@Override
    public void simpleUpdate(float tpf){
        Quaternion q = new Quaternion();
        
        if (offView.isEnabled()) {
            angle += tpf;
            angle %= FastMath.TWO_PI;
            q.fromAngles(angle, 0, angle);
            
            offBox.setLocalRotation(q);
            offBox.updateLogicalState(tpf);
            offBox.updateGeometricState();
        }
    }
This test renders a scene to a texture, then displays the texture on a cube.
jme3-examples/src/main/java/jme3test/post/TestRenderToTexture.java