smf_source: implement SMF::UsedChannels as a bitset; move midi screening into load_model()

we screen midi files for some aggregate info:
 used channels, used patches, and note-count

you can't do this from open() because there are cases (after importing)
 when the source exists but it is not yet written to disk

libs/ardour/ardour/smf_source.h

@@ -76,6 +76,9 @@ public:
 	void prevent_deletion ();
 	void set_path (const std::string& newpath);
 
+	/** Query the smf file for its channel info */
+	SMF::UsedChannels used_midi_channels();
+
   protected:
 	void close ();
 	void flush_midi (const Lock& lock);

libs/ardour/smf_source.cc

@@ -670,6 +670,11 @@ SMFSource::load_model (const Glib::Threads::Mutex::Lock& lock, bool force_reload
 	Evoral::event_id_t event_id;
 	bool have_event_id;
 
+	_num_channels     = 0;
+	_n_note_on_events = 0;
+	_has_pgm_change   = false;
+	_used_channels.reset ();
+
 	// TODO simplify event allocation
 	std::list< std::pair< Evoral::Event<Temporal::Beats>*, gint > > eventlist;
 
@@ -691,6 +696,23 @@ SMFSource::load_model (const Glib::Threads::Mutex::Lock& lock, bool force_reload
 				continue;
 			}
 
+			/* aggregate information about channels and pgm-changes */
+			uint8_t type = buf[0] & 0xf0;
+			uint8_t chan = buf[0] & 0x0f;
+			if (type >= 0x80 && type <= 0xE0) {
+				_used_channels.set(chan);
+				switch (type) {
+					case MIDI_CMD_NOTE_ON:
+						++_n_note_on_events;
+						break;
+					case MIDI_CMD_PGM_CHANGE:
+						_has_pgm_change = true;
+						break;
+					default:
+						break;
+				}
+			}
+
 			if (ret > 0) {
 				/* not a meta-event */
 
@@ -730,6 +752,8 @@ SMFSource::load_model (const Glib::Threads::Mutex::Lock& lock, bool force_reload
 		}
 	}
 
+	_num_channels = _used_channels.size();
+
 	eventlist.sort(compare_eventlist);
 
 	std::list< std::pair< Evoral::Event<Temporal::Beats>*, gint > >::iterator it;
@@ -749,6 +773,12 @@ SMFSource::load_model (const Glib::Threads::Mutex::Lock& lock, bool force_reload
 	free(buf);
 }
 
+Evoral::SMF::UsedChannels
+SMFSource::used_midi_channels()
+{
+	return _used_channels;
+}
+
 void
 SMFSource::destroy_model (const Glib::Threads::Mutex::Lock& lock)
 {

libs/evoral/SMF.cc

@@ -125,11 +125,6 @@ SMF::open(const std::string& path, int track)
 {
 	Glib::Threads::Mutex::Lock lm (_smf_lock);
 
-	_num_channels     = 0;
-	_n_note_on_events = 0;
-	_has_pgm_change   = false;
-	_used_channels.clear ();
-
 	assert(track >= 1);
 	if (_smf) {
 		smf_delete(_smf);
@@ -157,57 +152,11 @@ SMF::open(const std::string& path, int track)
 
 	fclose(f);
 
-	bool type0 = _smf->format==0;
-
 	lm.release ();
 	if (!_empty) {
-
-		for (int i = 1; i <= _smf->number_of_tracks; ++i) {
-
-			// scan file for used channels.
-			int ret;
-			uint32_t delta_t = 0;
-			uint32_t size    = 0;
-			uint8_t* buf     = NULL;
-			event_id_t event_id = 0;
-
-			if (type0) {
-				seek_to_start ();  //type0 files have no 'track' concept, just seek_to_start
-			} else {
-				seek_to_track (i);
-			}
-
-			std::set<uint8_t> used;
-			while ((ret = read_event (&delta_t, &size, &buf, &event_id)) >= 0) {
-				if (ret == 0) {
-					continue;
-				}
-				if (size == 0) {
-					break;
-				}
-				uint8_t type = buf[0] & 0xf0;
-				uint8_t chan = buf[0] & 0x0f;
-
-				if (type >= 0x80 && type <= 0xE0) {
-					_used_channels.insert(chan);
-					switch (type) {
-						case MIDI_CMD_NOTE_ON:
-							++_n_note_on_events;
-							break;
-						case MIDI_CMD_PGM_CHANGE:
-							_has_pgm_change = true;
-							break;
-						default:
-							break;
-					}
-				}
-			}
-			_num_channels += _used_channels.size();
-			free (buf);
-		}
-
 		seek_to_start();
 	}
+
 	return 0;
 }
 

libs/evoral/evoral/SMF.h

@@ -89,7 +89,9 @@ public:
 	int smf_format () const;
 
 	int num_channels () const { return _num_channels; }
-	std::set<uint8_t> const& used_channels () const { return _used_channels; }
+	typedef std::bitset<16> UsedChannels;
+	UsedChannels const& used_channels () const { return _used_channels; }
+	void set_used_channels (UsedChannels used) { _used_channels  = used; }
 	uint64_t n_note_on_events () const { return _n_note_on_events; }
 	bool has_pgm_change () const { return _has_pgm_change; }
 
@@ -134,18 +136,20 @@ public:
 	Markers const & markers() const { return _markers; }
 	void load_markers ();
 
+  protected:
+
+	uint64_t _n_note_on_events;
+	bool     _has_pgm_change;
+
+	int _num_channels;
+	UsedChannels _used_channels;
+
   private:
 	smf_t*       _smf;
 	smf_track_t* _smf_track;
 	bool         _empty; ///< true iff file contains(non-empty) events
 	mutable Glib::Threads::Mutex _smf_lock;
 
-	int _num_channels;
-	std::set<uint8_t> _used_channels;
-
-	uint64_t _n_note_on_events;
-	bool     _has_pgm_change;
-
 	mutable Markers _markers;
 };