small visual improvements to the timeline's timecode label

app/widget/slider/sliderbase.cpp

@@ -37,6 +37,7 @@ SliderBase::SliderBase(Mode mode, QWidget *parent) :
   setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Maximum);
 
   label_ = new SliderLabel(this);
+
   addWidget(label_);
 
   editor_ = new SliderLineEdit(this);
@@ -72,6 +73,11 @@ void SliderBase::SetRequireValidInput(bool e)
   require_valid_input_ = e;
 }
 
+void SliderBase::SetAlignment(Qt::Alignment alignment)
+{
+  label_->setAlignment(alignment);
+}
+
 const QVariant &SliderBase::Value()
 {
   if (dragged_) {

app/widget/slider/sliderbase.h

@@ -42,6 +42,8 @@ public:
 
   void SetRequireValidInput(bool e);
 
+  void SetAlignment(Qt::Alignment alignment);
+
 signals:
   void ValueChanged(QVariant v);
 

app/widget/timelinewidget/timelinewidget.cpp

@@ -24,6 +24,8 @@ TimelineWidget::TimelineWidget(QWidget *parent) :
   vert_layout->addLayout(ruler_and_time_layout);
 
   timecode_label_ = new TimeSlider();
+  timecode_label_->SetAlignment(Qt::AlignCenter);
+  timecode_label_->setVisible(false);
   connect(timecode_label_, SIGNAL(ValueChanged(int64_t)), this, SIGNAL(TimeChanged(const int64_t&)));
   connect(timecode_label_, SIGNAL(ValueChanged(int64_t)), this, SLOT(UpdateInternalTime(const int64_t&)));
   ruler_and_time_layout->addWidget(timecode_label_);
@@ -138,6 +140,8 @@ void TimelineWidget::SetTimebase(const rational &timebase)
   ruler_->SetTimebase(timebase);
   timecode_label_->SetTimebase(timebase);
 
+  timecode_label_->setVisible(!timebase.isNull());
+
   foreach (TimelineAndTrackView* view, views_) {
     view->view()->SetTimebase(timebase);
   }