completed zoom tool

app/widget/timelineview/timelineview.h

@@ -63,6 +63,8 @@ signals:
   void RequestReplaceBlock(Block* old, Block* replace, int track);
   void RequestSplitAtTime(rational time, int track);
 
+  void UserSetScale(double scale);
+
 protected:
   virtual void mousePressEvent(QMouseEvent *event) override;
   virtual void mouseMoveEvent(QMouseEvent *event) override;

app/widget/timelineview/tool/zoom.cpp

@@ -39,9 +39,9 @@ void TimelineView::ZoomTool::MouseRelease(QMouseEvent *event)
 {
   if (event->modifiers() & Qt::AltModifier) {
     // Zoom out if the user clicks while holding Alt
-    parent()->SetScale(parent()->scale_ * 0.5);
+    emit parent()->UserSetScale(parent()->scale_ * 0.5);
   } else {
     // Otherwise zoom in
-    parent()->SetScale(parent()->scale_ * 2);
+    emit parent()->UserSetScale(parent()->scale_ * 2);
   }
 }