After five years of having the Principled BSDF in Cycles, there's now an ongoing development effort to overhaul and modernize it.

This talk will present the background and current state of this work. After starting with the reasoning for why the current Principled BSDF is not good enough anymore, it will introduce the underlying theory of physically based shading, covering concepts such as microfacet models, dielectric vs. conductive materials, Fresnel terms, layering models, energy conservation and preservation etc.

Based on this, it'll cover the current plans for Cycles' new Principled BSDF - the design goals, the components it consists of, the theory that each of them is based on, and how they all combine and interact with each other, as well as the current status of the project and what remains to be done.