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

( function () {

	/**
 * 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/
 *
 */

	class DecalGeometry extends THREE.BufferGeometry {

		constructor( mesh, position, orientation, size ) {

			super();

			// buffers

			const vertices = [];
			const normals = [];
			const uvs = [];

			// helpers

			const plane = new THREE.Vector3();

			// this matrix represents the transformation of the decal projector

			const projectorMatrix = new THREE.Matrix4();
			projectorMatrix.makeRotationFromEuler( orientation );
			projectorMatrix.setPosition( position );
			const projectorMatrixInverse = new THREE.Matrix4();
			projectorMatrixInverse.copy( projectorMatrix ).invert();

			// generate buffers

			generate();

			// build geometry

			this.setAttribute( 'position', new THREE.Float32BufferAttribute( vertices, 3 ) );
			this.setAttribute( 'normal', new THREE.Float32BufferAttribute( normals, 3 ) );
			this.setAttribute( 'uv', new THREE.Float32BufferAttribute( uvs, 2 ) );
			function generate() {

				let decalVertices = [];
				const vertex = new THREE.Vector3();
				const normal = new THREE.Vector3();

				// handle different geometry types

				const geometry = mesh.geometry;
				const positionAttribute = geometry.attributes.position;
				const 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 THREE.BufferGeometry

					const index = geometry.index;
					for ( let 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 THREE.BufferGeometry

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

					const 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.matrixWorld );
				vertex.applyMatrix4( projectorMatrixInverse );
				normal.transformDirection( mesh.matrixWorld );
				decalVertices.push( new DecalVertex( vertex.clone(), normal.clone() ) );

			}

			function clipGeometry( inVertices, plane ) {

				const outVertices = [];
				const s = 0.5 * Math.abs( size.dot( plane ) );

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

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

					let total = 0;
					let nV1;
					let nV2;
					let nV3;
					let nV4;
					const d1 = inVertices[ i + 0 ].position.dot( plane ) - s;
					const d2 = inVertices[ i + 1 ].position.dot( plane ) - s;
					const d3 = inVertices[ i + 2 ].position.dot( plane ) - s;
					const v1Out = d1 > 0;
					const v2Out = d2 > 0;
					const 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 ) {

				const d0 = v0.position.dot( p ) - s;
				const d1 = v1.position.dot( p ) - s;
				const s0 = d0 / ( d0 - d1 );
				const 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;

			}

		}

	}

	// helper

	class DecalVertex {

		constructor( position, normal ) {

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

		}
		clone() {

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

		}

	}

	THREE.DecalGeometry = DecalGeometry;
	THREE.DecalVertex = DecalVertex;

} )();