when zooming any TimelineViewBase derivative, zoom towards the playhead

app/widget/timelinewidget/view/timelineviewbase.cpp

@@ -3,6 +3,7 @@
 #include <QGraphicsRectItem>
 #include <QMouseEvent>
 #include <QScrollBar>
+#include <QTimer>
 
 #include "common/timecodefunctions.h"
 
@@ -31,12 +32,16 @@ void TimelineViewBase::SetScale(const double &scale)
 {
   scale_ = scale;
 
-  // Force redraw for playhead
-  viewport()->update();
-
   end_item_->SetScale(scale_);
 
   ScaleChangedEvent(scale_);
+
+  // Force redraw for playhead
+  viewport()->update();
+
+  // Zoom towards the playhead
+  // (using a hacky singleShot so the scroll occurs after the scene and its scrollbars have updated)
+  QTimer::singleShot(0, this, &TimelineViewBase::CenterScrollOnPlayhead);
 }
 
 void TimelineViewBase::SetTimebase(const rational &timebase)
@@ -62,7 +67,7 @@ void TimelineViewBase::drawForeground(QPainter *painter, const QRectF &rect)
   if (!timebase().isNull()) {
     double width = TimeToScene(timebase());
 
-    playhead_scene_left_ = TimeToScene(rational(playhead_ * timebase().numerator(), timebase().denominator()));
+    playhead_scene_left_ = GetPlayheadX();
     playhead_scene_right_ = playhead_scene_left_ + width;
 
     playhead_style_.Draw(painter, QRectF(playhead_scene_left_, rect.top(), width, rect.height()));
@@ -105,6 +110,11 @@ bool TimelineViewBase::PlayheadRelease(QMouseEvent *event)
   return dragging_playhead_;
 }
 
+qreal TimelineViewBase::GetPlayheadX()
+{
+  return TimeToScene(rational(playhead_ * timebase().numerator(), timebase().denominator()));
+}
+
 void TimelineViewBase::SetEndTime(const rational &length)
 {
   end_item_->SetEndTime(length);
@@ -157,6 +167,11 @@ void TimelineViewBase::UpdateSceneRect()
   scene_.setSceneRect(bounding_rect);
 }
 
+void TimelineViewBase::CenterScrollOnPlayhead()
+{
+  horizontalScrollBar()->setValue(qRound(GetPlayheadX()) - viewport()->width()/2);
+}
+
 void TimelineViewBase::resizeEvent(QResizeEvent *event)
 {
   QGraphicsView::resizeEvent(event);

app/widget/timelinewidget/view/timelineviewbase.h

@@ -43,6 +43,8 @@ protected:
   bool PlayheadRelease(QMouseEvent* event);
 
 private:
+  qreal GetPlayheadX();
+
   int64_t playhead_;
 
   TimelinePlayhead playhead_style_;
@@ -64,6 +66,11 @@ private slots:
    */
   void UpdateSceneRect();
 
+  /**
+   * @brief Slot to center the horizontal scroll bar on the playhead's current position
+   */
+  void CenterScrollOnPlayhead();
+
 };
 
 #endif // TIMELINEVIEWBASE_H