public override void Dispose()
 {
     if (IsDisposed)
     {
         return;
     }
     base.Dispose();
     Instance = null;
 }
 public void Awake()
 {
     Instance = this;
     world    = new World(Vector2.Zero); //俯视角游戏,无重力
     // world.ContinuousPhysics = true;
 }