1 files changed, 121 insertions, 6 deletions

diff --git a/backends/platform/sdl/sdl.cpp b/backends/platform/sdl/sdl.cpp
index 290fe63663..76ac91c282 100644
--- a/backends/platform/sdl/sdl.cpp
+++ b/backends/platform/sdl/sdl.cpp
@@ -191,7 +191,7 @@ OSystem_SDL::OSystem_SDL()
 
 OSystem_SDL::~OSystem_SDL() {
 	SDL_RemoveTimer(_timerID);
-	SDL_CloseAudio();
+	closeMixer();
 
 	free(_dirtyChecksums);
 	free(_currentPalette);
@@ -199,7 +199,6 @@ OSystem_SDL::~OSystem_SDL() {
 	free(_mouseData);
 
 	delete _savefile;
-	delete _mixer;
 	delete _timer;
 }
 
@@ -306,7 +305,7 @@ void OSystem_SDL::quit() {
 	SDL_ShowCursor(SDL_ENABLE);
 
 	SDL_RemoveTimer(_timerID);
-	SDL_CloseAudio();
+	closeMixer();
 
 	free(_dirtyChecksums);
 	free(_currentPalette);
@@ -314,7 +313,6 @@ void OSystem_SDL::quit() {
 	free(_mouseData);
 
 	delete _savefile;
-	delete _mixer;
 	delete _timer;
 
 	SDL_Quit();
@@ -389,14 +387,110 @@ void OSystem_SDL::deleteMutex(MutexRef mutex) {
 #pragma mark --- Audio ---
 #pragma mark -
 
+#ifdef MIXER_DOUBLE_BUFFERING
+
+void OSystem_SDL::mixerProducerThread() {
+	byte nextSoundBuffer;
+
+	SDL_LockMutex(_soundMutex);
+	while (true) {
+		// Wait till we are allowed to produce data
+		SDL_CondWait(_soundCond, _soundMutex);
+
+		if (_soundThreadShouldQuit)
+			break;
+
+		// Generate samples and put them into the next buffer
+		nextSoundBuffer = _activeSoundBuf ^ 1;
+		_mixer->mixCallback(_soundBuffers[nextSoundBuffer], _soundBufSize);
+		
+		// Swap buffers
+		_activeSoundBuf = nextSoundBuffer;
+	}
+	SDL_UnlockMutex(_soundMutex);
+}
+
+int SDLCALL OSystem_SDL::mixerProducerThreadEntry(void *arg) {
+	OSystem_SDL *this_ = (OSystem_SDL *)arg;
+	assert(this_);
+	this_->mixerProducerThread();
+	return 0;
+}
+
+
+void OSystem_SDL::initThreadedMixer(Audio::MixerImpl *mixer, uint bufSize) {
+	_soundThreadIsRunning = false;
+	_soundThreadShouldQuit = false;
+
+	// Create mutex and condition variable
+	_soundMutex = SDL_CreateMutex();
+	_soundCond = SDL_CreateCond();
+
+	// Create two sound buffers
+	_activeSoundBuf = 0;
+	_soundBufSize = bufSize;
+	_soundBuffers[0] = (byte *)calloc(1, bufSize);
+	_soundBuffers[1] = (byte *)calloc(1, bufSize);
+
+	_soundThreadIsRunning = true;
+
+	// Finally start the thread
+	_soundThread = SDL_CreateThread(mixerProducerThreadEntry, this);
+}
+
+void OSystem_SDL::deinitThreadedMixer() {
+	// Kill thread?? _soundThread
+
+	if (_soundThreadIsRunning) {
+		// Signal the producer thread to end, and wait for it to actually finish.
+		_soundThreadShouldQuit = true;
+		SDL_CondBroadcast(_soundCond);
+		SDL_WaitThread(_soundThread, NULL);
+
+		// Kill the mutex & cond variables. 
+		// Attention: AT this point, the mixer callback must not be running
+		// anymore, else we will crash!
+		SDL_DestroyMutex(_soundMutex);
+		SDL_DestroyCond(_soundCond);
+
+		_soundThreadIsRunning = false;
+
+		free(_soundBuffers[0]);
+		free(_soundBuffers[1]);
+	}
+}
+
+
+void OSystem_SDL::mixCallback(void *arg, byte *samples, int len) {
+	OSystem_SDL *this_ = (OSystem_SDL *)arg;
+	assert(this_);
+	assert(this_->_mixer);
+
+	assert((int)this_->_soundBufSize == len);
+
+	// Lock mutex, to ensure our data is not overwritten by the producer thread
+	SDL_LockMutex(this_->_soundMutex);
+	
+	// Copy data from the current sound buffer
+	memcpy(samples, this_->_soundBuffers[this_->_activeSoundBuf], len);
+	
+	// Unlock mutex and wake up the produced thread
+	SDL_UnlockMutex(this_->_soundMutex);
+	SDL_CondSignal(this_->_soundCond);
+}
+
+#else
+
 void OSystem_SDL::mixCallback(void *sys, byte *samples, int len) {
 	OSystem_SDL *this_ = (OSystem_SDL *)sys;
 	assert(this_);
+	assert(this_->_mixer);
 
-	if (this_->_mixer)
-		this_->_mixer->mixCallback(samples, len);
+	this_->_mixer->mixCallback(samples, len);
 }
 
+#endif
+
 void OSystem_SDL::setupMixer() {
 	SDL_AudioSpec desired;
 	SDL_AudioSpec obtained;
@@ -443,10 +537,31 @@ void OSystem_SDL::setupMixer() {
 		// Tell the mixer that we are ready and start the sound processing
 		_mixer->setOutputRate(_samplesPerSec);
 		_mixer->setReady(true);
+
+#ifdef MIXER_DOUBLE_BUFFERING
+		initThreadedMixer(_mixer, obtained.samples * 4);
+#endif
+
+		// start the sound system
 		SDL_PauseAudio(0);
 	}
 }
 
+void OSystem_SDL::closeMixer() {
+	if (_mixer)
+		_mixer->setReady(false);
+
+	SDL_CloseAudio();
+
+	delete _mixer;
+	_mixer = 0;
+
+#ifdef MIXER_DOUBLE_BUFFERING
+	deinitThreadedMixer();
+#endif
+
+}
+
 Audio::Mixer *OSystem_SDL::getMixer() {
 	assert(_mixer);
 	return _mixer;