Initial commit

HTML/ThreeJS/node_modules/three/examples/jsm/math/MeshSurfaceSampler.js

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