mpd/src/output/plugins/OpenALOutputPlugin.cxx

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// SPDX-License-Identifier: GPL-2.0-or-later
// Copyright The Music Player Daemon Project
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#include "OpenALOutputPlugin.hxx"
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#include "../OutputAPI.hxx"
#include "lib/fmt/RuntimeError.hxx"
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#include <unistd.h>
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#ifndef __APPLE__
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#include <AL/al.h>
#include <AL/alc.h>
#else
#include <OpenAL/al.h>
#include <OpenAL/alc.h>
/* on macOS, OpenAL is deprecated, but since the user asked to enable
this plugin, let's ignore the compiler warnings */
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
#endif
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class OpenALOutput final : AudioOutput {
/* should be enough for buffer size = 2048 */
static constexpr unsigned NUM_BUFFERS = 16;
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const char *device_name;
ALCdevice *device;
ALCcontext *context;
ALuint buffers[NUM_BUFFERS];
unsigned filled;
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ALuint source;
ALenum format;
ALuint frequency;
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explicit OpenALOutput(const ConfigBlock &block);
public:
static AudioOutput *Create(EventLoop &,
const ConfigBlock &block) {
return new OpenALOutput(block);
}
private:
void Open(AudioFormat &audio_format) override;
void Close() noexcept override;
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[[nodiscard]] [[gnu::pure]]
std::chrono::steady_clock::duration Delay() const noexcept override {
return filled < NUM_BUFFERS || HasProcessed()
? std::chrono::steady_clock::duration::zero()
/* we don't know exactly how long we must wait
for the next buffer to finish, so this is a
random guess: */
: std::chrono::milliseconds(50);
}
std::size_t Play(std::span<const std::byte> src) override;
void Cancel() noexcept override;
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[[nodiscard]] [[gnu::pure]]
ALint GetSourceI(ALenum param) const noexcept {
ALint value;
alGetSourcei(source, param, &value);
return value;
}
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[[nodiscard]] [[gnu::pure]]
bool HasProcessed() const noexcept {
return GetSourceI(AL_BUFFERS_PROCESSED) > 0;
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}
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[[nodiscard]] [[gnu::pure]]
bool IsPlaying() const noexcept {
return GetSourceI(AL_SOURCE_STATE) == AL_PLAYING;
}
/**
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* Throws on error.
*/
void SetupContext();
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};
static ALenum
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openal_audio_format(AudioFormat &audio_format)
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{
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/* note: cannot map SampleFormat::S8 to AL_FORMAT_STEREO8 or
AL_FORMAT_MONO8 since OpenAL expects unsigned 8 bit
samples, while MPD uses signed samples */
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switch (audio_format.format) {
case SampleFormat::S16:
if (audio_format.channels == 2)
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return AL_FORMAT_STEREO16;
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if (audio_format.channels == 1)
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return AL_FORMAT_MONO16;
/* fall back to mono */
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audio_format.channels = 1;
return openal_audio_format(audio_format);
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default:
/* fall back to 16 bit */
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audio_format.format = SampleFormat::S16;
return openal_audio_format(audio_format);
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}
}
inline void
OpenALOutput::SetupContext()
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{
device = alcOpenDevice(device_name);
if (device == nullptr)
throw FmtRuntimeError("Error opening OpenAL device \"{}\"",
device_name);
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context = alcCreateContext(device, nullptr);
if (context == nullptr) {
alcCloseDevice(device);
throw FmtRuntimeError("Error creating context for \"{}\"",
device_name);
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}
}
OpenALOutput::OpenALOutput(const ConfigBlock &block)
:AudioOutput(0),
device_name(block.GetBlockValue("device"))
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{
if (device_name == nullptr)
device_name = alcGetString(nullptr,
ALC_DEFAULT_DEVICE_SPECIFIER);
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}
void
OpenALOutput::Open(AudioFormat &audio_format)
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{
format = openal_audio_format(audio_format);
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SetupContext();
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alcMakeContextCurrent(context);
alGenBuffers(NUM_BUFFERS, buffers);
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if (alGetError() != AL_NO_ERROR)
throw std::runtime_error("Failed to generate buffers");
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alGenSources(1, &source);
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if (alGetError() != AL_NO_ERROR) {
alDeleteBuffers(NUM_BUFFERS, buffers);
throw std::runtime_error("Failed to generate source");
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}
filled = 0;
frequency = audio_format.sample_rate;
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}
void
OpenALOutput::Close() noexcept
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{
alcMakeContextCurrent(context);
alDeleteSources(1, &source);
alDeleteBuffers(NUM_BUFFERS, buffers);
alcDestroyContext(context);
alcCloseDevice(device);
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}
std::size_t
OpenALOutput::Play(std::span<const std::byte> src)
{
if (alcGetCurrentContext() != context)
alcMakeContextCurrent(context);
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ALuint buffer;
if (filled < NUM_BUFFERS) {
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/* fill all buffers */
buffer = buffers[filled];
filled++;
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} else {
/* wait for processed buffer */
while (!HasProcessed())
usleep(10);
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alSourceUnqueueBuffers(source, 1, &buffer);
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}
alBufferData(buffer, format, src.data(), src.size(), frequency);
alSourceQueueBuffers(source, 1, &buffer);
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if (!IsPlaying())
alSourcePlay(source);
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return src.size();
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}
void
OpenALOutput::Cancel() noexcept
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{
filled = 0;
alcMakeContextCurrent(context);
alSourceStop(source);
/* force-unqueue all buffers */
alSourcei(source, AL_BUFFER, 0);
filled = 0;
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}
const struct AudioOutputPlugin openal_output_plugin = {
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"openal",
nullptr,
OpenALOutput::Create,
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nullptr,
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};