From: Vermaas, Joshua (
Date: Thu Apr 13 2017 - 20:53:52 CDT

Alright, I got fed up enough to try and fix this behavior. I failed
miserably at correcting it myself, so instead I have a quickish hack for
others that experience this: copy over OptiX* files from the src
directory of a VMD 1.9.2 install to replace the same files in the src
directory of VMD 1.9.3. This means you'll loose any of the VR-specific
changes made for 1.9.3, since you are effectively going back to the
1.9.2 rendering path. You'll need to patch FileRenderList.C to
accommodate this too.

Instead of:
    if (optixdevcount > 0) {
      // Emit a console message during OptiX renderer instantiation
      // since the JIT compilation and linkage of the 256+ shaders may
      // take several seconds on machines with several GPUs...
      if (vmdapp->nodecount == 1) {
        msgInfo << " Compiling "
                << OptiXRenderer::material_shader_table_size()
                << " OptiX shaders on " << optixdevcount << " target GPU"
                << ((optixdevcount > 1) ? "s" : "") << "..." << sendmsg;

      add(new OptiXDisplayDevice(vmdapp, 0));
      add(new OptiXDisplayDevice(vmdapp, 1, cluster_dev));

You go back to the simpler code from 1.9.2:

    if (optixdevcount > 0) {
      add(new OptiXDisplayDevice(vmdapp, 0));
      add(new OptiXDisplayDevice(vmdapp, 1));

After those changes are made, recompile. Rendering shadows then behaves
correctly when calling the non-interactive renderer. As a happy
accident, VMD startup times are reduced, since there isn't any shader
compilation at startup.


On 03/31/2017 01:25 PM, Vermaas, Joshua wrote:
> Heya folks,
> Has anyone else noticed strange behavior when using ambient occlusion &
> shadows coupled with the TachyonLOptiXInternal renderer in VMD 1.9.3?
> Relative to the Interactive renderer (see screenshots attached), the
> shadow edges look too straight, and are just wrong sometimes (compare
> the edges on the bottom of the rightmost aromatic ring, for example).
> The differences are huge compared to what they used to be in VMD 1.9.2.
> Interestingly the render times have gone down in VMD 1.9.3 as well, so I
> suspect internally its just a matter of not enough rays being cast in
> the current version, but I haven't found the knob to turn to get the
> look I want back. If I'm the only one experiencing this behavior, I can
> just go back to VMD 1.9.2 when I need to render animations, but if I'm
> not, I'd like to see what workarounds other folks have discovered.
> Thanks!
> -Josh Vermaas