text: /**
   * Based on http://www.emagix.net/academic/mscs-project/item/camera-sync-with-css3-and-webgl-threejs
   * @author mrdoob / http://mrdoob.com/
   * @author yomotsu / https://yomotsu.net/
   */
  
  THREE.CSS3DObject = function ( element ) {
  
  	THREE.Object3D.call( this );
  
  	this.element = element;
  	this.element.style.position = 'absolute';
  
  	this.addEventListener( 'removed', function () {
  
  		this.traverse( function ( object ) {
  
  			if ( object.element instanceof Element && object.element.parentNode !== null ) {
  
  				object.element.parentNode.removeChild( object.element );
  
  			}
  
  		} );
  
  	} );
  
  };
  
  THREE.CSS3DObject.prototype = Object.create( THREE.Object3D.prototype );
  THREE.CSS3DObject.prototype.constructor = THREE.CSS3DObject;
  
  THREE.CSS3DSprite = function ( element ) {
  
  	THREE.CSS3DObject.call( this, element );
  
  };
  
  THREE.CSS3DSprite.prototype = Object.create( THREE.CSS3DObject.prototype );
  THREE.CSS3DSprite.prototype.constructor = THREE.CSS3DSprite;
  
  //
  
  THREE.CSS3DRenderer = function () {
  
  	var _width, _height;
  	var _widthHalf, _heightHalf;
  
  	var matrix = new THREE.Matrix4();
  
  	var cache = {
  		camera: { fov: 0, style: '' },
  		objects: new WeakMap()
  	};
  
  	var domElement = document.createElement( 'div' );
  	domElement.style.overflow = 'hidden';
  
  	this.domElement = domElement;
  
  	var cameraElement = document.createElement( 'div' );
  
  	cameraElement.style.WebkitTransformStyle = 'preserve-3d';
  	cameraElement.style.transformStyle = 'preserve-3d';
  
  	domElement.appendChild( cameraElement );
  
  	var isIE = /Trident/i.test( navigator.userAgent );
  
  	this.getSize = function () {
  
  		return {
  			width: _width,
  			height: _height
  		};
  
  	};
  
  	this.setSize = function ( width, height ) {
  
  		_width = width;
  		_height = height;
  		_widthHalf = _width / 2;
  		_heightHalf = _height / 2;
  
  		domElement.style.width = width + 'px';
  		domElement.style.height = height + 'px';
  
  		cameraElement.style.width = width + 'px';
  		cameraElement.style.height = height + 'px';
  
  	};
  
  	function epsilon( value ) {
  
  		return Math.abs( value ) < 1e-10 ? 0 : value;
  
  	}
  
  	function getCameraCSSMatrix( matrix ) {
  
  		var elements = matrix.elements;
  
  		return 'matrix3d(' +
  			epsilon( elements[ 0 ] ) + ',' +
  			epsilon( - elements[ 1 ] ) + ',' +
  			epsilon( elements[ 2 ] ) + ',' +
  			epsilon( elements[ 3 ] ) + ',' +
  			epsilon( elements[ 4 ] ) + ',' +
  			epsilon( - elements[ 5 ] ) + ',' +
  			epsilon( elements[ 6 ] ) + ',' +
  			epsilon( elements[ 7 ] ) + ',' +
  			epsilon( elements[ 8 ] ) + ',' +
  			epsilon( - elements[ 9 ] ) + ',' +
  			epsilon( elements[ 10 ] ) + ',' +
  			epsilon( elements[ 11 ] ) + ',' +
  			epsilon( elements[ 12 ] ) + ',' +
  			epsilon( - elements[ 13 ] ) + ',' +
  			epsilon( elements[ 14 ] ) + ',' +
  			epsilon( elements[ 15 ] ) +
  		')';
  
  	}
  
  	function getObjectCSSMatrix( matrix, cameraCSSMatrix ) {
  
  		var elements = matrix.elements;
  		var matrix3d = 'matrix3d(' +
  			epsilon( elements[ 0 ] ) + ',' +
  			epsilon( elements[ 1 ] ) + ',' +
  			epsilon( elements[ 2 ] ) + ',' +
  			epsilon( elements[ 3 ] ) + ',' +
  			epsilon( - elements[ 4 ] ) + ',' +
  			epsilon( - elements[ 5 ] ) + ',' +
  			epsilon( - elements[ 6 ] ) + ',' +
  			epsilon( - elements[ 7 ] ) + ',' +
  			epsilon( elements[ 8 ] ) + ',' +
  			epsilon( elements[ 9 ] ) + ',' +
  			epsilon( elements[ 10 ] ) + ',' +
  			epsilon( elements[ 11 ] ) + ',' +
  			epsilon( elements[ 12 ] ) + ',' +
  			epsilon( elements[ 13 ] ) + ',' +
  			epsilon( elements[ 14 ] ) + ',' +
  			epsilon( elements[ 15 ] ) +
  		')';
  
  		if ( isIE ) {
  
  			return 'translate(-50%,-50%)' +
  				'translate(' + _widthHalf + 'px,' + _heightHalf + 'px)' +
  				cameraCSSMatrix +
  				matrix3d;
  
  		}
  
  		return 'translate(-50%,-50%)' + matrix3d;
  
  	}
  
  	function renderObject( object, camera, cameraCSSMatrix ) {
  
  		if ( object instanceof THREE.CSS3DObject ) {
  
  			var style;
  
  			if ( object instanceof THREE.CSS3DSprite ) {
  
  				// http://swiftcoder.wordpress.com/2008/11/25/constructing-a-billboard-matrix/
  
  				matrix.copy( camera.matrixWorldInverse );
  				matrix.transpose();
  				matrix.copyPosition( object.matrixWorld );
  				matrix.scale( object.scale );
  
  				matrix.elements[ 3 ] = 0;
  				matrix.elements[ 7 ] = 0;
  				matrix.elements[ 11 ] = 0;
  				matrix.elements[ 15 ] = 1;
  
  				style = getObjectCSSMatrix( matrix, cameraCSSMatrix );
  
  			} else {
  
  				style = getObjectCSSMatrix( object.matrixWorld, cameraCSSMatrix );
  
  			}
  
  			var element = object.element;
  			var cachedObject = cache.objects.get( object );
  
  			if ( cachedObject === undefined || cachedObject.style !== style ) {
  
  				element.style.WebkitTransform = style;
  				element.style.transform = style;
  
  				var objectData = { style: style };
  
  				if ( isIE ) {
  
  					objectData.distanceToCameraSquared = getDistanceToSquared( camera, object );
  
  				}
  
  				cache.objects.set( object, objectData );
  
  			}
  
  			if ( element.parentNode !== cameraElement ) {
  
  				cameraElement.appendChild( element );
  
  			}
  
  		}
  
  		for ( var i = 0, l = object.children.length; i < l; i ++ ) {
  
  			renderObject( object.children[ i ], camera, cameraCSSMatrix );
  
  		}
  
  	}
  
  	var getDistanceToSquared = function () {
  
  		var a = new THREE.Vector3();
  		var b = new THREE.Vector3();
  
  		return function ( object1, object2 ) {
  
  			a.setFromMatrixPosition( object1.matrixWorld );
  			b.setFromMatrixPosition( object2.matrixWorld );
  
  			return a.distanceToSquared( b );
  
  		};
  
  	}();
  
  	function filterAndFlatten( scene ) {
  
  		var result = [];
  
  		scene.traverse( function ( object ) {
  
  			if ( object instanceof THREE.CSS3DObject ) result.push( object );
  
  		} );
  
  		return result;
  
  	}
  
  	function zOrder( scene ) {
  
  		var sorted = filterAndFlatten( scene ).sort( function ( a, b ) {
  
  			var distanceA = cache.objects.get( a ).distanceToCameraSquared;
  			var distanceB = cache.objects.get( b ).distanceToCameraSquared;
  
  			return distanceA - distanceB;
  
  		} );
  
  		var zMax = sorted.length;
  
  		for ( var i = 0, l = sorted.length; i < l; i ++ ) {
  
  			sorted[ i ].element.style.zIndex = zMax - i;
  
  		}
  
  	}
  
  	this.render = function ( scene, camera ) {
  
  		var fov = camera.projectionMatrix.elements[ 5 ] * _heightHalf;
  
  		if ( cache.camera.fov !== fov ) {
  
  			if ( camera.isPerspectiveCamera ) {
  
  				domElement.style.WebkitPerspective = fov + 'px';
  				domElement.style.perspective = fov + 'px';
  
  			} else {
  
  				domElement.style.WebkitPerspective = '';
  				domElement.style.perspective = '';
  
  			}
  
  			cache.camera.fov = fov;
  
  		}
  
  		scene.updateMatrixWorld();
  
  		if ( camera.parent === null ) camera.updateMatrixWorld();
  
  		if ( camera.isOrthographicCamera ) {
  
  			var tx = - ( camera.right + camera.left ) / 2;
  			var ty = ( camera.top + camera.bottom ) / 2;
  
  		}
  
  		var cameraCSSMatrix = camera.isOrthographicCamera ?
  			'scale(' + fov + ')' + 'translate(' + epsilon( tx ) + 'px,' + epsilon( ty ) + 'px)' + getCameraCSSMatrix( camera.matrixWorldInverse ) :
  			'translateZ(' + fov + 'px)' + getCameraCSSMatrix( camera.matrixWorldInverse );
  
  		var style = cameraCSSMatrix +
  			'translate(' + _widthHalf + 'px,' + _heightHalf + 'px)';
  
  		if ( cache.camera.style !== style && ! isIE ) {
  
  			cameraElement.style.WebkitTransform = style;
  			cameraElement.style.transform = style;
  
  			cache.camera.style = style;
  
  		}
  
  		renderObject( scene, camera, cameraCSSMatrix );
  
  		if ( isIE ) {
  
  			// IE10 and 11 does not support 'preserve-3d'.
  			// Thus, z-order in 3D will not work.
  			// We have to calc z-order manually and set CSS z-index for IE.
  			// FYI: z-index can't handle object intersection
  			zOrder( scene );
  
  		}
  
  	};
  
  };
  