: |> 
: |> XmDrawingArea for drawing with Xlib.  But I would like to take advantage of
: |> the Graphics Library (GL) available on our IBM RS/6000 (SGI's GL i believe).
: |> Is it possible to mix X and GL in one application program?
: |> Can I use GL subroutines in an XmDrawingArea or in an X window opened by me
: |> with XOpenWindow?

You can't make GL calls in an XmDrawingArea widget for sure.  
: 
: There is a widget already defined for GL.  It is the GlxMDraw (motif) or
: GlxDraw (athena) widget.  It is similar to a XmDrawingArea, except that it
: allows you to use GL calls to render into the window.  Look at glxlink,
: glxunlink, glxgetconfig, and glxwinset in the man pages.
: 
: 
: The GlxMDraw widget works pretty well.  OpenGL will be an improvement.

I can vouch for that. The GL Widget works pretty well. I have been using it
for sometime now. I'm not sure though whether you can use Xlib calls to draw
into the GL widget. I haven't tried it yet nor have I read the accompanying
documentation completely. Try posting to comp.sys.sgi for more information.
Better still,you will find most of the answers in the  SGI manuals .. there
is a little transition guide which explains the "mixed-model programming"
paradigm(Mixing X and GL).

: |> Does PEX (graPHIGS?) have the same functionality of GL?
: 
: I think GL is a little easier to use and a little more powerful, but
: that's just an opinion.  Mileage may vary.

Well, PEX is designed as an extension to  X and will be more seamless  but 
then, it is buggy to start with .. opinions again.

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