implemented inverted timeline scroll axes

Timeline scrolls horizontally by default with a preference to disable that
functionality.

app/dialog/preferences/preferences.cpp

@@ -69,13 +69,6 @@ PreferencesDialog::PreferencesDialog(QWidget *parent, QMenuBar* main_menu_bar) :
 
   connect(list_widget_, SIGNAL(currentRowChanged(int)), preference_pane_stack_, SLOT(setCurrentIndex(int)));
 
-  // set up default sequence
-  /*default_sequence.set_name(tr("Default Sequence"));
-  default_sequence.set_width(olive::config.default_sequence_width);
-  default_sequence.set_height(olive::config.default_sequence_height);
-  default_sequence.set_frame_rate(olive::config.default_sequence_framerate);
-  default_sequence.set_audio_frequency(olive::config.default_sequence_audio_frequency);
-  default_sequence.set_audio_layout(olive::config.default_sequence_audio_channel_layout);*/
 }
 
 void PreferencesDialog::AddBoolPair(QCheckBox *ui, bool *value, bool restart_required)

app/dialog/preferences/tabs/preferencesbehaviortab.cpp

@@ -45,6 +45,7 @@ PreferencesBehaviorTab::PreferencesBehaviorTab()
           timeline_group);
   AddItem(tr("Invert Timeline Scroll Axes"),
           QStringLiteral("InvertTimelineScrollAxes"),
+          tr("Hold ALT on any UI element to switch scrolling axes"),
           timeline_group);
   AddItem(tr("Seek Also Selects"),
           QStringLiteral("SelectAlsoSeeks"),

app/widget/timelinewidget/view/timelineview.cpp

@@ -27,6 +27,7 @@
 #include <QtMath>
 #include <QPen>
 
+#include "config/config.h"
 #include "common/flipmodifiers.h"
 #include "common/timecodefunctions.h"
 #include "core.h"
@@ -113,6 +114,21 @@ void TimelineView::mouseDoubleClickEvent(QMouseEvent *event)
   emit MouseDoubleClicked(&timeline_event);
 }
 
+void TimelineView::wheelEvent(QWheelEvent *event)
+{
+  if (Config::Current()["InvertTimelineScrollAxes"].toBool()) {
+    QWheelEvent e(event->pos(),
+                  event->delta(),
+                  event->buttons(),
+                  event->modifiers(),
+                  event->orientation() == Qt::Horizontal ? Qt::Vertical : Qt::Horizontal);
+
+    QGraphicsView::wheelEvent(&e);
+  } else {
+    QGraphicsView::wheelEvent(event);
+  }
+}
+
 void TimelineView::dragEnterEvent(QDragEnterEvent *event)
 {
   TimelineViewMouseEvent timeline_event(ScreenToCoordinate(event->pos()),

app/widget/timelinewidget/view/timelineview.h

@@ -78,6 +78,8 @@ protected:
   virtual void mouseReleaseEvent(QMouseEvent *event) override;
   virtual void mouseDoubleClickEvent(QMouseEvent *event) override;
 
+  virtual void wheelEvent(QWheelEvent* event) override;
+
   virtual void dragEnterEvent(QDragEnterEvent *event) override;
   virtual void dragMoveEvent(QDragMoveEvent *event) override;
   virtual void dragLeaveEvent(QDragLeaveEvent *event) override;