code: public Sprite getHighestHitSprite (int x, int y)
      {
          // since they're stored in lowest -> highest order..
          for (int ii = _sprites.size() - 1; ii >= 0; ii--) {
              Sprite sprite = _sprites.get(ii);
              if (sprite.hitTest(x, y)) {
                  return sprite;
              }
          }
          return null;
      }
docs: Finds the sprite with the highest render order that hits the specified pixel.
  
  @param x the x (screen) coordinate to be checked
  @param y the y (screen) coordinate to be checked
  @return the highest sprite hit