text: /**
   * @author mrdoob / http://mrdoob.com/
   * @author supereggbert / http://www.paulbrunt.co.uk/
   * @author julianwa / https://github.com/julianwa
   */
  
  THREE.RenderableObject = function () {
  
  	this.id = 0;
  
  	this.object = null;
  	this.z = 0;
  
  };
  
  //
  
  THREE.RenderableFace = function () {
  
  	this.id = 0;
  
  	this.v1 = new THREE.RenderableVertex();
  	this.v2 = new THREE.RenderableVertex();
  	this.v3 = new THREE.RenderableVertex();
  
  	this.normalModel = new THREE.Vector3();
  
  	this.vertexNormalsModel = [ new THREE.Vector3(), new THREE.Vector3(), new THREE.Vector3() ];
  	this.vertexNormalsLength = 0;
  
  	this.color = new THREE.Color();
  	this.material = null;
  	this.uvs = [ new THREE.Vector2(), new THREE.Vector2(), new THREE.Vector2() ];
  
  	this.z = 0;
  
  };
  
  //
  
  THREE.RenderableVertex = function () {
  
  	this.position = new THREE.Vector3();
  	this.positionWorld = new THREE.Vector3();
  	this.positionScreen = new THREE.Vector4();
  
  	this.visible = true;
  
  };
  
  THREE.RenderableVertex.prototype.copy = function ( vertex ) {
  
  	this.positionWorld.copy( vertex.positionWorld );
  	this.positionScreen.copy( vertex.positionScreen );
  
  };
  
  //
  
  THREE.RenderableLine = function () {
  
  	this.id = 0;
  
  	this.v1 = new THREE.RenderableVertex();
  	this.v2 = new THREE.RenderableVertex();
  
  	this.vertexColors = [ new THREE.Color(), new THREE.Color() ];
  	this.material = null;
  
  	this.z = 0;
  
  };
  
  //
  
  THREE.RenderableSprite = function () {
  
  	this.id = 0;
  
  	this.object = null;
  
  	this.x = 0;
  	this.y = 0;
  	this.z = 0;
  
  	this.rotation = 0;
  	this.scale = new THREE.Vector2();
  
  	this.material = null;
  
  };
  
  //
  
  THREE.Projector = function () {
  
  	var _object, _objectCount, _objectPool = [], _objectPoolLength = 0,
  	_vertex, _vertexCount, _vertexPool = [], _vertexPoolLength = 0,
  	_face, _faceCount, _facePool = [], _facePoolLength = 0,
  	_line, _lineCount, _linePool = [], _linePoolLength = 0,
  	_sprite, _spriteCount, _spritePool = [], _spritePoolLength = 0,
  
  	_renderData = { objects: [], lights: [], elements: [] },
  
  	_vA = new THREE.Vector3(),
  	_vB = new THREE.Vector3(),
  	_vC = new THREE.Vector3(),
  
  	_vector3 = new THREE.Vector3(),
  	_vector4 = new THREE.Vector4(),
  
  	_clipBox = new THREE.Box3( new THREE.Vector3( - 1, - 1, - 1 ), new THREE.Vector3( 1, 1, 1 ) ),
  	_boundingBox = new THREE.Box3(),
  	_points3 = new Array( 3 ),
  	_points4 = new Array( 4 ),
  
  	_viewMatrix = new THREE.Matrix4(),
  	_viewProjectionMatrix = new THREE.Matrix4(),
  
  	_modelMatrix,
  	_modelViewProjectionMatrix = new THREE.Matrix4(),
  
  	_normalMatrix = new THREE.Matrix3(),
  
  	_frustum = new THREE.Frustum(),
  
  	_clippedVertex1PositionScreen = new THREE.Vector4(),
  	_clippedVertex2PositionScreen = new THREE.Vector4();
  
  	//
  
  	this.projectVector = function ( vector, camera ) {
  
  		console.warn( 'THREE.Projector: .projectVector() is now vector.project().' );
  		vector.project( camera );
  
  	};
  
  	this.unprojectVector = function ( vector, camera ) {
  
  		console.warn( 'THREE.Projector: .unprojectVector() is now vector.unproject().' );
  		vector.unproject( camera );
  
  	};
  
  	this.pickingRay = function ( vector, camera ) {
  
  		console.error( 'THREE.Projector: .pickingRay() has been removed.' );
  
  	};
  
  	//
  
  	var RenderList = function () {
  
  		var normals = [];
  		var uvs = [];
  
  		var object = null;
  		var material = null;
  
  		var normalMatrix = new THREE.Matrix3();
  
  		var setObject = function ( value ) {
  
  			object = value;
  			material = object.material;
  
  			normalMatrix.getNormalMatrix( object.matrixWorld );
  
  			normals.length = 0;
  			uvs.length = 0;
  
  		};
  
  		var projectVertex = function ( vertex ) {
  
  			var position = vertex.position;
  			var positionWorld = vertex.positionWorld;
  			var positionScreen = vertex.positionScreen;
  
  			positionWorld.copy( position ).applyMatrix4( _modelMatrix );
  			positionScreen.copy( positionWorld ).applyMatrix4( _viewProjectionMatrix );
  
  			var invW = 1 / positionScreen.w;
  
  			positionScreen.x *= invW;
  			positionScreen.y *= invW;
  			positionScreen.z *= invW;
  
  			vertex.visible = positionScreen.x >= - 1 && positionScreen.x <= 1 &&
  					 positionScreen.y >= - 1 && positionScreen.y <= 1 &&
  					 positionScreen.z >= - 1 && positionScreen.z <= 1;
  
  		};
  
  		var pushVertex = function ( x, y, z ) {
  
  			_vertex = getNextVertexInPool();
  			_vertex.position.set( x, y, z );
  
  			projectVertex( _vertex );
  
  		};
  
  		var pushNormal = function ( x, y, z ) {
  
  			normals.push( x, y, z );
  
  		};
  
  		var pushUv = function ( x, y ) {
  
  			uvs.push( x, y );
  
  		};
  
  		var checkTriangleVisibility = function ( v1, v2, v3 ) {
  
  			if ( v1.visible === true || v2.visible === true || v3.visible === true ) return true;
  
  			_points3[ 0 ] = v1.positionScreen;
  			_points3[ 1 ] = v2.positionScreen;
  			_points3[ 2 ] = v3.positionScreen;
  
  			return _clipBox.isIntersectionBox( _boundingBox.setFromPoints( _points3 ) );
  
  		};
  
  		var checkBackfaceCulling = function ( v1, v2, v3 ) {
  
  			return ( ( v3.positionScreen.x - v1.positionScreen.x ) *
  				    ( v2.positionScreen.y - v1.positionScreen.y ) -
  				    ( v3.positionScreen.y - v1.positionScreen.y ) *
  				    ( v2.positionScreen.x - v1.positionScreen.x ) ) < 0;
  
  		};
  
  		var pushLine = function ( a, b ) {
  
  			var v1 = _vertexPool[ a ];
  			var v2 = _vertexPool[ b ];
  
  			_line = getNextLineInPool();
  
  			_line.id = object.id;
  			_line.v1.copy( v1 );
  			_line.v2.copy( v2 );
  			_line.z = ( v1.positionScreen.z + v2.positionScreen.z ) / 2;
  
  			_line.material = object.material;
  
  			_renderData.elements.push( _line );
  
  		};
  
  		var pushTriangle = function ( a, b, c ) {
  
  			var v1 = _vertexPool[ a ];
  			var v2 = _vertexPool[ b ];
  			var v3 = _vertexPool[ c ];
  
  			if ( checkTriangleVisibility( v1, v2, v3 ) === false ) return;
  
  			if ( material.side === THREE.DoubleSide || checkBackfaceCulling( v1, v2, v3 ) === true ) {
  
  				_face = getNextFaceInPool();
  
  				_face.id = object.id;
  				_face.v1.copy( v1 );
  				_face.v2.copy( v2 );
  				_face.v3.copy( v3 );
  				_face.z = ( v1.positionScreen.z + v2.positionScreen.z + v3.positionScreen.z ) / 3;
  
  				for ( var i = 0; i < 3; i ++ ) {
  
  					var offset = arguments[ i ] * 3;
  					var normal = _face.vertexNormalsModel[ i ];
  
  					normal.set( normals[ offset ], normals[ offset + 1 ], normals[ offset + 2 ] );
  					normal.applyMatrix3( normalMatrix ).normalize();
  
  					var offset2 = arguments[ i ] * 2;
  
  					var uv = _face.uvs[ i ];
  					uv.set( uvs[ offset2 ], uvs[ offset2 + 1 ] );
  
  				}
  
  				_face.vertexNormalsLength = 3;
  
  				_face.material = object.material;
  
  				_renderData.elements.push( _face );
  
  			}
  
  		};
  
  		return {
  			setObject: setObject,
  			projectVertex: projectVertex,
  			checkTriangleVisibility: checkTriangleVisibility,
  			checkBackfaceCulling: checkBackfaceCulling,
  			pushVertex: pushVertex,
  			pushNormal: pushNormal,
  			pushUv: pushUv,
  			pushLine: pushLine,
  			pushTriangle: pushTriangle
  		}
  
  	};
  
  	var renderList = new RenderList();
  
  	this.projectScene = function ( scene, camera, sortObjects, sortElements ) {
  
  		_faceCount = 0;
  		_lineCount = 0;
  		_spriteCount = 0;
  
  		_renderData.elements.length = 0;
  
  		if ( scene.autoUpdate === true ) scene.updateMatrixWorld();
  		if ( camera.parent === undefined ) camera.updateMatrixWorld();
  
  		_viewMatrix.copy( camera.matrixWorldInverse.getInverse( camera.matrixWorld ) );
  		_viewProjectionMatrix.multiplyMatrices( camera.projectionMatrix, _viewMatrix );
  
  		_frustum.setFromMatrix( _viewProjectionMatrix );
  
  		//
  
  		_objectCount = 0;
  
  		_renderData.objects.length = 0;
  		_renderData.lights.length = 0;
  
  		scene.traverseVisible( function ( object ) {
  
  			if ( object instanceof THREE.Light ) {
  
  				_renderData.lights.push( object );
  
  			} else if ( object instanceof THREE.Mesh || object instanceof THREE.Line || object instanceof THREE.Sprite ) {
  
  				if ( object.material.visible === false ) return;
  
  				if ( object.frustumCulled === false || _frustum.intersectsObject( object ) === true ) {
  
  					_object = getNextObjectInPool();
  					_object.id = object.id;
  					_object.object = object;
  
  					if ( object.renderDepth !== null ) {
  
  						_object.z = object.renderDepth;
  
  					} else {
  
  						_vector3.setFromMatrixPosition( object.matrixWorld );
  						_vector3.applyProjection( _viewProjectionMatrix );
  						_object.z = _vector3.z;
  
  					}
  
  					_renderData.objects.push( _object );
  
  				}
  
  			}
  
  		} );
  
  		if ( sortObjects === true ) {
  
  			_renderData.objects.sort( painterSort );
  
  		}
  
  		//
  
  		for ( var o = 0, ol = _renderData.objects.length; o < ol; o ++ ) {
  
  			var object = _renderData.objects[ o ].object;
  			var geometry = object.geometry;
  
  			renderList.setObject( object );
  
  			_modelMatrix = object.matrixWorld;
  
  			_vertexCount = 0;
  
  			if ( object instanceof THREE.Mesh ) {
  
  				if ( geometry instanceof THREE.BufferGeometry ) {
  
  					var attributes = geometry.attributes;
  					var offsets = geometry.offsets;
  
  					if ( attributes.position === undefined ) continue;
  
  					var positions = attributes.position.array;
  
  					for ( var i = 0, l = positions.length; i < l; i += 3 ) {
  
  						renderList.pushVertex( positions[ i ], positions[ i + 1 ], positions[ i + 2 ] );
  
  					}
  
  					if ( attributes.normal !== undefined ) {
  
  						var normals = attributes.normal.array;
  
  						for ( var i = 0, l = normals.length; i < l; i += 3 ) {
  
  							renderList.pushNormal( normals[ i ], normals[ i + 1 ], normals[ i + 2 ] );
  
  						}
  
  					}
  
  					if ( attributes.uv !== undefined ) {
  
  						var uvs = attributes.uv.array;
  
  						for ( var i = 0, l = uvs.length; i < l; i += 2 ) {
  
  							renderList.pushUv( uvs[ i ], uvs[ i + 1 ] );
  
  						}
  
  					}
  
  					if ( attributes.index !== undefined ) {
  
  						var indices = attributes.index.array;
  
  						if ( offsets.length > 0 ) {
  
  							for ( var o = 0; o < offsets.length; o ++ ) {
  
  								var offset = offsets[ o ];
  								var index = offset.index;
  
  								for ( var i = offset.start, l = offset.start + offset.count; i < l; i += 3 ) {
  
  									renderList.pushTriangle( indices[ i ] + index, indices[ i + 1 ] + index, indices[ i + 2 ] + index );
  
  								}
  
  							}
  
  						} else {
  
  							for ( var i = 0, l = indices.length; i < l; i += 3 ) {
  
  								renderList.pushTriangle( indices[ i ], indices[ i + 1 ], indices[ i + 2 ] );
  
  							}
  
  						}
  
  					} else {
  
  						for ( var i = 0, l = positions.length / 3; i < l; i += 3 ) {
  
  							renderList.pushTriangle( i, i + 1, i + 2 );
  
  						}
  
  					}
  
  				} else if ( geometry instanceof THREE.Geometry ) {
  
  					var vertices = geometry.vertices;
  					var faces = geometry.faces;
  					var faceVertexUvs = geometry.faceVertexUvs[ 0 ];
  
  					_normalMatrix.getNormalMatrix( _modelMatrix );
  
  					var isFaceMaterial = object.material instanceof THREE.MeshFaceMaterial;
  					var objectMaterials = isFaceMaterial === true ? object.material : null;
  
  					for ( var v = 0, vl = vertices.length; v < vl; v ++ ) {
  
  						var vertex = vertices[ v ];
  						renderList.pushVertex( vertex.x, vertex.y, vertex.z );
  
  					}
  
  					for ( var f = 0, fl = faces.length; f < fl; f ++ ) {
  
  						var face = faces[ f ];
  
  						var material = isFaceMaterial === true
  							 ? objectMaterials.materials[ face.materialIndex ]
  							 : object.material;
  
  						if ( material === undefined ) continue;
  
  						var side = material.side;
  
  						var v1 = _vertexPool[ face.a ];
  						var v2 = _vertexPool[ face.b ];
  						var v3 = _vertexPool[ face.c ];
  
  						if ( material.morphTargets === true ) {
  
  							var morphTargets = geometry.morphTargets;
  							var morphInfluences = object.morphTargetInfluences;
  
  							var v1p = v1.position;
  							var v2p = v2.position;
  							var v3p = v3.position;
  
  							_vA.set( 0, 0, 0 );
  							_vB.set( 0, 0, 0 );
  							_vC.set( 0, 0, 0 );
  
  							for ( var t = 0, tl = morphTargets.length; t < tl; t ++ ) {
  
  								var influence = morphInfluences[ t ];
  
  								if ( influence === 0 ) continue;
  
  								var targets = morphTargets[ t ].vertices;
  
  								_vA.x += ( targets[ face.a ].x - v1p.x ) * influence;
  								_vA.y += ( targets[ face.a ].y - v1p.y ) * influence;
  								_vA.z += ( targets[ face.a ].z - v1p.z ) * influence;
  
  								_vB.x += ( targets[ face.b ].x - v2p.x ) * influence;
  								_vB.y += ( targets[ face.b ].y - v2p.y ) * influence;
  								_vB.z += ( targets[ face.b ].z - v2p.z ) * influence;
  
  								_vC.x += ( targets[ face.c ].x - v3p.x ) * influence;
  								_vC.y += ( targets[ face.c ].y - v3p.y ) * influence;
  								_vC.z += ( targets[ face.c ].z - v3p.z ) * influence;
  
  							}
  
  							v1.position.add( _vA );
  							v2.position.add( _vB );
  							v3.position.add( _vC );
  
  							renderList.projectVertex( v1 );
  							renderList.projectVertex( v2 );
  							renderList.projectVertex( v3 );
  
  						}
  
  						if ( renderList.checkTriangleVisibility( v1, v2, v3 ) === false ) continue;
  
  						var visible = renderList.checkBackfaceCulling( v1, v2, v3 );
  
  						if ( side !== THREE.DoubleSide ) {
  							if ( side === THREE.FrontSide && visible === false ) continue;
  							if ( side === THREE.BackSide && visible === true ) continue;
  						}
  
  						_face = getNextFaceInPool();
  
  						_face.id = object.id;
  						_face.v1.copy( v1 );
  						_face.v2.copy( v2 );
  						_face.v3.copy( v3 );
  
  						_face.normalModel.copy( face.normal );
  
  						if ( visible === false && ( side === THREE.BackSide || side === THREE.DoubleSide ) ) {
  
  							_face.normalModel.negate();
  
  						}
  
  						_face.normalModel.applyMatrix3( _normalMatrix ).normalize();
  
  						var faceVertexNormals = face.vertexNormals;
  
  						for ( var n = 0, nl = Math.min( faceVertexNormals.length, 3 ); n < nl; n ++ ) {
  
  							var normalModel = _face.vertexNormalsModel[ n ];
  							normalModel.copy( faceVertexNormals[ n ] );
  
  							if ( visible === false && ( side === THREE.BackSide || side === THREE.DoubleSide ) ) {
  
  								normalModel.negate();
  
  							}
  
  							normalModel.applyMatrix3( _normalMatrix ).normalize();
  
  						}
  
  						_face.vertexNormalsLength = faceVertexNormals.length;
  
  						var vertexUvs = faceVertexUvs[ f ];
  
  						if ( vertexUvs !== undefined ) {
  
  							for ( var u = 0; u < 3; u ++ ) {
  
  								_face.uvs[ u ].copy( vertexUvs[ u ] );
  
  							}
  
  						}
  
  						_face.color = face.color;
  						_face.material = material;
  
  						_face.z = ( v1.positionScreen.z + v2.positionScreen.z + v3.positionScreen.z ) / 3;
  
  						_renderData.elements.push( _face );
  
  					}
  
  				}
  
  			} else if ( object instanceof THREE.Line ) {
  
  				if ( geometry instanceof THREE.BufferGeometry ) {
  
  					var attributes = geometry.attributes;
  
  					if ( attributes.position !== undefined ) {
  
  						var positions = attributes.position.array;
  
  						for ( var i = 0, l = positions.length; i < l; i += 3 ) {
  
  							renderList.pushVertex( positions[ i ], positions[ i + 1 ], positions[ i + 2 ] );
  
  						}
  
  						if ( attributes.index !== undefined ) {
  
  							var indices = attributes.index.array;
  
  							for ( var i = 0, l = indices.length; i < l; i += 2 ) {
  
  								renderList.pushLine( indices[ i ], indices[ i + 1 ] );
  
  							}
  
  						} else {
  
  							var step = object.mode === THREE.LinePieces ? 2 : 1;
  
  							for ( var i = 0, l = ( positions.length / 3 ) - 1; i < l; i += step ) {
  
  								renderList.pushLine( i, i + 1 );
  
  							}
  
  						}
  
  					}
  
  				} else if ( geometry instanceof THREE.Geometry ) {
  
  					_modelViewProjectionMatrix.multiplyMatrices( _viewProjectionMatrix, _modelMatrix );
  
  					var vertices = object.geometry.vertices;
  
  					if ( vertices.length === 0 ) continue;
  
  					v1 = getNextVertexInPool();
  					v1.positionScreen.copy( vertices[ 0 ] ).applyMatrix4( _modelViewProjectionMatrix );
  
  					// Handle LineStrip and LinePieces
  					var step = object.mode === THREE.LinePieces ? 2 : 1;
  
  					for ( var v = 1, vl = vertices.length; v < vl; v ++ ) {
  
  						v1 = getNextVertexInPool();
  						v1.positionScreen.copy( vertices[ v ] ).applyMatrix4( _modelViewProjectionMatrix );
  
  						if ( ( v + 1 ) % step > 0 ) continue;
  
  						v2 = _vertexPool[ _vertexCount - 2 ];
  
  						_clippedVertex1PositionScreen.copy( v1.positionScreen );
  						_clippedVertex2PositionScreen.copy( v2.positionScreen );
  
  						if ( clipLine( _clippedVertex1PositionScreen, _clippedVertex2PositionScreen ) === true ) {
  
  							// Perform the perspective divide
  							_clippedVertex1PositionScreen.multiplyScalar( 1 / _clippedVertex1PositionScreen.w );
  							_clippedVertex2PositionScreen.multiplyScalar( 1 / _clippedVertex2PositionScreen.w );
  
  							_line = getNextLineInPool();
  
  							_line.id = object.id;
  							_line.v1.positionScreen.copy( _clippedVertex1PositionScreen );
  							_line.v2.positionScreen.copy( _clippedVertex2PositionScreen );
  
  							_line.z = Math.max( _clippedVertex1PositionScreen.z, _clippedVertex2PositionScreen.z );
  
  							_line.material = object.material;
  
  							if ( object.material.vertexColors === THREE.VertexColors ) {
  
  								_line.vertexColors[ 0 ].copy( object.geometry.colors[ v ] );
  								_line.vertexColors[ 1 ].copy( object.geometry.colors[ v - 1 ] );
  
  							}
  
  							_renderData.elements.push( _line );
  
  						}
  
  					}
  
  				}
  
  			} else if ( object instanceof THREE.Sprite ) {
  
  				_vector4.set( _modelMatrix.elements[ 12 ], _modelMatrix.elements[ 13 ], _modelMatrix.elements[ 14 ], 1 );
  				_vector4.applyMatrix4( _viewProjectionMatrix );
  
  				var invW = 1 / _vector4.w;
  
  				_vector4.z *= invW;
  
  				if ( _vector4.z >= - 1 && _vector4.z <= 1 ) {
  
  					_sprite = getNextSpriteInPool();
  					_sprite.id = object.id;
  					_sprite.x = _vector4.x * invW;
  					_sprite.y = _vector4.y * invW;
  					_sprite.z = _vector4.z;
  					_sprite.object = object;
  
  					_sprite.rotation = object.rotation;
  
  					_sprite.scale.x = object.scale.x * Math.abs( _sprite.x - ( _vector4.x + camera.projectionMatrix.elements[ 0 ] ) / ( _vector4.w + camera.projectionMatrix.elements[ 12 ] ) );
  					_sprite.scale.y = object.scale.y * Math.abs( _sprite.y - ( _vector4.y + camera.projectionMatrix.elements[ 5 ] ) / ( _vector4.w + camera.projectionMatrix.elements[ 13 ] ) );
  
  					_sprite.material = object.material;
  
  					_renderData.elements.push( _sprite );
  
  				}
  
  			}
  
  		}
  
  		if ( sortElements === true ) {
  
  			_renderData.elements.sort( painterSort );
  
  		}
  
  		return _renderData;
  
  	};
  
  	// Pools
  
  	function getNextObjectInPool() {
  
  		if ( _objectCount === _objectPoolLength ) {
  
  			var object = new THREE.RenderableObject();
  			_objectPool.push( object );
  			_objectPoolLength ++;
  			_objectCount ++;
  			return object;
  
  		}
  
  		return _objectPool[ _objectCount ++ ];
  
  	}
  
  	function getNextVertexInPool() {
  
  		if ( _vertexCount === _vertexPoolLength ) {
  
  			var vertex = new THREE.RenderableVertex();
  			_vertexPool.push( vertex );
  			_vertexPoolLength ++;
  			_vertexCount ++;
  			return vertex;
  
  		}
  
  		return _vertexPool[ _vertexCount ++ ];
  
  	}
  
  	function getNextFaceInPool() {
  
  		if ( _faceCount === _facePoolLength ) {
  
  			var face = new THREE.RenderableFace();
  			_facePool.push( face );
  			_facePoolLength ++;
  			_faceCount ++;
  			return face;
  
  		}
  
  		return _facePool[ _faceCount ++ ];
  
  
  	}
  
  	function getNextLineInPool() {
  
  		if ( _lineCount === _linePoolLength ) {
  
  			var line = new THREE.RenderableLine();
  			_linePool.push( line );
  			_linePoolLength ++;
  			_lineCount ++
  			return line;
  
  		}
  
  		return _linePool[ _lineCount ++ ];
  
  	}
  
  	function getNextSpriteInPool() {
  
  		if ( _spriteCount === _spritePoolLength ) {
  
  			var sprite = new THREE.RenderableSprite();
  			_spritePool.push( sprite );
  			_spritePoolLength ++;
  			_spriteCount ++
  			return sprite;
  
  		}
  
  		return _spritePool[ _spriteCount ++ ];
  
  	}
  
  	//
  
  	function painterSort( a, b ) {
  
  		if ( a.z !== b.z ) {
  
  			return b.z - a.z;
  
  		} else if ( a.id !== b.id ) {
  
  			return a.id - b.id;
  
  		} else {
  
  			return 0;
  
  		}
  
  	}
  
  	function clipLine( s1, s2 ) {
  
  		var alpha1 = 0, alpha2 = 1,
  
  		// Calculate the boundary coordinate of each vertex for the near and far clip planes,
  		// Z = -1 and Z = +1, respectively.
  		bc1near =  s1.z + s1.w,
  		bc2near =  s2.z + s2.w,
  		bc1far =  - s1.z + s1.w,
  		bc2far =  - s2.z + s2.w;
  
  		if ( bc1near >= 0 && bc2near >= 0 && bc1far >= 0 && bc2far >= 0 ) {
  
  			// Both vertices lie entirely within all clip planes.
  			return true;
  
  		} else if ( ( bc1near < 0 && bc2near < 0 ) || ( bc1far < 0 && bc2far < 0 ) ) {
  
  			// Both vertices lie entirely outside one of the clip planes.
  			return false;
  
  		} else {
  
  			// The line segment spans at least one clip plane.
  
  			if ( bc1near < 0 ) {
  
  				// v1 lies outside the near plane, v2 inside
  				alpha1 = Math.max( alpha1, bc1near / ( bc1near - bc2near ) );
  
  			} else if ( bc2near < 0 ) {
  
  				// v2 lies outside the near plane, v1 inside
  				alpha2 = Math.min( alpha2, bc1near / ( bc1near - bc2near ) );
  
  			}
  
  			if ( bc1far < 0 ) {
  
  				// v1 lies outside the far plane, v2 inside
  				alpha1 = Math.max( alpha1, bc1far / ( bc1far - bc2far ) );
  
  			} else if ( bc2far < 0 ) {
  
  				// v2 lies outside the far plane, v2 inside
  				alpha2 = Math.min( alpha2, bc1far / ( bc1far - bc2far ) );
  
  			}
  
  			if ( alpha2 < alpha1 ) {
  
  				// The line segment spans two boundaries, but is outside both of them.
  				// (This can't happen when we're only clipping against just near/far but good
  				//  to leave the check here for future usage if other clip planes are added.)
  				return false;
  
  			} else {
  
  				// Update the s1 and s2 vertices to match the clipped line segment.
  				s1.lerp( s2, alpha1 );
  				s2.lerp( s1, 1 - alpha2 );
  
  				return true;
  
  			}
  
  		}
  
  	}
  
  };
  