1) make sure AW does not fill the DS buffer, as semantics are unclear

2) process audio sooner, rather than a frame later
3) only 1 SDL buffer control (its size)
4) DS: Lock-Unlock probably reset the write cursor (in Windows)
5) DS: AW does not like DS buffer to be empty (or full??) at the begin

source/Speaker.cpp

@@ -569,8 +569,8 @@ static ULONG Spkr_SubmitWaveBuffer_FullSpeed(short* pSpeakerBuffer, ULONG nNumSa
 	UINT nBytesFree = g_dwDSSpkrBufferSize - nBytesRemaining;	// Calc free buffer space
 	ULONG nNumSamplesToUse = nNumSamples + nNumPadSamples;
 
-	if(nNumSamplesToUse * sizeof(short) > nBytesFree)
+	if(nNumSamplesToUse * sizeof(short) >= nBytesFree)
-		nNumSamplesToUse = nBytesFree / sizeof(short);
+		nNumSamplesToUse = nBytesFree / sizeof(short) - 1;
 
 	//
 
@@ -766,8 +766,8 @@ static ULONG Spkr_SubmitWaveBuffer(short* pSpeakerBuffer, ULONG nNumSamples)
 	UINT nBytesFree = g_dwDSSpkrBufferSize - nBytesRemaining;	// Calc free buffer space
 	ULONG nNumSamplesToUse = nNumSamples;
 
-	if(nNumSamplesToUse * sizeof(short) > nBytesFree)
+	if(nNumSamplesToUse * sizeof(short) >= nBytesFree)
-		nNumSamplesToUse = nBytesFree / sizeof(short);
+		nNumSamplesToUse = nBytesFree / sizeof(short) - 1;
 
 	if(bBufferError)
 		pSpeakerBuffer = &pSpeakerBuffer[nNumSamples - nNumSamplesToUse];

source/frontends/sdl/imgui/sdlsettings.cpp

@@ -500,22 +500,16 @@ namespace sa2
 
           ImGui::Separator();
 
-          int trigger;
+          int size;
-          int target;
+          getAudioBufferSize(size);
-          getAudioBufferSizes(trigger, target);
+          if (ImGui::SliderInt("Buffer size", &size, 0, 1000, "%d ms"))
-          if (ImGui::SliderInt("Trigger", &trigger, 0, 1000, "%d ms"))
           {
-            target = std::max(trigger, target);
+            setAudioBufferSize(size);
           }
-          if (ImGui::SliderInt("Target", &target, 0, 1000, "%d ms"))
-          {
-            trigger = std::min(trigger, target);
-          }
-          setAudioBufferSizes(trigger, target);
 
           ImGui::Separator();
 
-          if (ImGui::BeginTable("Devices", 5, ImGuiTableFlags_RowBg))
+          if (ImGui::BeginTable("Devices", 6, ImGuiTableFlags_RowBg))
           {
             myAudioInfo = getAudioInfo();
             ImGui::TableSetupColumn("Running");
@@ -523,6 +517,7 @@ namespace sa2
             ImGui::TableSetupColumn("Volume");
             ImGui::TableSetupColumn("Direct");
             ImGui::TableSetupColumn("SDL");
+            ImGui::TableSetupColumn("Total");
             ImGui::TableHeadersRow();
 
             ImGui::PushItemFlag(ImGuiItemFlags_Disabled, true); // this requires imgui_internal.h
@@ -538,6 +533,9 @@ namespace sa2
               ImGui::SliderFloat("", &device.buffer, 0.0f, device.size, "%.3f");
               ImGui::TableNextColumn();
               ImGui::SliderFloat("", &device.queue, 0.0f, device.size, "%.3f");
+              ImGui::TableNextColumn();
+              float total = device.buffer + device.queue;
+              ImGui::SliderFloat("", &total, 0.0f, 2 * device.size, "%.3f");
             }
             ImGui::PushItemFlag(ImGuiItemFlags_Disabled, false);
 

source/frontends/sdl/main.cpp

@@ -140,13 +140,13 @@ void run_sdl(int argc, const char * argv [])
       frameTimer.tic();
 
       eventTimer.tic();
-      sa2::writeAudio();
       processEventsUthernet2(5);
       frame->ProcessEvents(quit);
       eventTimer.toc();
 
       cpuTimer.tic();
       frame->ExecuteOneFrame(oneFrame);
+      sa2::writeAudio();
       cpuTimer.toc();
 
       if (!options.headless)

source/frontends/sdl/sdirectsound.cpp

@@ -24,8 +24,7 @@ namespace
     void printInfo() const;
     sa2::SoundInfo getInfo() const;
 
-    static int ourTrigger;
+    static int ourBufferSize;
-    static int ourTarget;
 
   private:
     IDirectSoundBuffer * myBuffer;
@@ -45,8 +44,7 @@ namespace
     void mixBuffer(const void * ptr, const size_t size);
   };
 
-  int DirectSoundGenerator::ourTrigger = 200;
+  int DirectSoundGenerator::ourBufferSize = 200;
-  int DirectSoundGenerator::ourTarget = 200;
 
   std::unordered_map<IDirectSoundBuffer *, std::shared_ptr<DirectSoundGenerator>> activeSoundGenerators;
 
@@ -141,7 +139,7 @@ namespace
       const float coeff = 1.0 / myBytesPerSecond;
       info.buffer = bytesInBuffer * coeff;
       info.queue = bytesInQueue * coeff;
-      info.size = myBuffer->bufferSize * coeff;
+      info.size = std::max(myBuffer->bufferSize * coeff, float(ourBufferSize / 1000.0));
     }
 
     return info;
@@ -186,13 +184,12 @@ namespace
     // and we loose sync
 
     const int queued = SDL_GetQueuedAudioSize(myAudioDevice);
-    const int trigger = myBytesPerSecond * DirectSoundGenerator::ourTrigger / 1000;
+    const int bufferSize = myBytesPerSecond * DirectSoundGenerator::ourBufferSize / 1000;
 
-    if (queued < trigger)  // trigger is already <= target
+    if (queued < bufferSize)  // trigger is already <= target
     {
-      const int target = myBytesPerSecond * DirectSoundGenerator::ourTarget / 1000;
       // make sure we only copy full frames
-      const int bytesToCopy = ((target - queued) / myBytesPerUnit) * myBytesPerUnit;
+      const int bytesToCopy = ((bufferSize - queued) / myBytesPerUnit) * myBytesPerUnit;
 
       LPVOID lpvAudioPtr1, lpvAudioPtr2;
       DWORD dwAudioBytes1, dwAudioBytes2;
@@ -272,16 +269,14 @@ namespace sa2
     return info;
   }
 
-  void getAudioBufferSizes(int & trigger, int & target)
+  void getAudioBufferSize(int & size)
   {
-    trigger = DirectSoundGenerator::ourTrigger;
+    size = DirectSoundGenerator::ourBufferSize;
-    target = DirectSoundGenerator::ourTarget;
   }
 
-  void setAudioBufferSizes(const int trigger, const int target)
+  void setAudioBufferSize(const int size)
   {
-    DirectSoundGenerator::ourTrigger = std::min(trigger, target);
+    DirectSoundGenerator::ourBufferSize = size;
-    DirectSoundGenerator::ourTarget = target;
   }
 
 }

source/frontends/sdl/sdirectsound.h

@@ -23,6 +23,6 @@ namespace sa2
   void printAudioInfo();
   std::vector<SoundInfo> getAudioInfo();
 
-  void getAudioBufferSizes(int & trigger, int & target);
+  void getAudioBufferSize(int & size);
-  void setAudioBufferSizes(const int trigger, const int target);
+  void setAudioBufferSize(const int size);
 }

source/linux/windows/dsound.cpp

@@ -97,6 +97,7 @@ HRESULT IDirectSoundBuffer::Lock( DWORD dwWriteCursor, DWORD dwWriteBytes, LPVOI
   }
   else
   {
+    myWritePosition = dwWriteCursor;
     const DWORD availableInFirstPart = this->mySoundBuffer.size() - dwWriteCursor;
 
     *lplpvAudioPtr1 = this->mySoundBuffer.data() + dwWriteCursor;

source/linux/windows/dsound.h

@@ -78,8 +78,8 @@ class IDirectSoundBuffer : public IUnknown
   const std::unique_ptr<IDirectSoundNotify> mySoundNotify;
   std::vector<char> mySoundBuffer;
 
-  size_t myPlayPosition = 0;
+  size_t myPlayPosition  = 0x0000;
-  size_t myWritePosition = 0;
+  size_t myWritePosition = 0x0100;
   WORD myStatus = 0;
   LONG myVolume = DSBVOLUME_MAX;