/// <summary>
/// Adds a halfedge to the halfedge list.
/// </summary>
/// <param name="halfedge">The halfedge to add.</param>
protected void AppendToHalfedgeList(DXHalfedge halfedge)
{
halfedge.Index = halfedges.Count;
halfedges.Add(halfedge);
}
/// <summary>
/// Adds a face to the mesh with the specified face traits.
/// </summary>
/// <param name="faceTraits">The custom traits for the face to add to the mesh.</param>
/// <param name="faceVertices">The vertices of the face in counterclockwise order.</param>
/// <returns>The face created by this method.</returns>
/// <exception cref="BadTopologyException">
/// Thrown when fewer than three vertices are given or the vertices cannot form a valid face.
/// </exception>
/// <exception cref="ArgumentNullException">Thrown when a null vertex is given.</exception>
private DXFace CreateFace(TFaceTraits faceTraits, params DXVertex[] faceVertices)
{
int n = faceVertices.Length;
// Require at least 3 vertices
if (n < 3)
{
throw new DXBadTopologyException("Cannot create a polygon with fewer than three vertices.");
}
DXEdge e;
DXFace f;
DXHalfedge[] faceHalfedges = new DXHalfedge[n];
bool[] isNewEdge = new bool[n], isUsedVertex = new bool[n];
// Make sure input is (mostly) acceptable before making any changes to the mesh
for (int i = 0; i < n; ++i)
{
int j = (i + 1) % n;
if (faceVertices[i] == null)
{
throw new ArgumentNullException("Can't add a null vertex to a face.");
}
if (!faceVertices[i].OnBoundary)
{
throw new DXBadTopologyException("Can't add an edge to a vertex on the interior of a mesh.");
}
// Find existing halfedges for this face
faceHalfedges[i] = faceVertices[i].FindHalfedgeTo(faceVertices[j]);
isNewEdge[i] = (faceHalfedges[i] == null);
isUsedVertex[i] = (faceVertices[i].Halfedge != null);
if (!isNewEdge[i] && !faceHalfedges[i].OnBoundary)
{
throw new DXBadTopologyException("Can't add more than two faces to an edge.");
}
}
// Create face
f = new DXFace(faceTraits);
mesh.AppendToFaceList(f);
// Create new edges
for (int i = 0; i < n; ++i)
{
int j = (i + 1) % n;
if (isNewEdge[i])
{
// Create new edge
e = new DXEdge();
mesh.AppendToEdgeList(e);
// Create new halfedges
faceHalfedges[i] = new DXHalfedge();
mesh.AppendToHalfedgeList(faceHalfedges[i]);
faceHalfedges[i].Opposite = new DXHalfedge();
mesh.AppendToHalfedgeList(faceHalfedges[i].Opposite);
// Connect opposite halfedge to inner halfedge
faceHalfedges[i].Opposite.Opposite = faceHalfedges[i];
// Connect edge to halfedges
e.Halfedge0 = faceHalfedges[i];
// Connect halfedges to edge
faceHalfedges[i].Edge = e;
faceHalfedges[i].Opposite.Edge = e;
// Connect halfedges to vertices
faceHalfedges[i].ToVertex = faceVertices[j];
faceHalfedges[i].Opposite.ToVertex = faceVertices[i];
// Connect vertex to outgoing halfedge if it doesn't have one yet
if (faceVertices[i].Halfedge == null)
{
faceVertices[i].Halfedge = faceHalfedges[i];
}
}
if (faceHalfedges[i].Face != null)
{
throw new DXBadTopologyException("An inner halfedge already has a face assigned to it.");
}
// Connect inner halfedge to face
faceHalfedges[i].Face = f;
//Debug.Assert(faceHalfedges[i].FromVertex == faceVertices[i] && faceHalfedges[i].ToVertex == faceVertices[j]);
}
// Connect next/previous halfedges
for (int i = 0; i < n; ++i)
{
int j = (i + 1) % n;
// Outer halfedges
if (isNewEdge[i] && isNewEdge[j] && isUsedVertex[j]) // Both edges are new and vertex has faces connected already
{
DXHalfedge closeHalfedge = null;
// Find the closing halfedge of the first available opening
foreach (DXHalfedge h in faceVertices[j].Halfedges)
{
if (h.Face == null)
{
closeHalfedge = h;
break;
}
}
//Debug.Assert(closeHalfedge != null);
DXHalfedge openHalfedge = closeHalfedge.Previous;
// Link new outer halfedges into this opening
faceHalfedges[i].Opposite.Previous = openHalfedge;
openHalfedge.Next = faceHalfedges[i].Opposite;
faceHalfedges[j].Opposite.Next = closeHalfedge;
closeHalfedge.Previous = faceHalfedges[j].Opposite;
}
else if (isNewEdge[i] && isNewEdge[j]) // Both edges are new
{
faceHalfedges[i].Opposite.Previous = faceHalfedges[j].Opposite;
faceHalfedges[j].Opposite.Next = faceHalfedges[i].Opposite;
}
else if (isNewEdge[i] && !isNewEdge[j]) // This is new, next is old
{
faceHalfedges[i].Opposite.Previous = faceHalfedges[j].Previous;
faceHalfedges[j].Previous.Next = faceHalfedges[i].Opposite;
}
else if (!isNewEdge[i] && isNewEdge[j]) // This is old, next is new
{
faceHalfedges[i].Next.Previous = faceHalfedges[j].Opposite;
faceHalfedges[j].Opposite.Next = faceHalfedges[i].Next;
}
else if (!isNewEdge[i] && !isNewEdge[j] && faceHalfedges[i].Next != faceHalfedges[j]) // Relink faces before adding new edges if they are in the way of a new face
{
DXHalfedge closeHalfedge = faceHalfedges[i].Opposite;
// Find the closing halfedge of the opening opposite the opening halfedge i is on
do
{
closeHalfedge = closeHalfedge.Previous.Opposite;
} while (closeHalfedge.Face != null && closeHalfedge != faceHalfedges[j] && closeHalfedge != faceHalfedges[i].Opposite);
if (closeHalfedge == faceHalfedges[j] || closeHalfedge == faceHalfedges[i].Opposite)
{
throw new DXBadTopologyException("Unable to find an opening to relink an existing face.");
}
DXHalfedge openHalfedge = closeHalfedge.Previous;
// Remove group of faces between two openings, close up gap to form one opening
openHalfedge.Next = faceHalfedges[i].Next;
faceHalfedges[i].Next.Previous = openHalfedge;
// Insert group of faces into target opening
faceHalfedges[j].Previous.Next = closeHalfedge;
closeHalfedge.Previous = faceHalfedges[j].Previous;
}
// Inner halfedges
faceHalfedges[i].Next = faceHalfedges[j];
faceHalfedges[j].Previous = faceHalfedges[i];
}
// Connect face to an inner halfedge
f.Halfedge = faceHalfedges[0];
return(f);
}
