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- import { tslFn, If, mat3, vec2, vec3 } from '../../shadernode/ShaderNode.js';
- import { max } from '../../math/MathNode.js';
- // Rect Area Light
- // Real-Time Polygonal-Light Shading with Linearly Transformed Cosines
- // by Eric Heitz, Jonathan Dupuy, Stephen Hill and David Neubelt
- // code: https://github.com/selfshadow/ltc_code/
- const LTC_Uv = tslFn( ( { N, V, roughness } ) => {
- const LUT_SIZE = 64.0;
- const LUT_SCALE = ( LUT_SIZE - 1.0 ) / LUT_SIZE;
- const LUT_BIAS = 0.5 / LUT_SIZE;
- const dotNV = N.dot( V ).saturate();
- // texture parameterized by sqrt( GGX alpha ) and sqrt( 1 - cos( theta ) )
- const uv = vec2( roughness, dotNV.oneMinus().sqrt() );
- uv.assign( uv.mul( LUT_SCALE ).add( LUT_BIAS ) );
- return uv;
- } ).setLayout( {
- name: 'LTC_Uv',
- type: 'vec2',
- inputs: [
- { name: 'N', type: 'vec3' },
- { name: 'V', type: 'vec3' },
- { name: 'roughness', type: 'float' }
- ]
- } );
- const LTC_ClippedSphereFormFactor = tslFn( ( { f } ) => {
- // Real-Time Area Lighting: a Journey from Research to Production (p.102)
- // An approximation of the form factor of a horizon-clipped rectangle.
- const l = f.length();
- return max( l.mul( l ).add( f.z ).div( l.add( 1.0 ) ), 0 );
- } ).setLayout( {
- name: 'LTC_ClippedSphereFormFactor',
- type: 'float',
- inputs: [
- { name: 'f', type: 'vec3' }
- ]
- } );
- const LTC_EdgeVectorFormFactor = tslFn( ( { v1, v2 } ) => {
- const x = v1.dot( v2 );
- const y = x.abs().toVar();
- // rational polynomial approximation to theta / sin( theta ) / 2PI
- const a = y.mul( 0.0145206 ).add( 0.4965155 ).mul( y ).add( 0.8543985 ).toVar();
- const b = y.add( 4.1616724 ).mul( y ).add( 3.4175940 ).toVar();
- const v = a.div( b );
- const theta_sintheta = x.greaterThan( 0.0 ).cond( v, max( x.mul( x ).oneMinus(), 1e-7 ).inverseSqrt().mul( 0.5 ).sub( v ) );
- return v1.cross( v2 ).mul( theta_sintheta );
- } ).setLayout( {
- name: 'LTC_EdgeVectorFormFactor',
- type: 'vec3',
- inputs: [
- { name: 'v1', type: 'vec3' },
- { name: 'v2', type: 'vec3' }
- ]
- } );
- const LTC_Evaluate = tslFn( ( { N, V, P, mInv, p0, p1, p2, p3 } ) => {
- // bail if point is on back side of plane of light
- // assumes ccw winding order of light vertices
- const v1 = p1.sub( p0 ).toVar();
- const v2 = p3.sub( p0 ).toVar();
- const lightNormal = v1.cross( v2 );
- const result = vec3().toVar();
- If( lightNormal.dot( P.sub( p0 ) ).greaterThanEqual( 0.0 ), () => {
- // construct orthonormal basis around N
- const T1 = V.sub( N.mul( V.dot( N ) ) ).normalize();
- const T2 = N.cross( T1 ).negate(); // negated from paper; possibly due to a different handedness of world coordinate system
- // compute transform
- const mat = mInv.mul( mat3( T1, T2, N ).transpose() ).toVar();
- // transform rect
- // & project rect onto sphere
- const coords0 = mat.mul( p0.sub( P ) ).normalize().toVar();
- const coords1 = mat.mul( p1.sub( P ) ).normalize().toVar();
- const coords2 = mat.mul( p2.sub( P ) ).normalize().toVar();
- const coords3 = mat.mul( p3.sub( P ) ).normalize().toVar();
- // calculate vector form factor
- const vectorFormFactor = vec3( 0 ).toVar();
- vectorFormFactor.addAssign( LTC_EdgeVectorFormFactor( { v1: coords0, v2: coords1 } ) );
- vectorFormFactor.addAssign( LTC_EdgeVectorFormFactor( { v1: coords1, v2: coords2 } ) );
- vectorFormFactor.addAssign( LTC_EdgeVectorFormFactor( { v1: coords2, v2: coords3 } ) );
- vectorFormFactor.addAssign( LTC_EdgeVectorFormFactor( { v1: coords3, v2: coords0 } ) );
- // adjust for horizon clipping
- result.assign( vec3( LTC_ClippedSphereFormFactor( { f: vectorFormFactor } ) ) );
- } );
- return result;
- } ).setLayout( {
- name: 'LTC_Evaluate',
- type: 'vec3',
- inputs: [
- { name: 'N', type: 'vec3' },
- { name: 'V', type: 'vec3' },
- { name: 'P', type: 'vec3' },
- { name: 'mInv', type: 'mat3' },
- { name: 'p0', type: 'vec3' },
- { name: 'p1', type: 'vec3' },
- { name: 'p2', type: 'vec3' },
- { name: 'p3', type: 'vec3' }
- ]
- } );
- export { LTC_Evaluate, LTC_Uv };
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