public void keyPressed(int keyCode, int rawKeyCode) {
        if (keyCode == GameCanvas.FIRE) {
            if (isBack) {
                MainMenu mainMenu = new MainMenu(engine);
                changeScene(mainMenu);
            } else {
                MainPlay mainPlay = new MainPlay(engine, level + 1);
                changeScene(mainPlay);
            }
        } else if (keyCode == GameCanvas.LEFT) {
            if (--level < 0) {
                level = 4;
            }
        } else if (keyCode == GameCanvas.RIGHT) {
            if (++level >= 5) {
                level = 0;
            }
        } else if (keyCode == GameCanvas.DOWN || keyCode == GameCanvas.UP) {
            isBack = !isBack;
        }
    }