Computing a Reflected Ray

NB : ||Rin|| = ||Rout|| = 1

Rin an Rout are unit vector

The projection of Rin onto N is -N cos (q) so

Rout - Rin = - 2N cos(q) = -2N.( N.Rin )

Rout = Rin - 2N(N.Rin)

You can form a losange with Rin and Rout