code: protected void updateBox ()
      {
          int hmin = _horz.getMinimum();
          int vmin = _vert.getMinimum();
          _hFactor = (_active.width) / (float) (_horz.getMaximum() - hmin);
          _vFactor = (_active.height) / (float) (_vert.getMaximum() - vmin);
  
          _box.x = _active.x + Math.round((_horz.getValue() - hmin) * _hFactor);
          _box.width = Math.round(_horz.getExtent() * _hFactor);
          _box.y = _active.y + Math.round((_vert.getValue() - vmin) * _vFactor);
          _box.height = Math.round(_vert.getExtent() * _vFactor);
      }
docs: Recalculate the size of the box.
  You shouldn't need to override this to provide custom functionality.
  Use the above three methods instead.