Hi, I made a Cg shader that does BRDF mapping, based on a nVidia technique which is using 2 cubemaps with pre-defined data. With the help of a light and eye vector, the shader can calculate the right coordinates to pick pixels from the cubemaps. This results in a value that describes how much light is reflected on that spot. Basically, its some sort of lighting model like Phong or Blinn but then with more physical correct data. Anyway, now I'd like to combine this technique with an environment map so that I can add some reflections. Instead of using stuff like Fresnell, I'd like to do it with the BRDF. However, there are some important differences though. The default nVidia BRDF approach is made for 1 lightspot (you give one light position) but when using a cubemap, the light could come from multiple directions of course (a env map with a few windows acting as light sources for example). How to handle that? Normally, the vertex shader calculates the BRDF cubemap coordinates with a eye position and camera position:

float3	half	= normalize( lightV + eyeV );
float3	hTex	= float3(
			dot(half,iTangent	),
	     		dot(half,iNrm	),
			dot(half,iBiNrm	)
			);

So I was thinking, what about replacing 'lightV' with the vector used to get a pixel from the cubemap? This code would move to the fragment shader and lightV would be something like "reflect( normal, eyeV )", instead of "normalize(vertexPos - lightPos)". However, this doesn't exactly work, otherwise I wouldn't ask of course :) Anyone an idea how to combine envmapping with the nVidia BRDF approach? Greetings

Thanks for the help guys! But for now, I think I stick on the good old Fresnell methods instead of BRDF for reflections :)

Greetings