What else about illumination ?
Control of the intensity with regards of the direction of a spot light.
Light sources are modeled as points on a reflecting surface, using the Phong
attenuation function applied to point light source
f(d) = 1/(a0 + a1.d + a2.d^2)
where d is the distance between the source and the illuminated surface
In Real Time API, a rough approximation with a percentage of refraction light.
no shifting of the path