public void FindCells()
{
// First we construct "wedges", which are pairs of sequential edges around each vtx.
// we then put all in a hash set, we will iterate until we use up all the available wedges.
// Edges are sorted by positive angle, so they are in clockwise order
// Hence, going from edge n to n+1 is a left-turn, and so "inside" cells are oriented clockwise
int NV = Graph.MaxVertexID;
var wedges = new Index2i[NV][];
var remaining = new HashSet <Index2i>();
foreach (int vid in Graph.VertexIndices())
{
int[] sorted = Graph.SortedVtxEdges(vid);
wedges[vid] = new Index2i[sorted.Length];
for (int k = 0; k < sorted.Length; ++k)
{
wedges[vid][k] = new Index2i(sorted[k], sorted[(k + 1) % sorted.Length]);
remaining.Add(new Index2i(vid, k));
}
}
CellLoops = new List <int[]>();
var loopv = new List <int>();
while (remaining.Count > 0)
{
Index2i idx = remaining.First();
remaining.Remove(idx);
int start_vid = idx.a;
int wid = idx.b;
int e0 = wedges[start_vid][wid].a; e0 = e0 + 1 - 1; // get rid of unused variable warning, want to keep this for debugging
int e1 = wedges[start_vid][wid].b;
loopv.Clear();
loopv.Add(start_vid);
int cur_v = start_vid;
int outgoing_e = e1;
// walk around loop taking immediate left-turns
bool done = false;
while (!done)
{
// find outgoing edge and vtx at far end
Index2i ev = Graph.GetEdgeV(outgoing_e);
int next_v = (ev.a == cur_v) ? ev.b : ev.a;
if (next_v == start_vid)
{
done = true;
continue;
}
// now find wedge at that vtx where this is incoming edge
Index2i[] next_wedges = wedges[next_v];
int use_wedge_idx = -1;
for (int k = 0; k < next_wedges.Length; ++k)
{
if (next_wedges[k].a == outgoing_e)
{
use_wedge_idx = k;
break;
}
}
if (use_wedge_idx == -1)
{
throw new Exception("could not find next wedge?");
}
remaining.Remove(new Index2i(next_v, use_wedge_idx));
loopv.Add(next_v);
cur_v = next_v;
outgoing_e = next_wedges[use_wedge_idx].b;
}
CellLoops.Add(loopv.ToArray());
}
}