AudioStream: Re-add SDL backend

src/core/host.cpp

@@ -365,6 +365,11 @@ std::unique_ptr<AudioStream> Host::CreateAudioStream(AudioBackend backend, u32 s
       return AudioStream::CreateCubebAudioStream(sample_rate, channels, buffer_ms, latency_ms, stretch);
 #endif
 
+#ifdef ENABLE_SDL2
+    case AudioBackend::SDL:
+      return AudioStream::CreateSDLAudioStream(sample_rate, channels, buffer_ms, latency_ms, stretch);
+#endif
+
 #ifdef _WIN32
     case AudioBackend::XAudio2:
       return AudioStream::CreateXAudio2Stream(sample_rate, channels, buffer_ms, latency_ms, stretch);

src/core/settings.cpp

@@ -1559,6 +1559,9 @@ static constexpr const std::array s_audio_backend_names = {
 #ifdef ENABLE_CUBEB
   "Cubeb",
 #endif
+#ifdef ENABLE_SDL2
+  "SDL",
+#endif
 #ifdef _WIN32
   "XAudio2",
 #endif
@@ -1571,6 +1574,9 @@ static constexpr const std::array s_audio_backend_display_names = {
 #ifdef ENABLE_CUBEB
   TRANSLATE_NOOP("AudioBackend", "Cubeb"),
 #endif
+#ifdef ENABLE_SDL2
+  TRANSLATE_NOOP("AudioBackend", "SDL"),
+#endif
 #ifdef _WIN32
   TRANSLATE_NOOP("AudioBackend", "XAudio2"),
 #endif

src/core/settings.h

@@ -484,6 +484,8 @@ struct Settings
   static constexpr AudioBackend DEFAULT_AUDIO_BACKEND = AudioBackend::XAudio2;
 #elif defined(__ANDROID__)
   static constexpr AudioBackend DEFAULT_AUDIO_BACKEND = AudioBackend::AAudio;
+#elif defined(ENABLE_SDL2)
+  static constexpr AudioBackend DEFAULT_AUDIO_BACKEND = AudioBackend::SDL;
 #else
   static constexpr AudioBackend DEFAULT_AUDIO_BACKEND = AudioBackend::Null;
 #endif

src/core/types.h

@@ -190,6 +190,9 @@ enum class AudioBackend : u8
 #ifdef ENABLE_CUBEB
   Cubeb,
 #endif
+#ifdef ENABLE_SDL2
+  SDL,
+#endif
 #ifdef _WIN32
   XAudio2,
 #endif

src/util/CMakeLists.txt

@@ -189,7 +189,8 @@ if(ENABLE_VULKAN)
 endif()
 
 if(ENABLE_SDL2)
-  target_sources(util PRIVATE 
+  target_sources(util PRIVATE
+    sdl_audio_stream.cpp
     sdl_input_source.cpp
     sdl_input_source.h
   )

src/util/audio_stream.cpp

@@ -89,10 +89,10 @@ u32 AudioStream::GetBufferedFramesRelaxed() const
   return (wpos + m_buffer_size - rpos) % m_buffer_size;
 }
 
-void AudioStream::ReadFrames(s16* bData, u32 nFrames)
+void AudioStream::ReadFrames(s16* samples, u32 num_frames)
 {
   const u32 available_frames = GetBufferedFramesRelaxed();
-  u32 frames_to_read = nFrames;
+  u32 frames_to_read = num_frames;
   u32 silence_frames = 0;
 
   if (m_filling)
@@ -102,7 +102,7 @@ void AudioStream::ReadFrames(s16* bData, u32 nFrames)
 
     if (available_frames < toFill)
     {
-      silence_frames = nFrames;
+      silence_frames = num_frames;
       frames_to_read = 0;
     }
     else
@@ -133,7 +133,7 @@ void AudioStream::ReadFrames(s16* bData, u32 nFrames)
     // towards the end of the buffer
     if (end > 0)
     {
-      std::memcpy(bData, &m_buffer[rpos], sizeof(s32) * end);
+      std::memcpy(samples, &m_buffer[rpos], sizeof(s32) * end);
       rpos += end;
       rpos = (rpos == m_buffer_size) ? 0 : rpos;
     }
@@ -142,7 +142,7 @@ void AudioStream::ReadFrames(s16* bData, u32 nFrames)
     const u32 start = frames_to_read - end;
     if (start > 0)
     {
-      std::memcpy(&bData[end * 2], &m_buffer[0], sizeof(s32) * start);
+      std::memcpy(&samples[end * 2], &m_buffer[0], sizeof(s32) * start);
       rpos = start;
     }
 
@@ -156,15 +156,15 @@ void AudioStream::ReadFrames(s16* bData, u32 nFrames)
       // super basic resampler - spread the input samples evenly across the output samples. will sound like ass and have
       // aliasing, but better than popping by inserting silence.
       const u32 increment =
-        static_cast<u32>(65536.0f * (static_cast<float>(frames_to_read / m_channels) / static_cast<float>(nFrames)));
+        static_cast<u32>(65536.0f * (static_cast<float>(frames_to_read / m_channels) / static_cast<float>(num_frames)));
 
       s16* resample_ptr = static_cast<s16*>(alloca(sizeof(s16) * frames_to_read));
-      std::memcpy(resample_ptr, bData, sizeof(s16) * frames_to_read);
+      std::memcpy(resample_ptr, samples, sizeof(s16) * frames_to_read);
 
-      s16* out_ptr = bData;
+      s16* out_ptr = samples;
       const u32 copy_stride = sizeof(SampleType) * m_channels;
       u32 resample_subpos = 0;
-      for (u32 i = 0; i < nFrames; i++)
+      for (u32 i = 0; i < num_frames; i++)
       {
         std::memcpy(out_ptr, resample_ptr, copy_stride);
         out_ptr += m_channels;
@@ -174,16 +174,28 @@ void AudioStream::ReadFrames(s16* bData, u32 nFrames)
         resample_subpos %= 65536u;
       }
 
-      Log_VerbosePrintf("Audio buffer underflow, resampled %u frames to %u", frames_to_read, nFrames);
+      Log_VerbosePrintf("Audio buffer underflow, resampled %u frames to %u", frames_to_read, num_frames);
     }
     else
     {
       // no data, fall back to silence
-      std::memset(bData + frames_to_read, 0, sizeof(s32) * silence_frames);
+      std::memset(samples + frames_to_read, 0, sizeof(s32) * silence_frames);
     }
   }
 }
 
+void AudioStream::ApplyVolume(s16* samples, u32 num_frames)
+{
+  if (m_volume == 100)
+    return;
+
+  const s32 volume_mult = static_cast<s32>(m_volume) * 32768;
+  const u32 num_samples = num_frames * m_channels;
+
+  while (num_samples > 0)
+    *samples = static_cast<s16>((static_cast<s16>(*samples) * volume_mult) >> 15);
+}
+
 void AudioStream::InternalWriteFrames(s32* bData, u32 nSamples)
 {
   const u32 free = m_buffer_size - GetBufferedFramesRelaxed();

src/util/audio_stream.h

@@ -85,6 +85,10 @@ public:
   static std::vector<std::string> GetCubebDriverNames();
   static std::vector<std::pair<std::string, std::string>> GetCubebOutputDevices(const char* driver);
 #endif
+#ifdef ENABLE_SDL2
+  static std::unique_ptr<AudioStream> CreateSDLAudioStream(u32 sample_rate, u32 channels, u32 buffer_ms, u32 latency_ms,
+                                                           AudioStretchMode stretch);
+#endif
 #ifdef _WIN32
   static std::unique_ptr<AudioStream> CreateXAudio2Stream(u32 sample_rate, u32 channels, u32 buffer_ms, u32 latency_ms,
                                                           AudioStretchMode stretch);
@@ -94,7 +98,8 @@ protected:
   AudioStream(u32 sample_rate, u32 channels, u32 buffer_ms, AudioStretchMode stretch);
   void BaseInitialize();
 
-  void ReadFrames(s16* bData, u32 nSamples);
+  void ReadFrames(s16* samples, u32 num_frames);
+  void ApplyVolume(s16* samples, u32 num_frames);
 
   u32 m_sample_rate = 0;
   u32 m_channels = 0;

src/util/sdl_audio_stream.cpp

@@ -0,0 +1,136 @@
+// SPDX-FileCopyrightText: 2019-2024 Connor McLaughlin <stenzek@gmail.com>
+// SPDX-License-Identifier: (GPL-3.0 OR CC-BY-NC-ND-4.0)
+
+#include "audio_stream.h"
+
+#include "common/assert.h"
+#include "common/log.h"
+
+#include <SDL.h>
+
+Log_SetChannel(SDLAudioStream);
+
+namespace {
+class SDLAudioStream final : public AudioStream
+{
+public:
+  SDLAudioStream(u32 sample_rate, u32 channels, u32 buffer_ms, AudioStretchMode stretch);
+  ~SDLAudioStream();
+
+  void SetPaused(bool paused) override;
+  void SetOutputVolume(u32 volume) override;
+
+  bool OpenDevice(u32 latency_ms);
+  void CloseDevice();
+
+protected:
+  ALWAYS_INLINE bool IsOpen() const { return (m_device_id != 0); }
+
+  static void AudioCallback(void* userdata, uint8_t* stream, int len);
+
+  u32 m_device_id = 0;
+};
+} // namespace
+
+static bool InitializeSDLAudio()
+{
+  static bool initialized = false;
+  if (initialized)
+    return true;
+
+  // May as well keep it alive until the process exits.
+  const int error = SDL_InitSubSystem(SDL_INIT_AUDIO);
+  if (error != 0)
+  {
+    Log_ErrorFmt("SDL_InitSubSystem(SDL_INIT_AUDIO) returned {}", error);
+    return false;
+  }
+
+  std::atexit([]() { SDL_QuitSubSystem(SDL_INIT_AUDIO); });
+
+  initialized = true;
+  return true;
+}
+
+SDLAudioStream::SDLAudioStream(u32 sample_rate, u32 channels, u32 buffer_ms, AudioStretchMode stretch)
+  : AudioStream(sample_rate, channels, buffer_ms, stretch)
+{
+}
+
+SDLAudioStream::~SDLAudioStream()
+{
+  if (IsOpen())
+    SDLAudioStream::CloseDevice();
+}
+
+std::unique_ptr<AudioStream> AudioStream::CreateSDLAudioStream(u32 sample_rate, u32 channels, u32 buffer_ms,
+                                                               u32 latency_ms, AudioStretchMode stretch)
+{
+  if (!InitializeSDLAudio())
+    return {};
+
+  std::unique_ptr<SDLAudioStream> stream = std::make_unique<SDLAudioStream>(sample_rate, channels, buffer_ms, stretch);
+  if (!stream->OpenDevice(latency_ms))
+    stream.reset();
+
+  return stream;
+}
+
+bool SDLAudioStream::OpenDevice(u32 latency_ms)
+{
+  DebugAssert(!IsOpen());
+
+  SDL_AudioSpec spec = {};
+  spec.freq = m_sample_rate;
+  spec.channels = static_cast<Uint8>(m_channels);
+  spec.format = AUDIO_S16;
+  spec.samples = static_cast<Uint16>(GetBufferSizeForMS(m_sample_rate, (latency_ms == 0) ? m_buffer_ms : latency_ms));
+  spec.callback = AudioCallback;
+  spec.userdata = static_cast<void*>(this);
+
+  SDL_AudioSpec obtained_spec = {};
+  m_device_id = SDL_OpenAudioDevice(nullptr, 0, &spec, &obtained_spec, SDL_AUDIO_ALLOW_SAMPLES_CHANGE);
+  if (m_device_id == 0)
+  {
+    Log_ErrorFmt("SDL_OpenAudioDevice() failed: {}", SDL_GetError());
+    return false;
+  }
+
+  Log_DevFmt("Requested {} frame buffer, got {} frame buffer", spec.samples, obtained_spec.samples);
+
+  BaseInitialize();
+  m_volume = 100;
+  m_paused = false;
+  SDL_PauseAudioDevice(m_device_id, 0);
+
+  return true;
+}
+
+void SDLAudioStream::SetPaused(bool paused)
+{
+  if (m_paused == paused)
+    return;
+
+  SDL_PauseAudioDevice(m_device_id, paused ? 1 : 0);
+  m_paused = paused;
+}
+
+void SDLAudioStream::CloseDevice()
+{
+  SDL_CloseAudioDevice(m_device_id);
+  m_device_id = 0;
+}
+
+void SDLAudioStream::AudioCallback(void* userdata, uint8_t* stream, int len)
+{
+  SDLAudioStream* const this_ptr = static_cast<SDLAudioStream*>(userdata);
+  const u32 num_frames = len / sizeof(SampleType) / this_ptr->m_channels;
+
+  this_ptr->ReadFrames(reinterpret_cast<SampleType*>(stream), num_frames);
+  this_ptr->ApplyVolume(reinterpret_cast<SampleType*>(stream), num_frames);
+}
+
+void SDLAudioStream::SetOutputVolume(u32 volume)
+{
+  m_volume = volume;
+}

src/util/util.vcxproj

@@ -203,6 +203,7 @@
     <ClCompile Include="postprocessing_shader.cpp" />
     <ClCompile Include="postprocessing_shader_fx.cpp" />
     <ClCompile Include="postprocessing_shader_glsl.cpp" />
+    <ClCompile Include="sdl_audio_stream.cpp" />
     <ClCompile Include="sdl_input_source.cpp" />
     <ClCompile Include="shadergen.cpp" />
     <ClCompile Include="shiftjis.cpp" />

src/util/util.vcxproj.filters

@@ -156,6 +156,7 @@
     <ClCompile Include="opengl_context_egl_x11.cpp" />
     <ClCompile Include="opengl_context_wgl.cpp" />
     <ClCompile Include="image.cpp" />
+    <ClCompile Include="sdl_audio_stream.cpp" />
   </ItemGroup>
   <ItemGroup>
     <None Include="metal_shaders.metal" />