[Radiance-general] Specular instead of lambertian for indirect

[Greg Ward]

Hi Lucio,

> As about using mixfunc, if understood it right, the problem would  
> be that direct calculation would be performed on both brdf and  
> specular, leading me to a quite correct result (due to brdf), but  
> influenced form the specular_bit.

This is why you would have to subtract the specular lobe from your  
BRDF model.  In effect the BRDF would be a "correction" to the  
Gaussian lobe model, or at least the direct part.  The indirect would  
be as good as it's going to be without writing your own BRDF sampler,  
which would be both difficult and extremely costly in any rendering  
you might do.

> As about the indirect calculation it would be influenced by  
> specular (which is ok) but also from lambertian (indirect  
> calculation of brdf).

If the diffuse part of your reflectance model is zero, then there's  
no Lambertian calculation.

-Greg