Merge remote-tracking branch 'origin/blender-v3.0-release'

6 files changed, 60 insertions, 20 deletions

diff --git a/source/blender/blenkernel/BKE_mesh_mirror.h b/source/blender/blenkernel/BKE_mesh_mirror.h
index 7b230b04410..eaa479be867 100644
--- a/source/blender/blenkernel/BKE_mesh_mirror.h
+++ b/source/blender/blenkernel/BKE_mesh_mirror.h
@@ -43,10 +43,12 @@ void BKE_mesh_mirror_apply_mirror_on_axis(struct Main *bmain,
                                           const int axis,
                                           const float dist);
 
-struct Mesh *BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(struct MirrorModifierData *mmd,
-                                                               struct Object *ob,
-                                                               const struct Mesh *mesh,
-                                                               const int axis);
+struct Mesh *BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(
+    struct MirrorModifierData *mmd,
+    struct Object *ob,
+    const struct Mesh *mesh,
+    const int axis,
+    const bool use_correct_order_on_merge);
 
 #ifdef __cplusplus
 }
diff --git a/source/blender/blenkernel/intern/mesh_mirror.c b/source/blender/blenkernel/intern/mesh_mirror.c
index 6df13e71e72..2756629b440 100644
--- a/source/blender/blenkernel/intern/mesh_mirror.c
+++ b/source/blender/blenkernel/intern/mesh_mirror.c
@@ -137,7 +137,8 @@ void BKE_mesh_mirror_apply_mirror_on_axis(struct Main *bmain,
 Mesh *BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(MirrorModifierData *mmd,
                                                         Object *ob,
                                                         const Mesh *mesh,
-                                                        const int axis)
+                                                        const int axis,
+                                                        const bool use_correct_order_on_merge)
 {
   const float tolerance_sq = mmd->tolerance * mmd->tolerance;
   const bool do_vtargetmap = (mmd->flag & MOD_MIR_NO_MERGE) == 0;
@@ -266,23 +267,46 @@ Mesh *BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(MirrorModifierData *mmd,
        * Always merge from the copied into the original vertices so it's possible to
        * generate a 1:1 mapping by scanning vertices from the beginning of the array
        * as is done in #BKE_editmesh_vert_coords_when_deformed. Without this,
-       * the coordinates returned will sometimes point to the copied vertex locations, see: T91444.
+       * the coordinates returned will sometimes point to the copied vertex locations, see:
+       * T91444.
+       *
+       * However, such a change also affects non-versionable things like some modifiers binding, so
+       * we cannot enforce that behavior on existing modifiers, in which case we keep using the
+       * old, incorrect behavior of merging the source vertex into its copy.
        */
-      if (UNLIKELY(len_squared_v3v3(mv_prev->co, mv->co) < tolerance_sq)) {
-        *vtmap_b = i;
-        tot_vtargetmap++;
+      if (use_correct_order_on_merge) {
+        if (UNLIKELY(len_squared_v3v3(mv_prev->co, mv->co) < tolerance_sq)) {
+          *vtmap_b = i;
+          tot_vtargetmap++;
+
+          /* average location */
+          mid_v3_v3v3(mv->co, mv_prev->co, mv->co);
+          copy_v3_v3(mv_prev->co, mv->co);
+        }
+        else {
+          *vtmap_b = -1;
+        }
 
-        /* average location */
-        mid_v3_v3v3(mv->co, mv_prev->co, mv->co);
-        copy_v3_v3(mv_prev->co, mv->co);
+        /* Fill here to avoid 2x loops. */
+        *vtmap_a = -1;
       }
       else {
+        if (UNLIKELY(len_squared_v3v3(mv_prev->co, mv->co) < tolerance_sq)) {
+          *vtmap_a = maxVerts + i;
+          tot_vtargetmap++;
+
+          /* average location */
+          mid_v3_v3v3(mv->co, mv_prev->co, mv->co);
+          copy_v3_v3(mv_prev->co, mv->co);
+        }
+        else {
+          *vtmap_a = -1;
+        }
+
+        /* Fill here to avoid 2x loops. */
         *vtmap_b = -1;
       }
 
-      /* Fill here to avoid 2x loops. */
-      *vtmap_a = -1;
-
       vtmap_a++;
       vtmap_b++;
     }
diff --git a/source/blender/editors/object/object_remesh.cc b/source/blender/editors/object/object_remesh.cc
index 3bdf7e0d34d..719ffd36f03 100644
--- a/source/blender/editors/object/object_remesh.cc
+++ b/source/blender/editors/object/object_remesh.cc
@@ -821,7 +821,8 @@ static Mesh *remesh_symmetry_mirror(Object *ob, Mesh *mesh, eSymmetryAxes symmet
       mmd.flag = 0;
       mmd.flag &= MOD_MIR_AXIS_X << i;
       mesh_mirror_temp = mesh_mirror;
-      mesh_mirror = BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(&mmd, ob, mesh_mirror, axis);
+      mesh_mirror = BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(
+          &mmd, ob, mesh_mirror, axis, true);
       if (mesh_mirror_temp != mesh_mirror) {
         BKE_id_free(nullptr, mesh_mirror_temp);
       }
diff --git a/source/blender/makesdna/DNA_modifier_defaults.h b/source/blender/makesdna/DNA_modifier_defaults.h
index 5b2694f420b..78ab41031a6 100644
--- a/source/blender/makesdna/DNA_modifier_defaults.h
+++ b/source/blender/makesdna/DNA_modifier_defaults.h
@@ -429,6 +429,7 @@
     .uv_offset = {0.0f, 0.0f}, \
     .uv_offset_copy = {0.0f, 0.0f}, \
     .mirror_ob = NULL, \
+    .use_correct_order_on_merge = true, \
   }
 
 #define _DNA_DEFAULT_MultiresModifierData \
diff --git a/source/blender/makesdna/DNA_modifier_types.h b/source/blender/makesdna/DNA_modifier_types.h
index 631db64ddd3..f7a468264c3 100644
--- a/source/blender/makesdna/DNA_modifier_types.h
+++ b/source/blender/makesdna/DNA_modifier_types.h
@@ -374,7 +374,15 @@ typedef struct MirrorModifierData {
   short flag;
   float tolerance;
   float bisect_threshold;
-  char _pad[4];
+
+  /** Mirror modifier used to merge the old vertex into its new copy, which would break code
+   * relying on access to the original geometry vertices. However, modifying this behavior to the
+   * correct one (i.e. merging the copy vertices into their original sources) has several potential
+   * effects on other modifiers and tools, so we need to keep that incorrect behavior for existing
+   * modifiers, and only use the new correct one for new modifiers. */
+  uint8_t use_correct_order_on_merge;
+
+  char _pad[3];
   float uv_offset[2];
   float uv_offset_copy[2];
   struct Object *mirror_ob;
diff --git a/source/blender/modifiers/intern/MOD_mirror.c b/source/blender/modifiers/intern/MOD_mirror.c
index 7fd90c71c9f..bbac6589577 100644
--- a/source/blender/modifiers/intern/MOD_mirror.c
+++ b/source/blender/modifiers/intern/MOD_mirror.c
@@ -84,14 +84,17 @@ static void updateDepsgraph(ModifierData *md, const ModifierUpdateDepsgraphConte
 static Mesh *mirrorModifier__doMirror(MirrorModifierData *mmd, Object *ob, Mesh *mesh)
 {
   Mesh *result = mesh;
+  const bool use_correct_order_on_merge = mmd->use_correct_order_on_merge;
 
   /* check which axes have been toggled and mirror accordingly */
   if (mmd->flag & MOD_MIR_AXIS_X) {
-    result = BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(mmd, ob, result, 0);
+    result = BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(
+        mmd, ob, result, 0, use_correct_order_on_merge);
   }
   if (mmd->flag & MOD_MIR_AXIS_Y) {
     Mesh *tmp = result;
-    result = BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(mmd, ob, result, 1);
+    result = BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(
+        mmd, ob, result, 1, use_correct_order_on_merge);
     if (tmp != mesh) {
       /* free intermediate results */
       BKE_id_free(NULL, tmp);
@@ -99,7 +102,8 @@ static Mesh *mirrorModifier__doMirror(MirrorModifierData *mmd, Object *ob, Mesh
   }
   if (mmd->flag & MOD_MIR_AXIS_Z) {
     Mesh *tmp = result;
-    result = BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(mmd, ob, result, 2);
+    result = BKE_mesh_mirror_apply_mirror_on_axis_for_modifier(
+        mmd, ob, result, 2, use_correct_order_on_merge);
     if (tmp != mesh) {
       /* free intermediate results */
       BKE_id_free(NULL, tmp);