@Override
    public void simpleInitApp() {
        /*
         * SimpleApplication creates 2 viewports:
         * 1. the default viewport (rendered first, after clearing all buffers)
         * 2. the GUI viewport (rendered last, without clearing any buffers)
         *
         * Create a 3rd ViewPort, named "background viewport",
         * to be rendered BEFORE the default viewport.
         */
        Camera backgroundCamera = guiViewPort.getCamera().clone();
        backgroundViewport = renderManager.createPreView(
                "background viewport", backgroundCamera);
        /*
         * Don't clear the color buffer before drawing the main viewport.
         * Clearing the color buffer would hide the background.
         */
        boolean clearColorBuffer = false;
        viewPort.setClearFlags(clearColorBuffer, true, true);
        /*
         * Create a quad to display the JMonkeyEngine logo,
         * assign it to the Gui bucket,
         * and attach it to the background viewport.
         */
        Texture quadTexture
                = assetManager.loadTexture("Interface/Logo/Monkey.png");
        Material quadMaterial = new Material(assetManager, Materials.UNSHADED);
        quadMaterial.setTexture("ColorMap", quadTexture);

        float quadHeight = backgroundCamera.getHeight();
        float quadWidth = backgroundCamera.getWidth();
        Mesh quadMesh = new Quad(quadWidth, quadHeight);

        Spatial quadGeometry = new Geometry("quad geometry", quadMesh);
        quadGeometry.setMaterial(quadMaterial);
        quadGeometry.setQueueBucket(RenderQueue.Bucket.Gui);
        backgroundViewport.attachScene(quadGeometry);
        /*
         * Add Jaime model and lighting to the default scene.
         */
        loadModel();
        setupLights();
        /*
         * Speed up camera motion for convenience.
         */
        flyCam.setMoveSpeed(8f);
    }
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