Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!tektronix!orca!tekecs!bobtl
From: bobtl@tekecs.GWD.TEK.COM (Bob Toole)
Newsgroups: comp.windows.x
Subject: Re: Drawing lines in windows with bitmaps
Message-ID: <11368@tekecs.GWD.TEK.COM>
Date: 3 May 89 21:32:07 GMT
References: <8905022004.AA09962@sae.com>
Reply-To: bobtl@tekecs.GWD.TEK.COM (Bob Toole)
Organization: Tektronix, Inc., Wilsonville, OR
Lines: 12

Sounds like what you need is an overlay plane.

You should be able to use XAllocColorCells with nplanes = 1,
assuming that you can control what pixels are used to build
your colormap.  If you need more than one line color, 
up the number of planes.

Basically, set up your colormap so that the color cells without
the plane bit set are the colors you want in your pixmap,
those with that bit set are your line color.
Then draw and erase your lines with XOR mode 
and foreground value of planemask.