Add SDL2 audio backend

5 files changed, 213 insertions, 2 deletions

diff --git a/externals/CMakeLists.txt b/externals/CMakeLists.txt
index aae0baa0b..ec3c0432b 100644
--- a/externals/CMakeLists.txt
+++ b/externals/CMakeLists.txt
@@ -48,10 +48,10 @@ target_include_directories(unicorn-headers INTERFACE ./unicorn/include)
 # SDL2
 if (NOT SDL2_FOUND AND ENABLE_SDL2)
     if (NOT WIN32)
-        # Yuzu itself needs: Events Joystick Haptic Sensor Timers
+        # Yuzu itself needs: Events Joystick Haptic Sensor Timers Audio
         # Yuzu-cmd also needs: Video (depends on Loadso/Dlopen)
         set(SDL_UNUSED_SUBSYSTEMS
-            Atomic Audio Render Power Threads
+            Atomic Render Power Threads
             File CPUinfo Filesystem Locale)
         foreach(_SUB ${SDL_UNUSED_SUBSYSTEMS})
           string(TOUPPER ${_SUB} _OPT)
diff --git a/src/audio_core/CMakeLists.txt b/src/audio_core/CMakeLists.txt
index a0ae07752..d25a1a645 100644
--- a/src/audio_core/CMakeLists.txt
+++ b/src/audio_core/CMakeLists.txt
@@ -42,6 +42,7 @@ add_library(audio_core STATIC
     voice_context.h
 
     $<$<BOOL:${ENABLE_CUBEB}>:cubeb_sink.cpp cubeb_sink.h>
+    $<$<BOOL:${ENABLE_SDL2}>:sdl2_sink.cpp sdl2_sink.h>
 )
 
 create_target_directory_groups(audio_core)
@@ -71,3 +72,7 @@ if(ENABLE_CUBEB)
     target_link_libraries(audio_core PRIVATE cubeb)
     target_compile_definitions(audio_core PRIVATE -DHAVE_CUBEB=1)
 endif()
+if(ENABLE_SDL2)
+    target_link_libraries(audio_core PRIVATE SDL2)
+    target_compile_definitions(audio_core PRIVATE HAVE_SDL2)
+endif()
diff --git a/src/audio_core/sdl2_sink.cpp b/src/audio_core/sdl2_sink.cpp
new file mode 100644
index 000000000..75c6202ef
--- /dev/null
+++ b/src/audio_core/sdl2_sink.cpp
@@ -0,0 +1,167 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <algorithm>
+#include <atomic>
+#include <cstring>
+#include "audio_core/sdl2_sink.h"
+#include "audio_core/stream.h"
+#include "audio_core/time_stretch.h"
+#include "common/assert.h"
+#include "common/logging/log.h"
+//#include "common/settings.h"
+
+// Ignore -Wimplicit-fallthrough due to https://github.com/libsdl-org/SDL/issues/4307
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wimplicit-fallthrough"
+#endif
+#include <SDL.h>
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
+namespace AudioCore {
+
+class SDLSinkStream final : public SinkStream {
+public:
+    SDLSinkStream(u32 sample_rate, u32 num_channels_, const std::string& output_device)
+        : num_channels{std::min(num_channels_, 6u)}, time_stretch{sample_rate, num_channels} {
+
+        SDL_AudioSpec spec;
+        spec.freq = sample_rate;
+        spec.channels = static_cast<u8>(num_channels);
+        spec.format = AUDIO_S16SYS;
+        spec.samples = 4096;
+        spec.callback = nullptr;
+
+        SDL_AudioSpec obtained;
+        if (output_device.empty())
+            dev = SDL_OpenAudioDevice(nullptr, 0, &spec, &obtained, 0);
+        else
+            dev = SDL_OpenAudioDevice(output_device.c_str(), 0, &spec, &obtained, 0);
+
+        if (dev == 0) {
+            LOG_CRITICAL(Audio_Sink, "Error opening sdl audio device: {}", SDL_GetError());
+            return;
+        }
+
+        SDL_PauseAudioDevice(dev, 0);
+    }
+
+    ~SDLSinkStream() override {
+        if (dev == 0) {
+            return;
+        }
+
+        SDL_PauseAudioDevice(dev, 1);
+        SDL_CloseAudioDevice(dev);
+    }
+
+    void EnqueueSamples(u32 source_num_channels, const std::vector<s16>& samples) override {
+        if (source_num_channels > num_channels) {
+            // Downsample 6 channels to 2
+            ASSERT_MSG(source_num_channels == 6, "Channel count must be 6");
+
+            std::vector<s16> buf;
+            buf.reserve(samples.size() * num_channels / source_num_channels);
+            for (std::size_t i = 0; i < samples.size(); i += source_num_channels) {
+                // Downmixing implementation taken from the ATSC standard
+                const s16 left{samples[i + 0]};
+                const s16 right{samples[i + 1]};
+                const s16 center{samples[i + 2]};
+                const s16 surround_left{samples[i + 4]};
+                const s16 surround_right{samples[i + 5]};
+                // Not used in the ATSC reference implementation
+                [[maybe_unused]] const s16 low_frequency_effects{samples[i + 3]};
+
+                constexpr s32 clev{707}; // center mixing level coefficient
+                constexpr s32 slev{707}; // surround mixing level coefficient
+
+                buf.push_back(static_cast<s16>(left + (clev * center / 1000) +
+                                               (slev * surround_left / 1000)));
+                buf.push_back(static_cast<s16>(right + (clev * center / 1000) +
+                                               (slev * surround_right / 1000)));
+            }
+            int ret = SDL_QueueAudio(dev, static_cast<const void*>(buf.data()),
+                                     static_cast<u32>(buf.size() * sizeof(s16)));
+            if (ret < 0)
+                LOG_WARNING(Audio_Sink, "Could not queue audio buffer: {}", SDL_GetError());
+            return;
+        }
+
+        int ret = SDL_QueueAudio(dev, static_cast<const void*>(samples.data()),
+                                 static_cast<u32>(samples.size() * sizeof(s16)));
+        if (ret < 0)
+            LOG_WARNING(Audio_Sink, "Could not queue audio buffer: {}", SDL_GetError());
+    }
+
+    std::size_t SamplesInQueue(u32 channel_count) const override {
+        if (dev == 0)
+            return 0;
+
+        return SDL_GetQueuedAudioSize(dev) / (channel_count * sizeof(s16));
+    }
+
+    void Flush() override {
+        should_flush = true;
+    }
+
+    u32 GetNumChannels() const {
+        return num_channels;
+    }
+
+private:
+    SDL_AudioDeviceID dev = 0;
+    u32 num_channels{};
+    std::atomic<bool> should_flush{};
+    TimeStretcher time_stretch;
+};
+
+SDLSink::SDLSink(std::string_view target_device_name) {
+    if (!SDL_WasInit(SDL_INIT_AUDIO)) {
+        if (SDL_InitSubSystem(SDL_INIT_AUDIO) < 0) {
+            LOG_CRITICAL(Audio_Sink, "SDL_InitSubSystem audio failed: {}", SDL_GetError());
+            return;
+        }
+    }
+
+    if (target_device_name != auto_device_name && !target_device_name.empty()) {
+        output_device = target_device_name;
+    } else {
+        output_device.clear();
+    }
+}
+
+SDLSink::~SDLSink() {
+    for (auto& sink_stream : sink_streams) {
+        sink_stream.reset();
+    }
+}
+
+SinkStream& SDLSink::AcquireSinkStream(u32 sample_rate, u32 num_channels, const std::string&) {
+    sink_streams.push_back(
+        std::make_unique<SDLSinkStream>(sample_rate, num_channels, output_device));
+    return *sink_streams.back();
+}
+
+std::vector<std::string> ListSDLSinkDevices() {
+    std::vector<std::string> device_list;
+
+    if (!SDL_WasInit(SDL_INIT_AUDIO)) {
+        if (SDL_InitSubSystem(SDL_INIT_AUDIO) < 0) {
+            LOG_CRITICAL(Audio_Sink, "SDL_InitSubSystem audio failed: {}", SDL_GetError());
+            return std::vector<std::string>();
+        }
+    }
+
+    int device_count = SDL_GetNumAudioDevices(0);
+    for (int i = 0; i < device_count; ++i) {
+        device_list.emplace_back(SDL_GetAudioDeviceName(i, 0));
+    }
+
+    return device_list;
+}
+
+} // namespace AudioCore
diff --git a/src/audio_core/sdl2_sink.h b/src/audio_core/sdl2_sink.h
new file mode 100644
index 000000000..8ec1526d8
--- /dev/null
+++ b/src/audio_core/sdl2_sink.h
@@ -0,0 +1,29 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "audio_core/sink.h"
+
+namespace AudioCore {
+
+class SDLSink final : public Sink {
+public:
+    explicit SDLSink(std::string_view device_id);
+    ~SDLSink() override;
+
+    SinkStream& AcquireSinkStream(u32 sample_rate, u32 num_channels,
+                                  const std::string& name) override;
+
+private:
+    std::string output_device;
+    std::vector<SinkStreamPtr> sink_streams;
+};
+
+std::vector<std::string> ListSDLSinkDevices();
+
+} // namespace AudioCore
diff --git a/src/audio_core/sink_details.cpp b/src/audio_core/sink_details.cpp
index a848eb1c9..de10aecd2 100644
--- a/src/audio_core/sink_details.cpp
+++ b/src/audio_core/sink_details.cpp
@@ -11,6 +11,9 @@
 #ifdef HAVE_CUBEB
 #include "audio_core/cubeb_sink.h"
 #endif
+#ifdef HAVE_SDL2
+#include "audio_core/sdl2_sink.h"
+#endif
 #include "common/logging/log.h"
 
 namespace AudioCore {
@@ -36,6 +39,13 @@ constexpr SinkDetails sink_details[] = {
                 },
                 &ListCubebSinkDevices},
 #endif
+#ifdef HAVE_SDL2
+    SinkDetails{"sdl2",
+                [](std::string_view device_id) -> std::unique_ptr<Sink> {
+                    return std::make_unique<SDLSink>(device_id);
+                },
+                &ListSDLSinkDevices},
+#endif
     SinkDetails{"null",
                 [](std::string_view device_id) -> std::unique_ptr<Sink> {
                     return std::make_unique<NullSink>(device_id);