fix waveout underruns cascading into decode underruns because the

decode buffer is smaller than the writeahead

stepmania/src/arch/Sound/RageSoundDriver_Generic_Software.cpp

@@ -8,8 +8,7 @@
 
 static const int channels = 2;
 static const int bytes_per_frame = channels*2; /* 16-bit */
-
-static const int frames_to_buffer = 4096;
+static int frames_to_buffer;
 
 static const int num_chunks = 8;
 static int chunksize() { return frames_to_buffer / num_chunks; }
@@ -18,7 +17,10 @@ RageSound_Generic_Software::sound::sound()
 {
 	snd = NULL;
 	state = STOPPED;
+}
 
+void RageSound_Generic_Software::sound::Init()
+{
 	/* Reserve enough blocks in the buffer to hold the buffer; plus some extra, since blocks
 	 * are partially read by Mix(); plus some more extra, since we can buffer one block
 	 * over frames_to_buffer (we buffer until filled >= frames_to_buffer). */
@@ -294,13 +296,26 @@ void RageSound_Generic_Software::StopMixing( RageSoundBase *snd )
 void RageSound_Generic_Software::StartDecodeThread()
 {
 	ASSERT( !m_DecodeThread.IsCreated() );
+
+	/* Initialize the sound buffers, now that frames_to_buffer is finalized. */
+	for( unsigned i = 0; i < ARRAYSIZE(sounds); ++i )
+		sounds[i].Init();
+
 	m_DecodeThread.Create( DecodeThread_start, this );
 }
 
+void RageSound_Generic_Software::SetDecodeBufferSize( int frames )
+{
+	ASSERT( !m_DecodeThread.IsCreated() );
+
+	frames_to_buffer = frames;
+}
+
 RageSound_Generic_Software::RageSound_Generic_Software()
 {
 	shutdown_decode_thread = false;
-
+	SetDecodeBufferSize( 4096 );
+	
 	m_DecodeThread.SetName("Decode thread");
 }
 

stepmania/src/arch/Sound/RageSoundDriver_Generic_Software.h

@@ -72,6 +72,7 @@ class RageSound_Generic_Software: public RageSoundDriver
 		} state;
 
 	    sound();
+		void Init();
 	};
 
 	/* List of currently playing sounds: XXX no vector */
@@ -89,6 +90,12 @@ protected:
 	/* Start the decoding.  This should be called once the hardware is set up and
 	 * GetSampleRate will return the correct value. */
 	void StartDecodeThread();
+
+	/* Call this before calling StartDecodeThread to set the desired decoding buffer
+	 * size.  This is the number of frames that Mix() will try to be able to return
+	 * at once.  This should generally be slightly larger than the sound writeahead,
+	 * to allow filling the buffer after an underrun.  The default is 4096 frames. */
+	void SetDecodeBufferSize( int frames );
 	
 	/* Override this to set the priority of the decoding thread, which should be above
 	 * normal priority but not realtime. */

stepmania/src/arch/Sound/RageSoundDriver_WaveOut.cpp

@@ -135,6 +135,9 @@ RageSound_WaveOut::RageSound_WaveOut()
 		buffers[b].dwFlags |= WHDR_DONE;
 	}
 
+	/* We have a very large writeahead; make sure we have a large enough decode
+	 * buffer to recover cleanly from underruns. */
+	SetDecodeBufferSize( buffersize_frames * 3/2 );
 	StartDecodeThread();
 
 	MixingThread.SetName("Mixer thread");