferranti International Controls Corporation.

Business: uunet.uu.net!ficc!peter, peter@ficc.uu.net, +1 713 274 5180.
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