private static void ConnectIntersections(SplitVertex start,
SplitVertex end,
List<SplitVertex> intersections,
bool? direction,
List<SplitVertex> polygon)
{
int index1 = intersections.IndexOf(start);
int index2 = intersections.IndexOf(end);
if (Math.Abs(index1 - index2) == 1)
return;
// int step = index2 > index1 ? 1 : -1;
// index2 -= step;
// index1 += step;
//
// for (; index2 != index1; index2 -= step)
// {
// var cornerDirection = intersections[index2].GetDirection (intersections[index2].GetNextIntersection ());
// if (cornerDirection != direction && cornerDirection != null)
// {
// do
// {
// polygon.Add (end);
// end = end.Next;
// } while (!end.IsIntersect);
// polygon.Add (end);
// }
// }
SplitVertex stop;
if (index2 > index1)
{
end = intersections [index2 - 1];
stop = intersections [index1 + 1];
}
else
{
end = intersections [index2 + 1];
stop = intersections [index1 - 1];
}
while(end != stop)
{
//connect vertex when encounter concave intersection
if (end.IsIntersect)
{
var cornerDirection = end.GetDirection (end.GetNextIntersection ());
if (cornerDirection != direction && cornerDirection != null)
{
double cp1 = SplitVertex.CrossProduct (intersections [0], intersections [intersections.Count - 1], start.Next);
double cp2 = SplitVertex.CrossProduct (intersections [0], intersections [intersections.Count - 1], end.Next);
if (cp1 * cp2 > 0)
{
do
{
polygon.Add (end);
end = end.Next;
} while (!end.IsIntersect);
polygon.Add (end);
var ind = intersections.IndexOf(end);
if (index2 > index1)
ind--;
else
ind++;
if(end != stop)
end = intersections[ind];
}
else
end = end.Next;
}
else
end = end.Next;
}
else
end = end.Next;
}
}
public static List<List<SplitVertex>> Split(SplitVertex polygon, Point p1, Point p2)
{
var ins = new List<SplitVertex>();
//phase 1 get all intersection
SplitVertex current = polygon;
do
{
var next = current.Next;
var cross = Line.IntersectWithSegment(p1, p2, current.ToPoint(), next.ToPoint());
if (cross.HasValue)
{
var iv = cross.Value.ToSplitVertex();
iv.IsIntersect = true;
iv.Next = next;
iv.Previous = current;
next.Previous = iv;
current.Next = iv;
if (ins.Count == 0)
ins.Add(iv);
else
{
int j = 0;
for (; j<ins.Count && (cross.Value.X > ins[j].X ||
(cross.Value.X == ins[j].X && cross.Value.Y >ins[j].Y));
j++);
if(j == ins.Count)
ins.Add(iv);
else
ins.Insert(j, iv);
}
}
current = next;
} while (current != polygon);
var result = new List<List<SplitVertex>>();
if (ins.Count == 0)
{
result.Add(polygon.ToList());
return result;
}
//phase 2
current = ins[0];
bool? direction = polygon.GetDirection();
do
{
//create new polygon when encouter convex intersection
if(current.IsIntersect && current.GetDirection(current.GetNextIntersection()) == direction)
{
var fi = current;
var sp = new List<SplitVertex>();
result.Add(sp);
do
{
sp.Add(current);
current = current.Next;
} while (!current.IsIntersect);
sp.Add(current);
ConnectIntersections(fi,current,ins,direction,sp);
}
else
current = current.Next;
} while (current != ins[0]);
return result;
}
public bool? GetDirection(SplitVertex end)
{
double signedArea = 0;
SplitVertex v = this;
do
{
signedArea += (v.X * v.Next.Y - v.Next.X * v.Y);
v = v.Next;
} while (v != end);
signedArea += (end.X * Y - X * end.Y);
if (signedArea == 0)
return null;
return signedArea > 0;
}
public static double CrossProduct(SplitVertex v1,SplitVertex v2,SplitVertex v3)
{
return (v2.X - v1.X) * (v3.Y - v2.Y) - (v2.Y - v1.Y) * (v3.X - v2.X);
}