1 files changed, 7 insertions, 2 deletions
diff --git a/source/blender/blenloader/BLO_readfile.h b/source/blender/blenloader/BLO_readfile.h
index 00dbe334356..8495caa91b5 100644
--- a/source/blender/blenloader/BLO_readfile.h
+++ b/source/blender/blenloader/BLO_readfile.h
@@ -76,8 +76,11 @@ typedef struct WorkspaceConfigFileData {
 } WorkspaceConfigFileData;
 
 struct BlendFileReadParams {
-  uint skip_flags : 2; /* eBLOReadSkip */
+  uint skip_flags : 3; /* eBLOReadSkip */
   uint is_startup : 1;
+
+  /** Whether we are reading the memfile for an undo (< 0) or a redo (> 0). */
+  int undo_direction : 2;
 };
 
 /* skip reading some data-block types (may want to skip screen data too). */
@@ -85,6 +88,8 @@ typedef enum eBLOReadSkip {
   BLO_READ_SKIP_NONE = 0,
   BLO_READ_SKIP_USERDEF = (1 << 0),
   BLO_READ_SKIP_DATA = (1 << 1),
+  /** Do not attempt to re-use IDs from old bmain for unchanged ones in case of undo. */
+  BLO_READ_SKIP_UNDO_OLD_MAIN = (1 << 2),
 } eBLOReadSkip;
 #define BLO_READ_SKIP_ALL (BLO_READ_SKIP_USERDEF | BLO_READ_SKIP_DATA)
 
@@ -98,7 +103,7 @@ BlendFileData *BLO_read_from_memory(const void *mem,
 BlendFileData *BLO_read_from_memfile(struct Main *oldmain,
                                      const char *filename,
                                      struct MemFile *memfile,
-                                     eBLOReadSkip skip_flags,
+                                     const struct BlendFileReadParams *params,
                                      struct ReportList *reports);
 
 void BLO_blendfiledata_free(BlendFileData *bfd);