From: Tristan Croll (
Date: Wed Feb 11 2015 - 15:07:43 CST

Hi John,

Somewhat oddly, this morning (without actually having shut down the machine) I can't seem to reproduce these issues. The interactive renderer now works fine when I close the window, and while the points still resolve as large spheres (each roughly 200 pixels diameter in a 1600 x 1500 OpenGL window) the system is handling the load fine. No idea why because I didn't actually close anything other than VMD itself before leaving it. For the record, this is on an Intel i915 GPU for display / GTX970M for CUDA, driving a somewhat ridiculous native screen resolution of 2880 x 1620 - so it wouldn't surprise me if I was simply running into memory issues. OS is Fedora 21, and up-to-date as of last week. Oh, and it is a final-release copy of VMD 1.9.2.



From: John Stone <>
Sent: Thursday, 12 February 2015 2:12 AM
To: Tristan Croll
Subject: Re: vmd-l: Handful of rendering issues


On Wed, Feb 11, 2015 at 11:15:19AM +0000, Tristan Croll wrote:
> Hi there,
> I have a few minor rendering-related issues/suggestions in VMD 1.9.2:
> - If I have an isosurface visualised in the default point representation
> and switch to GLSL rendermode, every point becomes a VERY large sphere and
> the system slows to a crawl.

What kind of GPU are you using? The point rendering in this case should be
relatively harmless on a normal GPU. I wonder if there's a bug in the video
driver affecting you there.

> - When a wireframe is rendered in Tachyon the lines are of course replaced
> by thin cylinders. This works out nicely in the CPU-only Tachyon
> (particularly if I use a transparent material, yielding a nicely
> unobtrusive mesh), but the cylinder diameter is much larger in
> Tachyon-OptiX. Is it possible to shrink this, or is this one of the
> trade-offs that allows the renderer to be so blazingly fast?

There are still a lot of minor differences between the full Tachyon and the
"light weight" GPU-accelerated version that I've implemented in VMD.
The behavior of line rendering on the GPU version leaves something to be
desired, I hope to improve that in the next release, and I will also
implement some of the missing features such as 3-D texturing and
user-defined clipping planes, which are not implemented in the GPU ray tracer
up to this point.

> - When using the interactive renderer, closing the rendering window with
> the mouse rather than pressing Esc or q crashes VMD.

This works fine for me using the final version of VMD 1.9.2.
If you're running a pre-release test version of VMD, you should upgrade
to the final release. If you're running the final version of VMD 1.9.2,
then I'm going to need to know a lot of other details about your machine,
such as what OS version you're running, what window manager, and so on.
The only way I've found to create a scenario similar to what you describe
is to use "xkill" on VMD, which terminates the program abruptly (but that's
the whole point of xkill, so I don't see that as wrong behavior).

> - I think it would be awesome if the interactive renderer had an option to
> render the scene at some multiple of the screen resolution, for when
> poster-quality images are needed.

This is something Axel had suggested early on, but it turns out to be
somewhat trickier than I had originally anticipated, due to the greatly
increased possibility for GPU kernel timeouts. I decided to leave this
feature for the next release so I can work on the code a bit more and
try to decrease the likelihood of GPU kernel timeouts on low-end GPUs.
That said, it's on the TODO list already with many other improvements.

  John Stone

> Cheers,
> Tristan

NIH Center for Macromolecular Modeling and Bioinformatics
Beckman Institute for Advanced Science and Technology
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