From 2fbbc7acbb3d4ca019e0d6e4ccbb4bf31fa33157 Mon Sep 17 00:00:00 2001
From: Jacques Lucke <jacques@blender.org>
Date: Mon, 8 May 2023 11:15:42 +0200
Subject: [PATCH] Fix: unnecessary depsgraph update when scrubbing in timeline

Previously, there was always a depsgraph update when the mouse moves
while scrubbing in the timeline. Even when the mouse movement does
not change the actual frame. This can happen when e.g. the mouse first
hovers over frame 5.2 and then it moves to frame 5.3. In both cases the
actual frame is rounded to 5, so no update is necessary (that is unless
subframes are used).
---
 source/blender/editors/animation/anim_ops.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/source/blender/editors/animation/anim_ops.c b/source/blender/editors/animation/anim_ops.c
index d3f563f5886..8cfbbc16b42 100644
--- a/source/blender/editors/animation/anim_ops.c
+++ b/source/blender/editors/animation/anim_ops.c
@@ -127,12 +127,15 @@ static int seq_frame_apply_snap(bContext *C, Scene *scene, const int timeline_fr
 }
 
 /* Set the new frame number */
-static void change_frame_apply(bContext *C, wmOperator *op)
+static void change_frame_apply(bContext *C, wmOperator *op, const bool always_update)
 {
   Scene *scene = CTX_data_scene(C);
   float frame = RNA_float_get(op->ptr, "frame");
   bool do_snap = RNA_boolean_get(op->ptr, "snap");
 
+  const int old_frame = scene->r.cfra;
+  const float old_subframe = scene->r.subframe;
+
   if (do_snap) {
     if (CTX_wm_space_seq(C) && SEQ_editing_get(scene) != NULL) {
       frame = seq_frame_apply_snap(C, scene, frame);
@@ -154,8 +157,11 @@ static void change_frame_apply(bContext *C, wmOperator *op)
   FRAMENUMBER_MIN_CLAMP(scene->r.cfra);
 
   /* do updates */
-  DEG_id_tag_update(&scene->id, ID_RECALC_FRAME_CHANGE);
-  WM_event_add_notifier(C, NC_SCENE | ND_FRAME, scene);
+  const bool frame_changed = (old_frame != scene->r.cfra) || (old_subframe != scene->r.subframe);
+  if (frame_changed || always_update) {
+    DEG_id_tag_update(&scene->id, ID_RECALC_FRAME_CHANGE);
+    WM_event_add_notifier(C, NC_SCENE | ND_FRAME, scene);
+  }
 }
 
 /* ---- */
@@ -163,7 +169,7 @@ static void change_frame_apply(bContext *C, wmOperator *op)
 /* Non-modal callback for running operator without user input */
 static int change_frame_exec(bContext *C, wmOperator *op)
 {
-  change_frame_apply(C, op);
+  change_frame_apply(C, op, true);
 
   return OPERATOR_FINISHED;
 }
@@ -258,7 +264,7 @@ static int change_frame_invoke(bContext *C, wmOperator *op, const wmEvent *event
 
   change_frame_seq_preview_begin(C, event);
 
-  change_frame_apply(C, op);
+  change_frame_apply(C, op, true);
 
   /* add temp handler */
   WM_event_add_modal_handler(C, op);
@@ -283,7 +289,7 @@ static int change_frame_modal(bContext *C, wmOperator *op, const wmEvent *event)
 
     case MOUSEMOVE:
       RNA_float_set(op->ptr, "frame", frame_from_event(C, event));
-      change_frame_apply(C, op);
+      change_frame_apply(C, op, false);
       break;
 
     case LEFTMOUSE: