code: protected boolean updateTileCoords (int sx, int sy, Point tpos)
      {
          Point npos = MisoUtil.screenToTile(_metrics, sx, sy, new Point());
          if (!tpos.equals(npos)) {
              tpos.setLocation(npos.x, npos.y);
              return true;
          } else {
              return false;
          }
      }
docs: Converts the supplied screen coordinates into tile coordinates, writing the values into the
  supplied {@link Point} instance and returning true if the screen coordinates translated
  into a different set of tile coordinates than were already contained in the point (so that
  the caller can know to update a highlight, for example).
  
  @return true if the tile coordinates have changed.