So respectively "if(Rdot,Rdot, -Rdot)" returns cos(theta) if both sides are similar. - By the way, I never realised before that modifiers "foreground" and "background" could refer to the concrete front and back of a surface...
Thanks very much,
Markku N.
···
At 14:02 2002-05-03 -0400, you wrote:
You can assign different materials/patterns/textures to the front
and back side of a surface simply by using "if(Rdot,1,0)" as the
coefficient for a mixture.