send midi messages from C++

Question

I'm using a raspberry pi, so it is sort of Debian (Raspbian)

I have a synthesizer running (Zynaddsubfx) and I want to send him midi messages from code and have it playing the music for me. I will use ALSA for that.

I managed to create a "emitting port" in my program by doing:

snd_seq_create_simple_port(seq_handle, "My own sequencer",
    SND_SEQ_PORT_CAP_READ|SND_SEQ_PORT_CAP_SUBS_READ,
    SND_SEQ_PORT_TYPE_APPLICATION)

now I can see ZynSubAddFX in aconnect -ol and my own sequencer in aconnect -il. And I'm able to connect them:

pi@cacharro:~/projects/tests$ aconnect 129:0 128:0
pi@cacharro:~/projects/tests$ Info, alsa midi port connected

for doing that, as sugested by CL I used opened snd_seq_open, stored the sequence and then used snd_seq_create_simple_port.. BUT :

As commented before I just wanna send commands to zynsubaddfx under user interaction so creating queues, adding tempo and so on is not the way to go.

Is there a way to send simple midi comands like note on/note off through my opened port ???

Answer 1

To send some events at a specific time:

• open the sequencer;
• create your own (source) port;
• construct and send some events.

To open the sequencer, call snd_seq_open. (You can get your client number with snd_seq_client_id.)

    snd_seq_t seq;
    snd_seq_open(&seq, "default", SND_SEQ_OPEN_DUPLEX, 0);

To create a port, allocate a port info object with snd_seq_port_info_alloca, set port parameters with snd_seq_port_info_set_xxx, and call snd_seq_create_port. Or simply call snd_seq_create_simple_port.

    int port;
    port = snd_seq_create_simple_port(seq, "my port",
            SND_SEQ_PORT_CAP_READ | SND_SEQ_POR_CAP_WRITE,
            SND_SEQ_PORT_TYPE_APPLICATION);

To send an event, allocate an event structure (just for a change, you can use a local snd_seq_event_t variable), and call various snd_seq_ev_xxx functions to set its properties. Then call snd_seq_event_output, and snd_seq_drain_output after you've sent all events.

    snd_seq_event_t ev;
    snd_seq_ev_clear(&ev);
    snd_seq_ev_set_direct(&ev);

    /* either */
    snd_seq_ev_set_dest(&ev, 64, 0); /* send to 64:0 */
    /* or */
    snd_seq_ev_set_subs(&ev);        /* send to subscribers of source port */

    snd_seq_ev_set_noteon(&ev, 0, 60, 127);
    snd_seq_event_output(seq, &ev);

    snd_seq_ev_set_noteon(&ev, 0, 67, 127);
    snd_seq_event_output(seq, &ev);

    snd_seq_drain_output(seq);