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This Bxdf is based on Brent Burley's extended material model, introduced in "Extending the Disney BRDF to a BSDF with Integrated Subsurface Scattering" at SIGGRAPH 2015.  It is a nice and simple physically-based model with a concise number of parameters, but at the same time it can represent a wide range of materials, including diffuse and specular reflection and transmission, clearcoat, sheen, and subsurface scattering.  All CG animations made at Walt Disney Animation Studios use this material model.  The source code for the Pixar version of this material, PxrDisneyBsdf, is available among the bxdf code examples.

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Examples of different material parameter settings for PxrDisneyBsdf: metallic reflection, thin diffuse transmission, thin specular transmission, subsurface scattering, and glass refraction and reflection.  Image inspired by Figure 1 of the Burley Bsdf paper.

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