public void init( )
    {
        // initialize the off-screen rendering buffer
        width = size().width;
        height = size().height;
        screen = createImage(width, height);
        gc = screen.getGraphics();
        gc.setColor(getBackground());
        gc.fillRect(0, 0, width, height);

        fov = 30;               // default horizonal field of view

        // Initialize various lists
        objectList = new Vector(CHUNKSIZE, CHUNKSIZE);
        lightList = new Vector(CHUNKSIZE, CHUNKSIZE);
        currentSurface = new Surface(0.8f, 0.2f, 0.9f, 0.2f, 0.4f, 0.4f, 10.0f, 0f, 0f, 1f);

        // Parse the scene file
        String filename = getParameter("datafile");
        showStatus("Parsing " + filename);
        InputStream is = null;
        try {
            is = new URL(getDocumentBase(), filename).openStream();
            ReadInput(is);
            is.close();
        } catch (IOException e) {
            showStatus("Error reading "+filename);
            System.err.println("Error reading "+filename);
            System.exit(-1);
        }

        // Initialize more defaults if they weren't specified
        if (eye == null) eye = new Vector3D(0, 0, 10);
        if (lookat == null) lookat = new Vector3D(0, 0, 0);
        if (up  == null) up = new Vector3D(0, 1, 0);
        if (background == null) background = new Color(0,0,0);

        // Compute viewing matrix that maps a
        // screen coordinate to a ray direction
        Vector3D look = new Vector3D(lookat.x - eye.x, lookat.y - eye.y, lookat.z - eye.z);
        Du = Vector3D.normalize(look.cross(up));
        Dv = Vector3D.normalize(look.cross(Du));
        float fl = (float)(width / (2*Math.tan((0.5*fov)*Math.PI/180)));
        Vp = Vector3D.normalize(look);
        Vp.x = Vp.x*fl - 0.5f*(width*Du.x + height*Dv.x);
        Vp.y = Vp.y*fl - 0.5f*(width*Du.y + height*Dv.y);
        Vp.z = Vp.z*fl - 0.5f*(width*Du.z + height*Dv.z);
    }