snell3d

Refraction of light at a surface in 3D vector form

Implementation of tutorial found on
http://starkeffects.com/snells-law-vector.shtml

s2 = snell3d(n1,n2,s1,N)
n1,n2: refractive indexes of first medium and surface respectively
s1: incident ray vector (xyz vector, will be normalized and made column)
N: surface normal (xyz vector, will be normalized and made column)
s2: refracted ray (normalized xyz vector)