Fix: Sequencer backdrop not updated during playback.

Caused by recent optimization in {7b76a160a4}.

source/blender/editors/include/ED_sequencer.h

@@ -42,7 +42,8 @@ bool ED_space_sequencer_maskedit_poll(struct bContext *C);
 
 bool ED_space_sequencer_check_show_imbuf(struct SpaceSeq *sseq);
 bool ED_space_sequencer_check_show_strip(struct SpaceSeq *sseq);
-bool ED_space_sequencer_has_visible_animation_on_strip(const struct Scene *scene);
+bool ED_space_sequencer_has_playback_animation(const struct SpaceSeq *sseq,
+                                               const struct Scene *scene);
 
 void ED_operatormacros_sequencer(void);
 

source/blender/editors/screen/screen_ops.c

@@ -4453,7 +4453,8 @@ static void screen_animation_region_tag_redraw(ScrArea *area,
     }
 
     if (area->spacetype == SPACE_SEQ) {
-      if (!ED_space_sequencer_has_visible_animation_on_strip(scene)) {
+      const SpaceSeq *sseq = area->spacedata.first;
+      if (!ED_space_sequencer_has_playback_animation(sseq, scene)) {
         return;
       }
     }

source/blender/editors/space_sequencer/sequencer_edit.c

@@ -153,12 +153,18 @@ static bool sequencer_fcurves_targets_color_strip(const FCurve *fcurve)
 }
 
 /*
- * Check if there is animation attached to a strip, that is shown on the strip in the UI.
+ * Check if there is animation shown during playback.
  *
  * - Colors of color strips are displayed on the strip itself.
+ * - Backdrop is drawn.
  */
-bool ED_space_sequencer_has_visible_animation_on_strip(const struct Scene *scene)
+bool ED_space_sequencer_has_playback_animation(const struct SpaceSeq *sseq,
+                                               const struct Scene *scene)
 {
+  if (sseq->draw_flag & SEQ_DRAW_BACKDROP) {
+    return true;
+  }
+
   if (!scene->adt) {
     return false;
   }