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171 lines
4.4 KiB
171 lines
4.4 KiB
( function () {
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/**
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* Utility class for sampling weighted random points on the surface of a mesh.
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*
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* Building the sampler is a one-time O(n) operation. Once built, any number of
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* random samples may be selected in O(logn) time. Memory usage is O(n).
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*
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* References:
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* - http://www.joesfer.com/?p=84
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* - https://stackoverflow.com/a/4322940/1314762
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*/
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const _face = new THREE.Triangle();
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const _color = new THREE.Vector3();
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class MeshSurfaceSampler {
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constructor( mesh ) {
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let geometry = mesh.geometry;
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if ( ! geometry.isBufferGeometry || geometry.attributes.position.itemSize !== 3 ) {
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throw new Error( 'THREE.MeshSurfaceSampler: Requires BufferGeometry triangle mesh.' );
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}
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if ( geometry.index ) {
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console.warn( 'THREE.MeshSurfaceSampler: Converting geometry to non-indexed BufferGeometry.' );
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geometry = geometry.toNonIndexed();
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}
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this.geometry = geometry;
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this.randomFunction = Math.random;
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this.positionAttribute = this.geometry.getAttribute( 'position' );
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this.colorAttribute = this.geometry.getAttribute( 'color' );
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this.weightAttribute = null;
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this.distribution = null;
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}
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setWeightAttribute( name ) {
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this.weightAttribute = name ? this.geometry.getAttribute( name ) : null;
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return this;
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}
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build() {
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const positionAttribute = this.positionAttribute;
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const weightAttribute = this.weightAttribute;
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const faceWeights = new Float32Array( positionAttribute.count / 3 );
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// Accumulate weights for each mesh face.
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for ( let i = 0; i < positionAttribute.count; i += 3 ) {
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let faceWeight = 1;
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if ( weightAttribute ) {
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faceWeight = weightAttribute.getX( i ) + weightAttribute.getX( i + 1 ) + weightAttribute.getX( i + 2 );
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}
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_face.a.fromBufferAttribute( positionAttribute, i );
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_face.b.fromBufferAttribute( positionAttribute, i + 1 );
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_face.c.fromBufferAttribute( positionAttribute, i + 2 );
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faceWeight *= _face.getArea();
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faceWeights[ i / 3 ] = faceWeight;
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}
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// Store cumulative total face weights in an array, where weight index
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// corresponds to face index.
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this.distribution = new Float32Array( positionAttribute.count / 3 );
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let cumulativeTotal = 0;
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for ( let i = 0; i < faceWeights.length; i ++ ) {
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cumulativeTotal += faceWeights[ i ];
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this.distribution[ i ] = cumulativeTotal;
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}
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return this;
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}
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setRandomGenerator( randomFunction ) {
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this.randomFunction = randomFunction;
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return this;
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}
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sample( targetPosition, targetNormal, targetColor ) {
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const cumulativeTotal = this.distribution[ this.distribution.length - 1 ];
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const faceIndex = this.binarySearch( this.randomFunction() * cumulativeTotal );
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return this.sampleFace( faceIndex, targetPosition, targetNormal, targetColor );
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}
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binarySearch( x ) {
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const dist = this.distribution;
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let start = 0;
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let end = dist.length - 1;
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let index = - 1;
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while ( start <= end ) {
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const mid = Math.ceil( ( start + end ) / 2 );
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if ( mid === 0 || dist[ mid - 1 ] <= x && dist[ mid ] > x ) {
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index = mid;
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break;
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} else if ( x < dist[ mid ] ) {
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end = mid - 1;
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} else {
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start = mid + 1;
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}
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}
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return index;
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}
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sampleFace( faceIndex, targetPosition, targetNormal, targetColor ) {
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let u = this.randomFunction();
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let v = this.randomFunction();
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if ( u + v > 1 ) {
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u = 1 - u;
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v = 1 - v;
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}
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_face.a.fromBufferAttribute( this.positionAttribute, faceIndex * 3 );
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_face.b.fromBufferAttribute( this.positionAttribute, faceIndex * 3 + 1 );
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_face.c.fromBufferAttribute( this.positionAttribute, faceIndex * 3 + 2 );
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targetPosition.set( 0, 0, 0 ).addScaledVector( _face.a, u ).addScaledVector( _face.b, v ).addScaledVector( _face.c, 1 - ( u + v ) );
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if ( targetNormal !== undefined ) {
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_face.getNormal( targetNormal );
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}
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if ( targetColor !== undefined && this.colorAttribute !== undefined ) {
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_face.a.fromBufferAttribute( this.colorAttribute, faceIndex * 3 );
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_face.b.fromBufferAttribute( this.colorAttribute, faceIndex * 3 + 1 );
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_face.c.fromBufferAttribute( this.colorAttribute, faceIndex * 3 + 2 );
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_color.set( 0, 0, 0 ).addScaledVector( _face.a, u ).addScaledVector( _face.b, v ).addScaledVector( _face.c, 1 - ( u + v ) );
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targetColor.r = _color.x;
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targetColor.g = _color.y;
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targetColor.b = _color.z;
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}
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return this;
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}
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}
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THREE.MeshSurfaceSampler = MeshSurfaceSampler;
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} )();
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