Add some libardour support for indicating MTC active status.

The general design here is wrong, because it should be more general and cover all possible sync sources.
But it does work, it is used in Tracks, and my attempt to do it correctly revealed the problem to be
an EXTREMELY difficult design issue (as in: two weeks of work on it did not really solve the
fundamental issues with slave design).

So, here it is for now, c/o Grygorii

libs/ardour/ardour/session.h

@@ -297,6 +297,9 @@ class LIBARDOUR_API Session : public PBD::StatefulDestructible, public PBD::Scop
 
 	PBD::Signal0<void> IOConnectionsComplete;
 
+	/* Timecode status signals */
+	PBD::Signal1<void, bool> MTCSyncStateChanged;
+	
 	/* Record status signals */
 
 	PBD::Signal0<void> RecordStateChanged; /* signals changes in recording state (i.e. are we recording) */
@@ -343,6 +346,9 @@ class LIBARDOUR_API Session : public PBD::StatefulDestructible, public PBD::Scop
 	/* Step Editing status changed */
 	PBD::Signal1<void,bool> StepEditStatusChange;
 
+	/* Timecode state signals */
+	PBD::Signal0<void> MtcOrLtcInputPortChanged;
+	
 	void queue_event (SessionEvent*);
 
 	void request_roll_at_and_return (framepos_t start, framepos_t return_to);
@@ -600,7 +606,8 @@ class LIBARDOUR_API Session : public PBD::StatefulDestructible, public PBD::Scop
 
 	void   request_sync_source (Slave*);
 	bool   synced_to_engine() const { return _slave && config.get_external_sync() && Config->get_sync_source() == Engine; }
-
+	bool   synced_to_mtc () const { return config.get_external_sync() && Config->get_sync_source() == MTC && g_atomic_int_get (const_cast<gint*>(&_mtc_active)); }
+	
 	double transport_speed() const { return _transport_speed; }
 	bool   transport_stopped() const { return _transport_speed == 0.0f; }
 	bool   transport_rolling() const { return _transport_speed != 0.0f; }
@@ -1070,6 +1077,9 @@ class LIBARDOUR_API Session : public PBD::StatefulDestructible, public PBD::Scop
 	bool                    _under_nsm_control;
 	unsigned int            _xrun_count;
 
+	void mtc_status_changed (bool);
+	PBD::ScopedConnection mtc_status_connection;
+	
 	void initialize_latencies ();
 	void set_worst_io_latencies ();
 	void set_worst_playback_latency ();
@@ -1107,6 +1117,7 @@ class LIBARDOUR_API Session : public PBD::StatefulDestructible, public PBD::Scop
 	bool have_first_delta_accumulator;
 
 	SlaveState _slave_state;
+	gint _mtc_active;
 	framepos_t slave_wait_end;
 
 	void reset_slave_state ();

libs/ardour/ardour/slave.h

@@ -273,6 +273,8 @@ class LIBARDOUR_API MTC_Slave : public TimecodeSlave {
         std::string approximate_current_position() const;
 	std::string approximate_current_delta() const;
 
+	PBD::Signal1<void, bool> ActiveChanged;
+    
   private:
 	Session&    session;
 	MidiPort*   port;

libs/ardour/mtc_slave.cc

@@ -213,6 +213,7 @@ MTC_Slave::reset (bool with_position)
 	window_end = 0;
 	transport_direction = 1;
 	current_delta = 0;
+	ActiveChanged(false);
 }
 
 void
@@ -468,6 +469,7 @@ MTC_Slave::update_mtc_time (const MIDI::byte *msg, bool was_full, framepos_t now
 				first_mtc_timestamp = now;
 				init_mtc_dll(mtc_frame, qtr);
 				mtc_frame_dll = mtc_frame;
+				ActiveChanged (true); // emit signal
 			}
 			current.guard1++;
 			current.position = mtc_frame;
@@ -626,6 +628,7 @@ MTC_Slave::speed_and_position (double& speed, framepos_t& pos)
 		session.request_transport_speed (0);
 		engine_dll_initstate = 0;
 		queue_reset (false);
+        ActiveChanged (false);
 		DEBUG_TRACE (DEBUG::MTC, "MTC not seen for 2 frames - reset pending\n");
 		return false;
 	}

libs/ardour/session.cc

@@ -184,6 +184,7 @@ Session::Session (AudioEngine &eng,
 	, average_dir (0)
 	, have_first_delta_accumulator (false)
 	, _slave_state (Stopped)
+    , _mtc_active (false)
 	, post_export_sync (false)
 	, post_export_position (0)
 	, _exporting (false)
@@ -2671,36 +2672,37 @@ Session::reconnect_midi_scene_ports(bool inputs)
 }
 
 void
-Session::reconnect_mtc_ports()
+Session::reconnect_mtc_ports ()
 {
-#if 0
 	boost::shared_ptr<MidiPort> mtc_in_ptr = _midi_ports->mtc_input_port();
 
-	if (mtc_in_ptr) {
-		mtc_in_ptr->disconnect_all ();
-        
-		std::vector<EngineStateController::MidiPortState> midi_port_states;
-		EngineStateController::instance()->get_physical_midi_input_states (midi_port_states);
-        
-		std::vector<EngineStateController::MidiPortState>::iterator state_iter = midi_port_states.begin();
-        
-		for (; state_iter != midi_port_states.end(); ++state_iter) {
-			if (state_iter->available && state_iter->mtc_in) {
-				mtc_in_ptr->connect (state_iter->name);
-			}
-		}
-        
-		if (!_midi_ports->mtc_input_port ()->connected () &&
-		    config.get_external_sync () &&
-		    (Config->get_sync_source () == MTC) ) {
-			config.set_external_sync (false);
-		}
-		if ( ARDOUR::Profile->get_trx () ) {
-			// Tracks need this signal to update timecode_source_dropdown
-			MtcOrLtcInputPortChanged (); //emit signal
+	if (!mtc_in_ptr) {
+		return;
+	}
+
+	mtc_in_ptr->disconnect_all ();
+	
+	std::vector<EngineStateController::MidiPortState> midi_port_states;
+	EngineStateController::instance()->get_physical_midi_input_states (midi_port_states);
+	
+	std::vector<EngineStateController::MidiPortState>::iterator state_iter = midi_port_states.begin();
+	
+	for (; state_iter != midi_port_states.end(); ++state_iter) {
+		if (state_iter->available && state_iter->mtc_in) {
+			mtc_in_ptr->connect (state_iter->name);
 		}
 	}
-#endif
+	
+	if (!_midi_ports->mtc_input_port ()->connected () &&
+	    config.get_external_sync () &&
+	    (Config->get_sync_source () == MTC) ) {
+		config.set_external_sync (false);
+	}
+	
+	if ( ARDOUR::Profile->get_trx () ) {
+		// Tracks need this signal to update timecode_source_dropdown
+		MtcOrLtcInputPortChanged (); //emit signal
+	}
 }
 
 void

libs/ardour/session_transport.cc

@@ -1542,6 +1542,13 @@ Session::reset_rf_scale (framecnt_t motion)
 	}
 }
 
+void
+Session::mtc_status_changed (bool yn)
+{
+	g_atomic_int_set (&_mtc_active, yn);
+	MTCSyncStateChanged( yn );
+}
+
 void
 Session::use_sync_source (Slave* new_slave)
 {
@@ -1554,6 +1561,18 @@ Session::use_sync_source (Slave* new_slave)
 	delete _slave;
 	_slave = new_slave;
 
+	MTC_Slave* mtc_slave = dynamic_cast<MTC_Slave*>(_slave);
+	if (mtc_slave) {
+		mtc_slave->ActiveChanged.connect_same_thread (mtc_status_connection, boost::bind (&Session::mtc_status_changed, this, _1));
+		MTCSyncStateChanged(mtc_slave->locked() );
+	} else {
+		if (g_atomic_int_get (&_mtc_active) ){
+			g_atomic_int_set (&_mtc_active, 0);
+			MTCSyncStateChanged( false );
+		}
+		mtc_status_connection.disconnect ();
+	}
+
 	DEBUG_TRACE (DEBUG::Slave, string_compose ("set new slave to %1\n", _slave));
 	
 	// need to queue this for next process() cycle