Playing MIDI with fluidsynth on OpenAL.

test.cpp

#include <OpenAL/al.h>
#include <OpenAL/alc.h>

#include <boost/assert.hpp>

#include <cstdint>
#include <cstdlib>

#include <chrono>
#include <iostream>
#include <memory>
#include <thread>
#include <vector>

#include <fluidsynth.h>
#include <fluidsynth/midi.h>
#include <fluidsynth/seq.h>
#include <fluidsynth/seqbind.h>


namespace {
void load_to_buffer(fluid_synth_t *synth, ALuint buffer, unsigned sample_rate) {
  std::vector<int16_t> buf_data(sample_rate * 2); // stereo
  fluid_synth_write_s16(synth, sample_rate,
                        buf_data.data(), 0, 2,
                        buf_data.data(), 1, 2);
  alBufferData(buffer, AL_FORMAT_STEREO16, buf_data.data(),
               sizeof(int16_t) * buf_data.size(), sample_rate);
}
}

int main(int argc, char *argv[]) {
  BOOST_ASSERT(argc == 3);

  std::shared_ptr<ALCdevice> dev(alcOpenDevice(nullptr), &alcCloseDevice);
  std::shared_ptr<ALCcontext> ctx(alcCreateContext(dev.get(), nullptr), &alcDestroyContext);

  alcMakeContextCurrent(ctx.get());

  std::shared_ptr<fluid_settings_t> settings(new_fluid_settings(), &delete_fluid_settings);
  fluid_settings_setstr(settings.get(), "player.timing-source", "sample");
  fluid_settings_setint(settings.get(), "synth.lock-memory", 0);

  std::shared_ptr<fluid_synth_t> synth(new_fluid_synth(settings.get()), &delete_fluid_synth);
  BOOST_VERIFY(fluid_synth_sfload(synth.get(), argv[1], 1) != -1);

  std::shared_ptr<fluid_sequencer_t> seq(new_fluid_sequencer2(false), &delete_fluid_sequencer);
  fluid_sequencer_register_fluidsynth(seq.get(), synth.get());

  double sample_rate;
  fluid_settings_getnum(settings.get(), "synth.sample-rate", &sample_rate);
  enum { BUFFER_NUM = 3 };

  std::cout << "synth.sample-rate: " << sample_rate << std::endl;

  std::shared_ptr<fluid_player_t> player(new_fluid_player(synth.get()), &delete_fluid_player);
  fluid_player_add(player.get(), argv[2]);
  fluid_player_play(player.get());

  ALuint buffers[BUFFER_NUM];
  alGenBuffers(BUFFER_NUM, buffers);
  for (int i = 0; i < BUFFER_NUM; ++i) {
    // std::cout << "Tick: " << fluid_sequencer_get_tick(seq.get()) << std::endl;
    load_to_buffer(synth.get(), buffers[i], sample_rate);
  }

  ALuint source;
  alGenSources(1, &source);
  alSourceQueueBuffers(source, 3, buffers);
  alSourcePlay(source);

  while (fluid_player_get_status(player.get()) == FLUID_PLAYER_PLAYING) {
    BOOST_ASSERT(alGetError() == AL_NO_ERROR);
    std::this_thread::sleep_for(std::chrono::milliseconds(1000));

    ALint val;
    alGetSourcei(source, AL_BUFFERS_PROCESSED, &val);
    if (val == 0) { continue; }

    ALuint unqueued[val];
    alSourceUnqueueBuffers(source, val, unqueued);
    for (int i = 0; i < val; ++i) {
      // std::cout << "Tick: " << fluid_sequencer_get_tick(seq.get()) << std::endl;
      load_to_buffer(synth.get(), unqueued[i], sample_rate);
    }
    alSourceQueueBuffers(source, val, unqueued);

    ALint source_type;
    alGetSourcei(source, AL_SOURCE_TYPE, &source_type);
    BOOST_ASSERT(source_type == AL_STREAMING);
  }

  std::cout << "End of midi" << std::endl;

  return EXIT_SUCCESS;
}