From 75d446c272063f51e0218b504f02edafaf29c995 Mon Sep 17 00:00:00 2001
From: Nik Henson <nik-m3@diablo-designs.co.uk>
Date: Mon, 12 Sep 2011 21:03:16 +0000
Subject: [PATCH] Changes to Audio.cpp: - audio buffer is now kept as full as
 possible with new audio buffering method rather than just half full like
 before (this is okay now that buffer overruns have been eliminated) - altered
 minimum size of audio buffer so that audio still works with a zero latency
 setting (obviously there will still be some latency)

---
 Src/OSD/SDL/Audio.cpp | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/Src/OSD/SDL/Audio.cpp b/Src/OSD/SDL/Audio.cpp
index e7e6f45..42b9bd5 100755
--- a/Src/OSD/SDL/Audio.cpp
+++ b/Src/OSD/SDL/Audio.cpp
@@ -38,8 +38,8 @@ static bool writeWrapped = false;   // True if write position has wrapped around
 static unsigned underRuns = 0;      // Number of buffer under-runs that have occured
 static unsigned overRuns = 0;       // Number of buffer over-runs that have occured
 
-static AudioCallbackFPtr callback = NULL;
-static void *callbackData = NULL;
+static AudioCallbackFPtr callback = NULL; // Pointer to audio callback that is called when audio buffer is less than half empty
+static void *callbackData = NULL;         // Pointer to data to be passed to audio callback when it is called
 
 void SetAudioCallback(AudioCallbackFPtr newCallback, void *newData)
 {
@@ -147,8 +147,8 @@ static void PlayCallback(void *data, Uint8 *stream, int len)
 	// Move play position forward for next time
 	playPos += len;
 
-	bool halfEmpty = adjWritePos + audioBufferSize / 2 - BYTES_PER_FRAME / 2 < playPos + audioBufferSize;
-	
+	bool bufferFull = adjWritePos + 2 * BYTES_PER_FRAME > playPos + audioBufferSize;
+
 	// Check if play position has moved past end of buffer
 	if (playPos >= audioBufferSize)
 	{
@@ -157,8 +157,8 @@ static void PlayCallback(void *data, Uint8 *stream, int len)
 		writeWrapped = false;
 	}
 
-	// If buffer is more than half empty then call callback
-	if (callback && halfEmpty)
+	// If buffer is not full then call audio callback
+	if (callback && !bufferFull)
 		callback(callbackData);
 }
 
@@ -228,8 +228,8 @@ bool OpenAudio()
 
 	// Create audio buffer
 	audioBufferSize = SAMPLE_RATE * BYTES_PER_SAMPLE * latency / MAX_LATENCY;
-	int roundBuffer = 2 * playSamples;
-	audioBufferSize = max<int>(roundBuffer, (audioBufferSize / roundBuffer) * roundBuffer);
+	int minBufferSize = 3 * BYTES_PER_FRAME;
+	audioBufferSize = max<int>(minBufferSize, audioBufferSize);
 	audioBuffer = new(std::nothrow) INT8[audioBufferSize];
 	if (audioBuffer == NULL)
 	{
@@ -240,7 +240,7 @@ bool OpenAudio()
 	
 	// Set initial play position to be beginning of buffer and initial write position to be half-way into buffer
 	playPos = 0;
-	writePos = (BYTES_PER_FRAME + audioBufferSize) / 2;
+	writePos = min<int>(audioBufferSize - BYTES_PER_FRAME, (BYTES_PER_FRAME + audioBufferSize) / 2);
 	writeWrapped = false;
 
 	// Reset counters
@@ -257,8 +257,6 @@ bool OutputAudio(unsigned numSamples, INT16 *leftBuffer, INT16 *rightBuffer)
 	//printf("OutputAudio(%u) [writePos = %u, writeWrapped = %s, playPos = %u, audioBufferSize = %u]\n",
 	//	numSamples, writePos, (writeWrapped ? "true" : "false"), playPos, audioBufferSize);
 
-	bool halfFull = false;
-
 	UINT32 bytesRemaining;
 	UINT32 bytesToCopy;
 	INT16 *src;
@@ -323,8 +321,7 @@ bool OutputAudio(unsigned numSamples, INT16 *leftBuffer, INT16 *rightBuffer)
 	// Check if write position has caught up with play region and now overlaps it (ie buffer over-run)
 	bool overRun = writePos + numBytes > playPos + audioBufferSize;
 	
-	if (writePos + audioBufferSize / 2 + BYTES_PER_FRAME / 2 > playPos + audioBufferSize)
-		halfFull = true;
+	bool bufferFull = writePos + 2 * BYTES_PER_FRAME > playPos + audioBufferSize;
 
 	// Move write position back to within buffer
 	if (writePos >= audioBufferSize)
@@ -338,7 +335,7 @@ bool OutputAudio(unsigned numSamples, INT16 *leftBuffer, INT16 *rightBuffer)
 		//printf("Audio buffer over-run #%u in OutputAudio(%u) [writePos = %u, writeWrapped = %s, playPos = %u, audioBufferSize = %u, numBytes = %u]\n",
 		//	overRuns, numSamples, writePos, (writeWrapped ? "true" : "false"), playPos, audioBufferSize, numBytes);
 		
-		halfFull = true;
+		bufferFull = true;
 
 		// Discard current chunk of data
 		goto Finish;
@@ -400,7 +397,7 @@ Finish:
 	SDL_UnlockAudio();
 
 	// Return whether buffer is half full
-	return halfFull;
+	return bufferFull;
 }
 
 void CloseAudio()