for ($i = 0; $i < $n; ++$i) {
                $title_xt = $colstarts[$i];
                $title_xb = $title_xt + $colwidth[$i];
                $coords   = "${title_xt},${yt},${title_xb},${yt},${title_xb},${yb},${title_xt},${yb}";