/// <summary>
/// Disconnect the given triangles from their neighbours, by duplicating "boundary" vertices, ie
/// vertices on edges for which one triangle is in-set and the other is not.
/// If bComputeEdgePairs is true, we return list of old/new edge pairs (useful for stitching)
/// [TODO] currently boundary-edge behaviour is to *not* duplicate boundary verts
/// </summary>
public bool SeparateTriangles(IEnumerable <int> triangles, bool bComputeEdgePairs, out List <Index2i> EdgePairs)
{
HashSet <int> in_set = new HashSet <int>(triangles);
Dictionary <int, int> VertexMap = new Dictionary <int, int>();
EdgePairs = null;
HashSet <int> edges = null;
List <Index2i> OldEdgeVerts = null;
if (bComputeEdgePairs)
{
EdgePairs = new List <Index2i>();
edges = new HashSet <int>();
OldEdgeVerts = new List <Index2i>();
}
// duplicate vertices on edges that are on boundary of triangles roi
foreach (int tid in triangles)
{
Index3i te = Mesh.GetTriEdges(tid);
for (int j = 0; j < 3; ++j)
{
Index2i et = Mesh.GetEdgeT(te[j]);
// [TODO] what about behavior where we want to also duplicate boundary verts??
if (et.b == DMesh3.InvalidID || (et.a == tid && in_set.Contains(et.b)) || (et.b == tid && in_set.Contains(et.a)))
{
te[j] = -1;
}
}
for (int j = 0; j < 3; ++j)
{
if (te[j] == -1)
{
continue;
}
Index2i ev = Mesh.GetEdgeV(te[j]);
if (VertexMap.ContainsKey(ev.a) == false)
{
VertexMap[ev.a] = Mesh.AppendVertex(Mesh, ev.a);
}
if (VertexMap.ContainsKey(ev.b) == false)
{
VertexMap[ev.b] = Mesh.AppendVertex(Mesh, ev.b);
}
if (bComputeEdgePairs && edges.Contains(te[j]) == false)
{
edges.Add(te[j]);
OldEdgeVerts.Add(ev);
EdgePairs.Add(new Index2i(te[j], -1));
}
}
}
// update triangles
foreach (int tid in triangles)
{
Index3i tv = Mesh.GetTriangle(tid);
Index3i tv_new = tv;
for (int j = 0; j < 3; ++j)
{
int newv;
if (VertexMap.TryGetValue(tv[j], out newv))
{
tv_new[j] = newv;
}
}
if (tv_new != tv)
{
Mesh.SetTriangle(tid, tv_new);
}
}
if (bComputeEdgePairs)
{
for (int k = 0; k < EdgePairs.Count; ++k)
{
Index2i old_ev = OldEdgeVerts[k];
int new_a = VertexMap[old_ev.a];
int new_b = VertexMap[old_ev.b];
int new_eid = Mesh.FindEdge(new_a, new_b);
Util.gDevAssert(new_eid != DMesh3.InvalidID);
EdgePairs[k] = new Index2i(EdgePairs[k].a, new_eid);
}
}
return(true);
}