scripts/startup/bl_ui/properties_data_mesh.py

@@ -198,9 +198,9 @@ class DATA_PT_normals(MeshButtonsPanel, Panel):
         mesh = context.mesh
 
         if mesh.has_custom_normals:
-            col.operator("mesh.customdata_custom_splitnormals_clear", icon='X')
+            layout.operator("mesh.customdata_custom_splitnormals_clear", icon='X')
         else:
-            col.operator("mesh.customdata_custom_splitnormals_add", icon='ADD')
+            layout.operator("mesh.customdata_custom_splitnormals_add", icon='ADD')
 
 
 class DATA_PT_texture_space(MeshButtonsPanel, Panel):

source/blender/blenloader/intern/versioning_400.cc

@@ -131,7 +131,17 @@ static void version_mesh_objects_replace_auto_smooth(Main &bmain)
     STRNCPY(md->modifier.name, DATA_("Auto Smooth"));
     BKE_modifier_unique_name(&object->modifiers, &md->modifier);
     md->node_group = auto_smooth_node_tree;
-    BLI_addtail(&object->modifiers, md);
+    if (!BLI_listbase_is_empty(&object->modifiers) &&
+        static_cast<ModifierData *>(object->modifiers.last)->type == eModifierType_Subsurf)
+    {
+      /* Add the auto smooth node group before the last subdivision surface modifier if possible.
+       * Subdivision surface modifiers have special handling for interpolating face corner normals,
+       * and recalculating them afterwards isn't usually helpful and can be much slower. */
+      BLI_insertlinkbefore(&object->modifiers, object->modifiers.last, md);
+    }
+    else {
+      BLI_addtail(&object->modifiers, md);
+    }
 
     md->settings.properties = bke::idprop::create_group("Nodes Modifier Settings").release();
     IDProperty *angle_prop = bke::idprop::create(DATA_("Input_1"), mesh->smoothresh).release();

source/blender/editors/mesh/mesh_data.cc

@@ -749,6 +749,7 @@ static int mesh_customdata_custom_splitnormals_add_exec(bContext *C, wmOperator
   }
   else {
     CustomData_add_layer(&me->ldata, CD_CUSTOMLOOPNORMAL, CD_SET_DEFAULT, me->totloop);
+    me->runtime->corner_normals_dirty = true;
   }
 
   DEG_id_tag_update(&me->id, 0);

source/blender/makesrna/intern/rna_mesh.c

@@ -2451,8 +2451,7 @@ static void rna_def_mlooptri(BlenderRNA *brna)
   RNA_def_property_ui_text(
       prop,
       "Split Normals",
-      "Local space unit length split normals vectors of the vertices of this triangle "
-      "(must be computed beforehand using calc_normals_split or calc_tangents)");
+      "Local space unit length split normal vectors of the face corners of this triangle");
 
   prop = RNA_def_property(srna, "area", PROP_FLOAT, PROP_UNSIGNED);
   RNA_def_property_clear_flag(prop, PROP_EDITABLE);