From: John Stone (
Date: Wed Jun 10 2020 - 09:57:06 CDT

  We have sometimes encountered a situation where the NICE DCV server
software interferes with interactive OptiX rendering for unknown reasons.
The same code runs without trouble on bare metal. But, under DCV I have
sometimes seen the display loop hang inside the DCV OpenGL interposer

When this has occured, I have sometimes had luck restarting
VMD and just repeating the same sequence and the next time it works.

I'm not sure if there's a threading issue in DCV (it gets stuck in a mutex IIRC)
or a bug in it's handling of certain combination of window / GL events,
but I've seen this issue crop up and go away, on and off over a few
generations of their software. We have 20 machines running DCV here,
and only some of them have ever exhibited this behavior.

Another thing you can try when this occurs is to limit VMD to talking
to just one of the GPUs, using VMDOPTIXDEVICEMASK 0x1 (or 0x2), and see
if that affects the behavior. My recollection has been that if I had
OptiX use a non-display GPU (that DCV was ignoring) then the hang never

I haven't had this happen in a while, but try the suggestions above
and see how it behaves.

Best regards,
  John Stone

On Wed, Jun 10, 2020 at 12:22:39PM +0200, Bart Bruininks wrote:
> Dear VMDers,
> When I try to use the GPU accelerated interactive rendering on our
> visualization server I get a black screen. Non-interactive rendering does
> render correctly. Also the CPU rendering (OSPRAY) works fine both
> interactively and non-interactively (though it is always so dark). I am
> not sure if it matters, but the interfacing takes place over a NICE portal
> streaming the screen.
> VMD:
> 1.9.4a42
> Nvidia Drivers:
> NVIDIA-SMI 440.82 Driver Version: 440.82 CUDA Version: 10.2
> GPU's:
> OptiXRenderer) Creating OptiX window: 672 x 805...
> OptiXRenderer) VMD TachyonL-OptiX Interactive Ray Tracer help:
> OptiXRenderer) ===============================================
> OptiXRenderer) Using 2 devices:
> OptiXRenderer) [0] Quadro RTX 8000 CUDA[0], 47.5GB RAM, KTO
> OptiXRenderer) [1] Quadro RTX 8000 CUDA[1], 47.5GB RAM
> Cheers,
> Bart

NIH Center for Macromolecular Modeling and Bioinformatics
Beckman Institute for Advanced Science and Technology
University of Illinois, 405 N. Mathews Ave, Urbana, IL 61801           Phone: 217-244-3349