RE: Any tips for using GLUT

["Champigny, Michael" <Michael Champigny compaq com>]

Blake,

Unfortunately, most X servers don't support INDEX mode in
bit depths over 8. When you think about it, you'd need
a color LUT of 2^16 entries for a 16-bit indexed visual. 
You wouldn't have the memory to contain that many cells!
For that reason, larger bit depths use a different visual.
For a 16-bit visual, usually the first 5 bits is the red
component, 6 bits for green, and the last 5 for blue. You
get this in GLUT via GLUT_RBG. 

This is an X server limitation. Some X servers allow overlays
so that you can overlay an 8-bit window over a 16-bit display.

I'm afraid you'll have to port your INDEX mode app to RGB mode.
This is why the OpenGL handbook recommends never using INDEX
mode in the first place.

I hope that helps,

Michael 

-----Original Message-----
From: Blake L. Carlson [mailto:blake-carlson@uiowa.edu]
Sent: Wednesday, October 13, 1999 6:27 PM
To: Champigny, Michael
Subject: Re: Any tips for using GLUT


Michael -

I've tracked down the bug to this GLUT init command:

      glutInitDisplayMode( GLUT_INDEX | GLUT_DOUBLE );

It seems that indexed mode is not working on my system. I know that this
initialization command does work:

      glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE );

(See /usr/lib/Mesa-3.0/demos/drawpix.c if you have the Mesa demos
installed)

We really need the GLUT_INDEX mode, otherwise I'm going to have to do a
major overhaul in some of our SGI libraries to port to alpha.  

Does this stir up any memories???

- Blake



Michael.Champigny@compaq.com wrote:
> 
> I've seen this "bug" appear on Tru64 UNIX so it's not Linux
> specific. It usually happens when the colormap is being maxed
> out. I don't remember how I fixed it...sorry I can't be more
> specific, but at least you know your not alone. :-) By the
> way, it also happens on NT but the colormap there seems to
> go further.
> 
> /Michael
> 
> -----Original Message-----
> From: Blake Carlson [mailto:blake-carlson@uiowa.edu]
> Sent: Wednesday, October 13, 1999 3:30 PM
> To: axp-list@redhat.com
> Subject: Any tips for using GLUT
> 
> Hello again -
> 
> While I have your attention, I'll ask if anyone has had any trouble
> getting GLUT to work.  I have a program that uses GLUT and works great
> on the SGI's.  Everything compiles okay on the alphalinux machine, but
> when I execute the program GLUT complains that the visual class is not
> sufficient (or some error similar).  Do I need to tweak X in some way to
> get this to work??
> 
> (I don't know if this question is alphalinux or just plain linux
> specific???)
> 
> Thanks -
> 
> Blake
> 
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