Modifier: Maintain per-modifier session UUID

Allows to keep track of modifiers, which is required, for example,
for runtime data preservation in depsgraph.

source/blender/blenkernel/BKE_modifier.h

@@ -413,9 +413,13 @@ void BKE_modifier_type_panel_id(ModifierType type, char *r_idname);
  * default values if pointer is optional.
  */
 struct ModifierData *BKE_modifier_new(int type);
+
 void BKE_modifier_free_ex(struct ModifierData *md, const int flag);
 void BKE_modifier_free(struct ModifierData *md);
 
+/* Generate new UUID for the given modifier. */
+void BKE_modifier_session_uuid_generate(struct ModifierData *md);
+
 bool BKE_modifier_unique_name(struct ListBase *modifiers, struct ModifierData *md);
 
 void BKE_modifier_copydata_generic(const struct ModifierData *md,
@@ -539,6 +543,8 @@ void BKE_modifier_deform_vertsEM(ModifierData *md,
 struct Mesh *BKE_modifier_get_evaluated_mesh_from_evaluated_object(struct Object *ob_eval,
                                                                    const bool get_cage_mesh);
 
+void BKE_modifier_check_uuids_unique_and_report(const struct Object *object);
+
 #ifdef __cplusplus
 }
 #endif

source/blender/blenkernel/BKE_object.h

@@ -409,6 +409,8 @@ struct Mesh *BKE_object_to_mesh(struct Depsgraph *depsgraph,
 
 void BKE_object_to_mesh_clear(struct Object *object);
 
+void BKE_object_check_uuids_unique_and_report(const struct Object *object);
+
 #ifdef __cplusplus
 }
 #endif

source/blender/blenkernel/intern/modifier.c

@@ -41,6 +41,7 @@
 #include "BLI_linklist.h"
 #include "BLI_listbase.h"
 #include "BLI_path_util.h"
+#include "BLI_session_uuid.h"
 #include "BLI_string.h"
 #include "BLI_string_utils.h"
 #include "BLI_utildefines.h"
@@ -150,6 +151,8 @@ ModifierData *BKE_modifier_new(int type)
     mti->initData(md);
   }
 
+  BKE_modifier_session_uuid_generate(md);
+
   return md;
 }
 
@@ -192,6 +195,11 @@ void BKE_modifier_free(ModifierData *md)
   BKE_modifier_free_ex(md, 0);
 }
 
+void BKE_modifier_session_uuid_generate(ModifierData *md)
+{
+  md->session_uuid = BLI_session_uuid_generate();
+}
+
 bool BKE_modifier_unique_name(ListBase *modifiers, ModifierData *md)
 {
   if (modifiers && md) {
@@ -368,6 +376,17 @@ void BKE_modifier_copydata_ex(ModifierData *md, ModifierData *target, const int
       mti->foreachObjectLink(target, NULL, (ObjectWalkFunc)modifier_copy_data_id_us_cb, NULL);
     }
   }
+
+  if (flag & LIB_ID_CREATE_NO_MAIN) {
+    /* Make sure UUID is the same between the source and the target.
+     * This is needed in the cases when UUID is to be preserved and when there is no copyData
+     * callback, or the copyData does not do full byte copy of the modifier data. */
+    target->session_uuid = md->session_uuid;
+  }
+  else {
+    /* In the case copyData made full byte copy force UUID to be re-generated. */
+    BKE_modifier_session_uuid_generate(md);
+  }
 }
 
 void BKE_modifier_copydata(ModifierData *md, ModifierData *target)
@@ -1071,3 +1090,26 @@ struct ModifierData *BKE_modifier_get_evaluated(Depsgraph *depsgraph,
   }
   return BKE_modifiers_findby_name(object_eval, md->name);
 }
+
+void BKE_modifier_check_uuids_unique_and_report(const Object *object)
+{
+  struct GSet *used_uuids = BLI_gset_new(
+      BLI_session_uuid_ghash_hash, BLI_session_uuid_ghash_compare, "modifier used uuids");
+
+  LISTBASE_FOREACH (ModifierData *, md, &object->modifiers) {
+    const SessionUUID *session_uuid = &md->session_uuid;
+    if (!BLI_session_uuid_is_generated(session_uuid)) {
+      printf("Modifier %s -> %s does not have UUID generated.\n", object->id.name + 2, md->name);
+      continue;
+    }
+
+    if (BLI_gset_lookup(used_uuids, session_uuid) != NULL) {
+      printf("Modifier %s -> %s has duplicate UUID generated.\n", object->id.name + 2, md->name);
+      continue;
+    }
+
+    BLI_gset_insert(used_uuids, (void *)session_uuid);
+  }
+
+  BLI_gset_free(used_uuids, NULL);
+}

source/blender/blenkernel/intern/object.c

@@ -4714,3 +4714,9 @@ void BKE_object_to_mesh_clear(Object *object)
   BKE_id_free(NULL, object->runtime.object_as_temp_mesh);
   object->runtime.object_as_temp_mesh = NULL;
 }
+
+void BKE_object_check_uuids_unique_and_report(const Object *object)
+{
+  BKE_pose_check_uuids_unique_and_report(object->pose);
+  BKE_modifier_check_uuids_unique_and_report(object);
+}

source/blender/blenloader/intern/readfile.c

@@ -5296,6 +5296,8 @@ static void direct_link_modifiers(BlendDataReader *reader, ListBase *lb, Object
   BLO_read_list(reader, lb);
 
   for (md = lb->first; md; md = md->next) {
+    BKE_modifier_session_uuid_generate(md);
+
     md->error = NULL;
     md->runtime = NULL;
 

source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.cc

@@ -292,7 +292,7 @@ bool id_copy_inplace_no_main(const ID *id, ID *newid)
     const ID_Type id_type = GS(id_for_copy->name);
     if (id_type == ID_OB) {
       const Object *object = reinterpret_cast<const Object *>(id_for_copy);
-      BKE_pose_check_uuids_unique_and_report(object->pose);
+      BKE_object_check_uuids_unique_and_report(object);
     }
   }
 

source/blender/makesdna/DNA_modifier_types.h

@@ -22,6 +22,7 @@
 
 #include "DNA_defs.h"
 #include "DNA_listBase.h"
+#include "DNA_session_uuid_types.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -124,6 +125,11 @@ typedef struct ModifierData {
 
   /* Pointer to a ModifierData in the original domain. */
   struct ModifierData *orig_modifier_data;
+
+  /* Runtime field which contains unique identifier of the modifier. */
+  SessionUUID session_uuid;
+
+  /* Runtime field which contains runtime data which is specific to a modifier type. */
   void *runtime;
 } ModifierData;