From 111e378366e389fda300e0f5317d0c9b95bbd8fb Mon Sep 17 00:00:00 2001
From: Hans Goudey <h.goudey@me.com>
Date: Sun, 16 Jul 2023 00:08:23 -0400
Subject: [PATCH] Revert "Fix #109236: Split Edges node skips loose edges"

This reverts commit b226c115e263afbb1c2ded1e5a73e954690945c2.

Fixes #110005.

I have been working on a fix branch, but the problem was fairly
fundamental to the algorithm and the fix ended up being a rewrite
that I didn't quite finish yet, and I will be away next week. Since
the other bug is a crash rather than a change in behavior, better to
have the other bug than this one in the meantime.
---
 .../geometry/intern/mesh_split_edges.cc       | 53 ++-----------------
 1 file changed, 3 insertions(+), 50 deletions(-)

diff --git a/source/blender/geometry/intern/mesh_split_edges.cc b/source/blender/geometry/intern/mesh_split_edges.cc
index 2538a4fbd22..9bc7be7ed0b 100644
--- a/source/blender/geometry/intern/mesh_split_edges.cc
+++ b/source/blender/geometry/intern/mesh_split_edges.cc
@@ -180,33 +180,6 @@ static void split_vertex_per_fan(const int vertex,
   }
 }
 
-/** Assign the newly created vertex duplicates to the loose edges around this vertex. */
-static void reassign_loose_edge_verts(const int vertex,
-                                      const int start_offset,
-                                      const Span<int> fans,
-                                      const Span<int> fan_sizes,
-                                      const BoundedBitSpan loose_edges,
-                                      MutableSpan<int2> edges)
-{
-  int fan_start = 0;
-  /* We don't need to create a new vertex for the last fan. That fan can just be connected to the
-   * original vertex. */
-  for (const int i : fan_sizes.index_range().drop_back(1)) {
-    const int new_vert = start_offset + i;
-    for (const int edge_i : fans.slice(fan_start, fan_sizes[i])) {
-      if (loose_edges[edge_i]) {
-        if (edges[edge_i][0] == vertex) {
-          edges[edge_i][0] = new_vert;
-        }
-        else if (edges[edge_i][1] == vertex) {
-          edges[edge_i][1] = new_vert;
-        }
-      }
-    }
-    fan_start += fan_sizes[i];
-  }
-}
-
 /**
  * Get the index of the adjacent edge to a loop connected to a vertex. In other words, for the
  * given polygon return the unique edge connected to the given vertex and not on the given loop.
@@ -410,7 +383,7 @@ void split_edges(Mesh &mesh,
     }
   });
 
-  /* Calculate result indices per source vertex as offsets for parallelizing the next step. */
+  /* Step 2.5: Calculate offsets for next step. */
   Array<int> vert_offsets(mesh.totvert);
   int total_verts_num = mesh.totvert;
   for (const int vert : IndexRange(mesh.totvert)) {
@@ -422,7 +395,7 @@ void split_edges(Mesh &mesh,
     total_verts_num += vertex_fan_sizes[vert].size() - 1;
   }
 
-  /* Split the vertices into their duplicates so that each fan has its own result vertex.
+  /* Step 3: Split the vertices.
    * Build a map from each new vertex to an old vertex to use for transferring attributes later. */
   const int new_verts_num = total_verts_num - mesh.totvert;
   Array<int> new_to_old_verts_map(new_verts_num);
@@ -442,7 +415,6 @@ void split_edges(Mesh &mesh,
     }
   });
 
-  /* Create deduplicated new edges based on the corner vertices at each polygon. */
   VectorSet<OrderedEdge> new_edges;
   new_edges.reserve(new_edges_size + loose_edges.size());
   for (const int i : polys.index_range()) {
@@ -455,7 +427,6 @@ void split_edges(Mesh &mesh,
   }
   loose_edges.foreach_index([&](const int64_t i) { new_edges.add(OrderedEdge(edges[i])); });
 
-  /* Build a map of old to new edges for transferring attributes. */
   Array<int> new_to_old_edges_map(new_edges.size());
   loose_edges.to_indices(new_to_old_edges_map.as_mutable_span().take_back(loose_edges.size()));
   for (const int i : polys.index_range()) {
@@ -467,28 +438,10 @@ void split_edges(Mesh &mesh,
     }
   }
 
-  /* Resize the mesh to add the new vertices and rebuild the edges. */
+  /* Step 5: Resize the mesh to add the new vertices and rebuild the edges. */
   add_new_vertices(mesh, new_to_old_verts_map);
   add_new_edges(mesh, new_edges.as_span().cast<int2>(), new_to_old_edges_map, propagation_info);
 
-  /* Connect loose edges to duplicated vertices. */
-  if (loose_edges_cache.count > 0) {
-    MutableSpan<int2> new_edges_span = mesh.edges_for_write();
-    threading::parallel_for(should_split_vert.index_range(), 512, [&](IndexRange range) {
-      for (const int vert : range) {
-        if (!should_split_vert[vert]) {
-          continue;
-        }
-        reassign_loose_edge_verts(vert,
-                                  vert_offsets[vert],
-                                  vert_to_edge_map[vert],
-                                  vertex_fan_sizes[vert],
-                                  loose_edges_cache.is_loose_bits,
-                                  new_edges_span);
-      }
-    });
-  }
-
   BKE_mesh_tag_edges_split(&mesh);
 }