prevent suggestion that MIDI tracks can be set to stacked view

gtk2_ardour/midi_streamview.cc

@@ -242,6 +242,16 @@ MidiStreamView::update_data_note_range(uint8_t min, uint8_t max)
 	return dirty;
 }
 
+void
+MidiStreamView::set_layer_display (LayerDisplay d)
+{
+	if (d != Overlaid) {
+		return;
+	}
+
+	StreamView::set_layer_display (d);
+}
+
 void
 MidiStreamView::redisplay_track ()
 {

gtk2_ardour/midi_streamview.h

@@ -77,6 +77,8 @@ class MidiStreamView : public StreamView
 
 	void update_note_range(uint8_t note_num);
 
+	void set_layer_display (LayerDisplay);
+	bool can_change_layer_display() const { return false; }
 	void redisplay_track ();
 
 	inline double contents_height() const

gtk2_ardour/route_time_axis.cc

@@ -632,21 +632,27 @@ RouteTimeAxisView::build_display_menu ()
 
 		int overlaid = 0;
 		int stacked = 0;
+		int unchangeable = 0;
 		TrackSelection const & s = _editor.get_selection().tracks;
+
 		for (TrackSelection::const_iterator i = s.begin(); i != s.end(); ++i) {
 			StreamView* v = (*i)->view ();
 			if (!v) {
 				continue;
 			}
 
-			switch (v->layer_display ()) {
-			case Overlaid:
-				++overlaid;
-				break;
-			case Stacked:
-			case Expanded:
-				++stacked;
-				break;
+			if (v->can_change_layer_display()) {
+				switch (v->layer_display ()) {
+				case Overlaid:
+					++overlaid;
+					break;
+				case Stacked:
+				case Expanded:
+					++stacked;
+					break;
+				}
+			} else {
+				unchangeable++;
 			}
 		}
 
@@ -664,12 +670,20 @@ RouteTimeAxisView::build_display_menu ()
 		i->set_inconsistent (overlaid != 0 && stacked != 0);
 		i->signal_activate().connect (sigc::bind (sigc::mem_fun (*this, &RouteTimeAxisView::set_layer_display), Overlaid, true));
 
+		if (unchangeable) {
+			i->set_sensitive (false);
+		}
+
 		layers_items.push_back (RadioMenuElem (layers_group, _("Stacked")));
 		i = dynamic_cast<RadioMenuItem*> (&layers_items.back ());
 		i->set_active (overlaid == 0 && stacked != 0);
 		i->set_inconsistent (overlaid != 0 && stacked != 0);
 		i->signal_activate().connect (sigc::bind (sigc::mem_fun (*this, &RouteTimeAxisView::set_layer_display), Stacked, true));
 
+		if (unchangeable) {
+			i->set_sensitive (false);
+		}
+
 		_ignore_set_layer_display = false;
 
 		items.push_back (MenuElem (_("Layers"), *layers_menu));

gtk2_ardour/streamview.h

@@ -76,7 +76,8 @@ public:
 	virtual int set_samples_per_pixel (double);
 	gdouble     get_samples_per_pixel () const { return _samples_per_pixel; }
 
- 	void set_layer_display (LayerDisplay);
+	virtual void set_layer_display (LayerDisplay);
+	virtual bool can_change_layer_display() const { return true; }
 	LayerDisplay layer_display () const { return _layer_display; }
 
 	ArdourCanvas::Container* canvas_item() { return _canvas_group; }