three
Version:
JavaScript 3D library
316 lines (226 loc) • 8.16 kB
JavaScript
import {
Triangle,
Vector2,
Vector3
} from 'three';
const _face = new Triangle();
const _color = new Vector3();
const _uva = new Vector2(), _uvb = new Vector2(), _uvc = new Vector2();
/**
* 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:
* - {@link http://www.joesfer.com/?p=84}
* - {@link https://stackoverflow.com/a/4322940/1314762}
*
* ```js
* const sampler = new MeshSurfaceSampler( surfaceMesh )
* .setWeightAttribute( 'color' )
* .build();
*
* const mesh = new THREE.InstancedMesh( sampleGeometry, sampleMaterial, 100 );
*
* const position = new THREE.Vector3();
* const matrix = new THREE.Matrix4();
*
* // Sample randomly from the surface, creating an instance of the sample geometry at each sample point.
*
* for ( let i = 0; i < 100; i ++ ) {
*
* sampler.sample( position );
* matrix.makeTranslation( position.x, position.y, position.z );
* mesh.setMatrixAt( i, matrix );
*
* }
*
* scene.add( mesh );
* ```
*
* @three_import import { MeshSurfaceSampler } from 'three/addons/math/MeshSurfaceSampler.js';
*/
class MeshSurfaceSampler {
/**
* Constructs a mesh surface sampler.
*
* @param {Mesh} mesh - Surface mesh from which to sample.
*/
constructor( mesh ) {
this.geometry = mesh.geometry;
this.randomFunction = Math.random;
this.indexAttribute = this.geometry.index;
this.positionAttribute = this.geometry.getAttribute( 'position' );
this.normalAttribute = this.geometry.getAttribute( 'normal' );
this.colorAttribute = this.geometry.getAttribute( 'color' );
this.uvAttribute = this.geometry.getAttribute( 'uv' );
this.weightAttribute = null;
this.distribution = null;
}
/**
* Specifies a vertex attribute to be used as a weight when sampling from the surface.
* Faces with higher weights are more likely to be sampled, and those with weights of
* zero will not be sampled at all. For vector attributes, only .x is used in sampling.
*
* If no weight attribute is selected, sampling is randomly distributed by area.
*
* @param {string} name - The attribute name.
* @return {MeshSurfaceSampler} A reference to this sampler.
*/
setWeightAttribute( name ) {
this.weightAttribute = name ? this.geometry.getAttribute( name ) : null;
return this;
}
/**
* Processes the input geometry and prepares to return samples. Any configuration of the
* geometry or sampler must occur before this method is called. Time complexity is O(n)
* for a surface with n faces.
*
* @return {MeshSurfaceSampler} A reference to this sampler.
*/
build() {
const indexAttribute = this.indexAttribute;
const positionAttribute = this.positionAttribute;
const weightAttribute = this.weightAttribute;
const totalFaces = indexAttribute ? ( indexAttribute.count / 3 ) : ( positionAttribute.count / 3 );
const faceWeights = new Float32Array( totalFaces );
// Accumulate weights for each mesh face.
for ( let i = 0; i < totalFaces; i ++ ) {
let faceWeight = 1;
let i0 = 3 * i;
let i1 = 3 * i + 1;
let i2 = 3 * i + 2;
if ( indexAttribute ) {
i0 = indexAttribute.getX( i0 );
i1 = indexAttribute.getX( i1 );
i2 = indexAttribute.getX( i2 );
}
if ( weightAttribute ) {
faceWeight = weightAttribute.getX( i0 )
+ weightAttribute.getX( i1 )
+ weightAttribute.getX( i2 );
}
_face.a.fromBufferAttribute( positionAttribute, i0 );
_face.b.fromBufferAttribute( positionAttribute, i1 );
_face.c.fromBufferAttribute( positionAttribute, i2 );
faceWeight *= _face.getArea();
faceWeights[ i ] = faceWeight;
}
// Store cumulative total face weights in an array, where weight index
// corresponds to face index.
const distribution = new Float32Array( totalFaces );
let cumulativeTotal = 0;
for ( let i = 0; i < totalFaces; i ++ ) {
cumulativeTotal += faceWeights[ i ];
distribution[ i ] = cumulativeTotal;
}
this.distribution = distribution;
return this;
}
/**
* Allows to set a custom random number generator. Default is `Math.random()`.
*
* @param {Function} randomFunction - A random number generator.
* @return {MeshSurfaceSampler} A reference to this sampler.
*/
setRandomGenerator( randomFunction ) {
this.randomFunction = randomFunction;
return this;
}
/**
* Selects a random point on the surface of the input geometry, returning the
* position and optionally the normal vector, color and UV Coordinate at that point.
* Time complexity is O(log n) for a surface with n faces.
*
* @param {Vector3} targetPosition - The target object holding the sampled position.
* @param {Vector3} targetNormal - The target object holding the sampled normal.
* @param {Color} targetColor - The target object holding the sampled color.
* @param {Vector2} targetUV - The target object holding the sampled uv coordinates.
* @return {MeshSurfaceSampler} A reference to this sampler.
*/
sample( targetPosition, targetNormal, targetColor, targetUV ) {
const faceIndex = this._sampleFaceIndex();
return this._sampleFace( faceIndex, targetPosition, targetNormal, targetColor, targetUV );
}
// private
_sampleFaceIndex() {
const cumulativeTotal = this.distribution[ this.distribution.length - 1 ];
return this._binarySearch( this.randomFunction() * cumulativeTotal );
}
_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, targetUV ) {
let u = this.randomFunction();
let v = this.randomFunction();
if ( u + v > 1 ) {
u = 1 - u;
v = 1 - v;
}
// get the vertex attribute indices
const indexAttribute = this.indexAttribute;
let i0 = faceIndex * 3;
let i1 = faceIndex * 3 + 1;
let i2 = faceIndex * 3 + 2;
if ( indexAttribute ) {
i0 = indexAttribute.getX( i0 );
i1 = indexAttribute.getX( i1 );
i2 = indexAttribute.getX( i2 );
}
_face.a.fromBufferAttribute( this.positionAttribute, i0 );
_face.b.fromBufferAttribute( this.positionAttribute, i1 );
_face.c.fromBufferAttribute( this.positionAttribute, i2 );
targetPosition
.set( 0, 0, 0 )
.addScaledVector( _face.a, u )
.addScaledVector( _face.b, v )
.addScaledVector( _face.c, 1 - ( u + v ) );
if ( targetNormal !== undefined ) {
if ( this.normalAttribute !== undefined ) {
_face.a.fromBufferAttribute( this.normalAttribute, i0 );
_face.b.fromBufferAttribute( this.normalAttribute, i1 );
_face.c.fromBufferAttribute( this.normalAttribute, i2 );
targetNormal.set( 0, 0, 0 ).addScaledVector( _face.a, u ).addScaledVector( _face.b, v ).addScaledVector( _face.c, 1 - ( u + v ) ).normalize();
} else {
_face.getNormal( targetNormal );
}
}
if ( targetColor !== undefined && this.colorAttribute !== undefined ) {
_face.a.fromBufferAttribute( this.colorAttribute, i0 );
_face.b.fromBufferAttribute( this.colorAttribute, i1 );
_face.c.fromBufferAttribute( this.colorAttribute, i2 );
_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;
}
if ( targetUV !== undefined && this.uvAttribute !== undefined ) {
_uva.fromBufferAttribute( this.uvAttribute, i0 );
_uvb.fromBufferAttribute( this.uvAttribute, i1 );
_uvc.fromBufferAttribute( this.uvAttribute, i2 );
targetUV.set( 0, 0 ).addScaledVector( _uva, u ).addScaledVector( _uvb, v ).addScaledVector( _uvc, 1 - ( u + v ) );
}
return this;
}
}
export { MeshSurfaceSampler };