Fix T96294: Crash and error with shape key normal calculation

A mistake in the mesh normal refactor caused the wrong mesh to
be used when calculating normals with a shape key's deformation.

This commit fixes the normal calculation by using the correct mesh,
with just adjusted vertex positions, and calculating the results
directly into the result arrays when possible. This completely avoids
the need to make a local copy of the mesh, which makes sense,
since the only thing that changes is the vertex positions.

Differential Revision: https://developer.blender.org/D14317

7 files changed, 100 insertions, 74 deletions

diff --git a/source/blender/blenkernel/BKE_key.h b/source/blender/blenkernel/BKE_key.h
index 07e816558df..ee83427d620 100644
--- a/source/blender/blenkernel/BKE_key.h
+++ b/source/blender/blenkernel/BKE_key.h
@@ -29,6 +29,7 @@ struct Lattice;
 struct ListBase;
 struct Main;
 struct Mesh;
+struct MVert;
 struct Object;
 
 /* Kernel prototypes */
@@ -135,7 +136,8 @@ void BKE_keyblock_convert_to_curve(struct KeyBlock *kb, struct Curve *cu, struct
 
 void BKE_keyblock_update_from_mesh(struct Mesh *me, struct KeyBlock *kb);
 void BKE_keyblock_convert_from_mesh(struct Mesh *me, struct Key *key, struct KeyBlock *kb);
-void BKE_keyblock_convert_to_mesh(struct KeyBlock *kb, struct Mesh *me);
+void BKE_keyblock_convert_to_mesh(struct KeyBlock *kb, struct MVert *mvert, int totvert);
+
 /**
  * Computes normals (vertices, polygons and/or loops ones) of given mesh for given shape key.
  *
diff --git a/source/blender/blenkernel/BKE_mesh.h b/source/blender/blenkernel/BKE_mesh.h
index b6296fdffc3..27f4fe94dbd 100644
--- a/source/blender/blenkernel/BKE_mesh.h
+++ b/source/blender/blenkernel/BKE_mesh.h
@@ -488,6 +488,21 @@ void BKE_mesh_calc_normals_poly(const struct MVert *mvert,
                                 float (*r_poly_normals)[3]);
 
 /**
+ * Calculate face and vertex normals directly into result arrays.
+ *
+ * \note Usually #BKE_mesh_vertex_normals_ensure is the preferred way to access vertex normals,
+ * since they may already be calculated and cached on the mesh.
+ */
+void BKE_mesh_calc_normals_poly_and_vertex(struct MVert *mvert,
+                                           int mvert_len,
+                                           const struct MLoop *mloop,
+                                           int mloop_len,
+                                           const struct MPoly *mpoly,
+                                           int mpoly_len,
+                                           float (*r_poly_normals)[3],
+                                           float (*r_vert_normals)[3]);
+
+/**
  * Calculate vertex and face normals, storing the result in custom data layers on the mesh.
  *
  * \note It is usually preferable to calculate normals lazily with
diff --git a/source/blender/blenkernel/intern/key.c b/source/blender/blenkernel/intern/key.c
index 0df493e28c0..21630d0aea7 100644
--- a/source/blender/blenkernel/intern/key.c
+++ b/source/blender/blenkernel/intern/key.c
@@ -2186,16 +2186,14 @@ void BKE_keyblock_convert_from_mesh(Mesh *me, Key *key, KeyBlock *kb)
   BKE_keyblock_update_from_mesh(me, kb);
 }
 
-void BKE_keyblock_convert_to_mesh(KeyBlock *kb, Mesh *me)
+void BKE_keyblock_convert_to_mesh(KeyBlock *kb, struct MVert *mvert, int totvert)
 {
-  MVert *mvert;
   const float(*fp)[3];
   int a, tot;
 
-  mvert = me->mvert;
   fp = kb->data;
 
-  tot = min_ii(kb->totelem, me->totvert);
+  tot = min_ii(kb->totelem, totvert);
 
   for (a = 0; a < tot; a++, fp++, mvert++) {
     copy_v3_v3(mvert->co, *fp);
@@ -2208,68 +2206,77 @@ void BKE_keyblock_mesh_calc_normals(struct KeyBlock *kb,
                                     float (*r_polynors)[3],
                                     float (*r_loopnors)[3])
 {
-  /* We use a temp, shallow copy of mesh to work. */
-  Mesh me;
-  bool free_polynors = false;
-
   if (r_vertnors == NULL && r_polynors == NULL && r_loopnors == NULL) {
     return;
   }
 
-  me = *mesh;
-  me.mvert = MEM_dupallocN(mesh->mvert);
-  CustomData_reset(&me.vdata);
-  CustomData_reset(&me.edata);
-  CustomData_reset(&me.pdata);
-  CustomData_reset(&me.ldata);
-  CustomData_reset(&me.fdata);
-
-  BKE_keyblock_convert_to_mesh(kb, &me);
-
-  if (r_polynors == NULL && r_loopnors != NULL) {
-    r_polynors = MEM_mallocN(sizeof(float[3]) * me.totpoly, __func__);
-    free_polynors = true;
-  }
-
-  const float(*vert_normals)[3] = BKE_mesh_vertex_normals_ensure(mesh);
-  if (r_vertnors) {
-    memcpy(r_vertnors, vert_normals, sizeof(float[3]) * me.totvert);
-  }
-
-  const float(*face_normals)[3] = BKE_mesh_poly_normals_ensure(mesh);
-  memcpy(r_polynors, face_normals, sizeof(float[3]) * me.totpoly);
-
-  if (r_loopnors) {
+  MVert *mvert = MEM_dupallocN(mesh->mvert);
+  BKE_keyblock_convert_to_mesh(kb, mesh->mvert, mesh->totvert);
+
+  const bool loop_normals_needed = r_loopnors != NULL;
+  const bool vert_normals_needed = r_vertnors != NULL || loop_normals_needed;
+  const bool poly_normals_needed = r_polynors != NULL || vert_normals_needed ||
+                                   loop_normals_needed;
+
+  float(*vert_normals)[3] = r_vertnors;
+  float(*poly_normals)[3] = r_polynors;
+  bool free_vert_normals = false;
+  bool free_poly_normals = false;
+  if (vert_normals_needed && r_vertnors == NULL) {
+    vert_normals = MEM_malloc_arrayN(mesh->totvert, sizeof(float[3]), __func__);
+    free_vert_normals = true;
+  }
+  if (poly_normals_needed && r_polynors == NULL) {
+    poly_normals = MEM_malloc_arrayN(mesh->totpoly, sizeof(float[3]), __func__);
+    free_poly_normals = true;
+  }
+
+  if (poly_normals_needed) {
+    BKE_mesh_calc_normals_poly(mvert,
+                               mesh->totvert,
+                               mesh->mloop,
+                               mesh->totloop,
+                               mesh->mpoly,
+                               mesh->totpoly,
+                               poly_normals);
+  }
+  if (vert_normals_needed) {
+    BKE_mesh_calc_normals_poly_and_vertex(mvert,
+                                          mesh->totvert,
+                                          mesh->mloop,
+                                          mesh->totloop,
+                                          mesh->mpoly,
+                                          mesh->totpoly,
+                                          poly_normals,
+                                          vert_normals);
+  }
+  if (loop_normals_needed) {
     short(*clnors)[2] = CustomData_get_layer(&mesh->ldata, CD_CUSTOMLOOPNORMAL); /* May be NULL. */
-
-    BKE_mesh_normals_loop_split(me.mvert,
+    BKE_mesh_normals_loop_split(mesh->mvert,
                                 vert_normals,
-                                me.totvert,
-                                me.medge,
-                                me.totedge,
-                                me.mloop,
+                                mesh->totvert,
+                                mesh->medge,
+                                mesh->totedge,
+                                mesh->mloop,
                                 r_loopnors,
-                                me.totloop,
-                                me.mpoly,
-                                face_normals,
-                                me.totpoly,
-                                (me.flag & ME_AUTOSMOOTH) != 0,
-                                me.smoothresh,
+                                mesh->totloop,
+                                mesh->mpoly,
+                                poly_normals,
+                                mesh->totpoly,
+                                (mesh->flag & ME_AUTOSMOOTH) != 0,
+                                mesh->smoothresh,
                                 NULL,
                                 clnors,
                                 NULL);
   }
 
-  CustomData_free(&me.vdata, me.totvert);
-  CustomData_free(&me.edata, me.totedge);
-  CustomData_free(&me.pdata, me.totpoly);
-  CustomData_free(&me.ldata, me.totloop);
-  CustomData_free(&me.fdata, me.totface);
-  MEM_freeN(me.mvert);
-
-  if (free_polynors) {
-    MEM_freeN(r_polynors);
+  if (free_vert_normals) {
+    MEM_freeN(vert_normals);
+  }
+  if (free_poly_normals) {
+    MEM_freeN(poly_normals);
   }
+  MEM_freeN(mvert);
 }
 
 /************************* raw coords ************************/
diff --git a/source/blender/blenkernel/intern/mesh_convert.cc b/source/blender/blenkernel/intern/mesh_convert.cc
index 1db17c950b3..9bf7d14eb80 100644
--- a/source/blender/blenkernel/intern/mesh_convert.cc
+++ b/source/blender/blenkernel/intern/mesh_convert.cc
@@ -1321,7 +1321,7 @@ Mesh *BKE_mesh_create_derived_for_modifier(struct Depsgraph *depsgraph,
 
   if (build_shapekey_layers && me->key &&
       (kb = (KeyBlock *)BLI_findlink(&me->key->block, ob_eval->shapenr - 1))) {
-    BKE_keyblock_convert_to_mesh(kb, me);
+    BKE_keyblock_convert_to_mesh(kb, me->mvert, me->totvert);
   }
 
   Mesh *mesh_temp = (Mesh *)BKE_id_copy_ex(nullptr, &me->id, nullptr, LIB_ID_COPY_LOCALIZE);
diff --git a/source/blender/blenkernel/intern/mesh_normals.cc b/source/blender/blenkernel/intern/mesh_normals.cc
index b690d7f1e32..276e823126d 100644
--- a/source/blender/blenkernel/intern/mesh_normals.cc
+++ b/source/blender/blenkernel/intern/mesh_normals.cc
@@ -323,14 +323,14 @@ static void mesh_calc_normals_poly_and_vertex_finalize_fn(
   }
 }
 
-static void mesh_calc_normals_poly_and_vertex(MVert *mvert,
-                                              const int mvert_len,
-                                              const MLoop *mloop,
-                                              const int UNUSED(mloop_len),
-                                              const MPoly *mpoly,
-                                              const int mpoly_len,
-                                              float (*r_poly_normals)[3],
-                                              float (*r_vert_normals)[3])
+void BKE_mesh_calc_normals_poly_and_vertex(MVert *mvert,
+                                           const int mvert_len,
+                                           const MLoop *mloop,
+                                           const int UNUSED(mloop_len),
+                                           const MPoly *mpoly,
+                                           const int mpoly_len,
+                                           float (*r_poly_normals)[3],
+                                           float (*r_vert_normals)[3])
 {
   TaskParallelSettings settings;
   BLI_parallel_range_settings_defaults(&settings);
@@ -403,14 +403,14 @@ const float (*BKE_mesh_vertex_normals_ensure(const Mesh *mesh))[3]
     vert_normals = BKE_mesh_vertex_normals_for_write(&mesh_mutable);
     poly_normals = BKE_mesh_poly_normals_for_write(&mesh_mutable);
 
-    mesh_calc_normals_poly_and_vertex(mesh_mutable.mvert,
-                                      mesh_mutable.totvert,
-                                      mesh_mutable.mloop,
-                                      mesh_mutable.totloop,
-                                      mesh_mutable.mpoly,
-                                      mesh_mutable.totpoly,
-                                      poly_normals,
-                                      vert_normals);
+    BKE_mesh_calc_normals_poly_and_vertex(mesh_mutable.mvert,
+                                          mesh_mutable.totvert,
+                                          mesh_mutable.mloop,
+                                          mesh_mutable.totloop,
+                                          mesh_mutable.mpoly,
+                                          mesh_mutable.totpoly,
+                                          poly_normals,
+                                          vert_normals);
 
     BKE_mesh_vertex_normals_clear_dirty(&mesh_mutable);
     BKE_mesh_poly_normals_clear_dirty(&mesh_mutable);
diff --git a/source/blender/blenkernel/intern/object.cc b/source/blender/blenkernel/intern/object.cc
index 6dc6e37de27..ef86647000d 100644
--- a/source/blender/blenkernel/intern/object.cc
+++ b/source/blender/blenkernel/intern/object.cc
@@ -4902,9 +4902,11 @@ bool BKE_object_shapekey_remove(Main *bmain, Object *ob, KeyBlock *kb)
     if (key->refkey) {
       /* apply new basis key on original data */
       switch (ob->type) {
-        case OB_MESH:
-          BKE_keyblock_convert_to_mesh(key->refkey, (Mesh *)ob->data);
+        case OB_MESH: {
+          Mesh *mesh = (Mesh *)ob->data;
+          BKE_keyblock_convert_to_mesh(key->refkey, mesh->mvert, mesh->totvert);
           break;
+        }
         case OB_CURVE:
         case OB_SURF:
           BKE_keyblock_convert_to_curve(
diff --git a/source/blender/io/collada/GeometryExporter.cpp b/source/blender/io/collada/GeometryExporter.cpp
index 73e3eeda462..2bfe3f16582 100644
--- a/source/blender/io/collada/GeometryExporter.cpp
+++ b/source/blender/io/collada/GeometryExporter.cpp
@@ -134,7 +134,7 @@ void GeometryExporter::operator()(Object *ob)
       /* skip the basis */
       kb = kb->next;
       for (; kb; kb = kb->next) {
-        BKE_keyblock_convert_to_mesh(kb, me);
+        BKE_keyblock_convert_to_mesh(kb, me->mvert, me->totvert);
         export_key_mesh(ob, me, kb);
       }
     }