Normal Mapping Vectors with Wrapping

It's worth trying it both ways so you can learn to recognize this kind of artifact. :)

Ben

BenLuna at 2007-9-9 >

The actual algorithm that it uses is fairly simple, what wrapping does is essentially give you 3 options to place the texture coordinate at in a given dimension. So that means that a texture coordinate (u, v) in the range [0,1) x [0,1) (you can get this pretty easily by taking the floating point modulus wrt 1), if wrapping in both dimensions is enabled, is equivalent to (u +/- 1, v +/- 1).

What this means is that in this case, there are 9 possible locations that you might want to make the actual texture coordinate be located at, for the purpose of calculating partial derivatives. What ComputeTangent does is it locks the first vertex location, and then tries the 81 possible locations of the other two vertices, and chooses the combination with the smallest perimeter (only because choosing based solely on area could prefer long skinny triangles over reasonably sized fat ones).

It's not perfect (nor particularly fast), but if the triangles are relatively small in tangent space, then it works relatively well. It's not a well defined problem, so there will always be cases where it won't work.

If you're only wrapping u (as your reference to a cylindrical mapping suggests), then you only have to check 3 locations per vertex, and 9 combinations of the two vertices, which will probably be faster, if that's important to you.

JohnRapp at 2007-9-9 >