Cleanup/refactor: Undosys: Get rid of the magic values for undo direction.

Move `eUndoStepDir` to `BKE_undo_system.h` and use its values
everywhere.

Note that this also introduce the `STEP_INVALID` value in that enum.

Finally, kept the matching struct members in some lower-level readfile
code as an `int` to avoid having to include `BKE_undo_system.h` in a lot
of unrelated files.

3 files changed, 12 insertions, 10 deletions

diff --git a/source/blender/blenloader/BLO_readfile.h b/source/blender/blenloader/BLO_readfile.h
index 7dbe73cbd6a..237294a6017 100644
--- a/source/blender/blenloader/BLO_readfile.h
+++ b/source/blender/blenloader/BLO_readfile.h
@@ -84,8 +84,8 @@ struct BlendFileReadParams {
   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;
+  /** Whether we are reading the memfile for an undo or a redo. */
+  int undo_direction; /* eUndoStepDir */
 };
 
 /* skip reading some data-block types (may want to skip screen data too). */
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 2192e9a378f..a63d95c1823 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -94,6 +94,7 @@
 #include "BKE_report.h"
 #include "BKE_scene.h"
 #include "BKE_screen.h"
+#include "BKE_undo_system.h"
 #include "BKE_workspace.h"
 
 #include "DRW_engine.h"
@@ -1294,12 +1295,12 @@ static ssize_t fd_read_from_memfile(FileData *filedata,
       seek += readsize;
       if (r_is_memchunck_identical != NULL) {
         /* `is_identical` of current chunk represents whether it changed compared to previous undo
-         * step. this is fine in redo case (filedata->undo_direction > 0), but not in undo case,
-         * where we need an extra flag defined when saving the next (future) step after the one we
-         * want to restore, as we are supposed to 'come from' that future undo step, and not the
-         * one before current one. */
-        *r_is_memchunck_identical &= filedata->undo_direction > 0 ? chunk->is_identical :
-                                                                    chunk->is_identical_future;
+         * step. this is fine in redo case, but not in undo case, where we need an extra flag
+         * defined when saving the next (future) step after the one we want to restore, as we are
+         * supposed to 'come from' that future undo step, and not the one before current one. */
+        *r_is_memchunck_identical &= filedata->undo_direction == STEP_REDO ?
+                                         chunk->is_identical :
+                                         chunk->is_identical_future;
       }
     } while (totread < size);
 
@@ -2400,11 +2401,12 @@ static int direct_link_id_restore_recalc(const FileData *fd,
 
     /* Tags that were set between the target state and the current state,
      * that we need to perform again. */
-    if (fd->undo_direction < 0) {
+    if (fd->undo_direction == STEP_UNDO) {
       /* Undo: tags from target to the current state. */
       recalc |= id_current->recalc_up_to_undo_push;
     }
     else {
+      BLI_assert(fd->undo_direction == STEP_REDO);
       /* Redo: tags from current to the target state. */
       recalc |= id_target->recalc_up_to_undo_push;
     }
diff --git a/source/blender/blenloader/intern/readfile.h b/source/blender/blenloader/intern/readfile.h
index 86f05eda7b7..e007d42b283 100644
--- a/source/blender/blenloader/intern/readfile.h
+++ b/source/blender/blenloader/intern/readfile.h
@@ -91,7 +91,7 @@ typedef struct FileData {
   struct MemFile *memfile;
   /** Whether we are undoing (< 0) or redoing (> 0), used to choose which 'unchanged' flag to use
    * to detect unchanged data from memfile. */
-  short undo_direction;
+  int undo_direction; /* eUndoStepDir */
 
   /** Variables needed for reading from file. */
   gzFile gzfiledes;