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import F_Schlick from './F_Schlick.js';
import V_GGX_SmithCorrelated from './V_GGX_SmithCorrelated.js';
import D_GGX from './D_GGX.js';
import {
ShaderNode, dotNV, add, mul, clamp, dot, pow2, normalize,
transformedNormalView, positionViewDirection
} from '../../shadernode/ShaderNodeBaseElements.js';
// GGX Distribution, Schlick Fresnel, GGX_SmithCorrelated Visibility
const BRDF_GGX = new ShaderNode( ( inputs ) => {
const { lightDirection, f0, f90, roughness } = inputs;
const alpha = pow2( roughness ); // UE4's roughness
const halfDir = normalize( add( lightDirection, positionViewDirection ) );
const dotNL = clamp( dot( transformedNormalView, lightDirection ) );
//const dotNV = clamp( dot( transformedNormalView, positionViewDirection ) );
const dotNH = clamp( dot( transformedNormalView, halfDir ) );
const dotVH = clamp( dot( positionViewDirection, halfDir ) );
const F = F_Schlick.call( { f0, f90, dotVH } );
const V = V_GGX_SmithCorrelated.call( { alpha, dotNL, dotNV } );
const D = D_GGX.call( { alpha, dotNH } );
return mul( F, mul( V, D ) );
} ); // validated
export default BRDF_GGX;