Variable BRDFCharlieConst
BRDFCharlie: "\n// https://github.com/google/filament/blob/main/shaders/src/surface_brdf.fs#L94\nfn D_Charlie( roughness: f32, NdotH: f32 ) -> f32 {\n let alpha: f32 = pow2( roughness );\n\n // Estevez and Kulla 2017, \"Production Friendly Microfacet Sheen BRDF\"\n let invAlpha: f32 = 1.0 / max(alpha, EPSILON);\n let cos2h: f32 = NdotH * NdotH;\n let sin2h: f32 = max( 1.0 - cos2h, 0.0078125 ); // 2^(-14/2), so sin2h^2 > 0 in fp16\n\n return ( 2.0 + invAlpha ) * pow( sin2h, invAlpha * 0.5 ) / ( 2.0 * PI );\n}\n\n// https://github.com/google/filament/blob/main/shaders/src/surface_brdf.fs#L139\nfn V_Neubelt( NdotL: f32, NdotV: f32 ) -> f32 {\n // Neubelt and Pettineo 2013, \"Crafting a Next-gen Material Pipeline for The Order: 1886\"\n return saturate( 1.0 / ( 4.0 * max( NdotL + NdotV - NdotL * NdotV, EPSILON ) ) );\n}\n" = ...
BRDF "Charlie" sheen Distribution and Visibility helper functions.