timeline: allow dropping on trackviewitem to overwrite at 0

Fixes #1928

app/widget/timelinewidget/timelinewidget.cpp

@@ -157,6 +157,11 @@ TimelineWidget::TimelineWidget(QWidget *parent) :
     connect(view, &TimelineView::DragLeft, this, &TimelineWidget::ViewDragLeft);
     connect(view, &TimelineView::DragDropped, this, &TimelineWidget::ViewDragDropped);
 
+    TrackView *tv = tview->track_view();
+    connect(tv, &TrackView::DragEntered, this, &TimelineWidget::ViewDragEntered);
+    connect(tv, &TrackView::DragLeft, this, &TimelineWidget::ViewDragLeft);
+    connect(tv, &TrackView::DragDropped, this, &TimelineWidget::ViewDragDropped);
+
     connect(tview->splitter(), &QSplitter::splitterMoved, this, &TimelineWidget::UpdateHorizontalSplitters);
 
     // Connect each view's scroll to each other

app/widget/timelinewidget/trackview/trackview.cpp

@@ -124,6 +124,9 @@ void TrackView::InsertTrack(Track *track)
   TrackViewItem *tvi = new TrackViewItem(track);
 
   connect(tvi, &TrackViewItem::AboutToDeleteTrack, this, &TrackView::AboutToDeleteTrack);
+  connect(tvi, &TrackViewItem::DragEntered, this, &TrackView::DragEntered);
+  connect(tvi, &TrackViewItem::DragLeft, this, &TrackView::DragLeft);
+  connect(tvi, &TrackViewItem::DragDropped, this, &TrackView::DragDropped);
 
   splitter_->Insert(track->Index(),
                     track->GetTrackHeightInPixels(),

app/widget/timelinewidget/trackview/trackview.h

@@ -43,6 +43,10 @@ public:
 signals:
   void AboutToDeleteTrack(Track *track);
 
+  void DragEntered(TimelineViewMouseEvent* event);
+  void DragLeft(QDragLeaveEvent* event);
+  void DragDropped(TimelineViewMouseEvent* event);
+
 protected:
   virtual void resizeEvent(QResizeEvent *e) override;
 

app/widget/timelinewidget/trackview/trackviewitem.cpp

@@ -76,11 +76,33 @@ TrackViewItem::TrackViewItem(Track* track, QWidget *parent) :
 
   setMinimumHeight(mute_button_->height());
   setContextMenuPolicy(Qt::CustomContextMenu);
+  setAcceptDrops(true);
 
   connect(track, &Track::MutedChanged, mute_button_, &QPushButton::setChecked);
   connect(this, &QWidget::customContextMenuRequested, this, &TrackViewItem::ShowContextMenu);
 }
 
+void TrackViewItem::dragEnterEvent(QDragEnterEvent *event)
+{
+  TimelineViewMouseEvent e(0, 1, 1, track_->ToReference(), Qt::NoButton, event->keyboardModifiers());
+  e.SetMimeData(event->mimeData());
+  e.SetEvent(event);
+  emit DragEntered(&e);
+}
+
+void TrackViewItem::dragLeaveEvent(QDragLeaveEvent *event)
+{
+  emit DragLeft(event);
+}
+
+void TrackViewItem::dropEvent(QDropEvent *event)
+{
+  TimelineViewMouseEvent e(0, 1, 1, track_->ToReference(), Qt::NoButton, event->keyboardModifiers());
+  e.SetMimeData(event->mimeData());
+  e.SetEvent(event);
+  emit DragDropped(&e);
+}
+
 QPushButton *TrackViewItem::CreateMSLButton(const QColor& checked_color) const
 {
   QPushButton* button = new QPushButton();

app/widget/timelinewidget/trackview/trackviewitem.h

@@ -28,6 +28,7 @@
 #include "node/output/track/track.h"
 #include "widget/clickablelabel/clickablelabel.h"
 #include "widget/focusablelineedit/focusablelineedit.h"
+#include "widget/timelinewidget/view/timelineviewmouseevent.h"
 
 namespace olive {
 
@@ -41,6 +42,15 @@ public:
 signals:
   void AboutToDeleteTrack(Track *track);
 
+  void DragEntered(TimelineViewMouseEvent* event);
+  void DragLeft(QDragLeaveEvent* event);
+  void DragDropped(TimelineViewMouseEvent* event);
+
+protected:
+  virtual void dragEnterEvent(QDragEnterEvent *event) override;
+  virtual void dragLeaveEvent(QDragLeaveEvent *event) override;
+  virtual void dropEvent(QDropEvent *event) override;
+
 private:
   QPushButton* CreateMSLButton(const QColor &checked_color) const;
 

app/widget/timelinewidget/view/timelineviewmouseevent.h

@@ -21,6 +21,7 @@
 #ifndef TIMELINEVIEWMOUSEEVENT_H
 #define TIMELINEVIEWMOUSEEVENT_H
 
+#include <QEvent>
 #include <QMimeData>
 #include <QPointF>
 #include <QPoint>