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From: klee@wsl.dec.com (Ken Lee)
Newsgroups: comp.windows.x
Subject: Re: question on using GC Functions for levels of overlap
Keywords: Graphical Context
Message-ID: <1991Apr18.110603@wsl.dec.com>
Date: 18 Apr 91 18:06:03 GMT
References: <1991Apr18.013051.24770@iscnvx.uucp>
Sender: news@pa.dec.com (News)
Reply-To: klee@wsl.dec.com
Organization: DEC Western Software Laboratory
Lines: 17

In article <1991Apr18.013051.24770@iscnvx.uucp>, greggw@iscnvx.uucp (William E. Gregg) writes:
|> Can anyone give me some ideas on drawing overlapping objects on the screen
|> in such a way that the colors indicate the level of overlap (i.e. single,
|> double, triple, ...).

Most college text books on raster graphics describe techniques for
setting up a colormap to do what you want.  The idea is to chose your
pixel values so that addition and subtraction do intelligent things.
These techniques were pretty popular in early CAD and image processing
applications, but are not well supported in many modern window systems
(other than X).

-- 
Ken Lee
DEC Western Software Laboratory, Palo Alto, Calif.
Internet: klee@wsl.dec.com
uucp: uunet!decwrl!klee