Derivative Calculation
‘w’ will be interpolated just like Z, R, G, etc…
- we do not want to do division, so we set w’ = 1/w (do division only one time)
- Compute dw’/dx, dw’/dy, dw’_dscan
Correct starting S, T values at each vertex via:
- S’ = S * w’
- T’ = T * w’
- Compute all derivatives for S, T using corrected S’, T’ values