Path: utzoo!attcan!uunet!lll-winken!ames!apple!bloom-beacon!ai-lab!tmb
From: tmb@wheaties.ai.mit.edu (Thomas M. Breuel)
Newsgroups: comp.windows.x
Subject: Re: Fast, infinitely undoable graphics.
Message-ID: <2532@wheat-chex.ai.mit.edu>
Date: 20 May 89 02:20:31 GMT
References: <2483@rice-chex.ai.mit.edu> <4243@ficc.uu.net>
Organization: MIT AI Lab, Cambridge, MA
Lines: 13
In-reply-to: peter@ficc.uu.net's message of 19 May 89 15:03:11 GMT

In article <4243@ficc.uu.net> peter@ficc.uu.net (Peter da Silva) writes:
   [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).

Obviously. However, if you have a system that is built on the paradigm
of putting up individual "objects" on the screen such that you can
remove them or manipulate them individually, it doesn't even really
make sense just to draw a rectangle in the background color.

However, you can repeat the same trick of counting pixels for several
"layers" or several "colors" (with the obvious semantics of one layer
shadowing another).