@Override
    public void simpleRender(RenderManager rm){
        Renderer r = rm.getRenderer();

        //do FBO rendering
        r.setFrameBuffer(fb);

        rm.setCamera(cam, false); // FBO uses current camera
        r.clearBuffers(true, true, true);
        rm.renderScene(fbNode, viewPort);
        rm.flushQueue(viewPort);

        //go back to default rendering and let
        //SimpleApplication render the default scene
        r.setFrameBuffer(null);
    }
Demonstrates FrameBuffer usage.
The scene is first rendered to an FB with a texture attached,
the texture is then rendered onto the screen in ortho mode.

@author Kirill
jme3-examples/src/main/java/jme3test/post/TestFBOPassthrough.java