/**
  * Set the kerning groups associated to a character
  * @param mixed $ch the character
  * @param mixed $group the group
  */
 public function setKerningGroup($ch, $group)
 {
     if ($this->direction == -1) {
         foreach ($this->directions as $direction) {
             $this->font_metrics[$direction]->setKerningGroup($ch, $group);
         }
         parent::setKerningGroup($ch, $group);
     } else {
         $this->font_metrics[$this->direction]->setKerningGroup($ch, $group);
     }
 }