Fix T57652: Multires undo broken with shared object data

source/blender/blenkernel/BKE_multires.h

@@ -49,7 +49,9 @@ void multires_customdata_delete(struct Mesh *me);
 
 void multires_set_tot_level(struct Object *ob, struct MultiresModifierData *mmd, int lvl);
 
-void multires_mark_as_modified(struct Object *ob, enum MultiresModifiedFlags flags);
+void multires_mark_as_modified(struct Depsgraph *depsgraph,
+                               struct Object *object,
+                               enum MultiresModifiedFlags flags);
 
 void multires_force_update(struct Object *ob);
 void multires_force_render_update(struct Object *ob);

source/blender/blenkernel/intern/multires.c

@@ -385,12 +385,20 @@ static void multires_ccg_mark_as_modified(SubdivCCG *subdiv_ccg, MultiresModifie
   }
 }
 
-void multires_mark_as_modified(Object *ob, MultiresModifiedFlags flags)
+void multires_mark_as_modified(Depsgraph *depsgraph, Object *object, MultiresModifiedFlags flags)
 {
-  if (ob == NULL) {
+  if (object == NULL) {
     return;
   }
-  Mesh *mesh = ob->data;
+  /* NOTE: CCG live inside of evaluated object.
+   *
+   * While this is a bit weird to tag the only one, this is how other areas were built
+   * historically: they are tagging multires for update and then rely on object re-evaluation to
+   * do an actual update.
+   *
+   * In a longer term maybe special dependency graph tag can help sanitizing this a bit. */
+  Object *object_eval = DEG_get_evaluated_object(depsgraph, object);
+  Mesh *mesh = object_eval->data;
   SubdivCCG *subdiv_ccg = mesh->runtime.subdiv_ccg;
   if (subdiv_ccg == NULL) {
     return;

source/blender/editors/sculpt_paint/paint_hide.c

@@ -126,7 +126,8 @@ static void partialvis_update_mesh(Object *ob,
 
 /* Hide or show elements in multires grids with a special GridFlags
  * customdata layer. */
-static void partialvis_update_grids(Object *ob,
+static void partialvis_update_grids(Depsgraph *depsgraph,
+                                    Object *ob,
                                     PBVH *pbvh,
                                     PBVHNode *node,
                                     PartialVisAction action,
@@ -208,7 +209,7 @@ static void partialvis_update_grids(Object *ob,
   if (any_changed) {
     BKE_pbvh_node_mark_rebuild_draw(node);
     BKE_pbvh_node_fully_hidden_set(node, !any_visible);
-    multires_mark_as_modified(ob, MULTIRES_HIDDEN_MODIFIED);
+    multires_mark_as_modified(depsgraph, ob, MULTIRES_HIDDEN_MODIFIED);
   }
 }
 
@@ -378,7 +379,7 @@ static int hide_show_exec(bContext *C, wmOperator *op)
         partialvis_update_mesh(ob, pbvh, nodes[i], action, area, clip_planes);
         break;
       case PBVH_GRIDS:
-        partialvis_update_grids(ob, pbvh, nodes[i], action, area, clip_planes);
+        partialvis_update_grids(depsgraph, ob, pbvh, nodes[i], action, area, clip_planes);
         break;
       case PBVH_BMESH:
         partialvis_update_bmesh(ob, pbvh, nodes[i], action, area, clip_planes);

source/blender/editors/sculpt_paint/paint_mask.c

@@ -167,7 +167,7 @@ static int mask_flood_fill_exec(bContext *C, wmOperator *op)
       0, totnode, &data, mask_flood_fill_task_cb, &settings);
 
   if (multires) {
-    multires_mark_as_modified(ob, MULTIRES_COORDS_MODIFIED);
+    multires_mark_as_modified(depsgraph, ob, MULTIRES_COORDS_MODIFIED);
   }
 
   sculpt_undo_push_end();
@@ -341,7 +341,7 @@ bool ED_sculpt_mask_box_select(struct bContext *C, ViewContext *vc, const rcti *
   }
 
   if (multires) {
-    multires_mark_as_modified(ob, MULTIRES_COORDS_MODIFIED);
+    multires_mark_as_modified(depsgraph, ob, MULTIRES_COORDS_MODIFIED);
   }
 
   sculpt_undo_push_end();
@@ -528,7 +528,7 @@ static int paint_mask_gesture_lasso_exec(bContext *C, wmOperator *op)
     }
 
     if (multires) {
-      multires_mark_as_modified(ob, MULTIRES_COORDS_MODIFIED);
+      multires_mark_as_modified(depsgraph, ob, MULTIRES_COORDS_MODIFIED);
     }
 
     sculpt_undo_push_end();

source/blender/editors/sculpt_paint/sculpt.c

@@ -5186,15 +5186,13 @@ static void sculpt_flush_update_step(bContext *C)
 {
   Depsgraph *depsgraph = CTX_data_depsgraph(C);
   Object *ob = CTX_data_active_object(C);
-  Object *ob_eval = DEG_get_evaluated_object(depsgraph, ob);
   SculptSession *ss = ob->sculpt;
   ARegion *ar = CTX_wm_region(C);
   MultiresModifierData *mmd = ss->multires;
   View3D *v3d = CTX_wm_view3d(C);
 
   if (mmd != NULL) {
-    /* NOTE: SubdivCCG is living in the evaluated object. */
-    multires_mark_as_modified(ob_eval, MULTIRES_COORDS_MODIFIED);
+    multires_mark_as_modified(depsgraph, ob, MULTIRES_COORDS_MODIFIED);
   }
 
   DEG_id_tag_update(&ob->id, ID_RECALC_SHADING);

source/blender/editors/sculpt_paint/sculpt_undo.c

@@ -554,10 +554,10 @@ static void sculpt_undo_restore_list(bContext *C, ListBase *lb)
 
     if (BKE_sculpt_multires_active(scene, ob)) {
       if (rebuild) {
-        multires_mark_as_modified(ob, MULTIRES_HIDDEN_MODIFIED);
+        multires_mark_as_modified(depsgraph, ob, MULTIRES_HIDDEN_MODIFIED);
       }
       else {
-        multires_mark_as_modified(ob, MULTIRES_COORDS_MODIFIED);
+        multires_mark_as_modified(depsgraph, ob, MULTIRES_COORDS_MODIFIED);
       }
     }