function clipping_rectangle($x1, $y1, $w, $h)
 {
     $this->_pdf->save();
     $y1 = $this->y($y1) - $h;
     $this->_pdf->rect(floatval($x1), floatval($y1), floatval($w), floatval($h));
     $this->_pdf->clip();
 }