three.js/examples/js/renderers/CSS3DRenderer.js

/**
 * Based on http://www.emagix.net/academic/mscs-project/item/camera-sync-with-css3-and-webgl-threejs
 */

THREE.CSS3DObject = function ( element ) {

	THREE.Object3D.call( this );

	this.element = element || document.createElement( 'div' );
	this.element.style.position = 'absolute';
	this.element.style.pointerEvents = 'auto';

	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.assign( Object.create( THREE.Object3D.prototype ), {

	constructor: THREE.CSS3DObject,

	copy: function ( source, recursive ) {

		THREE.Object3D.prototype.copy.call( this, source, recursive );

		this.element = source.element.cloneNode( true );

		return this;

	}

} );

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 _this = this;

	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.transformStyle = 'preserve-3d';
	cameraElement.style.pointerEvents = 'none';

	domElement.appendChild( cameraElement );

	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 ) {

		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 ] ) +
		')';

		return 'translate(-50%,-50%)' + matrix3d;

	}

	function renderObject( object, scene, camera, cameraCSSMatrix ) {

		if ( object instanceof THREE.CSS3DObject ) {

			object.onBeforeRender( _this, scene, camera );

			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 );

			} else {

				style = getObjectCSSMatrix( object.matrixWorld );

			}

			var element = object.element;
			var cachedObject = cache.objects.get( object );

			if ( cachedObject === undefined || cachedObject.style !== style ) {

				element.style.transform = style;

				var objectData = { style: style };
				cache.objects.set( object, objectData );

			}

			element.style.display = object.visible ? '' : 'none';

			if ( element.parentNode !== cameraElement ) {

				cameraElement.appendChild( element );

			}

			object.onAfterRender( _this, scene, camera );

		}

		for ( var i = 0, l = object.children.length; i < l; i ++ ) {

			renderObject( object.children[ i ], scene, camera, cameraCSSMatrix );

		}

	}

	this.render = function ( scene, camera ) {

		var fov = camera.projectionMatrix.elements[ 5 ] * _heightHalf;

		if ( cache.camera.fov !== fov ) {

			domElement.style.perspective = camera.isPerspectiveCamera ? fov + 'px' : '';
			cache.camera.fov = fov;

		}

		if ( scene.autoUpdate === true ) 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 ) {

			cameraElement.style.transform = style;

			cache.camera.style = style;

		}

		renderObject( scene, scene, camera, cameraCSSMatrix );

	};

};