Fix T78650: Lattice evaluation writes to shared data

Fix the data management bug where evaluation of lattice objects would
write back to the CoW copy of the Lattice ID, even when that copy was
shared between objects.

Each lattice object evaluation now stores its own evaluated data copy
via `BKE_object_eval_assign_data()`.

Reviewed By: sergey

Maniphest Tasks: T78650

Differential Revision: https://developer.blender.org/D10790

5 files changed, 60 insertions, 45 deletions

diff --git a/source/blender/blenkernel/BKE_object.h b/source/blender/blenkernel/BKE_object.h
index 12c40e891c9..0c2c6313dde 100644
--- a/source/blender/blenkernel/BKE_object.h
+++ b/source/blender/blenkernel/BKE_object.h
@@ -336,6 +336,12 @@ struct Mesh *BKE_object_get_evaluated_mesh(struct Object *object);
 struct Mesh *BKE_object_get_pre_modified_mesh(struct Object *object);
 struct Mesh *BKE_object_get_original_mesh(struct Object *object);
 
+/* Lattice accessors.
+ * These functions return either the regular lattice, or the edit-mode lattice,
+ * whichever is currently in use. */
+struct Lattice *BKE_object_get_lattice(const struct Object *object);
+struct Lattice *BKE_object_get_evaluated_lattice(const struct Object *object);
+
 int BKE_object_insert_ptcache(struct Object *ob);
 void BKE_object_delete_ptcache(struct Object *ob, int index);
 struct KeyBlock *BKE_object_shapekey_insert(struct Main *bmain,
diff --git a/source/blender/blenkernel/intern/lattice.c b/source/blender/blenkernel/intern/lattice.c
index 7c451051727..48104e72825 100644
--- a/source/blender/blenkernel/intern/lattice.c
+++ b/source/blender/blenkernel/intern/lattice.c
@@ -540,10 +540,12 @@ void BKE_lattice_vert_coords_apply(Lattice *lt, const float (*vert_coords)[3])
 
 void BKE_lattice_modifiers_calc(struct Depsgraph *depsgraph, Scene *scene, Object *ob)
 {
+  BKE_object_free_derived_caches(ob);
+  if (ob->runtime.curve_cache == NULL) {
+    ob->runtime.curve_cache = MEM_callocN(sizeof(CurveCache), "CurveCache for lattice");
+  }
+
   Lattice *lt = ob->data;
-  /* Get vertex coordinates from the original copy;
-   * otherwise we get already-modified coordinates. */
-  Object *ob_orig = DEG_get_original_object(ob);
   VirtualModifierData virtualModifierData;
   ModifierData *md = BKE_modifiers_get_virtual_modifierlist(ob, &virtualModifierData);
   float(*vert_coords)[3] = NULL;
@@ -551,13 +553,6 @@ void BKE_lattice_modifiers_calc(struct Depsgraph *depsgraph, Scene *scene, Objec
   const bool is_editmode = (lt->editlatt != NULL);
   const ModifierEvalContext mectx = {depsgraph, ob, 0};
 
-  if (ob->runtime.curve_cache) {
-    BKE_displist_free(&ob->runtime.curve_cache->disp);
-  }
-  else {
-    ob->runtime.curve_cache = MEM_callocN(sizeof(CurveCache), "CurveCache for lattice");
-  }
-
   for (; md; md = md->next) {
     const ModifierTypeInfo *mti = BKE_modifier_get_info(md->type);
 
@@ -577,49 +572,33 @@ void BKE_lattice_modifiers_calc(struct Depsgraph *depsgraph, Scene *scene, Objec
       continue;
     }
 
-    if (!vert_coords) {
-      Lattice *lt_orig = ob_orig->data;
-      if (lt_orig->editlatt) {
-        lt_orig = lt_orig->editlatt->latt;
-      }
-      vert_coords = BKE_lattice_vert_coords_alloc(lt_orig, &numVerts);
+    if (vert_coords == NULL) {
+      /* Get either the edit-mode or regular lattice, whichever is in use now. */
+      const Lattice *effective_lattice = BKE_object_get_lattice(ob);
+      vert_coords = BKE_lattice_vert_coords_alloc(effective_lattice, &numVerts);
     }
+
     mti->deformVerts(md, &mectx, NULL, vert_coords, numVerts);
   }
 
-  if (ob->id.tag & LIB_TAG_COPIED_ON_WRITE) {
-    if (vert_coords) {
-      BKE_lattice_vert_coords_apply(ob->data, vert_coords);
-      MEM_freeN(vert_coords);
-    }
+  if (vert_coords == NULL) {
+    return;
   }
-  else {
-    /* Displist won't do anything; this is just for posterity's sake until we remove it. */
-    if (!vert_coords) {
-      Lattice *lt_orig = ob_orig->data;
-      if (lt_orig->editlatt) {
-        lt_orig = lt_orig->editlatt->latt;
-      }
-      vert_coords = BKE_lattice_vert_coords_alloc(lt_orig, &numVerts);
-    }
-
-    DispList *dl = MEM_callocN(sizeof(*dl), "lt_dl");
-    dl->type = DL_VERTS;
-    dl->parts = 1;
-    dl->nr = numVerts;
-    dl->verts = (float *)vert_coords;
 
-    BLI_addtail(&ob->runtime.curve_cache->disp, dl);
+  Lattice *lt_eval = BKE_object_get_evaluated_lattice(ob);
+  if (lt_eval == NULL) {
+    BKE_id_copy_ex(NULL, &lt->id, (ID **)&lt_eval, LIB_ID_COPY_LOCALIZE);
+    BKE_object_eval_assign_data(ob, &lt_eval->id, true);
   }
+
+  BKE_lattice_vert_coords_apply(lt_eval, vert_coords);
+  MEM_freeN(vert_coords);
 }
 
 struct MDeformVert *BKE_lattice_deform_verts_get(const struct Object *oblatt)
 {
-  Lattice *lt = (Lattice *)oblatt->data;
   BLI_assert(oblatt->type == OB_LATTICE);
-  if (lt->editlatt) {
-    lt = lt->editlatt->latt;
-  }
+  Lattice *lt = BKE_object_get_lattice(oblatt);
   return lt->dvert;
 }
 
diff --git a/source/blender/blenkernel/intern/lattice_deform.c b/source/blender/blenkernel/intern/lattice_deform.c
index 2651042939f..4a926ee3d96 100644
--- a/source/blender/blenkernel/intern/lattice_deform.c
+++ b/source/blender/blenkernel/intern/lattice_deform.c
@@ -47,6 +47,7 @@
 #include "BKE_key.h"
 #include "BKE_lattice.h"
 #include "BKE_modifier.h"
+#include "BKE_object.h"
 
 #include "BKE_deform.h"
 
@@ -69,7 +70,7 @@ typedef struct LatticeDeformData {
 LatticeDeformData *BKE_lattice_deform_data_create(const Object *oblatt, const Object *ob)
 {
   /* we make an array with all differences */
-  Lattice *lt = oblatt->data;
+  Lattice *lt = BKE_object_get_lattice(oblatt);
   BPoint *bp;
   DispList *dl = oblatt->runtime.curve_cache ?
                      BKE_displist_find(&oblatt->runtime.curve_cache->disp, DL_VERTS) :
@@ -83,9 +84,6 @@ LatticeDeformData *BKE_lattice_deform_data_create(const Object *oblatt, const Ob
   float latmat[4][4];
   LatticeDeformData *lattice_deform_data;
 
-  if (lt->editlatt) {
-    lt = lt->editlatt->latt;
-  }
   bp = lt->def;
 
   const int32_t num_points = lt->pntsu * lt->pntsv * lt->pntsw;
diff --git a/source/blender/blenkernel/intern/lattice_deform_test.cc b/source/blender/blenkernel/intern/lattice_deform_test.cc
index f08d0349598..a7cd5c36ec2 100644
--- a/source/blender/blenkernel/intern/lattice_deform_test.cc
+++ b/source/blender/blenkernel/intern/lattice_deform_test.cc
@@ -51,6 +51,7 @@ static void test_lattice_deform_init(LatticeDeformTestContext *ctx,
     ctx->coords[index][2] = (rng->get_float() - 0.5f) * 10;
   }
   IDType_ID_LT.init_data(&ctx->lattice.id);
+  strcpy(ctx->lattice.id.name, "LTLattice");
   IDType_ID_OB.init_data(&ctx->ob_lattice.id);
   ctx->ob_lattice.type = OB_LATTICE;
   ctx->ob_lattice.data = &ctx->lattice;
diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index b07c4b22c39..a8224094919 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -4474,6 +4474,37 @@ Mesh *BKE_object_get_original_mesh(Object *object)
   return result;
 }
 
+Lattice *BKE_object_get_lattice(const Object *object)
+{
+  ID *data = object->data;
+  if (data == NULL || GS(data->name) != ID_LT) {
+    return NULL;
+  }
+
+  Lattice *lt = (Lattice *)data;
+  if (lt->editlatt) {
+    return lt->editlatt->latt;
+  }
+
+  return lt;
+}
+
+Lattice *BKE_object_get_evaluated_lattice(const Object *object)
+{
+  ID *data_eval = object->runtime.data_eval;
+
+  if (data_eval == NULL || GS(data_eval->name) != ID_LT) {
+    return NULL;
+  }
+
+  Lattice *lt_eval = (Lattice *)data_eval;
+  if (lt_eval->editlatt) {
+    return lt_eval->editlatt->latt;
+  }
+
+  return lt_eval;
+}
+
 static int pc_cmp(const void *a, const void *b)
 {
   const LinkData *ad = a, *bd = b;