old-ruby/audio/alsa.cpp

#include <alsa/asoundlib.h>

struct AudioALSA : Audio {
  ~AudioALSA() { term(); }

  struct {
    snd_pcm_t* handle = nullptr;
    snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE;
    snd_pcm_uframes_t buffer_size;
    snd_pcm_uframes_t period_size;
    int channels = 2;
    const char* name = "default";
  } device;

  struct {
    uint32_t* data = nullptr;
    unsigned length = 0;
  } buffer;

  struct {
    bool synchronize = false;
    unsigned frequency = 48000;
    unsigned latency = 60;
  } settings;

  auto cap(const string& name) -> bool {
    if(name == Audio::Synchronize) return true;
    if(name == Audio::Frequency) return true;
    if(name == Audio::Latency) return true;
    return false;
  }

  auto get(const string& name) -> any {
    if(name == Audio::Synchronize) return settings.synchronize;
    if(name == Audio::Frequency) return settings.frequency;
    if(name == Audio::Latency) return settings.latency;
    return {};
  }

  auto set(const string& name, const any& value) -> bool {
    if(name == Audio::Synchronize && value.is<bool>()) {
      if(settings.synchronize != value.get<bool>()) {
        settings.synchronize = value.get<bool>();
        if(device.handle) init();
      }
      return true;
    }

    if(name == Audio::Frequency && value.is<unsigned>()) {
      if(settings.frequency != value.get<unsigned>()) {
        settings.frequency = value.get<unsigned>();
        if(device.handle) init();
      }
      return true;
    }

    if(name == Audio::Latency && value.is<unsigned>()) {
      if(settings.latency != value.get<unsigned>()) {
        settings.latency = value.get<unsigned>();
        if(device.handle) init();
      }
      return true;
    }

    return false;
  }

  auto sample(int16_t left, int16_t right) -> void {
    if(!device.handle) return;

    buffer.data[buffer.length++] = (uint16_t)left << 0 | (uint16_t)right << 16;
    if(buffer.length < device.period_size) return;

    snd_pcm_sframes_t avail;
    do {
      avail = snd_pcm_avail_update(device.handle);
      if(avail < 0) snd_pcm_recover(device.handle, avail, 1);
      if(avail < buffer.length) {
        if(settings.synchronize == false) {
          buffer.length = 0;
          return;
        }
        int error = snd_pcm_wait(device.handle, -1);
        if(error < 0) snd_pcm_recover(device.handle, error, 1);
      }
    } while(avail < buffer.length);

    //below code has issues with PulseAudio sound server
    #if 0
    if(settings.synchronize == false) {
      snd_pcm_sframes_t avail = snd_pcm_avail_update(device.handle);
      if(avail < device.period_size) {
        buffer.length = 0;
        return;
      }
    }
    #endif

    uint32_t* buffer_ptr = buffer.data;
    int i = 4;

    while((buffer.length > 0) && i--) {
      snd_pcm_sframes_t written = snd_pcm_writei(device.handle, buffer_ptr, buffer.length);
      if(written < 0) {
        //no samples written
        snd_pcm_recover(device.handle, written, 1);
      } else if(written <= buffer.length) {
        buffer.length -= written;
        buffer_ptr += written;
      }
    }

    if(i < 0) {
      if(buffer.data == buffer_ptr) {
        buffer.length--;
        buffer_ptr++;
      }
      memmove(buffer.data, buffer_ptr, buffer.length * sizeof(uint32_t));
    }
  }

  auto clear() -> void {
  }

  auto init() -> bool {
    if(snd_pcm_open(&device.handle, device.name, SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK) < 0) {
      term();
      return false;
    }

    //below code will not work with 24khz frequency rate (ALSA library bug)
    #if 0
    if(snd_pcm_set_params(device.handle, device.format, SND_PCM_ACCESS_RW_INTERLEAVED,
      device.channels, settings.frequency, 1, settings.latency * 1000) < 0) {
      //failed to set device parameters
      term();
      return false;
    }

    if(snd_pcm_get_params(device.handle, &device.buffer_size, &device.period_size) < 0) {
      device.period_size = settings.latency * 1000 * 1e-6 * settings.frequency / 4;
    }
    #endif

    snd_pcm_hw_params_t* hwparams;
    snd_pcm_sw_params_t* swparams;
    unsigned rate = settings.frequency;
    unsigned buffer_time = settings.latency * 1000;
    unsigned period_time = settings.latency * 1000 / 4;

    snd_pcm_hw_params_alloca(&hwparams);
    if(snd_pcm_hw_params_any(device.handle, hwparams) < 0) {
      term();
      return false;
    }

    if(snd_pcm_hw_params_set_access(device.handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0
    || snd_pcm_hw_params_set_format(device.handle, hwparams, device.format) < 0
    || snd_pcm_hw_params_set_channels(device.handle, hwparams, device.channels) < 0
    || snd_pcm_hw_params_set_rate_near(device.handle, hwparams, &rate, 0) < 0
    || snd_pcm_hw_params_set_period_time_near(device.handle, hwparams, &period_time, 0) < 0
    || snd_pcm_hw_params_set_buffer_time_near(device.handle, hwparams, &buffer_time, 0) < 0
    ) {
      term();
      return false;
    }

    if(snd_pcm_hw_params(device.handle, hwparams) < 0) {
      term();
      return false;
    }

    if(snd_pcm_get_params(device.handle, &device.buffer_size, &device.period_size) < 0) {
      term();
      return false;
    }

    snd_pcm_sw_params_alloca(&swparams);
    if(snd_pcm_sw_params_current(device.handle, swparams) < 0) {
      term();
      return false;
    }

    if(snd_pcm_sw_params_set_start_threshold(device.handle, swparams,
      (device.buffer_size / device.period_size) * device.period_size) < 0
    ) {
      term();
      return false;
    }

    if(snd_pcm_sw_params(device.handle, swparams) < 0) {
      term();
      return false;
    }

    buffer.data = new uint32_t[device.period_size];
    return true;
  }

  auto term() -> void {
    if(device.handle) {
    //snd_pcm_drain(device.handle);  //prevents popping noise; but causes multi-second lag
      snd_pcm_close(device.handle);
      device.handle = 0;
    }

    if(buffer.data) {
      delete[] buffer.data;
      buffer.data = 0;
	}
  }
};