PyAPI: add undo redo handlers

Useful so Python can clean up before/after undo steps.

3 files changed, 45 insertions, 2 deletions

diff --git a/source/blender/blenlib/BLI_callbacks.h b/source/blender/blenlib/BLI_callbacks.h
index 6eb45107488..3db7d2d87f1 100644
--- a/source/blender/blenlib/BLI_callbacks.h
+++ b/source/blender/blenlib/BLI_callbacks.h
@@ -49,6 +49,10 @@ typedef enum {
 	BLI_CB_EVT_LOAD_POST,
 	BLI_CB_EVT_SAVE_PRE,
 	BLI_CB_EVT_SAVE_POST,
+	BLI_CB_EVT_UNDO_PRE,
+	BLI_CB_EVT_UNDO_POST,
+	BLI_CB_EVT_REDO_PRE,
+	BLI_CB_EVT_REDO_POST,
 	BLI_CB_EVT_SCENE_UPDATE_PRE,
 	BLI_CB_EVT_SCENE_UPDATE_POST,
 	BLI_CB_EVT_GAME_PRE,
diff --git a/source/blender/editors/undo/ed_undo.c b/source/blender/editors/undo/ed_undo.c
index 5f5b7b330f9..b4268dac863 100644
--- a/source/blender/editors/undo/ed_undo.c
+++ b/source/blender/editors/undo/ed_undo.c
@@ -38,6 +38,8 @@
 #include "DNA_scene_types.h"
 
 #include "BLI_utildefines.h"
+#include "BLI_callbacks.h"
+#include "BLI_listbase.h"
 
 #include "BLT_translation.h"
 
@@ -119,17 +121,50 @@ static int ed_undo_step(bContext *C, int step, const char *undoname)
 		return ED_undo_gpencil_step(C, step, undoname);
 	}
 
+	UndoStep *step_data_from_name = NULL;
+	int step_for_callback = step;
+	if (undoname != NULL) {
+		step_data_from_name = BKE_undosys_step_find_by_name(wm->undo_stack, undoname);
+		if (step_data_from_name == NULL) {
+			return OPERATOR_CANCELLED;
+		}
+
+		/* TODO(campbell), could use simple optimization. */
+		BLI_assert(step_data_from_name != wm->undo_stack->step_active);
+		step_for_callback = (
+		        BLI_findindex(&wm->undo_stack->steps, step_data_from_name) <
+		        BLI_findindex(&wm->undo_stack->steps, wm->undo_stack->step_active)) ? 1 : -1;
+	}
+
+	/* App-Handlers (pre). */
+	{
+		/* Note: ignore grease pencil for now. */
+		Main *bmain = CTX_data_main(C);
+		wm->op_undo_depth++;
+		BLI_callback_exec(bmain, &scene->id, (step_for_callback > 0) ? BLI_CB_EVT_UNDO_PRE : BLI_CB_EVT_REDO_PRE);
+		wm->op_undo_depth--;
+	}
+
+
 	/* Undo System */
 	{
 		if (undoname) {
-			UndoStep *step_data = BKE_undosys_step_find_by_name(wm->undo_stack, undoname);
-			BKE_undosys_step_undo_with_data(wm->undo_stack, C, step_data);
+			BKE_undosys_step_undo_with_data(wm->undo_stack, C, step_data_from_name);
 		}
 		else {
 			BKE_undosys_step_undo_compat_only(wm->undo_stack, C, step);
 		}
 	}
 
+	/* App-Handlers (post). */
+	{
+		Main *bmain = CTX_data_main(C);
+		scene = CTX_data_scene(C);
+		wm->op_undo_depth++;
+		BLI_callback_exec(bmain, &scene->id, step_for_callback > 0 ? BLI_CB_EVT_UNDO_PRE : BLI_CB_EVT_REDO_PRE);
+		wm->op_undo_depth--;
+	}
+
 	WM_event_add_notifier(C, NC_WINDOW, NULL);
 	WM_event_add_notifier(C, NC_WM | ND_UNDO, NULL);
 
diff --git a/source/blender/python/intern/bpy_app_handlers.c b/source/blender/python/intern/bpy_app_handlers.c
index 90aa22de5bf..ded5ead93aa 100644
--- a/source/blender/python/intern/bpy_app_handlers.c
+++ b/source/blender/python/intern/bpy_app_handlers.c
@@ -59,6 +59,10 @@ static PyStructSequence_Field app_cb_info_fields[] = {
 	{(char *)"load_post",         (char *)"on loading a new blend file (after)"},
 	{(char *)"save_pre",          (char *)"on saving a blend file (before)"},
 	{(char *)"save_post",         (char *)"on saving a blend file (after)"},
+	{(char *)"undo_pre",          (char *)"on loading an undo step (before)"},
+	{(char *)"undo_post",         (char *)"on loading an undo step (after)"},
+	{(char *)"redo_pre",          (char *)"on loading a redo step (before)"},
+	{(char *)"redo_post",         (char *)"on loading a redo step (after)"},
 	{(char *)"scene_update_pre",  (char *)"on every scene data update. Does not imply that anything changed in the "
                                           "scene, just that the dependency graph is about to be reevaluated, and the "
                                           "scene is about to be updated by Blender's animation system."},