EditMesh: Improve AutoMerge with Split Edges & Faces

Previously, compared to `Auto Merge` without `Split Edges & Faces`,
`Auto Merge` with this option ignored duplicates between selected
vertices. It only considered duplicates between selected vertices and
unselected vertices.

This is a regress and not a progress.

This commit implements this behavior, so this option matches the other
`Auto Merge`.

2 files changed, 47 insertions, 11 deletions

diff --git a/source/blender/editors/include/ED_mesh.h b/source/blender/editors/include/ED_mesh.h
index 90ad90058e7..b28f645e982 100644
--- a/source/blender/editors/include/ED_mesh.h
+++ b/source/blender/editors/include/ED_mesh.h
@@ -144,9 +144,9 @@ bool BMBVH_EdgeVisible(struct BMBVHTree *tree,
 /* editmesh_automerge.c */
 void EDBM_automerge(struct Object *ob, bool update, const char hflag, const float dist);
 void EDBM_automerge_and_split(struct Object *ob,
-                              bool split_edges,
-                              bool split_faces,
-                              bool update,
+                              const bool split_edges,
+                              const bool split_faces,
+                              const bool update,
                               const char hflag,
                               const float dist);
 
diff --git a/source/blender/editors/mesh/editmesh_automerge.c b/source/blender/editors/mesh/editmesh_automerge.c
index fb8ee85f9db..55b52e01fc3 100644
--- a/source/blender/editors/mesh/editmesh_automerge.c
+++ b/source/blender/editors/mesh/editmesh_automerge.c
@@ -92,9 +92,9 @@ void EDBM_automerge(Object *obedit, bool update, const char hflag, const float d
  * \{ */
 
 void EDBM_automerge_and_split(Object *obedit,
-                              bool UNUSED(split_edges),
-                              bool split_faces,
-                              bool update,
+                              const bool UNUSED(split_edges),
+                              const bool split_faces,
+                              const bool update,
                               const char hflag,
                               const float dist)
 {
@@ -126,18 +126,54 @@ void EDBM_automerge_and_split(Object *obedit,
   ok = BM_mesh_intersect_edges(bm, hflag, dist, ghash_targetmap);
 
   if (ok) {
+    GHashIterator gh_iter;
+    BMVert **v_survivors, **v_iter;
+    uint v_survivors_len = 0;
+    if (split_faces) {
+      BMVert *v_src, *v_dst;
+      GHASH_ITER (gh_iter, ghash_targetmap) {
+        v_src = BLI_ghashIterator_getKey(&gh_iter);
+        v_dst = BLI_ghashIterator_getValue(&gh_iter);
+        BM_elem_flag_disable(v_src, BM_ELEM_TAG);
+        BM_elem_flag_disable(v_dst, BM_ELEM_TAG);
+      }
+
+      int v_survivors_len_max = BLI_ghash_len(ghash_targetmap);
+      GHASH_ITER (gh_iter, ghash_targetmap) {
+        v_src = BLI_ghashIterator_getKey(&gh_iter);
+        v_dst = BLI_ghashIterator_getValue(&gh_iter);
+        if (!BM_elem_flag_test(v_src, BM_ELEM_TAG)) {
+          BM_elem_flag_enable(v_src, BM_ELEM_TAG);
+        }
+        if (BM_elem_flag_test(v_dst, BM_ELEM_TAG)) {
+          v_survivors_len_max--;
+        }
+      }
+
+      v_survivors = MEM_mallocN(sizeof(*v_survivors) * v_survivors_len_max, __func__);
+      v_iter = &v_survivors[0];
+      GHASH_ITER (gh_iter, ghash_targetmap) {
+        v_dst = BLI_ghashIterator_getValue(&gh_iter);
+        if (!BM_elem_flag_test(v_dst, BM_ELEM_TAG)) {
+          *v_iter = v_dst;
+          v_iter++;
+          v_survivors_len++;
+        }
+      }
+    }
+
     BMO_op_exec(bm, &weldop);
 
     BMEdge **edgenet = NULL;
     int edgenet_alloc_len = 0;
     if (split_faces) {
-      GHashIterator gh_iter;
-      GHASH_ITER (gh_iter, ghash_targetmap) {
-        BMVert *v = BLI_ghashIterator_getValue(&gh_iter);
-        // BLI_assert(BM_elem_flag_test(v, hflag) || hflag == BM_ELEM_TAG);
+      v_iter = &v_survivors[0];
+      for (int i = v_survivors_len; i--; v_iter++) {
         BM_vert_weld_linked_wire_edges_into_linked_faces(
-            bm, v, dist, &edgenet, &edgenet_alloc_len);
+            bm, *v_iter, dist, &edgenet, &edgenet_alloc_len);
       }
+
+      MEM_freeN(v_survivors);
     }
 
     if (edgenet) {