If you''re using shaders, you may have forgotten to transform the normals of your mesh along with its position. When you rotate a mesh, the normals of the mesh need to be tranformed as well.

However, because of the way the 3D math works, you can''t always transform the normals of a mesh with the same matrix you use to transform the vertices of the mesh. Do a search for something like "transforming normals" if you''re not sure what I mean.

If I remember correctly (brain is mush right now after having pulled an all-nighter), the matrix to transform normals is:

Mn = ( (M)^-1 )^T

This says that the Matrix to transform normals (Mn) is equal to the transpose (that''s the ^T part) of the inverse (that''s the ^-1 part) of the mesh''s original transformation matrix used to move the mesh around the scene.

neneboricua

If you''re using the fixed function pipeline, D3D takes care of transforming the normals for you. That''s why you''ve never run into that problem. When you use shaders, you''re responsible for all this kind of work. It''s easy to forget to transform normals when writing your shaders.

Your problem still sounds like it has something to do with the normals. If rotating your mesh causes lighting to work at some orientations and not others, it really sounds like a problem with your normals. Double check how the normals are being exported and that all your code dealing them is ok.

Perhaps other forum members will have other ideas about what could be the problem.

neneboricua