public void union(Viewport v) {
        union(v.left, v.top, v.right, v.bottom);
    }
Update this Viewport to enclose itself and the specified viewport. If the specified viewport is empty, nothing is
done. If this viewport is empty it is set to the specified viewport.

@param v The viewport being unioned with this viewport
hellocharts-library/src/lecho/lib/hellocharts/model/Viewport.java