( function () {
/**
* 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 THREE.Triangle();
const _color = new THREE.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;
}
}
THREE.MeshSurfaceSampler = MeshSurfaceSampler;
} )();
