function add(Vertex $nv)
{
if ($this->cnt == 0) {
$this->first =& $nv;
// Save a reference to it in the polygon
$this->first->setNext($nv);
// Set its pointer to point to itself
$this->first->setPrev($nv);
// because it is the only vertex in the list
$ps =& $this->first->Nseg();
// Get ref to the Next segment object
$this->first->setPseg($ps);
// and save it as Prev segment as well
} else {
// $p <-> $nv <-> $n
// $ps $ns
$n =& $this->first;
// Get a ref to the first vertex in the list
$p =& $n->Prev();
// Get ref to previous vertex
$n->setPrev($nv);
// Add at end of list (just before first)
$nv->setNext($n);
// link the new vertex to it
$nv->setPrev($p);
// link to the pervious EOL vertex
$p->setNext($nv);
// And finally link the previous EOL vertex
// Segments
$ns =& $nv->Nseg();
// Get ref to the new next segment
$ps =& $p->Nseg();
// Get ref to the previous segment
$n->setPseg($ns);
// Set new previous seg for $this->first
$nv->setPseg($ps);
// Set previous seg of the new vertex
}
$this->cnt++;
// Increment the count of vertices
}