three
Version:
JavaScript 3D library
186 lines (108 loc) • 3.84 kB
JavaScript
import {
Triangle
} from "../../../build/three.module.js";
/**
* 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
*/
var MeshSurfaceSampler = ( function () {
var _face = new Triangle();
function MeshSurfaceSampler( mesh ) {
var 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.positionAttribute = this.geometry.getAttribute( 'position' );
this.weightAttribute = null;
this.distribution = null;
}
MeshSurfaceSampler.prototype = {
constructor: MeshSurfaceSampler,
setWeightAttribute: function ( name ) {
this.weightAttribute = name ? this.geometry.getAttribute( name ) : null;
return this;
},
build: function () {
var positionAttribute = this.positionAttribute;
var weightAttribute = this.weightAttribute;
var faceWeights = new Float32Array( positionAttribute.count / 3 );
// Accumulate weights for each mesh face.
for ( var i = 0; i < positionAttribute.count; i += 3 ) {
var 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 );
var cumulativeTotal = 0;
for ( var i = 0; i < faceWeights.length; i ++ ) {
cumulativeTotal += faceWeights[ i ];
this.distribution[ i ] = cumulativeTotal;
}
return this;
},
sample: function ( targetPosition, targetNormal ) {
var cumulativeTotal = this.distribution[ this.distribution.length - 1 ];
var faceIndex = this.binarySearch( Math.random() * cumulativeTotal );
return this.sampleFace( faceIndex, targetPosition, targetNormal );
},
binarySearch: function ( x ) {
var dist = this.distribution;
var start = 0;
var end = dist.length - 1;
var index = - 1;
while ( start <= end ) {
var 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: function ( faceIndex, targetPosition, targetNormal ) {
var u = Math.random();
var v = Math.random();
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 ) );
_face.getNormal( targetNormal );
return this;
}
};
return MeshSurfaceSampler;
} )();
export { MeshSurfaceSampler };