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).