# Blinn & Torrance Variation

Jim Blinn introduced another approach for computing Phong-like illumination
based on the work of Ken Torrance.

His illumination function uses the following equation:

In this equation the angle of specular dispersion is computed by how far the
surface's normal is from a vector bisecting the incoming light direction and
the viewing direction.

### q + f = a +
g q + a
= g =>
f - a = a

## f = 2a

On your own you should consider how this approach and
the previous one differ.

N : Normal to the real plan

H : Normal to the plane that would create higher reflexion
towards the viewer

Advantage : the angle (N,H) will always remains between
0 and PI/2

Careful : nshiny should introduce a factor 2 with the
previous expression.