From: John Stone (
Date: Tue Sep 14 2004 - 21:35:21 CDT

  The reason OpenGL programmable shading is disabled in 64-bit mode
on your NVidia card on Linux AMD64 is because the current version of the
64-bit NVidia drivers return a NULL pointer for one of the required
OpenGL extension functions needed for programmable shading to work.
This was in fact one of the causes of the crashing that occured in
previous versions. VMD now contains explicit checks for this bogus
behavior and will disable programmable shading rather than crash, which
is the only alternative :-) I suspect this is a minor mix-up in NVidia's
drivers, and I'd expect them to fix it in a subsequent release. I don't
know how many other apps are already using GLSL, VMD is pretty
bleeding-edge in that regard, so NVidia probably hasn't tested their
drivers thoroughly on this. All of the other OpenGL extensions appear
to work ok on the 64-bit NVidia drivers so far. If any other problems
like this one crop up, this latest version of VMD contains special code
to allow one to set an environment variable to prevent VMD from using
OpenGL features that are broken in buggy graphics drivers, so if this
sort of thing comes up again, I can just give you an environment variable
to set rather than recompiling the code to avoid the buggy video driver's
problem :-)

  John Stone

On Tue, Sep 14, 2004 at 06:48:44PM +0000, Jerry Ebalunode wrote:
> Hi John,
> First thanks for resolving this problem. The nvidia driver now works with a23
> release of vmd for my Linux AMD64.
> However opengl shading is not available, probably because the vmd does not see
> this feature on my FX 5600 XT card. When I boot the same machine to run in
> 32 bit linux os, opengl shading is available for this card.
> Thanks again for tuning vmd code to work with the flaky nv drivers in 64 bit
> mode.
> On Tuesday 14 September 2004 09:49 pm, John Stone wrote:
> > Hi,
> > I've just found and fixed a bug in the AMD64 builds of VMD
> > and written a workaround for bugs in the current NVidia AMD64
> > drivers that caused the 64-bit Opteron builds of VMD to crash
> > on the newest generation NVidia cards. (NVidia's driver provides
> > false information about the availability of one of the OpenGL
> > shading language extensions, which had been making VMD crash
> > on the higher-end FX-series cards..) The new code no longer
> > trusts the OpenGL driver and now double-checks everything
> > it gets back from the video driver.
> >
> > I've just been running the new code on a demo box we have in the lab
> > and it seems to run quite well now. Anyone else that's interested in
> > testing VMD 1.8.3 on Opteron can download the new binary here:
> >
> >
> > John Stone
> >
> --
> Jerry Ebalunode
> Ph.D. Candidate
> RM 402F Houston Science Center
> Phone: 713-743-8367
> Dept. of Biology and Biochemistry
> University of Houston
> 4800 Calhoun Road
> Houston, TX 77204

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