Fix T82388: Sculpt mode: Unexpected undo behavior.

Issue exposed by rB4c7b1766a7f1.

Main idea is that non-memfile first undo step should check into previous
memfile and tag the ID it is editing as `future_changed`.

That way, when we go back and undo to the memfile, said IDs are properly
detected as changed and re-read from the memfile.

Otherwise, undo system sees them as unchanged, and just re-use the
current data instead.

Note that currently only Sculpt mode seems affected (probably because it
is storing the mode switch itself as a Sculpt undo step instead of a
memfile one), but similar action might be needed in some other cases
too.

Maniphest Tasks: T82388

Differential Revision: https://developer.blender.org/D9510

1 files changed, 35 insertions, 0 deletions

diff --git a/source/blender/editors/undo/memfile_undo.c b/source/blender/editors/undo/memfile_undo.c
index 2df26abe8b3..ace82f82a78 100644
--- a/source/blender/editors/undo/memfile_undo.c
+++ b/source/blender/editors/undo/memfile_undo.c
@@ -24,7 +24,9 @@
 #include "BLI_utildefines.h"
 
 #include "BLI_ghash.h"
+#include "BLI_listbase.h"
 
+#include "DNA_ID.h"
 #include "DNA_node_types.h"
 #include "DNA_object_enums.h"
 #include "DNA_object_types.h"
@@ -52,6 +54,8 @@
 
 #include "undo_intern.h"
 
+#include <stdio.h>
+
 /* -------------------------------------------------------------------- */
 /** \name Implements ED Undo System
  * \{ */
@@ -307,4 +311,35 @@ struct MemFile *ED_undosys_stack_memfile_get_active(UndoStack *ustack)
   return NULL;
 }
 
+/**
+ * If the last undo step is a memfile one, find the first memchunk matching given ID (using its
+ * seesion uuid), and tag it as 'changed in the future'.
+ *
+ * Since non-memfile undos cannot automatically set this flag in the previous step as done with
+ * memfile ones, this has to be called manually by relevant undo code.
+ *
+ * \note Only current known case for this is undoing a switch from Pbject to Sculpt mode (see
+ * T82388).
+ *
+ * \note Calling this ID by ID is not optimal, as it will loop over all memchunks until it find
+ * expected one. If this becomes an issue we'll have to add a mapping from session uuid to first
+ * memchunk in #MemFile itself (currently we only do that in #MemFileWriteData when writing a new
+ * step).
+ */
+void ED_undosys_stack_memfile_id_changed_tag(UndoStack *ustack, ID *id)
+{
+  UndoStep *us = ustack->step_active;
+  if (id == NULL || us == NULL || us->type != BKE_UNDOSYS_TYPE_MEMFILE) {
+    return;
+  }
+
+  MemFile *memfile = &((MemFileUndoStep *)us)->data->memfile;
+  LISTBASE_FOREACH (MemFileChunk *, mem_chunk, &memfile->chunks) {
+    if (mem_chunk->id_session_uuid == id->session_uuid) {
+      mem_chunk->is_identical_future = false;
+      break;
+    }
+  }
+}
+
 /** \} */