From: John Stone (
Date: Tue Oct 26 2004 - 15:20:48 CDT

  Thanks for the feedback, I hadn't seen the issue you encountered
with the ribbons, that's good to know about. I'll see if I can
figure out why POV is upset about that, it might be something trivial.
Regarding the gradient issue you mentioned:
  - color gradients are lost in POV-Ray because they don't have
    a way to draw vertex-interpolated colors (as far as I know)
  - for Tachyon, I ended up writing special rendering code so that
    Tachyon could render color-per-vertex triangles.
    Very few ray tracing packages bother to implement color-per-vertex
    triangles or polygon primitives, this is something that hardware
    accelerators do, but most ray tracing packages make heavy use of
    curved geometry and texture maps for complex scenes.
    This is one of those annoying problems one encounters rendering
    purely polygonal data with ray tracing software.

If anyone knows of a way to convince POV to output color-per-vertex
triangles, I'd love to hear about it since it'd probably be easy to
change VMD's POV export code to use it.

  John Stone

On Tue, Oct 26, 2004 at 03:11:53PM -0500, Luis Rosales wrote:
> Dear John,
> I just tried the new alpha version of vmd (Linux)!!! (a couple of images are
> attached on the mail...)
> The Pov export of surfaces is really good, a lot cleaner than the previous
> versions.
> I generated surfaces on small proteins like ubiquitin and big complexes like
> the nucleosome, on every case the parsing of the files was just fine,
> without the degenerate triangle warning.
> Also, I think that the size of the generated Pov files is a lot smaller than
> the previous versions (I only checked ubiquitin and the size difference was
> 8Mb in vmd 1.8.3a vs. 11Mb in vmd 1.8.2).
> The only trouble I found was on the rendering of the "new ribbons"
> representation of proteins. On every case I got the message "all
> determinants too small". Even as I tried warious ribbons resolutions, I was
> unable to avoid the warning. I am not sure, but I wonder if this could be
> related to the curvature asociated to the "sides" of the ribbon??
> One last question,
> I wonder why color gradients are not conserved when you render them on a
> surface, (why a surface colored by position is made of discrete colored
> "patches" of tringles instead of a true gradient?).
> Thank you and best regards,
> Luis
> > -----Mensaje original-----
> > > >
> > > > I tested on both linux and windows (I use VMD 1.8.2 and Povray 3.5),
> > > > but to no avail. I used VMD/povray already before, and I don't
> remember
> > > > to have had problems then. My structures consists mainly of
> > > > Bonds, VDW and NewRibbons Graphical Representations.
> > > >
> > > > Any clues?
> > > >
> > > > Regards,
> > > >
> > > > Dominique

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