+ virtual void paint_label(QPainter &p, const QRect &rect,
+ unsigned int prefix) = 0;
+
+ /**
+ * Returns a list of context menu items to show in the context
+ * bar.
+ */
+ const std::list<QAction*> get_context_bar_actions();
+
+private slots:
+ void on_value_changed(double value);
+
+signals:
+ void time_changed();