perf: optimize planting triangles removal

This commit improves triangle removal performance by approximately 2.5%
in the planting seed step. Additionally, it reduces temporary memory
allocation by eliminating the `map` buffer entirely.

Runtime/Triangulator.cs

@@ -2536,7 +2536,7 @@ private struct PlantingSeedStep
             private NativeArray<T2> holes;
 
             private readonly Args args;
-            private bool anyTriangleVisited;
+            private int tIdMinVisited;
 
             public PlantingSeedStep(InputData<T2> input, OutputData<T2> output, Args args) : this(output, args, input.HoleSeeds) { }
 
@@ -2554,7 +2554,7 @@ public PlantingSeedStep(OutputData<T2> output, Args args, NativeArray<T2> localH
                 visitedTriangles = default;
                 trianglesQueue = default;
 
-                anyTriangleVisited = false;
+                tIdMinVisited = -1;
             }
 
             public void Execute(Allocator allocator, bool constraintsIsCreated)
@@ -2573,7 +2573,7 @@ public void Execute(Allocator allocator, bool constraintsIsCreated)
                 if (holes.IsCreated) PlantHoleSeeds(holes);
                 if (args.RestoreBoundary) PlantBoundarySeeds();
 
-                RemoveVisitedTriangles(allocator);
+                RemoveVisitedTriangles();
             }
 
             private bool HalfedgeIsIgnored(int he) => ignoredHalfedges.IsCreated && ignoredHalfedges[he];
@@ -2603,54 +2603,60 @@ private void PlantHoleSeeds(NativeArray<T2> holeSeeds)
                 }
             }
 
-            private void RemoveVisitedTriangles(Allocator allocator)
+            private void RemoveVisitedTriangles()
             {
-                if (!anyTriangleVisited)
+                static void DisableHe(NativeList<int> halfedges, int he, int rId)
                 {
-                    return;
+                    var ohe = halfedges[3 * rId + he];
+                    if (ohe != -1)
+                    {
+                        halfedges[ohe] = -1;
+                    }
                 }
 
-                // Triangles to remove are marked with -1, otherwise they are assigned with incremental id.
-                var map = new NativeArray<int>(triangles.Length / 3, allocator);
-                var count = 0;
-                for (int tId = 0; tId < visitedTriangles.Length; tId++)
+                static void AdaptHe(NativeList<int> halfedges, int he, int rId, int wId)
                 {
-                    map[tId] = visitedTriangles[tId] ? -1 : count++;
+                    var ohe = halfedges[3 * rId + he];
+                    halfedges[3 * wId + he] = ohe;
+                    if (ohe != -1)
+                    {
+                        halfedges[ohe] = 3 * wId + he;
+                    }
                 }
 
-                int RemapHalfedge(int ohe)
+                if (tIdMinVisited == -1)
                 {
-                    if (ohe == -1)
-                    {
-                        return -1;
-                    }
-                    var tId = map[ohe / 3];
-                    return tId == -1 ? -1 : 3 * tId + ohe % 3;
+                    return;
                 }
 
                 // Reinterpret to a larger struct to make copies of whole triangles slightly more efficient
                 var constrainedHalfedges3 = constrainedHalfedges.AsArray().Reinterpret<bool3>(1);
                 var triangles3 = triangles.AsArray().Reinterpret<int3>(4);
 
-                for (int tId = 0; tId < map.Length; tId++)
+                var wId = tIdMinVisited;
+                for (int rId = tIdMinVisited; rId < triangles3.Length; rId++)
                 {
-                    var tIdNew = map[tId];
-                    if (tIdNew != -1)
+                    if (!visitedTriangles[rId])
+                    {
+                        triangles3[wId] = triangles3[rId];
+                        constrainedHalfedges3[wId] = constrainedHalfedges3[rId];
+                        AdaptHe(halfedges, 0, rId, wId);
+                        AdaptHe(halfedges, 1, rId, wId);
+                        AdaptHe(halfedges, 2, rId, wId);
+                        wId++;
+                    }
+                    else
                     {
-                        triangles3[tIdNew] = triangles3[tId];
-                        constrainedHalfedges3[tIdNew] = constrainedHalfedges3[tId];
-                        halfedges[3 * tIdNew + 0] = RemapHalfedge(ohe: halfedges[3 * tId + 0]);
-                        halfedges[3 * tIdNew + 1] = RemapHalfedge(ohe: halfedges[3 * tId + 1]);
-                        halfedges[3 * tIdNew + 2] = RemapHalfedge(ohe: halfedges[3 * tId + 2]);
+                        DisableHe(halfedges, 0, rId);
+                        DisableHe(halfedges, 1, rId);
+                        DisableHe(halfedges, 2, rId);
                     }
                 }
 
                 // Trim the data to reflect removed triangles.
-                triangles.Length = 3 * count;
-                constrainedHalfedges.Length = 3 * count;
-                halfedges.Length = 3 * count;
-
-                map.Dispose();
+                triangles.Length = 3 * wId;
+                constrainedHalfedges.Length = 3 * wId;
+                halfedges.Length = 3 * wId;
             }
 
             private void PlantSeed(int tId)
@@ -2662,7 +2668,7 @@ private void PlantSeed(int tId)
 
                 visitedTriangles[tId] = true;
                 trianglesQueue.Enqueue(tId);
-                anyTriangleVisited = true;
+                tIdMinVisited = tIdMinVisited == -1 ? tId : math.min(tId, tIdMinVisited);
 
                 // Search outwards from the seed triangle and mark all triangles
                 // until we get to a constrained edge, or a previously visited triangle.
@@ -2682,6 +2688,7 @@ private void PlantSeed(int tId)
                         {
                             visitedTriangles[otherId] = true;
                             trianglesQueue.Enqueue(otherId);
+                            tIdMinVisited = math.min(otherId, tIdMinVisited);
                         }
                     }
                 }