public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";

            // Frame rate is 30 fps by default for Windows Phone.
            TargetElapsedTime = TimeSpan.FromTicks(333333);

            // Extend battery life under lock.
            InactiveSleepTime = TimeSpan.FromSeconds(1);
            manager = SceneManager.GetInstance(this);
        }
 public static SceneManager GetInstance(Microsoft.Xna.Framework.Game game)
 {
     if (manager == null)
         manager = new SceneManager(game);
     return manager;
 }