frontface VEX function

If dot(I, Nref) is less than zero, N will be negated.

Contexts: image3d, chop, cop, pop, sop, surface, displace, fog, light, shadow, photon, cvex

  1. vector frontface(vector N, vector I)

    This form (which doesn’t take a reference vector) is only available in the shading contexts, where the Ng variable is used.

  2. vector frontface(vector N, vector I, vector Nref)

If dot(I, Nref) is less than zero, N will be negated.