/*
* implicit parameters: nsites, sqrt_nsites, xmin, xmax, ymin, ymax, deltax,
* deltay (can all be estimates). Performance suffers if they are wrong;
* better to make nsites, deltax, and deltay too big than too small. (?)
*/
private bool voronoi_bd()
{
Site newsite, bot, top, temp, p;
Site v;
Point newintstar = null;
int pm;
Halfedge lbnd, rbnd, llbnd, rrbnd, bisector;
Edge e;
PQinitialize();
ELinitialize();
bottomsite = nextone();
newsite = nextone();
while (true)
{
if (!PQempty())
{
newintstar = PQ_min();
}
// if the lowest site has a smaller y value than the lowest vector
// intersection,
// process the site otherwise process the vector intersection
if (newsite != null && (PQempty()
|| newsite.coord.y < newintstar.y
|| (newsite.coord.y == newintstar.y
&& newsite.coord.x < newintstar.x)))
{
/* new site is smallest -this is a site event */
// get the first HalfEdge to the LEFT of the new site
lbnd = ELleftbnd((newsite.coord));
// get the first HalfEdge to the RIGHT of the new site
rbnd = ELright(lbnd);
// if this halfedge has no edge,bot =bottom site (whatever that
// is)
bot = rightreg(lbnd);
// create a new edge that bisects
e = bisect(bot, newsite);
// create a new HalfEdge, setting its ELpm field to 0
bisector = HEcreate(e, LE);
// insert this new bisector edge between the left and right
// vectors in a linked list
ELinsert(lbnd, bisector);
// if the new bisector intersects with the left edge,
// remove the left edge's vertex, and put in the new one
if ((p = intersect(lbnd, bisector)) != null)
{
PQdelete(lbnd);
PQinsert(lbnd, p, dist(p, newsite));
}
lbnd = bisector;
// create a new HalfEdge, setting its ELpm field to 1
bisector = HEcreate(e, RE);
// insert the new HE to the right of the original bisector
// earlier in the IF stmt
ELinsert(lbnd, bisector);
// if this new bisector intersects with the new HalfEdge
if ((p = intersect(bisector, rbnd)) != null)
{
// push the HE into the ordered linked list of vertices
PQinsert(bisector, p, dist(p, newsite));
}
newsite = nextone();
}
else if (!PQempty())
/* intersection is smallest - this is a vector event */
{
// pop the HalfEdge with the lowest vector off the ordered list
// of vectors
lbnd = PQextractmin();
// get the HalfEdge to the left of the above HE
llbnd = ELleft(lbnd);
// get the HalfEdge to the right of the above HE
rbnd = ELright(lbnd);
// get the HalfEdge to the right of the HE to the right of the
// lowest HE
rrbnd = ELright(rbnd);
// get the Site to the left of the left HE which it bisects
bot = leftreg(lbnd);
// get the Site to the right of the right HE which it bisects
top = rightreg(rbnd);
v = lbnd.vertex; // get the vertex that caused this event
makevertex(v); // set the vertex number - couldn't do this
// earlier since we didn't know when it would be processed
endpoint(lbnd.ELedge, lbnd.ELpm, v);
// set the endpoint of
// the left HalfEdge to be this vector
endpoint(rbnd.ELedge, rbnd.ELpm, v);
// set the endpoint of the right HalfEdge to
// be this vector
ELdelete(lbnd); // mark the lowest HE for
// deletion - can't delete yet because there might be pointers
// to it in Hash Map
PQdelete(rbnd);
// remove all vertex events to do with the right HE
ELdelete(rbnd); // mark the right HE for
// deletion - can't delete yet because there might be pointers
// to it in Hash Map
pm = LE; // set the pm variable to zero
if (bot.coord.y > top.coord.y)
// if the site to the left of the event is higher than the
// Site
{ // to the right of it, then swap them and set the 'pm'
// variable to 1
temp = bot;
bot = top;
top = temp;
pm = RE;
}
e = bisect(bot, top); // create an Edge (or line)
// that is between the two Sites. This creates the formula of
// the line, and assigns a line number to it
bisector = HEcreate(e, pm); // create a HE from the Edge 'e',
// and make it point to that edge
// with its ELedge field
ELinsert(llbnd, bisector); // insert the new bisector to the
// right of the left HE
endpoint(e, RE - pm, v); // set one endpoint to the new edge
// to be the vector point 'v'.
// If the site to the left of this bisector is higher than the
// right Site, then this endpoint
// is put in position 0; otherwise in pos 1
// if left HE and the new bisector intersect, then delete
// the left HE, and reinsert it
if ((p = intersect(llbnd, bisector)) != null)
{
PQdelete(llbnd);
PQinsert(llbnd, p, dist(p, bot));
}
// if right HE and the new bisector intersect, then
// reinsert it
if ((p = intersect(bisector, rrbnd)) != null)
{
PQinsert(bisector, p, dist(p, bot));
}
}
else
{
break;
}
}
for (lbnd = ELright(ELleftend); lbnd != ELrightend; lbnd = ELright(lbnd))
{
e = lbnd.ELedge;
clip_line(e);
}
return true;
}
private void makevertex(Site v)
{
v.sitenbr = nvertices;
nvertices++;
}
