Fix T69822: Switching sculpt objects breaks undo

This introduces object mode tagging for data which hasn't yet been
written back to the ID data.

Now when selecting other sculpt objects, the original objects data is
flushed back to the ID before writing a memfile undo step.

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_paint.h b/source/blender/blenkernel/BKE_paint.h
index 4413ad2a70f..48f9e1fd95e 100644
--- a/source/blender/blenkernel/BKE_paint.h
+++ b/source/blender/blenkernel/BKE_paint.h
@@ -306,6 +306,13 @@ typedef struct SculptSession {
 
   /* This flag prevents PBVH from being freed when creating the vp_handle for texture paint. */
   bool building_vp_handle;
+
+  /**
+   * ID data is older than sculpt-mode data.
+   * Set #Main.is_memfile_undo_flush_needed when enabling.
+   */
+  char needs_flush_to_id;
+
 } SculptSession;
 
 void BKE_sculptsession_free(struct Object *ob);