public void flushQueue(ViewPort vp) {
        renderViewPortQueues(vp, true);
    }
Flushes the ViewPort's {@link ViewPort#getQueue() render queue}
by rendering each of its visible buckets.
By default, the queues will be cleared automatically after rendering,
so there's no need to clear them manually.

@param vp The ViewPort of which the queue will be flushed

@see RenderQueue#renderQueue(com.jme3.renderer.queue.RenderQueue.Bucket,
    com.jme3.renderer.RenderManager, com.jme3.renderer.Camera)
@see #renderGeometryList(com.jme3.renderer.queue.GeometryList)
jme3-core/src/main/java/com/jme3/renderer/RenderManager.java