A faster technique for normalization without
using texture maps is to use the register combiners extension
[11]. With register combiners only addition, subtraction,
multiplication and dot products are possible
(Section 3.3). Direct computation of the
normalization equation shown in Formula 4 is not possible.
Given that the vector is derived from the interpolation of a
unit-length vector across the polygon and the angle between the per-vertex
vectors is not too big, this expression can be approximated by a Taylor series
(Formula 5).