private static bool PreconditionLegalCollapse(Halfedge he, Vector3D pos)
{
if (he.IsDestroyed())
{
return(false);
}
if (he.CollapsePrecondition(pos, Halfedge.CollapsePreconditionReason.NormalFlipped) != Halfedge.CollapsePreconditionReason.Ok)
{
return(false);
}
HMesh hmesh = he.hmesh;
HashSet <int> uniqueLabels = new HashSet <int>();
List <Vector3D> vertexPositions = new List <Vector3D>();
int index = 0;
int indexOfHe = 0;
var prevVertCirculated = he.prev.vert.Circulate();
// Check that all normals (of same label) are facing the same way
var prev = he.prev;
int thisLabel = he.face.label;
Vector3D normal = he.face.GetNormal();
Vector3D otherNormal = Vector3D.zero;
foreach (var vHe in prev.vert.Circulate())
{
uniqueLabels.Add(vHe.face.label);
if (vHe.face.label != thisLabel)
{
otherNormal = vHe.face.GetNormal();
}
}
if (uniqueLabels.Count > 2)
{
// currently not simplified
return(false);
}
// 2. all face normals of the same label must be equal when having the same label
foreach (var vHe in prev.vert.Circulate())
{
var circulateFaceNormal = vHe.face.GetNormal();
if (vHe.face.label == thisLabel)
{
if (!hmesh.AreNormalsEqual(circulateFaceNormal, normal))
{
return(false);
}
}
else
{
if (!hmesh.AreNormalsEqual(circulateFaceNormal, otherNormal))
{
return(false);
}
}
}
// if more labels, make sure that the collapse does not change any boundary between labels
if (uniqueLabels.Count == 2)
{
if (he.opp != null && he.face.label == he.opp.face.label)
{
return(false);
}
foreach (var otherHe in prevVertCirculated)
{
bool compareToSelf = otherHe.id == he.id;
if (compareToSelf)
{
continue;
}
bool isLabelBoundary = otherHe.opp != null && otherHe.opp.face.label != otherHe.face.label;
if (isLabelBoundary)
{
var dir1 = he.GetDirection();
var dir2 = otherHe.GetDirection();
bool oppositeDir = Vector3D.Dot(dir1, dir2) > 0;
// if boundary between labels then they must be parallel in same direction
if (Vector3D.IsParallelDist(dir1, dir2, hmesh.zeroMagnitudeTresholdSqr) == false || oppositeDir)
{
return(false);
}
}
}
}
return(true);
}