private void setupLights() {
        AmbientLight ambient = new AmbientLight();
        ambient.setColor(new ColorRGBA(0.2f, 0.2f, 0.2f, 1f));
        rootNode.addLight(ambient);

        DirectionalLight sun = new DirectionalLight();
        sun.setDirection(new Vector3f(0f, -1f, -1f).normalizeLocal());
        sun.setColor(ColorRGBA.White.mult(1.5f));
        rootNode.addLight(sun);
    }
Demonstrates how to render a non-moving background image using a pre
ViewPort.

@author Stephen Gold sgold@sonic.net
jme3-examples/src/main/java/jme3test/renderer/TestBackgroundImage.java