native_midi: Send reset messages on track stop

The ALSA device we're sending messages to will continue playing them
even if the program quits, and we don't want to leave notes hanging. So
when stopping the current track, send the "notes all off" and "reset all
controllers" messages to every channel, and also send an ALSA reset
event as well for good measure (the Timidity++ daemon seems to respond
to it)

src/codecs/native_midi/native_midi_alsa.c

@@ -209,6 +209,34 @@ static void set_queue_tempo(Uint16 division)
     }
 }
 
+static void send_reset(void)
+{
+    static snd_seq_event_t alsa_ev;
+    int i;
+
+    snd_seq_ev_clear(&alsa_ev);
+    snd_seq_ev_set_source(&alsa_ev, local_port);
+    snd_seq_ev_set_subs(&alsa_ev);
+    snd_seq_ev_schedule_tick(&alsa_ev, output_queue, 0, 0);
+
+    // We send an ALSA reset event, but first send the standard MIDI control
+    // events to stop all notes on all channels, just in case.
+    for (i = 0; i < 16; i++) {
+        alsa_ev.type = SND_SEQ_EVENT_CONTROLLER;
+        snd_seq_ev_set_fixed(&alsa_ev);
+        alsa_ev.data.control.channel = i;
+        alsa_ev.data.control.param = MIDI_CTL_ALL_NOTES_OFF;
+        alsa_ev.data.control.value = 0;
+        snd_seq_event_output(output, &alsa_ev);
+
+        alsa_ev.data.control.param = MIDI_CTL_RESET_CONTROLLERS;
+        snd_seq_event_output(output, &alsa_ev);
+    }
+
+    alsa_ev.type = SND_SEQ_EVENT_RESET;
+    snd_seq_event_output(output, &alsa_ev);
+}
+
 static int playback_thread(void *data)
 {
     NativeMidiSong *song = data;
@@ -219,6 +247,7 @@ static int playback_thread(void *data)
     snd_seq_drop_output(output);
     set_queue_tempo(song->division);
     snd_seq_start_queue(output, output_queue, NULL);
+    send_reset();
 
     while (state == PLAYING) {
         if (ev == NULL) {
@@ -284,6 +313,8 @@ void native_midi_stop(void)
     SDL_WaitThread(native_midi_thread, NULL);
 
     snd_seq_drop_output(output);
+    send_reset();
+    snd_seq_drain_output(output);
     snd_seq_stop_queue(output, output_queue, NULL);
 }