nCine::SdlAudioDevice class
#include <nCine/Audio/Backends/SDL/SdlAudioDevice.h>

Implementation of IAudioDevice on top of SDL2's audio queue.

For platforms that have a working SDL2 but no OpenAL: AmigaOS 4 and MorphOS today, where SDL2 is the mature and maintained media layer and OpenAL is not part of the SDK at all.

The mixer is the classic Amiga backend's, which is the N64 one before it: sources are software- mixed by hand into a single 16-bit stereo stream (32-bit integer accumulator, 32.32 fixed-point cursors, Q15 gains). What differs is only where the stream goes - blocks are handed to SDL_QueueAudio(), and how much is already waiting is read back with SDL_GetQueuedAudioSize().

The queue API is used rather than a callback deliberately. A callback would run the mixer on SDL's audio thread and every source operation the game makes would then need a lock around it, for no gain: the mixer is cheap, and running it where the rest of the frame runs keeps this backend the same shape as the console ones. What the queue costs instead is latency, bounded here by TargetQueuedFrames.

Base classes

class AudioDeviceBase: Backend-independent part of an audio device.

Constructors, destructors, conversion operators

SdlAudioDevice()
~SdlAudioDevice() override

Public functions

auto isValid() const -> bool override: Returns true if the device was initialized successfully.
auto name() const -> const char* override: Returns the name of the underlying device.
void setGain(float gain) override: Sets the listener gain (master volume).
void updateListener(const Vector3f& position, const Vector3f& velocity) override: Updates the position and velocity of the listener.
auto nativeFrequency() -> std::int32_t override: Returns the native sample rate of the device.
auto registerPlayer(IAudioPlayer* player) -> std::uint32_t override: Registers a player so it receives state and buffer queue updates, returning its source id.
void updatePlayers() override: Updates the state of every registered player, including the buffer queue of stream players.
auto createBuffer(BufferUsage usage) -> std::uint32_t override: Creates an empty backend buffer, returning its id or 0 on failure.
void deleteBuffer(std::uint32_t bufferId) override: Destroys a buffer previously returned by createBuffer().
auto uploadBuffer(std::uint32_t bufferId, BufferFormat format, const void* data, std::int32_t size, std::int32_t frequency) -> bool override: Replaces the contents of a buffer with the specified samples.
void setSourceBuffer(std::uint32_t sourceId, std::uint32_t bufferId) override: Attaches a buffer to a source for non-streamed playback, 0 detaches the current one.
void setSourceGain(std::uint32_t sourceId, float gain) override: Sets the gain of a source.
void setSourcePitch(std::uint32_t sourceId, float pitch) override: Sets the pitch of a source, as a multiplier of its natural playback rate.
void setSourceLooping(std::uint32_t sourceId, bool looping) override: Sets whether a source repeats its attached buffer.
void setSourceRelative(std::uint32_t sourceId, bool relative) override: Sets whether the position of a source is relative to the listener.
void setSourcePosition(std::uint32_t sourceId, const Vector3f& position) override: Sets the position of a source, in physical units.
void setSourceLowPass(std::uint32_t sourceId, float value) override: Sets the low-pass amount of a source, 1.0f disables the filter.
auto sourceSampleOffset(std::uint32_t sourceId) -> std::int32_t override: Returns the playback position of a source in samples.
void setSourceSampleOffset(std::uint32_t sourceId, std::int32_t offset) override: Sets the playback position of a source in samples.
void playSource(std::uint32_t sourceId) override: Starts or resumes a source.
void pauseSource(std::uint32_t sourceId) override: Pauses a source at its current position.
void stopSource(std::uint32_t sourceId) override: Stops a source.
auto isSourcePlaying(std::uint32_t sourceId) -> bool override: Returns true if a source is still producing sound.
void queueBuffer(std::uint32_t sourceId, std::uint32_t bufferId) override: Appends a buffer to the streaming queue of a source.
auto numProcessedBuffers(std::uint32_t sourceId) -> std::int32_t override: Returns the number of queued buffers a source has finished playing.
void unqueueBuffers(std::uint32_t sourceId, std::int32_t count, std::uint32_t* bufferIds) override: Removes the specified number of played buffers from the front of the queue.
void suspendDevice() override: Suspends the audio device.
void resumeDevice() override: Resumes the audio device.

Function documentation

void nCine::SdlAudioDevice::unqueueBuffers(std::uint32_t sourceId, std::int32_t count, std::uint32_t* bufferIds) override

Removes the specified number of played buffers from the front of the queue.