code: public void viewLocationDidChange (int dx, int dy)
      {
          if (_perfRect != null) {
              Rectangle sdirty = new Rectangle(_perfRect);
              sdirty.translate(-dx, -dy);
              _remgr.addDirtyRegion(sdirty);
          }
  
          // let our sprites and animations know what's up
          _animmgr.viewLocationDidChange(dx, dy);
          _spritemgr.viewLocationDidChange(dx, dy);
      }
docs: If our host supports scrolling around in a virtual view, it should call this method when the
  view origin changes.