mjs1

06-04-2005, 06:32 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!

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!