shader development

[joevenzon]

So the ambient map is actually an irradiance environment map generated from the static environment map?

Yep! That's all done offline though, and really the only reason for it is to try to make the track geometry look less flat, so I'm willing to change it if needed.

Spherical harmonics are similar to the way you can build up any function using a sum of simple sine or cosine waves of different frequencies (fourier series) but using a basis function appropriate for a sphere instead of a sine/cosine. Representing an irradiance environment map is fairly easy with spherical harmonics because it's so low frequency:
http://graphics.stanford.edu/papers/envmap/

Also, valve uses an "ambient cube" approach which is a little faster (but not as general as spherical harmonics) and easier to understand:
http://www.valvesoftware.com/publication...Engine.pdf