Revert Monitor-Section to be per session

This partially reverts 639dff3a7c7. When loading a session,
the monitor-bus that was saved with the session is used.

This changes semantics of the monitor-section/config.

Config::set_use_monitor_bus(bool) is used to initiate a change!
Notification about the change is sent asynchronously by
Session::MonitorBusAddedOrRemoved

It is no longer possible to directly call add/remove_monitor_section()
and leave the session + config in an inconsistent state.

4 files changed, 34 insertions, 11 deletions

diff --git a/libs/ardour/ardour/session.h b/libs/ardour/ardour/session.h
index 539b6595c2..560ccbf2c4 100644
--- a/libs/ardour/ardour/session.h
+++ b/libs/ardour/ardour/session.h
@@ -873,15 +873,14 @@ public:
 	PBD::Signal0<void> MuteChanged;
 	PBD::Signal0<void> IsolatedChanged;
 	PBD::Signal0<void> MonitorChanged;
+	PBD::Signal0<void> MonitorBusAddedOrRemoved;
 
 	PBD::Signal0<void> session_routes_reconnected;
 
 	/* monitor/master out */
 	int add_master_bus (ChanCount const&);
 
-	void add_monitor_section ();
 	void reset_monitor_section ();
-	void remove_monitor_section ();
 	bool monitor_active() const { return (_monitor_out && _monitor_out->monitor_control () && _monitor_out->monitor_control ()->monitor_active()); }
 
 	boost::shared_ptr<Route> monitor_out() const { return _monitor_out; }
@@ -1276,6 +1275,9 @@ private:
 
 	std::string             _missing_file_replacement;
 
+	void add_monitor_section ();
+	void remove_monitor_section ();
+
 	void initialize_latencies ();
 	void update_latency (bool playback);
 	bool update_route_latency (bool reverse, bool apply_to_delayline);
diff --git a/libs/ardour/luabindings.cc b/libs/ardour/luabindings.cc
index 4191a44d7a..dcb83ebe44 100644
--- a/libs/ardour/luabindings.cc
+++ b/libs/ardour/luabindings.cc
@@ -2240,8 +2240,6 @@ LuaBindings::common (lua_State* L)
 		.addFunction ("new_midi_route", &Session::new_midi_route)
 
 		.addFunction ("add_master_bus", &Session::add_master_bus)
-		.addFunction ("add_monitor_section", &Session::add_monitor_section)
-		.addFunction ("remove_monitor_section", &Session::remove_monitor_section)
 
 		.addFunction ("get_routes", &Session::get_routes)
 		.addFunction ("get_tracks", &Session::get_tracks)
diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index dc55a2daeb..52c4e580ba 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -1213,7 +1213,7 @@ Session::remove_monitor_section ()
 		auditioner->connect ();
 	}
 
-	Config->ParameterChanged ("use-monitor-bus");
+	MonitorBusAddedOrRemoved (); /* EMIT SIGNAL */
 }
 
 void
@@ -1369,7 +1369,8 @@ Session::add_monitor_section ()
 	if (auditioner) {
 		auditioner->connect ();
 	}
-	Config->ParameterChanged ("use-monitor-bus");
+
+	MonitorBusAddedOrRemoved (); /* EMIT SIGNAL */
 }
 
 void
diff --git a/libs/ardour/session_state.cc b/libs/ardour/session_state.cc
index e23df492b1..b7c4faf5a4 100644
--- a/libs/ardour/session_state.cc
+++ b/libs/ardour/session_state.cc
@@ -4135,11 +4135,33 @@ Session::config_changed (std::string p, bool ours)
 	} else if (p == "auto-return-target-list") {
 		follow_playhead_priority ();
 	} else if (p == "use-monitor-bus") {
-		bool yn = Config->get_use_monitor_bus();
-		if (yn && !_monitor_out) {
-			add_monitor_section ();
-		} else if (!yn && _monitor_out) {
-			remove_monitor_section ();
+		/* NB. This is always called when constructing a session,
+		 * after restoring session state (if any),
+		 * via post_engine_init() -> Config->map_parameters()
+		 */
+		bool want_ms = Config->get_use_monitor_bus();
+		bool have_ms = _monitor_out ? true : false;
+		if (loading ()) {
+			/* When loading an existing session, the config "use-monitor-bus"
+			 * is ignored. Instead the sesion-state (xml) will have added the
+			 * "monitor-route" and restored its state (and connections)
+			 * if the session has a monitor-section.
+			 * Update the config to reflect this.
+			 */
+			if (want_ms != have_ms) {
+				Config->set_use_monitor_bus (have_ms);
+			}
+			MonitorBusAddedOrRemoved (); /* EMIT SIGNAL */
+		} else  {
+			/* Otherwise, Config::set_use_monitor_bus() does
+			 * control the the presence of the monitor-section
+			 * (new sessions, user initiated change)
+			 */
+			if (want_ms && !have_ms) {
+				add_monitor_section ();
+			} else if (!want_ms && have_ms) {
+				remove_monitor_section ();
+			}
 		}
 	}