@Override
    public void start(Stage primaryStage) {
        byte[] datafile = getDatafile("/sample.h2.db");
        int pageSize = readInt(datafile, 48);
        System.out.println(String.format("pageSize: %d ", pageSize));
        int pages = (int) datafile.length / pageSize;
        int cnt = 0;
        Group root = new Group();
        for (int i = 0; cnt < pages; i++) {
            for (int j = 0; j < 10; j++) {
                if (cnt < pages) {
                    Rectangle rect = createRectangle(cnt, root, datafile, pageSize);
                    rect.setX(10 + j * 40);
                    rect.setY(10 + i * 40);
                    root.getChildren().add(rect);
                    cnt++;
                }
            }
        }
        Scene scene = new Scene(root, 800, 600, Color.BLACK);
        scene.getStylesheets().add(getClass().getResource("H2PageStoreVisualizer.css").toExternalForm());
        primaryStage.setTitle("Hello World!? " + pageSize + " * " + pages);
        primaryStage.setScene(scene);
        primaryStage.show();
    }