From: John Stone (
Date: Wed Jun 09 2010 - 10:06:06 CDT

  I haven't implemented background-free images for Tachyon yet.
Actually what this type of feature actually does is add an alpha-channel
to the image corresponding to the amount of background visible through
each rendered pixel. While the math involved in computing the alpha
channel is relatively inexpensive, adding support for it in Tachyon would
likely mean making changes all throughout the rendering code so it gets
passed around everywhere, which adds some overhead in cases when you don't
need it. If you want to superimpose a Tachyon image on a background, an
alternative way to do this is to load your background image as a texture
map and put it on a plane at the very back of the view volume, and set
the material properties for the plane to be entirely diffuse.

If you're interested in doing something like that, I could probably write
you a little Tcl script for VMD that would do this by appending commands
to an existing Tachyon scene file. I won't have time to work on it until
next week however.

  John Stone

On Wed, Jun 09, 2010 at 04:33:25PM +0200, maria goranovic wrote:
> Is it possible to render images to background-free .png format images?
> From the mailing list, it seems that it is not included in the
> downloadable binary formats?
> --
> Maria G.
> Technical University of Denmark
> Copenhagen

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