anchor.diff:    SpriteSheet spriteSheetUI;
     Sprite sprtBgScore;
     Sprite sprtBgShield;
  +  bool _dirtyScore = true;
   
     int _score = 0;
   
  
positive.code:     }
      return true;
    }
  }
  
  // Game objects
  
negative.code:     _hud = new Hud(_spriteSheetUI);
      _hud.zPosition = 1000.0;
      addChild(_hud);
  
      // Setup level
      setupLevel(0);
    }
  
    void setupLevel(int level) {
      int numLargeAsteroids = 5 + level * 2;
      int numMediumAsteroids = 5 + level * 2;
  
      // Add some asteroids to the game world
      for (int i = 0; i < numLargeAsteroids; i++) {
        addAsteroid(AsteroidSize.large);
      }
      for (int i = 0; i < numMediumAsteroids; i++) {
        addAsteroid(AsteroidSize.medium);
      }
  
      _numFrames = 0;
      _shield.visible = true;
    }
  
    // Methods for adding game objects
  