higan/ruby/audio/alsa.cpp

#include <alsa/asoundlib.h>

struct AudioALSA : AudioDriver {
  AudioALSA& self = *this;
  AudioALSA(Audio& super) : AudioDriver(super) {}
  ~AudioALSA() { terminate(); }

  auto create() -> bool override {
    super.setDevice("default");
    super.setChannels(2);
    super.setFrequency(48000);
    super.setLatency(20);
    return initialize();
  }

  auto driver() -> string override { return "ALSA"; }
  auto ready() -> bool override { return _ready; }

  auto hasBlocking() -> bool override { return true; }
  auto hasDynamic() -> bool override { return true; }

  auto hasDevices() -> vector<string> override {
    vector<string> devices;

    char** list;
    if(snd_device_name_hint(-1, "pcm", (void***)&list) == 0) {
      uint index = 0;
      while(list[index]) {
        char* deviceName = snd_device_name_get_hint(list[index], "NAME");
        if(deviceName) devices.append(deviceName);
        free(deviceName);
        index++;
      }
    }

    snd_device_name_free_hint((void**)list);
    return devices;
  }

  auto hasChannels() -> vector<uint> override {
    return {2};
  }

  auto hasFrequencies() -> vector<uint> override {
    return {44100, 48000, 96000};
  }

  auto hasLatencies() -> vector<uint> override {
    return {20, 40, 60, 80, 100};
  }

  auto setDevice(string device) -> bool override { return initialize(); }
  auto setBlocking(bool blocking) -> bool override { return true; }
  auto setChannels(uint channels) -> bool override { return true; }
  auto setFrequency(uint frequency) -> bool override { return initialize(); }
  auto setLatency(uint latency) -> bool override { return initialize(); }

  auto level() -> double override {
    snd_pcm_sframes_t available;
    for(uint timeout : range(256)) {
      available = snd_pcm_avail_update(_interface);
      if(available >= 0) break;
      snd_pcm_recover(_interface, available, 1);
    }
    return (double)(_bufferSize - available) / _bufferSize;
  }

  auto output(const double samples[]) -> void override {
    _buffer[_offset]  = (uint16_t)sclamp<16>(samples[0] * 32767.0) <<  0;
    _buffer[_offset] |= (uint16_t)sclamp<16>(samples[1] * 32767.0) << 16;
    if(++_offset < _periodSize) return;

    snd_pcm_sframes_t available;
    do {
      available = snd_pcm_avail_update(_interface);
      if(available < 0) {
        snd_pcm_recover(_interface, available, 1);
        continue;
      }
      if(available < _offset) {
        if(!self.blocking) {
          _offset = 0;
          return;
        }
        int error = snd_pcm_wait(_interface, -1);
        if(error < 0) snd_pcm_recover(_interface, error, 1);
      }
    } while(available < _offset);

    uint32_t* output = _buffer;
    int i = 4;

    while(_offset > 0 && i--) {
      snd_pcm_sframes_t written = snd_pcm_writei(_interface, output, _offset);
      if(written < 0) {
        //no samples written
        snd_pcm_recover(_interface, written, 1);
      } else if(written <= _offset) {
        _offset -= written;
        output += written;
      }
    }

    if(i < 0) {
      if(_buffer == output) {
        _offset--;
        output++;
      }
      memory::move<uint32_t>(_buffer, output, _offset);
    }
  }

private:
  auto initialize() -> bool {
    terminate();

    if(!hasDevices().find(self.device)) self.device = "default";
    if(snd_pcm_open(&_interface, self.device, SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK) < 0) return terminate(), false;

    uint rate = self.frequency;
    uint bufferTime = self.latency * 1000;
    uint periodTime = self.latency * 1000 / 8;

    snd_pcm_hw_params_t* hardwareParameters;
    snd_pcm_hw_params_alloca(&hardwareParameters);
    if(snd_pcm_hw_params_any(_interface, hardwareParameters) < 0) return terminate(), false;

    if(snd_pcm_hw_params_set_access(_interface, hardwareParameters, SND_PCM_ACCESS_RW_INTERLEAVED) < 0
    || snd_pcm_hw_params_set_format(_interface, hardwareParameters, SND_PCM_FORMAT_S16_LE) < 0
    || snd_pcm_hw_params_set_channels(_interface, hardwareParameters, 2) < 0
    || snd_pcm_hw_params_set_rate_near(_interface, hardwareParameters, &rate, 0) < 0
    || snd_pcm_hw_params_set_period_time_near(_interface, hardwareParameters, &periodTime, 0) < 0
    || snd_pcm_hw_params_set_buffer_time_near(_interface, hardwareParameters, &bufferTime, 0) < 0
    ) return terminate(), false;

    if(snd_pcm_hw_params(_interface, hardwareParameters) < 0) return terminate(), false;
    if(snd_pcm_get_params(_interface, &_bufferSize, &_periodSize) < 0) return terminate(), false;

    snd_pcm_sw_params_t* softwareParameters;
    snd_pcm_sw_params_alloca(&softwareParameters);
    if(snd_pcm_sw_params_current(_interface, softwareParameters) < 0) return terminate(), false;
    if(snd_pcm_sw_params_set_start_threshold(_interface, softwareParameters, _bufferSize / 2) < 0) return terminate(), false;
    if(snd_pcm_sw_params(_interface, softwareParameters) < 0) return terminate(), false;

    _buffer = new uint32_t[_periodSize]();
    _offset = 0;
    return _ready = true;
  }

  auto terminate() -> void {
    _ready = false;

    if(_interface) {
    //snd_pcm_drain(_interface);  //prevents popping noise; but causes multi-second lag
      snd_pcm_close(_interface);
      _interface = nullptr;
    }

    if(_buffer) {
      delete[] _buffer;
      _buffer = nullptr;
    }
  }

  bool _ready = false;

  snd_pcm_t* _interface = nullptr;
  snd_pcm_uframes_t _bufferSize;
  snd_pcm_uframes_t _periodSize;

  uint32_t* _buffer = nullptr;
  uint _offset = 0;
};