public function transformVertex(Vertex $vtx)
{
$tmp_array = array();
$tmp_array[0][0] = $vtx->getX();
$tmp_array[1][0] = $vtx->getY();
$tmp_array[2][0] = $vtx->getZ();
$tmp_array[3][0] = $vtx->getW();
return new Vertex(array('x' => $this->_mult_line_row($tmp_array, 0, 0), 'y' => $this->_mult_line_row($tmp_array, 1, 0), 'z' => $this->_mult_line_row($tmp_array, 2, 0), 'color' => $vtx->getColor()));
}