three.js/examples/js/geometries/DecalGeometry.js

/**
 * @author Mugen87 / https://github.com/Mugen87
 * @author spite / https://github.com/spite
 *
 * You can use this geometry to create a decal mesh, that serves different kinds of purposes.
 * e.g. adding unique details to models, performing dynamic visual environmental changes or covering seams.
 *
 * Constructor parameter:
 *
 * mesh — Any mesh object
 * position — Position of the decal projector
 * orientation — Orientation of the decal projector
 * size — Size of the decal projector
 *
 * reference: http://blog.wolfire.com/2009/06/how-to-project-decals/
 *
 */

( function () {

	function DecalGeometry( mesh, position, orientation, size ) {

  	THREE.BufferGeometry.call( this );

  	this.type = 'DecalGeometry';

  	// buffers

  	var vertices = [];
  	var normals = [];
  	var uvs = [];

  	// helpers

  	var plane = new THREE.Vector3();

  	// this matrix represents the transformation of the decal projector

  	var projectorMatrix = new THREE.Matrix4();
  	projectorMatrix.makeRotationFromEuler( orientation );
  	projectorMatrix.setPosition( position );

  	var projectorMatrixInverse = new THREE.Matrix4().getInverse( projectorMatrix );

  	// generate buffers

  	generate();

  	// build geometry

  	this.addAttribute( 'position', new THREE.Float32BufferAttribute( vertices, 3 ) );
  	this.addAttribute( 'normal', new THREE.Float32BufferAttribute( normals, 3 ) );
  	this.addAttribute( 'uv', new THREE.Float32BufferAttribute( uvs, 2 ) );

  	function generate() {

  		var i;
  		var geometry = new THREE.BufferGeometry();
  		var decalVertices = [];

  		var vertex = new THREE.Vector3();
  		var normal = new THREE.Vector3();

  		// handle different geometry types

  		if ( mesh.geometry.isGeometry ) {

  			geometry.fromGeometry( mesh.geometry );

  		} else {

  			geometry.copy( mesh.geometry );

  		}

  		var positionAttribute = geometry.attributes.position;
  		var normalAttribute = geometry.attributes.normal;

  		// first, create an array of 'DecalVertex' objects
  		// three consecutive 'DecalVertex' objects represent a single face
  		//
  		// this data structure will be later used to perform the clipping

  		if ( geometry.index !== null ) {

  			// indexed BufferGeometry

  			var index = geometry.index;

  			for ( i = 0; i < index.count; i ++ ) {

  				vertex.fromBufferAttribute( positionAttribute, index.getX( i ) );
  				normal.fromBufferAttribute( normalAttribute, index.getX( i ) );

  				pushDecalVertex( decalVertices, vertex, normal );

  			}

  		} else {

  			// non-indexed BufferGeometry

  			for ( i = 0; i < positionAttribute.count; i ++ ) {

  				vertex.fromBufferAttribute( positionAttribute, i );
  				normal.fromBufferAttribute( normalAttribute, i );

  				pushDecalVertex( decalVertices, vertex, normal );

  			}

  		}

  		// second, clip the geometry so that it doesn't extend out from the projector

  		decalVertices = clipGeometry( decalVertices, plane.set( 1, 0, 0 ) );
  		decalVertices = clipGeometry( decalVertices, plane.set( - 1, 0, 0 ) );
  		decalVertices = clipGeometry( decalVertices, plane.set( 0, 1, 0 ) );
  		decalVertices = clipGeometry( decalVertices, plane.set( 0, - 1, 0 ) );
  		decalVertices = clipGeometry( decalVertices, plane.set( 0, 0, 1 ) );
  		decalVertices = clipGeometry( decalVertices, plane.set( 0, 0, - 1 ) );

  		// third, generate final vertices, normals and uvs

  		for ( i = 0; i < decalVertices.length; i ++ ) {

  			var decalVertex = decalVertices[ i ];

  			// create texture coordinates (we are still in projector space)

  			uvs.push(
  				0.5 + ( decalVertex.position.x / size.x ),
  				0.5 + ( decalVertex.position.y / size.y )
  			);

  			// transform the vertex back to world space

  			decalVertex.position.applyMatrix4( projectorMatrix );

  			// now create vertex and normal buffer data

  			vertices.push( decalVertex.position.x, decalVertex.position.y, decalVertex.position.z );
  			normals.push( decalVertex.normal.x, decalVertex.normal.y, decalVertex.normal.z );

  		}

  	}

  	function pushDecalVertex( decalVertices, vertex, normal ) {

  		// transform the vertex to world space, then to projector space

  		vertex.applyMatrix4( mesh.matrix );
  		vertex.applyMatrix4( projectorMatrixInverse );

  		decalVertices.push( new DecalVertex( vertex.clone(), normal.clone() ) );

  	}

  	function clipGeometry( inVertices, plane ) {

  		var outVertices = [];

  		var s = 0.5 * Math.abs( size.dot( plane ) );

  		// a single iteration clips one face,
  		// which consists of three consecutive 'DecalVertex' objects

  		for ( var i = 0; i < inVertices.length; i += 3 ) {

  			var v1Out, v2Out, v3Out, total = 0;
  			var nV1, nV2, nV3, nV4;

  			var d1 = inVertices[ i + 0 ].position.dot( plane ) - s;
  			var d2 = inVertices[ i + 1 ].position.dot( plane ) - s;
  			var d3 = inVertices[ i + 2 ].position.dot( plane ) - s;

  			v1Out = d1 > 0;
  			v2Out = d2 > 0;
  			v3Out = d3 > 0;

  			// calculate, how many vertices of the face lie outside of the clipping plane

  			total = ( v1Out ? 1 : 0 ) + ( v2Out ? 1 : 0 ) + ( v3Out ? 1 : 0 );

  			switch ( total ) {

  				case 0: {

  					// the entire face lies inside of the plane, no clipping needed

  					outVertices.push( inVertices[ i ] );
  					outVertices.push( inVertices[ i + 1 ] );
  					outVertices.push( inVertices[ i + 2 ] );
  					break;

  				}

  				case 1: {

  					// one vertex lies outside of the plane, perform clipping

  					if ( v1Out ) {

  						nV1 = inVertices[ i + 1 ];
  						nV2 = inVertices[ i + 2 ];
  						nV3 = clip( inVertices[ i ], nV1, plane, s );
  						nV4 = clip( inVertices[ i ], nV2, plane, s );

  					}

  					if ( v2Out ) {

  						nV1 = inVertices[ i ];
  						nV2 = inVertices[ i + 2 ];
  						nV3 = clip( inVertices[ i + 1 ], nV1, plane, s );
  						nV4 = clip( inVertices[ i + 1 ], nV2, plane, s );

  						outVertices.push( nV3 );
  						outVertices.push( nV2.clone() );
  						outVertices.push( nV1.clone() );

  						outVertices.push( nV2.clone() );
  						outVertices.push( nV3.clone() );
  						outVertices.push( nV4 );
  						break;

  					}

  					if ( v3Out ) {

  						nV1 = inVertices[ i ];
  						nV2 = inVertices[ i + 1 ];
  						nV3 = clip( inVertices[ i + 2 ], nV1, plane, s );
  						nV4 = clip( inVertices[ i + 2 ], nV2, plane, s );

  					}

  					outVertices.push( nV1.clone() );
  					outVertices.push( nV2.clone() );
  					outVertices.push( nV3 );

  					outVertices.push( nV4 );
  					outVertices.push( nV3.clone() );
  					outVertices.push( nV2.clone() );

  					break;

  				}

  				case 2: {

  					// two vertices lies outside of the plane, perform clipping

  					if ( ! v1Out ) {

  						nV1 = inVertices[ i ].clone();
  						nV2 = clip( nV1, inVertices[ i + 1 ], plane, s );
  						nV3 = clip( nV1, inVertices[ i + 2 ], plane, s );
  						outVertices.push( nV1 );
  						outVertices.push( nV2 );
  						outVertices.push( nV3 );

  					}

  					if ( ! v2Out ) {

  						nV1 = inVertices[ i + 1 ].clone();
  						nV2 = clip( nV1, inVertices[ i + 2 ], plane, s );
  						nV3 = clip( nV1, inVertices[ i ], plane, s );
  						outVertices.push( nV1 );
  						outVertices.push( nV2 );
  						outVertices.push( nV3 );

  					}

  					if ( ! v3Out ) {

  						nV1 = inVertices[ i + 2 ].clone();
  						nV2 = clip( nV1, inVertices[ i ], plane, s );
  						nV3 = clip( nV1, inVertices[ i + 1 ], plane, s );
  						outVertices.push( nV1 );
  						outVertices.push( nV2 );
  						outVertices.push( nV3 );

  					}

  					break;

  				}

  				case 3: {

  					// the entire face lies outside of the plane, so let's discard the corresponding vertices

  					break;

  				}

  			}

  		}

  		return outVertices;

  	}

  	function clip( v0, v1, p, s ) {

  		var d0 = v0.position.dot( p ) - s;
  		var d1 = v1.position.dot( p ) - s;

  		var s0 = d0 / ( d0 - d1 );

  		var v = new DecalVertex(
  			new THREE.Vector3(
  				v0.position.x + s0 * ( v1.position.x - v0.position.x ),
  				v0.position.y + s0 * ( v1.position.y - v0.position.y ),
  				v0.position.z + s0 * ( v1.position.z - v0.position.z )
  			),
  			new THREE.Vector3(
  				v0.normal.x + s0 * ( v1.normal.x - v0.normal.x ),
  				v0.normal.y + s0 * ( v1.normal.y - v0.normal.y ),
  				v0.normal.z + s0 * ( v1.normal.z - v0.normal.z )
  			)
  		);

  		// need to clip more values (texture coordinates)? do it this way:
  		// intersectpoint.value = a.value + s * ( b.value - a.value );

  		return v;

  	}

	}

	DecalGeometry.prototype = Object.create( THREE.BufferGeometry.prototype );
	DecalGeometry.prototype.constructor = DecalGeometry;

	// helper

	function DecalVertex( position, normal ) {

		this.position = position;
		this.normal = normal;

	}

	DecalVertex.prototype.clone = function () {

		return new DecalVertex( this.position.clone(), this.normal.clone() );

	};

	// export

	THREE.DecalGeometry = DecalGeometry;

} )();