Where do we Illuminate ?...

From Illumination (a costly process), lighting model to...

To this point we have discussed how to compute an illumination model at a point on a surface.

But, at which points on the surface is the illumination model applied? Where and how often it is applied has a noticable effect on the result.

Illuminating can be a costly process involving the computation of and normalizing of vectors to multiple light sources and the viewer.

... Shading or Surface rendering algorithm

For models defined by collections of polygonal facets or triangles: