Workaround T81065: Merge UV's when applying modifiers

Support merging UV's that share the same vertex and are very close when
applying modifiers.

This is needed to prevent UV's becoming "detached" which can happen when
applying the subdivision surface modifier.

This regression was caused by [0] which removed selection threshold for
nearby coordinates. While restoring the UV selection threshold could be
done - some selection operations that walk around connected UV fans
wouldn't behave in a deterministic way (such as select shortest path).
There are also other cases where UV's may be compared without a
threshold such as tangent calculation and exporters which have their own
logic to handling UV's.

Also resolves T86896, T89903.

[0]: b88dd3b8e7b9c02ae08d4679bb427963c5d21250

Reviewed By: sergey

Ref D14841

1 files changed, 27 insertions, 0 deletions

diff --git a/source/blender/editors/object/object_modifier.cc b/source/blender/editors/object/object_modifier.cc
index f90a31a7cbe..3328fe65f2e 100644
--- a/source/blender/editors/object/object_modifier.cc
+++ b/source/blender/editors/object/object_modifier.cc
@@ -1434,8 +1434,10 @@ static int modifier_apply_exec_ex(bContext *C, wmOperator *op, int apply_as, boo
   Scene *scene = CTX_data_scene(C);
   Object *ob = ED_object_active_context(C);
   ModifierData *md = edit_modifier_property_get(op, ob, 0);
+  const ModifierTypeInfo *mti = BKE_modifier_get_info((ModifierType)md->type);
   const bool do_report = RNA_boolean_get(op->ptr, "report");
   const bool do_single_user = RNA_boolean_get(op->ptr, "single_user");
+  const bool do_merge_customdata = RNA_boolean_get(op->ptr, "merge_customdata");
 
   if (md == nullptr) {
     return OPERATOR_CANCELLED;
@@ -1460,6 +1462,11 @@ static int modifier_apply_exec_ex(bContext *C, wmOperator *op, int apply_as, boo
     return OPERATOR_CANCELLED;
   }
 
+  if (do_merge_customdata &&
+      (mti->type & (eModifierTypeType_Constructive | eModifierTypeType_Nonconstructive))) {
+    BKE_mesh_merge_customdata_for_apply_modifier((Mesh *)ob->data);
+  }
+
   DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
   DEG_relations_tag_update(bmain);
   WM_event_add_notifier(C, NC_OBJECT | ND_MODIFIER, ob);
@@ -1518,6 +1525,12 @@ void OBJECT_OT_modifier_apply(wmOperatorType *ot)
   edit_modifier_properties(ot);
   edit_modifier_report_property(ot);
 
+  RNA_def_boolean(
+      ot->srna,
+      "merge_customdata",
+      true,
+      "Merge UV's",
+      "Merge UV coordinates that share a vertex to account for imprecision in some modifiers");
   PropertyRNA *prop = RNA_def_boolean(ot->srna,
                                       "single_user",
                                       false,
@@ -1599,11 +1612,18 @@ static int modifier_convert_exec(bContext *C, wmOperator *op)
   ViewLayer *view_layer = CTX_data_view_layer(C);
   Object *ob = ED_object_active_context(C);
   ModifierData *md = edit_modifier_property_get(op, ob, 0);
+  const ModifierTypeInfo *mti = BKE_modifier_get_info((ModifierType)md->type);
+  const bool do_merge_customdata = RNA_boolean_get(op->ptr, "merge_customdata");
 
   if (!md || !ED_object_modifier_convert(op->reports, bmain, depsgraph, view_layer, ob, md)) {
     return OPERATOR_CANCELLED;
   }
 
+  if (do_merge_customdata &&
+      (mti->type & (eModifierTypeType_Constructive | eModifierTypeType_Nonconstructive))) {
+    BKE_mesh_merge_customdata_for_apply_modifier((Mesh *)ob->data);
+  }
+
   DEG_id_tag_update(&ob->id, ID_RECALC_GEOMETRY);
   WM_event_add_notifier(C, NC_OBJECT | ND_MODIFIER, ob);
 
@@ -1631,6 +1651,13 @@ void OBJECT_OT_modifier_convert(wmOperatorType *ot)
   /* flags */
   ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
   edit_modifier_properties(ot);
+
+  RNA_def_boolean(
+      ot->srna,
+      "merge_customdata",
+      true,
+      "Merge UV's",
+      "Merge UV coordinates that share a vertex to account for imprecision in some modifiers");
 }
 
 /** \} */