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, 31 insertions, 0 deletions

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;