Undo System: avoid redundant decoding on undo

In most cases the undo system was loading undo steps twice.

This was needed since some undo systems (sculpt, paint, text)
require stepping out of the current undo step.

Use a flag to limit this to the undo systems that need it.

This improves performance for other undo systems.
This gives around 1.96x speedup in edit-mesh for high-poly objects.

Reviewed by: mont29

Ref D11893

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_undo_system.h b/source/blender/blenkernel/BKE_undo_system.h
index efac5d9097f..2973a432723 100644
--- a/source/blender/blenkernel/BKE_undo_system.h
+++ b/source/blender/blenkernel/BKE_undo_system.h
@@ -162,6 +162,13 @@ typedef enum UndoTypeFlags {
    * \note Callback is still supposed to properly deal with a NULL context pointer.
    */
   UNDOTYPE_FLAG_NEED_CONTEXT_FOR_ENCODE = 1 << 0,
+
+  /**
+   * When the active undo step is of this type, it must be read before loading other undo steps.
+   *
+   * This is typically used for undo systems that store both before/after states.
+   */
+  UNDOTYPE_FLAG_DECODE_ACTIVE_STEP = 1 << 1,
 } UndoTypeFlags;
 
 /* Expose since we need to perform operations on specific undo types (rarely). */