SceneJS_math_subVec2 = function(u, v, dest) {
    if (!dest) {
        dest = u;
    }

    dest[0] = u[0] - v[0];
    dest[1] = u[1] - v[1];

    return dest;
}
@param u vec2
@param v vec2
@param dest vec2 - optional destination
@return {vec2} dest if specified, u otherwise
@private