From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Russ Cox" <rsc@plan9.bell-labs.com>
Date: Fri, 29 Sep 2000 10:55:18 -0400
To: 9fans@cse.psu.edu
Subject: Re: [9fans] =?iso-8859-1?Q?R=E9f._:_Re:_[9fans]_Re:_moving_things_in_a_window?=
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	guess you can go a ways with xor :)

I think xor had little to do with it.  You could
do it with the current draw about as easily.
It seems to have come out of the trick of looking at
the color of the pixels in your way to see if
you are going to hit anything, rather than 
keeping higher-level objects.

See http://research.microsoft.com/Users/luca/Papers/Crabs/Crabs.ps