timeline views can be siblings

app/widget/timelineview/timelineview.cpp

@@ -483,3 +483,24 @@ void TimelineView::SetEndTime(const rational &length)
 {
   end_item_->SetEndTime(length);
 }
+
+void TimelineView::SetSiblings(TimelineView *a, TimelineView *b)
+{
+  if (a == b)
+    return;
+
+  if (!a->siblings_.contains(b))
+    a->siblings_.append(b);
+
+  if (!b->siblings_.contains(a))
+    b->siblings_.append(a);
+}
+
+void TimelineView::SetSiblings(const QList<TimelineView *> &siblings)
+{
+  foreach (TimelineView* view, siblings) {
+    foreach (TimelineView* sibling, siblings) {
+      SetSiblings(view, sibling);
+    }
+  }
+}

app/widget/timelineview/timelineview.h

@@ -61,6 +61,10 @@ public:
 
   void SetEndTime(const rational& length);
 
+  static void SetSiblings(TimelineView* a, TimelineView* b);
+
+  static void SetSiblings(const QList<TimelineView*>& siblings);
+
 public slots:
   void SetTimebase(const rational& timebase);
 
@@ -385,6 +389,8 @@ private:
 
   bool use_tracklist_length_directly_;
 
+  QVector<TimelineView*> siblings_;
+
 private slots:
   /**
    * @brief Slot for when a Block node changes its parameters and the graphics need to update