Burley states about metallic parameter:
"This is a linear blend between two different models. ..."
What are the two models? I can't see this described in the Frostbite or the Unreal papers either.
Is it simply a blend between the diffuse and specular terms or a scaling factor on the specular term?
If I'm reading this right, the answer seems to be right there in the continuation of that line:
metallic - the metallic-ness (0 = dielectric, 1 = metallic). This is a linear blend between two different models. The metallic model has no diffuse component and also has a tinted incident specular, equal to the base color.
(With the implication that the dielectric model is defined by not having those specific traits)
ie...
Dielectric Model:
Metallic Model:
