[Radiance-general] Re: Help with transfunc

[Greg Ward]

Hi Mark,

This is what you want:

void brightfunc trans_mod
2 1-.6667/Rdot .
0
0

trans_mod trans surf_dens
0
0
7 1 1 1 0 0 1 1

The modifier will alter the specular transmission, and the trans has no  
diffuse component or specular reflection.  The reason transfunc didn't  
work for you was because the specularity you can modify is only used  
for light sources in that material.  You could use BRDTfunc, but the  
above is simpler.

-Greg

> From: Mark Stock <mstock@umich.edu>
> Date: January 24, 2004 12:36:37 PM PST
>
> I am confused about the use of the transfunc. Function files took
> me a little while to understand anyways, but what I can't figure out
> is how to specify only a change in transmittance in a material.
>
>         mod transfunc id
>         2+ brtd funcfile transform
>         0
>         6+ red green blue rspec trans tspec A7 ..
>
> I'd like to render a mesh object in "x-ray" form, but visualizing
> its surface and not its volume. I'd like a material that diffuses
> and reflects no light, and transmits light based on the "thickness"
> of the surface (assuming that the object is a thin shell of fixed
> thickness). I'd like the transmittance to be something like
> 1.0-(const/Rdot), but when I try the following:
>
>         void transfunc meshcolor
>         2 1.0-A5/Rdot .
>         0
>         6 0.5 0.5 0.5  1 0.66667 1
>
> I've tried several different values for the function, and everything
> gives me a totally opaque object, or an "undefined function" error.
> I'd like to get something like this:
>
> http://mark.technolope.org/vort3d/bd10/run168_first_sphere/burn1/ 
> run05/save_0053.jpg
>
> Mark