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From: klee@wsl.dec.com (Ken Lee)
Newsgroups: comp.windows.x
Subject: Re: Combining Two drawables (Pixmaps)
Message-ID: <4589@bacchus.dec.com>
Date: 30 May 90 00:33:15 GMT
References: <436@hal.CSS.GOV>
Sender: news@decwrl.dec.com
Reply-To: klee@wsl.dec.com
Organization: DEC Western Software Laboratory
Lines: 17

In article <436@hal.CSS.GOV>, nancie@hal.CSS.GOV (Nancie Matson) writes:
> Is it possible to XOR two Pixmaps and still retain the colors?

This is a fairly common graphics problem.  Simple binary logic
functions like XOR are not usually appropriate when dealing with
multi-bit color pixel values.  A little arithmetic with your pixels
will show you why.  There are 2 ways to work around this.  First, you
can use images and whatever logic you want to combine pixels.  Second,
you can prepare your colormap so that the logic functions give you the
results you want.  The second technique is much faster and is commonly
used with CAD applications.  Any good computer graphics text should
have examples of such colormaps.

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