/// <summary>
/// Inserts a pair of HalfEdges between two (non adjacent) vertices of a Face.
/// </summary>
/// <param name="geometry">The Geometry to insert a dignonal</param>
/// <param name="p">First Vertex handle.</param>
/// <param name="q">Second Vertex handle.</param>
/// <exception cref="Exception"></exception>
public static void InsertDiagonal(this Geometry geometry, int p, int q)
{
var pStartHe = new HalfEdge();
var qStartHe = new HalfEdge();
var face = geometry.GetFaceToInsertDiag(p, q, ref pStartHe, ref qStartHe);
if (geometry.IsVertexAdjacentToVertex(p, q, pStartHe, qStartHe))
{
throw new ArgumentException("A diagonal can't be inserted between adjacent Vertices!");
}
var newFromP = new HalfEdge(geometry.CreateHalfEdgeHandleId());
var newFromQ = new HalfEdge(geometry.CreateHalfEdgeHandleId());
newFromP.OriginVertex = p;
newFromP.NextHalfEdge = qStartHe.Handle;
newFromP.PrevHalfEdge = pStartHe.PrevHalfEdge;
newFromP.IncidentFace = face.Handle;
newFromQ.OriginVertex = q;
newFromQ.NextHalfEdge = pStartHe.Handle;
newFromQ.PrevHalfEdge = qStartHe.PrevHalfEdge;
newFromQ.IncidentFace = face.Handle;
newFromP.TwinHalfEdge = newFromQ.Handle;
newFromQ.TwinHalfEdge = newFromP.Handle;
geometry.DictHalfEdges.Add(newFromP.Handle, newFromP);
geometry.DictHalfEdges.Add(newFromQ.Handle, newFromQ);
//Assign new sucessor to previous HalfEdges from p and q & assign new predecessor for qStartHe and pStartHe.
var prevHeP = geometry.GetHalfEdgeByHandle(pStartHe.PrevHalfEdge);
var prevHeQ = geometry.GetHalfEdgeByHandle(qStartHe.PrevHalfEdge);
var prevHePUpdate = geometry.DictHalfEdges[prevHeP.Handle];
prevHePUpdate.NextHalfEdge = newFromP.Handle;
geometry.DictHalfEdges[prevHeP.Handle] = prevHePUpdate;
var prevHeQUpdate = geometry.DictHalfEdges[prevHeQ.Handle];
prevHeQUpdate.NextHalfEdge = newFromQ.Handle;
geometry.DictHalfEdges[prevHeQ.Handle] = prevHeQUpdate;
var nextHePUpdate = geometry.DictHalfEdges[pStartHe.Handle];
nextHePUpdate.PrevHalfEdge = newFromQ.Handle;
geometry.DictHalfEdges[pStartHe.Handle] = nextHePUpdate;
var nextHeQUpdate = geometry.DictHalfEdges[qStartHe.Handle];
nextHeQUpdate.PrevHalfEdge = newFromP.Handle;
geometry.DictHalfEdges[qStartHe.Handle] = nextHeQUpdate;
var holes = geometry.GetHoles(face);
if (holes.Count != 0 && IsNewEdgeToHole(holes, p, q, face))
{
return;
}
var newFace = new Face(geometry.CreateFaceHandleId(), newFromQ.Handle);
//The face normal of the newFace equals the normal of the original Face because adding a diagonal does not change the face vertices position.
var newFaceData = newFace.FaceData;
newFaceData.FaceNormal = face.FaceData.FaceNormal;
newFace.FaceData = newFaceData;
geometry.DictFaces.Add(newFace.Handle, newFace);
//Assign the handle of the new Face to its HalfEdges.
geometry.AssignFaceHandle(newFace.OuterHalfEdge, newFace);
//Set Face.OuterHalfEdge to newFromP - old OuterHalfEdge can be part of new Face now!
var currentFace = face;
currentFace.OuterHalfEdge = newFromP.Handle;
face = currentFace;
geometry.DictFaces[face.Handle] = face;
}