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

1 files changed, 2 insertions, 4 deletions

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;