[Radiance-general] accessing interpolated normals in a .cal file

[Roland William Fleming]

Hi ---

I've written a .cal shader for use with colorpict that makes use of Nx, 
Ny and Nz.  But now I want to apply it to a mesh, (or object generated 
with gensurf with the smoothing option on).  Instead of receiving the 
perturbed (interpolated) vertex normals, it just applies to the local 
surface normal, leading to faceted appearance.

How do I access the interpolated surface normals in a .cal file?

Cheers,
Roland