Lommel-Seeliger diffuse model

PBR CG 


// Quoted from http://www.shlyaev.com/rnd/37-cpp-category/60-diffuseshaders

The Lommel-Seeliger volumetric scattering BRDF is a simple BRDF predicting scattering from a dusty surface.
Dusty surfaces scatter the reflected light in all directions toward grazing angles to the surface.
The BRDF is: brdf(wi,wo) = 1 / (N.wi)+(N.wo)
The Lommel-Seeliger function is essentially a "distillation" of the Hapke function
that does not contain more complicated terms.

It relies on the incidence and emergence angles alone.
It ignores masking and shadowing.
The Lambert and Lommel-Seeliger functions represent end-members on a scale
that ranges from an "icy-type" surface (Lambert) to a "lunar-type" surface (Lommel-Seeliger).