Mesh: support face-maps when joining

Resolves T64320

source/blender/blenkernel/BKE_object_facemap.h

@@ -40,6 +40,11 @@ void BKE_object_facemap_unique_name(struct Object *ob, struct bFaceMap *fmap);
 struct bFaceMap *BKE_object_facemap_find_name(struct Object *ob, const char *name);
 void BKE_object_facemap_copy_list(struct ListBase *outbase, const struct ListBase *inbase);
 
+int *BKE_object_facemap_index_map_create(struct Object *ob_src,
+                                         struct Object *ob_dst,
+                                         int *r_map_len);
+void BKE_object_facemap_index_map_apply(int *fmap, int fmap_len, const int *map, int map_len);
+
 #ifdef __cplusplus
 }
 #endif

source/blender/blenkernel/intern/object_facemap.c

@@ -261,3 +261,41 @@ bFaceMap *BKE_object_facemap_find_name(Object *ob, const char *name)
 {
   return BLI_findstring(&ob->fmaps, name, offsetof(bFaceMap, name));
 }
+
+int *BKE_object_facemap_index_map_create(Object *ob_src, Object *ob_dst, int *r_map_len)
+{
+  /* Build src to merged mapping of facemap indices. */
+  if (BLI_listbase_is_empty(&ob_src->fmaps) || BLI_listbase_is_empty(&ob_dst->fmaps)) {
+    *r_map_len = 0;
+    return NULL;
+  }
+
+  *r_map_len = BLI_listbase_count(&ob_src->fmaps);
+  int *fmap_index_map = MEM_malloc_arrayN(
+      *r_map_len, sizeof(*fmap_index_map), "defgroup index map create");
+  bool is_fmap_remap_needed = false;
+
+  int i = 0;
+  for (bFaceMap *fmap_src = ob_src->fmaps.first; fmap_src; fmap_src = fmap_src->next, i++) {
+    fmap_index_map[i] = BKE_object_facemap_name_index(ob_dst, fmap_src->name);
+    is_fmap_remap_needed = is_fmap_remap_needed || (fmap_index_map[i] != i);
+  }
+
+  if (!is_fmap_remap_needed) {
+    MEM_freeN(fmap_index_map);
+    fmap_index_map = NULL;
+    *r_map_len = 0;
+  }
+
+  return fmap_index_map;
+}
+
+void BKE_object_facemap_index_map_apply(int *fmap, int fmap_len, const int *map, int map_len)
+{
+  if (map == NULL || map_len == 0) {
+    return;
+  }
+  for (int i = 0; i < fmap_len; i++, fmap++) {
+    *fmap = (*fmap < map_len && *fmap != -1) ? map[*fmap] : -1;
+  }
+}

source/blender/editors/mesh/meshtools.c

@@ -54,6 +54,7 @@
 #include "BKE_multires.h"
 #include "BKE_object.h"
 #include "BKE_object_deform.h"
+#include "BKE_object_facemap.h"
 #include "BKE_report.h"
 
 #include "DEG_depsgraph.h"
@@ -267,6 +268,22 @@ static void join_mesh_single(Depsgraph *depsgraph,
       mpoly->loopstart += *loopofs;
       mpoly->mat_nr = matmap ? matmap[mpoly->mat_nr] : 0;
     }
+
+    /* Face maps. */
+    int *fmap = CustomData_get(pdata, *polyofs, CD_FACEMAP);
+    int *fmap_src = CustomData_get(&me->pdata, 0, CD_FACEMAP);
+
+    /* Remap to correct new face-map indices, if needed. */
+    if (fmap_src) {
+      BLI_assert(fmap != NULL);
+      int *fmap_index_map;
+      int fmap_index_map_len;
+      fmap_index_map = BKE_object_facemap_index_map_create(ob_src, ob_dst, &fmap_index_map_len);
+      BKE_object_facemap_index_map_apply(fmap, me->totpoly, fmap_index_map, fmap_index_map_len);
+      if (fmap_index_map != NULL) {
+        MEM_freeN(fmap_index_map);
+      }
+    }
   }
 
   /* these are used for relinking (cannot be set earlier, or else reattaching goes wrong) */
@@ -403,7 +420,7 @@ int join_mesh_exec(bContext *C, wmOperator *op)
     key->type = KEY_RELATIVE;
   }
 
-  /* first pass over objects - copying materials and vertexgroups across */
+  /* First pass over objects: Copying materials, vertex-groups & face-maps across. */
   CTX_DATA_BEGIN (C, Object *, ob_iter, selected_editable_objects) {
     /* only act if a mesh, and not the one we're joining to */
     if ((ob != ob_iter) && (ob_iter->type == OB_MESH)) {
@@ -422,6 +439,19 @@ int join_mesh_exec(bContext *C, wmOperator *op)
         ob->actdef = 1;
       }
 
+      /* Join this object's face maps to the base one's. */
+      for (bFaceMap *fmap = ob_iter->fmaps.first; fmap; fmap = fmap->next) {
+        /* See if this group exists in the object (if it doesn't, add it to the end) */
+        if (BKE_object_facemap_find_name(ob, fmap->name) == NULL) {
+          bFaceMap *fmap_new = MEM_callocN(sizeof(bFaceMap), "join faceMap");
+          memcpy(fmap_new, fmap, sizeof(bFaceMap));
+          BLI_addtail(&ob->fmaps, fmap_new);
+        }
+      }
+      if (ob->fmaps.first && ob->actfmap == 0) {
+        ob->actfmap = 1;
+      }
+
       if (me->totvert) {
         /* Add this object's materials to the base one's if they don't exist already
          * (but only if limits not exceeded yet) */