@Override
    public void render(RenderManager rm) {
        super.render(rm);
        if (viewPort != null) {
            rm.renderScene(physicsDebugRootNode, viewPort);
        }
    }
Render this state. Should be invoked only by a subclass or by the
AppStateManager. Invoked once per frame, provided the state is attached
and enabled.

@param rm the render manager (not null)
jme3-jbullet/src/main/java/com/jme3/bullet/debug/BulletDebugAppState.java