private HalfEdge Flip(HalfEdge edge)
{
var twin = edge.Twin;
var edgeNext = edge.Next;
var twinNext = twin.Next;
edge.Prev.Next = twinNext;
twin.Prev.Next = edgeNext;
edge.Detach();
twin.Detach();
edge = new HalfEdge(edgeNext.Next.Origin)
{
Next = twinNext.Next
};
twin = new HalfEdge(twinNext.Next.Origin)
{
Next = edgeNext.Next
};
edge.TwinWith(twin);
edgeNext.Next = edge;
twinNext.Next = twin;
return(edge);
}