public HalfEdge2D Split()
{
var m = (to.p + p) * 0.5f;
var e = new HalfEdge2D(m);
to.from = e; e.to = to;
this.to = e; e.from = this;
return(e);
}
// Disable to intersect more than two edges
static List <HalfEdge2D> SplitEdges(List <HalfEdge2D> edges)
{
HalfEdge2D start = edges[0];
HalfEdge2D cur = start;
while (true)
{
HalfEdge2D from = cur, to = from.to;
HalfEdge2D from2 = to.to, to2 = from2.to;
int intersections = 0;
while (to2 != from.from)
{
if (Utils2D.Intersect(from.p, to.p, from2.p, to2.p))
{
intersections++;
if (intersections >= 2)
{
break;
}
}
// next
from2 = from2.to;
to2 = to2.to;
}
if (intersections >= 2)
{
edges.Add(cur.Split());
}
else
{
// next
cur = cur.to;
if (cur == start)
{
break;
}
}
}
return(edges);
}
public static Polygon2D Contour(Vector2[] points)
{
var n = points.Length;
var edges = new List <HalfEdge2D>();
for (int i = 0; i < n; i++)
{
edges.Add(new HalfEdge2D(points[i]));
}
for (int i = 0; i < n; i++)
{
var e = edges[i];
e.from = edges[(i == 0) ? (n - 1) : (i - 1)];
e.to = edges[(i + 1) % n];
}
edges = Polygon2D.SplitEdges(edges);
var result = new List <Vector2>();
HalfEdge2D start = edges[0];
result.Add(start.p);
HalfEdge2D current = start;
while (true)
{
HalfEdge2D from = current, to = current.to;
HalfEdge2D from2 = to.to, to2 = from2.to;
bool flag = false;
while (from2 != start && to2 != from)
{
if (flag = Utils2D.Intersect(from.p, to.p, from2.p, to2.p))
{
break;
}
from2 = to2;
to2 = to2.to;
}
if (!flag)
{
result.Add(to.p);
current = to; // step to next
}
else
{
result.Add(from2.p);
// reconnect
from.to = from2;
from2.to = from; // invert this edge later
to.from = to2;
to.Invert();
to2.from = to;
HalfEdge2D e = from2;
while (e != to)
{
e.Invert();
e = e.to;
}
current = from2;
}
if (current == start)
{
break;
}
}
result.RemoveAt(result.Count - 1); // remove last
return(new Polygon2D(result.ToArray()));
}
public void Invert()
{
var tmp = from; from = to; to = tmp;
}