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From: nancie@hal.CSS.GOV (Nancie Matson)
Newsgroups: comp.windows.x
Subject: Combining Two drawables (Pixmaps)
Message-ID: <436@hal.CSS.GOV>
Date: 29 May 90 18:42:44 GMT
Article-I.D.: hal.436
Reply-To: nancie@hal.css.gov (Nancie Matson)
Organization: ENSCO Inc., Melbourne FL
Lines: 30

This is probably a novice question, but I would like to know
how to go about combining two Pixmaps (drawables) on the
screen.  I have a map generated by drawing an XImage structure
into a Pixmap and using the XCopyArea function drawing it to 
the window.  Now I have another drawable with some reference
lines that I would like to "overlay" onto the first Pixmap.
Both are in color and each time I try to use the XOR function
I get the reference lines appearing in all black.

Is it possible to XOR two Pixmaps and still retain the colors?
It seems to work great with Black, when I try white, I get
a reverse-video effect where if I have a blue background and
green foreground and try to overlay white lines, I get black
lines wherever there was foreground color and white lines where-
ever there was background color.

Does this make any sense???  If you have any idea what I
may be talking about, Please E-mail your comments.  I have
a lot of "overlays"  that I would like to place on the
map, and I wanted to be able to draw each one in a different
color as well as remove them at any time (that's why I
chose to use XOR).

If this is of any interest to anyone else, I'll be glad to
summarize later on.  Let me know!

Thanx in advance!

-Nancie
nancie@hal.CSS.GOV