protected override void Update(GameTime gameTime)
        {
            base.Update(gameTime);

            if (m_InputManager.KeyPressed(Keys.OemMinus))
            {
                SpaceInvadersSettings.GetInstance(this).IsSoundOff = !SpaceInvadersSettings.GetInstance(this).IsSoundOff;
            }

            if (m_InputManager.KeyPressed(Keys.Escape))
            {
                this.Exit();
            }
        }
        public SpaceInvaders()
        {
            m_GraphicsMgr = new GraphicsDeviceManager(this);
            m_GraphicsMgr.PreferredBackBufferHeight = 600;
            m_GraphicsMgr.PreferredBackBufferWidth  = 800;
            this.Content.RootDirectory = "Content";
            SpaceInvadersSettings settings = SpaceInvadersSettings.GetInstance(this);

            settings.GraphicsManager = m_GraphicsMgr;

            m_InputManager     = new InputManager(this);
            m_SoundManager     = SoundEffectsManager.GetInstance(this);
            m_TransitionScreen = new LevelTransitionScreeen(this, 1);
            m_PlayGameScreen   = new PlayGameScreen(this, m_TransitionScreen);
            m_WelcomeScreen    = new WelcomeScreen(this, m_PlayGameScreen, m_TransitionScreen);
            m_ScreensManager   = new ScreensMananger(this);

            m_ScreensManager.Push(m_PlayGameScreen);
            m_ScreensManager.Push(m_TransitionScreen);
            m_ScreensManager.SetCurrentScreen(m_WelcomeScreen);
        }