static MStatus extract_smoothing_groups(MFnMesh& mesh_fn, std::vector<uint32_t>& sgroups)
{
MStatus status = MS::kSuccess;

MIntArray connected;

temp_edge* temp_edges = new temp_edge[unsigned(mesh_fn.numEdges() & INT_MAX)];
for (MItMeshEdge it(mesh_fn.object()); !it.isDone(); it.next()) {
if (it.isSmooth()) {
it.getConnectedFaces(connected, &status);
CHECK_MSTATUS(status);
unsigned n = connected.length();
if (n <= 2) {
temp_edge& edge = temp_edges[it.index()];
while (n) {
--n;
edge.faces[n] = uint32_t(connected[n] & INT_MAX);
}
}
}
}

unsigned num_faces = unsigned(mesh_fn.numPolygons() & INT_MAX);
temp_face* temp_faces = new temp_face[num_faces];
for (MItMeshPolygon it(mesh_fn.object()); !it.isDone(); it.next()) {
status = it.getEdges(connected);
CHECK_MSTATUS(status);
unsigned n = connected.length();
if (n != 3) {
msg("can't build smoothing groups");
delete[] temp_edges;
delete[] temp_faces;
return MS::kInvalidParameter;
}
temp_face& face = temp_faces[it.index(&status)];
CHECK_MSTATUS(status);
while (n) {
--n;
face.edges[n] = uint32_t(connected[n] & INT_MAX);
}
}

sgroups.assign(num_faces, EMESH_NO_SG);
std::vector<uint32_t> adjacents;
adjacents.reserve(512);
uint32_t sgroup = 0;
for (uint_fast32_t base_idx = num_faces; base_idx != 0;) {
if (sgroups[--base_idx] != EMESH_NO_SG)
continue;
bool new_sgroup = false;
for (uint_fast32_t face_idx = base_idx;;) {
const temp_face& face = temp_faces[face_idx];
for (uint_fast32_t i = 3; i != 0;) {
temp_edge& edge = temp_edges[face.edges[--i]];
if (edge.faces[0] == UINT32_MAX || edge.faces[1] == UINT32_MAX)
continue;
if (!new_sgroup) {
new_sgroup = true;
sgroups[face_idx] = sgroup;
}
uint32_t adj_face_idx = edge.faces[0] == face_idx ?
edge.faces[1] : edge.faces[0];
if (sgroups[adj_face_idx] == EMESH_NO_SG) {
adjacents.push_back(adj_face_idx);
sgroups[adj_face_idx] = sgroup;
}
}
if (adjacents.empty())
break;
face_idx = adjacents.back();
adjacents.pop_back();
}
if (new_sgroup)
++sgroup;
}

delete[] temp_edges;
delete[] temp_faces;

return status;
}