From: John Stone (
Date: Tue Oct 19 2021 - 13:27:56 CDT

  There are lots of things coming in new VMD builds.

One of the new features that I know many people are
interested in is a new VMD full-time ray tracing display mode
that currently runs on NVIDIA GPUs, and allows you to
use interactive ray tracing in the main VMD graphical
interface full-time. Something that the new display mode
enables for the first time is the ability to animate
a trajectory while also using ray tracing features like
shadows, ambient occlusion lighting, etc.

The new display mode is primarily designed to target
molecular scenes from structures of up to about one million
atoms or thereabouts. The RTRT rendering performance
depends greatly on whether there are reflective or
transmissive (transparent) objects in the scene, as they
have a mauch stronger impact on performance than atom
count does.

Unlike OpenGL, the new RTRT display mode requires that the
entire VMD molecular scene as well as associated ray tracing
acceleration structure (bounding volume hierarchy) can fit
in the on-board GPU memory. This means that older GPUs that
have less than 6GB of memory are not well suited to RTRT mode.
For the best results, I recommend using recent NVIDIA GPUs
such as the original "Turing" RTX GPUs, or the most recent
"Ampere" GPU generation, although the new code will currently work
on any GPU generation all the way back to "Maxwell" (9xx series).

For the time being, I'm calling this display mode
"Tachyon RTX RTRT" (RTX real-time ray tracing), because
it is currently specific to NVIDIA GPU hardware.
In VMD builds where it is available, it is listed in the
Display -> Rendermode menu, as "Tachyon RTX RTRT", and
is the menu entry immediately following "GLSL".

In the current VMD RTRT test build, not every display primitive
is implemented in the interactive ray tracing code path, so
if/when you encounter those cases, you can just switch back
to "Normal" or "GLSL" when needed. This is primarily an issue
when rendering things like lines and points, that don't have
a directly analogous implementation in a ray tracing engine.
I'm expecting the RTRT implementation to continue to progress
rapidly in the next several weeks, and that user feedback about
bugs and existing limitations will be helpful.

At present I have made the first RTRT-enabled VMD builds
for 64-bit Linux, although I expect that I will also be able to
make a 64-bit Windows build available at a later time.

The first RTRT test build is posted here, at the top of the
alpha build page you'll see when you login:

Best regards,
  John Stone

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