SOURCE

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

THREE.CSS3DObject = function (element) {

    THREE.Object3D.call(this);

    this.element = element;
    this.element.style.position = 'absolute';

    this.addEventListener('removed', function (event) {

        if (this.element.parentNode !== null) {

            this.element.parentNode.removeChild(this.element);

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

                this.children[i].dispatchEvent(event);

            }

        }

    });

};

THREE.CSS3DObject.prototype = Object.create(THREE.Object3D.prototype);

THREE.CSS3DSprite = function (element) {

    THREE.CSS3DObject.call(this, element);

};

THREE.CSS3DSprite.prototype = Object.create(THREE.CSS3DObject.prototype);

//

THREE.CSS3DRenderer = function () {

    console.log('THREE.CSS3DRenderer', THREE.REVISION);

    var _width, _height;
    var _widthHalf, _heightHalf;

    var matrix = new THREE.Matrix4();

    var domElement = document.createElement('div');
    domElement.style.overflow = 'hidden';

    domElement.style.WebkitTransformStyle = 'preserve-3d';
    domElement.style.MozTransformStyle = 'preserve-3d';
    domElement.style.oTransformStyle = 'preserve-3d';
    domElement.style.transformStyle = 'preserve-3d';

    this.domElement = domElement;

    var cameraElement = document.createElement('div');

    cameraElement.style.WebkitTransformStyle = 'preserve-3d';
    cameraElement.style.MozTransformStyle = 'preserve-3d';
    cameraElement.style.oTransformStyle = 'preserve-3d';
    cameraElement.style.transformStyle = 'preserve-3d';

    domElement.appendChild(cameraElement);

    this.setClearColor = function () {

    };

    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';

    };

    var epsilon = function (value) {

        return Math.abs(value) < 0.000001 ? 0 : value;

    };

    var getCameraCSSMatrix = function (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]) +
            ')';

    };

    var getObjectCSSMatrix = function (matrix) {

        var elements = matrix.elements;

        return 'translate3d(-50%,-50%,0) 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]) +
            ')';

    };

    var renderObject = function (object, camera) {

        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);

            } else {

                style = getObjectCSSMatrix(object.matrixWorld);

            }

            var element = object.element;

            element.style.WebkitTransform = style;
            element.style.MozTransform = style;
            element.style.oTransform = style;
            element.style.transform = style;

            if (element.parentNode !== cameraElement) {

                cameraElement.appendChild(element);

            }

        }

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

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

        }

    };

    this.render = function (scene, camera) {

        var fov = 0.5 / Math.tan(THREE.Math.degToRad(camera.fov * 0.5)) * _height;

        domElement.style.WebkitPerspective = fov + "px";
        domElement.style.MozPerspective = fov + "px";
        domElement.style.oPerspective = fov + "px";
        domElement.style.perspective = fov + "px";

        scene.updateMatrixWorld();

        if (camera.parent === undefined) camera.updateMatrixWorld();

        camera.matrixWorldInverse.getInverse(camera.matrixWorld);

        var style = "translate3d(0,0," + fov + "px)" + getCameraCSSMatrix(camera.matrixWorldInverse) +
            " translate3d(" + _widthHalf + "px," + _heightHalf + "px, 0)";

        cameraElement.style.WebkitTransform = style;
        cameraElement.style.MozTransform = style;
        cameraElement.style.oTransform = style;
        cameraElement.style.transform = style;

        renderObject(scene, camera);

    };

};