/// <summary>
/// Return true if the collapse results in a valid mesh (otherwise normals may be flipped)
/// Return false if boundary face
/// </summary>
/// <returns></returns>
public bool Collapse()
{
var hm = hmesh;
var hes = Circulate();
var center = GetCenter();
Halfedge opp = null;
var firstVert = hes[0].vert;
List <Vector3D> potentialCollapsedPositions = new List <Vector3D>();
// faces that share edges with this face
List <Face> adjacentFaces = new List <Face>();
potentialCollapsedPositions.Add(center);
foreach (var he in hes)
{
potentialCollapsedPositions.Add(he.vert.positionD);
if (he.opp != null)
{
adjacentFaces.Add(he.opp.face);
}
if (he.vert.IsBoundary())
{
// cannot collapse boundary
return(false);
}
}
adjacentFaces.Add(this);
// faces that are affected by a collapse and their associated face normal
Dictionary <Face, Vector3D> affectedFaceNormals = new Dictionary <Face, Vector3D>();
foreach (var he in hes)
{
if (!he.vert.IsBoundary())
{
foreach (var halfedge in he.vert.Circulate())
{
var face = halfedge.face;
if (!adjacentFaces.Contains(face))
{
affectedFaceNormals.Add(face, face.GetNormal());
}
}
}
}
// prepare removal/disconnect of face
foreach (var he in hes)
{
if (he.opp != null)
{
opp = he.opp;
he.opp.opp = null; // remove reference to opp
}
}
Vertex survivingVertes = null;
foreach (var he in hes)
{
hm.Destroy(he);
}
hm.Destroy(this);
if (opp != null)
{
var vert = opp.CollapseBoundaryLoop();
bool validPosition = true;
// find position where adjacent faces are not flipped
for (int i = 0; i < potentialCollapsedPositions.Count; i++)
{
vert.positionD = potentialCollapsedPositions[i];
validPosition = true;
foreach (var faceNormal in affectedFaceNormals)
{
var newNormal = faceNormal.Key.GetNormal();
bool isNormalFlipped = Vector3D.Dot(newNormal, faceNormal.Value) < 0;
if (isNormalFlipped)
{
validPosition = false;
}
}
if (validPosition)
{
return(true);
}
bool didNotSucceedInFindingValidPosition = (i == potentialCollapsedPositions.Count);
if (didNotSucceedInFindingValidPosition)
{
// assume center position has least damage
vert.positionD = potentialCollapsedPositions[i];
}
}
}
return(false);
}
