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mjs1
06-04-2005, 05:32 AM
I was reading up on bump mapping and was wondering why you needed to
construct the two temp vectors (A and B) from the cross products of the
surface normal and the Pu and Pv surface partial derivatives. As I
understand it you create these two vectors in order to create a tangent
plane with respect to the surface at point P. Then you take these two
vectors and multiply them respectively by the s and t partial
derivatives from the bump map (Fs and Ft) to find the offset vector D for N.

Since the surface normal was created via the cross product of the
partial derivatives in the first place, couldn't you save time and
multiply the P/u, P/v partial derivative vectors directly with the s, t
partial derivative vectors from the texture map to find D?


A = N X P , B = N X P , and D = F A - F B
v u s t


Thanks!

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