function _getPath(ev) {
    // TODO move into _triggerEvent, avoid object allocation
    var path = [];
    var node = ev.target;
    while (node !== document.body) {
        path.push(node);
        node = node.parentNode;
    }
    return path;
}
getSizeOf gets the dom size of a particular DOM element.  This is
needed for render sizing in the scene graph.

@method

@param {String} path path of the Node in the scene graph

@return {Array} a vec3 of the offset size of the dom element