godot/drivers/alsa/audio_driver_alsa.cpp

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/*  audio_driver_alsa.cpp                                                */
/*************************************************************************/
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#include "audio_driver_alsa.h"

#ifdef ALSA_ENABLED

#include "core/os/os.h"
#include "core/project_settings.h"

#include <errno.h>

Error AudioDriverALSA::init_device() {
	mix_rate = GLOBAL_GET("audio/mix_rate");
	speaker_mode = SPEAKER_MODE_STEREO;
	channels = 2;

	// If there is a specified device check that it is really present
	if (device_name != "Default") {
		Array list = get_device_list();
		if (list.find(device_name) == -1) {
			device_name = "Default";
			new_device = "Default";
		}
	}

	int status;
	snd_pcm_hw_params_t *hwparams;
	snd_pcm_sw_params_t *swparams;

#define CHECK_FAIL(m_cond)                                       \
	if (m_cond) {                                                \
		fprintf(stderr, "ALSA ERR: %s\n", snd_strerror(status)); \
		if (pcm_handle) {                                        \
			snd_pcm_close(pcm_handle);                           \
			pcm_handle = nullptr;                                \
		}                                                        \
		ERR_FAIL_COND_V(m_cond, ERR_CANT_OPEN);                  \
	}

	//todo, add
	//6 chans - "plug:surround51"
	//4 chans - "plug:surround40";

	if (device_name == "Default") {
		status = snd_pcm_open(&pcm_handle, "default", SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK);
	} else {
		String device = device_name;
		int pos = device.find(";");
		if (pos != -1) {
			device = device.substr(0, pos);
		}
		status = snd_pcm_open(&pcm_handle, device.utf8().get_data(), SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK);
	}

	ERR_FAIL_COND_V(status < 0, ERR_CANT_OPEN);

	snd_pcm_hw_params_alloca(&hwparams);

	status = snd_pcm_hw_params_any(pcm_handle, hwparams);
	CHECK_FAIL(status < 0);

	status = snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED);
	CHECK_FAIL(status < 0);

	//not interested in anything else
	status = snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_S16_LE);
	CHECK_FAIL(status < 0);

	//todo: support 4 and 6
	status = snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2);
	CHECK_FAIL(status < 0);

	status = snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &mix_rate, nullptr);
	CHECK_FAIL(status < 0);

	// In ALSA the period size seems to be the one that will determine the actual latency
	// Ref: https://www.alsa-project.org/main/index.php/FramesPeriods
	unsigned int periods = 2;
	int latency = GLOBAL_GET("audio/output_latency");
	buffer_frames = closest_power_of_2(latency * mix_rate / 1000);
	buffer_size = buffer_frames * periods;
	period_size = buffer_frames;

	// set buffer size from project settings
	status = snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams, &buffer_size);
	CHECK_FAIL(status < 0);

	status = snd_pcm_hw_params_set_period_size_near(pcm_handle, hwparams, &period_size, nullptr);
	CHECK_FAIL(status < 0);

	print_verbose("Audio buffer frames: " + itos(period_size) + " calculated latency: " + itos(period_size * 1000 / mix_rate) + "ms");

	status = snd_pcm_hw_params_set_periods_near(pcm_handle, hwparams, &periods, nullptr);
	CHECK_FAIL(status < 0);

	status = snd_pcm_hw_params(pcm_handle, hwparams);
	CHECK_FAIL(status < 0);

	//snd_pcm_hw_params_free(&hwparams);

	snd_pcm_sw_params_alloca(&swparams);

	status = snd_pcm_sw_params_current(pcm_handle, swparams);
	CHECK_FAIL(status < 0);

	status = snd_pcm_sw_params_set_avail_min(pcm_handle, swparams, period_size);
	CHECK_FAIL(status < 0);

	status = snd_pcm_sw_params_set_start_threshold(pcm_handle, swparams, 1);
	CHECK_FAIL(status < 0);

	status = snd_pcm_sw_params(pcm_handle, swparams);
	CHECK_FAIL(status < 0);

	samples_in.resize(period_size * channels);
	samples_out.resize(period_size * channels);

	return OK;
}

Error AudioDriverALSA::init() {
	active = false;
	thread_exited = false;
	exit_thread = false;

	Error err = init_device();
	if (err == OK) {
		thread = Thread::create(AudioDriverALSA::thread_func, this);
	}

	return err;
}

void AudioDriverALSA::thread_func(void *p_udata) {
	AudioDriverALSA *ad = (AudioDriverALSA *)p_udata;

	while (!ad->exit_thread) {
		ad->lock();
		ad->start_counting_ticks();

		if (!ad->active) {
			for (uint64_t i = 0; i < ad->period_size * ad->channels; i++) {
				ad->samples_out.write[i] = 0;
			}

		} else {
			ad->audio_server_process(ad->period_size, ad->samples_in.ptrw());

			for (uint64_t i = 0; i < ad->period_size * ad->channels; i++) {
				ad->samples_out.write[i] = ad->samples_in[i] >> 16;
			}
		}

		int todo = ad->period_size;
		int total = 0;

		while (todo && !ad->exit_thread) {
			uint8_t *src = (uint8_t *)ad->samples_out.ptr();
			int wrote = snd_pcm_writei(ad->pcm_handle, (void *)(src + (total * ad->channels)), todo);

			if (wrote > 0) {
				total += wrote;
				todo -= wrote;
			} else if (wrote == -EAGAIN) {
				ad->stop_counting_ticks();
				ad->unlock();

				OS::get_singleton()->delay_usec(1000);

				ad->lock();
				ad->start_counting_ticks();
			} else {
				wrote = snd_pcm_recover(ad->pcm_handle, wrote, 0);
				if (wrote < 0) {
					ERR_PRINT("ALSA: Failed and can't recover: " + String(snd_strerror(wrote)));
					ad->active = false;
					ad->exit_thread = true;
				}
			}
		}

		// User selected a new device, finish the current one so we'll init the new device
		if (ad->device_name != ad->new_device) {
			ad->device_name = ad->new_device;
			ad->finish_device();

			Error err = ad->init_device();
			if (err != OK) {
				ERR_PRINT("ALSA: init_device error");
				ad->device_name = "Default";
				ad->new_device = "Default";

				err = ad->init_device();
				if (err != OK) {
					ad->active = false;
					ad->exit_thread = true;
				}
			}
		}

		ad->stop_counting_ticks();
		ad->unlock();
	}

	ad->thread_exited = true;
}

void AudioDriverALSA::start() {
	active = true;
}

int AudioDriverALSA::get_mix_rate() const {
	return mix_rate;
}

AudioDriver::SpeakerMode AudioDriverALSA::get_speaker_mode() const {
	return speaker_mode;
}

Array AudioDriverALSA::get_device_list() {
	Array list;

	list.push_back("Default");

	void **hints;

	if (snd_device_name_hint(-1, "pcm", &hints) < 0) {
		return list;
	}

	for (void **n = hints; *n != nullptr; n++) {
		char *name = snd_device_name_get_hint(*n, "NAME");
		char *desc = snd_device_name_get_hint(*n, "DESC");

		if (name != nullptr && !strncmp(name, "plughw", 6)) {
			if (desc) {
				list.push_back(String(name) + ";" + String(desc));
			} else {
				list.push_back(String(name));
			}
		}

		if (desc != nullptr) {
			free(desc);
		}
		if (name != nullptr) {
			free(name);
		}
	}
	snd_device_name_free_hint(hints);

	return list;
}

String AudioDriverALSA::get_device() {
	return device_name;
}

void AudioDriverALSA::set_device(String device) {
	lock();
	new_device = device;
	unlock();
}

void AudioDriverALSA::lock() {
	if (!thread) {
		return;
	}
	mutex.lock();
}

void AudioDriverALSA::unlock() {
	if (!thread) {
		return;
	}
	mutex.unlock();
}

void AudioDriverALSA::finish_device() {
	if (pcm_handle) {
		snd_pcm_close(pcm_handle);
		pcm_handle = nullptr;
	}
}

void AudioDriverALSA::finish() {
	if (thread) {
		exit_thread = true;
		Thread::wait_to_finish(thread);

		memdelete(thread);
		thread = nullptr;
	}

	finish_device();
}

#endif // ALSA_ENABLED