No, there are many methods to generate the t/b vectors, given a normal. Any t/b/n basis per vertex is valid, provided they're all perpendicular. This means if you rotate the basis around the normal axis, you've still got valid data. You can even flip one axis in the reverse direction (e.g. Do Binormal = -Binormal), and you've still got a valid t/b/n basis.Since I'm at least respecting the normal information in the model, shouldn't this have a close to or maybe even identical result to what the modelling program was using?
Also, art tools generally try to take the UV/texture coordinates into account when generating the t/b vectors, so that the Tangent points in the same direction the U (x texture coord) is increasing, and the Binormal/Bitangent point in the direction the V (y) is increasing. This makes the normal map texture make a but more sense to look at and edit by hand ;) This also means that if the UVs are flipped at one point (e.g. The artist only textured half a face, but then used he same UV layout on both sides of the face, causing a mirroring in the tex-coords down he centre) then your binormals might also flip direction arbitrarily. If you're using artist-generated data, you often can't throw out the Binormal and just recreate it with a cross product -- you need to at least store a single bit encoding whether the cross product should be multiplied with 1 or -1.
This means that unless you know the algorithm being used by your art tools, it's very likely that your engine will produce different results...
Putting a normal map onto a brick wall is fairly simple, but handling all the little problems that come up when modeling a character is a lot more complex ;(
That model format is from the Source engine, right? Maybe there's source code for a loader/importer/compiler/viewer in the Source SDK, and you can copy their TBN generation algorithm?
