more refactoring, audio loopback kinda working

src/content/sdl_audio_frame_stream2.cpp

@@ -1,10 +1,9 @@
 #include "./sdl_audio_frame_stream2.hpp"
-#include "SDL_audio.h"
 
 #include <iostream>
 #include <vector>
 
-SDLAudioInputDevice::SDLAudioInputDevice(void) : _stream{nullptr, &SDL_DestroyAudioStream} {
+SDLAudioInputDeviceDefault::SDLAudioInputDeviceDefault(void) : _stream{nullptr, &SDL_DestroyAudioStream} {
 	constexpr SDL_AudioSpec spec = { SDL_AUDIO_S16, 1, 48000 };
 
 	_stream = {
@@ -70,10 +69,102 @@ SDLAudioInputDevice::SDLAudioInputDevice(void) : _stream{nullptr, &SDL_DestroyAu
 	});
 }
 
-SDLAudioInputDevice::~SDLAudioInputDevice(void) {
+SDLAudioInputDeviceDefault::~SDLAudioInputDeviceDefault(void) {
 	// TODO: pause audio device?
 	_thread_should_quit = true;
 	_thread.join();
 	// TODO: what to do if readers are still present?
 }
 
+int32_t SDLAudioOutputDeviceDefaultInstance::size(void) {
+	return -1;
+}
+
+std::optional<AudioFrame> SDLAudioOutputDeviceDefaultInstance::pop(void) {
+	assert(false);
+	// this is an output device, there is no data to pop
+	return std::nullopt;
+}
+
+bool SDLAudioOutputDeviceDefaultInstance::push(const AudioFrame& value) {
+	if (!static_cast<bool>(_stream)) {
+		return false;
+	}
+
+	// verify here the fame has the same sample type, channel count and sample freq
+	// if something changed, we need to either use a temporary stream, just for conversion, or reopen _stream with the new params
+	// because of data temporality, the second options looks like a better candidate
+	if (
+		value.sample_rate != _last_sample_rate ||
+		value.channels != _last_channels ||
+		(value.isF32() && _last_format != SDL_AUDIO_F32) ||
+		(value.isS16() && _last_format != SDL_AUDIO_S16)
+	) {
+		const auto device_id = SDL_GetAudioStreamDevice(_stream.get());
+		SDL_FlushAudioStream(_stream.get());
+
+		const SDL_AudioSpec spec = {
+			static_cast<SDL_AudioFormat>((value.isF32() ? SDL_AUDIO_F32 :  SDL_AUDIO_S16)),
+			static_cast<int>(value.channels),
+			static_cast<int>(value.sample_rate)
+		};
+
+		_stream = {
+			SDL_OpenAudioDeviceStream(device_id, &spec, nullptr, nullptr),
+			&SDL_DestroyAudioStream
+		};
+	}
+
+	// HACK
+	assert(value.isS16());
+
+	auto data = value.getSpan<int16_t>();
+
+	if (data.size == 0) {
+		std::cerr << "empty audio frame??\n";
+	}
+
+	if (SDL_PutAudioStreamData(_stream.get(), data.ptr, data.size * sizeof(int16_t)) < 0) {
+		std::cerr << "put data error\n";
+		return false; // return true?
+	}
+
+	_last_sample_rate = value.sample_rate;
+	_last_channels = value.channels;
+	_last_format = value.isF32() ? SDL_AUDIO_F32 :  SDL_AUDIO_S16;
+
+	return true;
+}
+
+SDLAudioOutputDeviceDefaultInstance::SDLAudioOutputDeviceDefaultInstance(void) : _stream(nullptr, nullptr) {
+}
+
+SDLAudioOutputDeviceDefaultInstance::SDLAudioOutputDeviceDefaultInstance(SDLAudioOutputDeviceDefaultInstance&& other) : _stream(std::move(other._stream)) {
+}
+
+SDLAudioOutputDeviceDefaultInstance::~SDLAudioOutputDeviceDefaultInstance(void) {
+}
+
+SDLAudioOutputDeviceDefaultInstance SDLAudioOutputDeviceDefaultFactory::create(void) {
+	SDLAudioOutputDeviceDefaultInstance new_instance;
+
+	constexpr SDL_AudioSpec spec = { SDL_AUDIO_S16, 1, 48000 };
+
+	new_instance._stream = {
+		SDL_OpenAudioDeviceStream(SDL_AUDIO_DEVICE_DEFAULT_OUTPUT, &spec, nullptr, nullptr),
+		&SDL_DestroyAudioStream
+	};
+	new_instance._last_sample_rate = spec.freq;
+	new_instance._last_channels = spec.channels;
+	new_instance._last_format = spec.format;
+
+	if (!static_cast<bool>(new_instance._stream)) {
+		std::cerr << "SDL open audio device failed!\n";
+	}
+
+	const auto audio_device_id = SDL_GetAudioStreamDevice(new_instance._stream.get());
+	SDL_ResumeAudioDevice(audio_device_id);
+
+	return new_instance;
+}
+