Add 6 channel downmixing support for Audout

The specific attenuations used for each channel are taken from Ryujinx.

app/src/main/cpp/skyline/audio.cpp

@@ -5,7 +5,7 @@
 
 namespace skyline::audio {
     Audio::Audio(const DeviceState &state) : oboe::AudioStreamCallback() {
-        builder.setChannelCount(constant::ChannelCount);
+        builder.setChannelCount(constant::StereoChannelCount);
         builder.setSampleRate(constant::SampleRate);
         builder.setFormat(constant::PcmFormat);
         builder.setFramesPerCallback(constant::MixBufferSize);

app/src/main/cpp/skyline/audio/common.h

@@ -9,9 +9,10 @@
 namespace skyline {
     namespace constant {
         constexpr u16 SampleRate{48000}; //!< The common sampling rate to use for audio output
-        constexpr u8 ChannelCount{2}; //!< The common amount of channels to use for audio output
+        constexpr u8 StereoChannelCount{2}; //!< Channels to use for stereo audio output
-        constexpr u16 MixBufferSize{960}; //!< The size of the mix buffer by default
+        constexpr u8 SurroundChannelCount{6}; //!< Channels to use for surround audio output (downsampled by backend)
-        constexpr auto PcmFormat{oboe::AudioFormat::I16}; //!< The common PCM data format to use for audio output
+        constexpr u16 MixBufferSize{960}; //!< Default size of the audren mix buffer
+        constexpr auto PcmFormat{oboe::AudioFormat::I16}; //!< PCM data format to use for audio output
     }
 
     namespace audio {

app/src/main/cpp/skyline/audio/downmixer.h

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright © 2022 Skyline Team and Contributors (https://github.com/skyline-emu/)
+
+#pragma once
+
+#include <common.h>
+#include "common.h"
+
+namespace skyline::audio {
+    /**
+     * @brief Format of a 5.1 channel audio sample
+     */
+    struct Surround51Sample {
+        i16 frontLeft;
+        i16 frontRight;
+        i16 centre;
+        i16 lowFrequency;
+        i16 backLeft;
+        i16 backRight;
+    };
+
+    /**
+     * @brief Format of a stereo audio sample
+     */
+    struct StereoSample {
+        i16 left;
+        i16 right;
+    };
+
+    /**
+     * @brief Downmixes a buffer of 5.1 surround audio to stereo
+     */
+    std::vector<StereoSample> DownMix(span<Surround51Sample> surroundSamples) {
+        constexpr i16 FixedPointMultiplier{1000}; //!< Avoids using floating point maths
+        constexpr i16 Attenuation3Db{707}; //! 10^(-3/20)
+        constexpr i16 Attenuation6Db{501}; //! 10^(-6/20)
+        constexpr i16 Attenuation12Db{251}; //! 10^(-6/20)
+
+        auto downmixChannel{[](i32 front, i32 centre, i32 lowFrequency, i32 back) {
+            return static_cast<i16>(front +
+                                    (centre * Attenuation3Db +
+                                     lowFrequency * Attenuation12Db +
+                                     back * Attenuation6Db) / FixedPointMultiplier);
+        }};
+
+        std::vector<StereoSample> stereoSamples(surroundSamples.size());
+        for (size_t i{}; i < surroundSamples.size(); i++) {
+            auto &surroundSample = surroundSamples[i];
+            auto &stereoSample = stereoSamples[i];
+
+            stereoSample.left = downmixChannel(surroundSample.frontLeft, surroundSample.centre, surroundSample.lowFrequency, surroundSample.backLeft);
+            stereoSample.right = downmixChannel(surroundSample.frontRight, surroundSample.centre, surroundSample.lowFrequency, surroundSample.backRight);
+        }
+
+        return stereoSamples;
+    }
+}

app/src/main/cpp/skyline/audio/track.cpp

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 // Copyright © 2020 Skyline Team and Contributors (https://github.com/skyline-emu/)
 
+#include "downmixer.h"
 #include "track.h"
 
 namespace skyline::audio {
@@ -11,7 +12,7 @@ namespace skyline::audio {
         if (sampleRate != constant::SampleRate)
             throw exception("Unsupported audio sample rate: {}", sampleRate);
 
-        if (channelCount != constant::ChannelCount)
+        if (channelCount != constant::StereoChannelCount && channelCount != constant::SurroundChannelCount)
             throw exception("Unsupported quantity of audio channels: {}", channelCount);
     }
 
@@ -64,7 +65,13 @@ namespace skyline::audio {
         };
 
         identifiers.push_front(identifier);
-        samples.Append(buffer);
+
+        if (channelCount == constant::SurroundChannelCount) {
+            auto stereoBuffer{DownMix(buffer.cast<Surround51Sample>())};
+            samples.Append(span(stereoBuffer).cast<i16>());
+        } else {
+            samples.Append(buffer);
+        }
     }
 
     void AudioTrack::CheckReleasedBuffers() {

app/src/main/cpp/skyline/audio/track.h

@@ -20,7 +20,7 @@ namespace skyline::audio {
         u32 sampleRate;
 
       public:
-        CircularBuffer<i16, constant::SampleRate * constant::ChannelCount * 10> samples; //!< A circular buffer with all appended audio samples
+        CircularBuffer<i16, constant::SampleRate * constant::StereoChannelCount * 10> samples; //!< A circular buffer with all appended audio samples
         std::mutex bufferLock; //!< Synchronizes appending to audio buffers
 
         AudioOutState playbackState{AudioOutState::Stopped}; //!< The current state of playback

app/src/main/cpp/skyline/services/audio/IAudioDevice.cpp

@@ -41,7 +41,7 @@ namespace skyline::service::audio {
     }
 
     Result IAudioDevice::GetActiveChannelCount(type::KSession &session, ipc::IpcRequest &request, ipc::IpcResponse &response) {
-        response.Push<u32>(constant::ChannelCount);
+        response.Push<u32>(constant::StereoChannelCount);
         return {};
     }
 }

app/src/main/cpp/skyline/services/audio/IAudioOutManager.cpp

@@ -14,21 +14,27 @@ namespace skyline::service::audio {
     }
 
     Result IAudioOutManager::OpenAudioOut(type::KSession &session, ipc::IpcRequest &request, ipc::IpcResponse &response) {
-        auto sampleRate{request.Pop<u32>()};
+        struct AudioInputParams {
-        auto channelCount{static_cast<u16>(request.Pop<u32>())};
+            u32 sampleRate;
+            u16 channelCount;
+            u16 _pad_;
+        };
+        auto &inputParams{request.Pop<AudioInputParams>()};
 
-        Logger::Debug("Opening an IAudioOut with sample rate: {}, channel count: {}", sampleRate, channelCount);
+        inputParams.sampleRate = inputParams.sampleRate ? inputParams.sampleRate : constant::SampleRate;
-
+        inputParams.channelCount = inputParams.channelCount <= constant::StereoChannelCount ? constant::StereoChannelCount : constant::SurroundChannelCount;
-        sampleRate = sampleRate ? sampleRate : constant::SampleRate;
+        inputParams._pad_ = 0;
-        channelCount = channelCount ? channelCount : constant::ChannelCount;
+        Logger::Debug("Opening an IAudioOut with sample rate: {}, channel count: {}", inputParams.sampleRate, inputParams.channelCount);
-        manager.RegisterService(std::make_shared<IAudioOut>(state, manager, channelCount, sampleRate), session, response);
+        manager.RegisterService(std::make_shared<IAudioOut>(state, manager, inputParams.channelCount, inputParams.sampleRate), session, response);
-
+        response.Push<AudioInputParams>(inputParams);
-        response.Push<u32>(sampleRate);
-        response.Push<u16>(channelCount);
-        response.Push<u16>(0);
         response.Push(static_cast<u32>(skyline::audio::AudioFormat::Int16));
         response.Push(static_cast<u32>(skyline::audio::AudioOutState::Stopped));
 
+        if (request.inputBuf.at(0).empty() || !request.inputBuf.at(0)[0])
+            request.outputBuf.at(0).copy_from(constant::DefaultAudioOutName);
+        else
+            request.outputBuf.at(0).copy_from(request.inputBuf.at(0));
+
         return {};
     }
 }

app/src/main/cpp/skyline/services/audio/IAudioRenderer/IAudioRenderer.cpp

@@ -7,7 +7,7 @@
 namespace skyline::service::audio::IAudioRenderer {
     IAudioRenderer::IAudioRenderer(const DeviceState &state, ServiceManager &manager, AudioRendererParameters &parameters)
         : systemEvent(std::make_shared<type::KEvent>(state, true)), parameters(parameters), BaseService(state, manager) {
-        track = state.audio->OpenTrack(constant::ChannelCount, constant::SampleRate, [&]() { systemEvent->Signal(); });
+        track = state.audio->OpenTrack(constant::StereoChannelCount, constant::SampleRate, [&]() { systemEvent->Signal(); });
         track->Start();
 
         memoryPools.resize(parameters.effectCount + parameters.voiceCount * 4);
@@ -144,7 +144,7 @@ namespace skyline::service::audio::IAudioRenderer {
                 if (voiceBufferSize == 0)
                     break;
 
-                pendingSamples -= voiceBufferSize / constant::ChannelCount;
+                pendingSamples -= voiceBufferSize / constant::StereoChannelCount;
 
                 for (auto index{voiceBufferOffset}; index < voiceBufferOffset + voiceBufferSize; index++) {
                     if (writtenSamples == bufferOffset) {

app/src/main/cpp/skyline/services/audio/IAudioRenderer/IAudioRenderer.h

@@ -69,7 +69,7 @@ namespace skyline {
             std::vector<MemoryPool> memoryPools;
             std::vector<Effect> effects;
             std::vector<Voice> voices;
-            std::array<i16, constant::MixBufferSize * constant::ChannelCount> sampleBuffer{}; //!< The final output data that is appended to the stream
+            std::array<i16, constant::MixBufferSize * constant::StereoChannelCount> sampleBuffer{}; //!< The final output data that is appended to the stream
             skyline::audio::AudioOutState playbackState{skyline::audio::AudioOutState::Stopped};
 
             /**

app/src/main/cpp/skyline/services/audio/IAudioRenderer/voice.cpp

@@ -79,13 +79,13 @@ namespace skyline::service::audio::IAudioRenderer {
         if (sampleRate != constant::SampleRate)
             samples = resampler.ResampleBuffer(samples, static_cast<double>(sampleRate) / constant::SampleRate, channelCount);
 
-        if (channelCount == 1 && constant::ChannelCount != channelCount) {
+        if (channelCount == 1 && constant::StereoChannelCount != channelCount) {
             auto originalSize{samples.size()};
-            samples.resize((originalSize / channelCount) * constant::ChannelCount);
+            samples.resize((originalSize / channelCount) * constant::StereoChannelCount);
 
             for (auto monoIndex{originalSize - 1}, targetIndex{samples.size()}; monoIndex > 0; monoIndex--) {
                 auto sample{samples[monoIndex]};
-                for (u8 i{}; i < constant::ChannelCount; i++)
+                for (u8 i{}; i < constant::StereoChannelCount; i++)
                     samples[--targetIndex] = sample;
             }
         }
@@ -105,9 +105,9 @@ namespace skyline::service::audio::IAudioRenderer {
         }
 
         outOffset = sampleOffset;
-        outSize = std::min(maxSamples * constant::ChannelCount, static_cast<u32>(samples.size() - sampleOffset));
+        outSize = std::min(maxSamples * constant::StereoChannelCount, static_cast<u32>(samples.size() - sampleOffset));
 
-        output.playedSamplesCount += outSize / constant::ChannelCount;
+        output.playedSamplesCount += outSize / constant::StereoChannelCount;
         sampleOffset += outSize;
 
         if (sampleOffset == samples.size()) {