FACEFORWARD

THE BOX'S MAIN HELP:

Result is NN, if NN and II form an acute angle when placed head to tail,
otherwise the result is -NN.
refer to page 328 in the RenderMan Companion.

NN (input):

A normal in space.  The default is the surface normal, N.

II (input):

A vector in space.  The default is the incidence vector, I.

OUT (output):

Result is NN, if NN and II form an acute angle when placed head to tail,
otherwise the result is -NN.
refer to page 328 in the RenderMan Companion.