make AxisView::marked_for_display() be virtual so we can use the a Stripable's PresentationInfo hidden() status

gtk2_ardour/axis_view.h

@@ -74,7 +74,7 @@ class AxisView : public virtual Selectable, public PBD::ScopedConnectionList, pu
 		property_hashtable.clear ();
 	}
 
-	bool marked_for_display () const;
+	virtual bool marked_for_display () const;
 	virtual bool set_marked_for_display (bool);
 
 	static GUIObjectState& gui_object_state();

gtk2_ardour/mixer_strip.cc

@@ -2616,3 +2616,15 @@ MixerStrip::update_track_number_visibility ()
 		number_label.hide ();
 	}
 }
+bool
+MixerStrip::marked_for_display () const
+{
+	return !_route->presentation_info().hidden();
+}
+
+bool
+MixerStrip::set_marked_for_display (bool yn)
+{
+	return RouteUI::mark_hidden (!yn);
+}
+

gtk2_ardour/mixer_strip.h

@@ -81,6 +81,9 @@ class MixerStrip : public RouteUI, public Gtk::EventBox
 	MixerStrip (Mixer_UI&, ARDOUR::Session*, bool in_mixer = true);
 	~MixerStrip ();
 
+	bool marked_for_display () const;
+	bool set_marked_for_display (bool);
+
 	void set_width_enum (Width, void* owner);
 	Width get_width_enum () const { return _width; }
 	void* width_owner () const { return _width_owner; }

gtk2_ardour/route_time_axis.cc

@@ -2931,3 +2931,15 @@ RouteTimeAxisView::stripable () const
 {
 	return _route;
 }
+
+bool
+RouteTimeAxisView::marked_for_display () const
+{
+	return !_route->presentation_info().hidden();
+}
+
+bool
+RouteTimeAxisView::set_marked_for_display (bool yn)
+{
+	return RouteUI::mark_hidden (!yn);
+}

gtk2_ardour/route_ui.cc

@@ -2356,3 +2356,13 @@ RouteUI::manage_pins ()
 		proxy->present();
 	}
 }
+
+bool
+RouteUI::mark_hidden (bool yn)
+{
+	if (yn != _route->presentation_info().hidden()) {
+		_route->presentation_info().set_hidden (yn);
+		return true; // things changed
+	}
+	return false;
+}

gtk2_ardour/route_ui.h

@@ -299,6 +299,8 @@ class RouteUI : public virtual AxisView
 
 	static std::string program_port_prefix;
 
+	bool mark_hidden (bool yn);
+
   private:
 	void parameter_changed (std::string const &);
 	void relabel_solo_button ();