Normal maps need tangents and binormals to do dotproduct (dot3) bumpmapping. A "tutorial" (a chunk of code without much comments) can be found here

http://www.nitrogl.com

There are also tutorials on nVidia''s and ATI''s developer sites (check ATI''s "simple dot3 bumpmapping"-application).

The lighting is calculated using N dotproduct L per pixel (well, per texel could be more accurate).

Basically you get the vector N from a normal map, and the vector L is the light direction calculated per vertex (light position - vertex position). Then the light direction is rotated to tangent space using the vert tangent and binormal (so we actually get the vector L'' = L in "tangent space"). Note that some may also refer to tangent space as texture space. A bit of 3D-card magic, and you''ve got bumps on your flat sufraces.

Check the sites i mentioned for a better explanation & code.


--BerLan