[Scummvm-git-logs] scummvm master -> d725cae79eb47300b07ae509f7e11c4b0002e3c3

[eriktorbjorn]

This automated email contains information about 1 new commit which have been
pushed to the 'scummvm' repo located at https://github.com/scummvm/scummvm .

Summary:
d725cae79e SCUMM: Fix audio distortion in Loom for PC-Engine


Commit: d725cae79eb47300b07ae509f7e11c4b0002e3c3
    https://github.com/scummvm/scummvm/commit/d725cae79eb47300b07ae509f7e11c4b0002e3c3
Author: Torbjörn Andersson (eriktorbjorn at users.sourceforge.net)
Date: 2021-01-29T14:42:17+01:00

Commit Message:
SCUMM: Fix audio distortion in Loom for PC-Engine

There are two buffers when generating audio. The output buffer that
readBuffer() fills, and the sample buffer where new samples are
generated. The sample buffer is the larger of the two.

When readBuffer() is called, samples are copied from the sample buffer
to the output buffer. Usually it will copy some samples to the output
buffer, generate new ones to the sample buffer, and copy the remaining
ones needed to the output buffer.

At the end, the remaining samples in the sample buffer are moved to the
beginning of the buffer. It works out so that samples are always copied
from the beginning of the sample buffer to somewhere in the output
buffer.

But here's where things went wrong: If the sample buffer was not full,
but still contained enough samples to fill the output buffer, it would
still copy the last samples in the sample buffer. It should copy the
samples from right after the ones that had already been copied to the
output buffer.

I spent far too long beating my head against this bug, and I don't know
how well I've explained it here. But the audio corruption appears to be
gone now...

Foo

Changed paths:
    engines/scumm/players/player_pce.cpp


diff --git a/engines/scumm/players/player_pce.cpp b/engines/scumm/players/player_pce.cpp
index 31210025ca..8efa3c6510 100644
--- a/engines/scumm/players/player_pce.cpp
+++ b/engines/scumm/players/player_pce.cpp
@@ -511,6 +511,7 @@ void Player_PCE::updateSound() {
 int Player_PCE::readBuffer(int16 *buffer, const int numSamples) {
 	int sampleCopyCnt;
 	int samplesLeft = numSamples;
+	int16 *sampleBufferPtr = _sampleBuffer;
 
 	Common::StackLock lock(_mutex);
 
@@ -518,10 +519,11 @@ int Player_PCE::readBuffer(int16 *buffer, const int numSamples) {
 		// copy samples to output buffer
 		sampleCopyCnt = (samplesLeft < _sampleBufferCnt) ? samplesLeft : _sampleBufferCnt;
 		if (sampleCopyCnt > 0) {
-			memcpy(buffer, _sampleBuffer, sampleCopyCnt * sizeof(int16));
+			memcpy(buffer, sampleBufferPtr, sampleCopyCnt * sizeof(int16));
 			buffer += sampleCopyCnt;
 			samplesLeft -= sampleCopyCnt;
 			_sampleBufferCnt -= sampleCopyCnt;
+			sampleBufferPtr += sampleCopyCnt;
 		}
 
 		if (samplesLeft == 0)
@@ -531,12 +533,13 @@ int Player_PCE::readBuffer(int16 *buffer, const int numSamples) {
 		updateSound();
 		_psg->update(_sampleBuffer, _samplesPerPeriod / 2);
 		_sampleBufferCnt = _samplesPerPeriod;
+		sampleBufferPtr = _sampleBuffer;
 	}
 
 	// copy remaining samples to the front of the buffer
 	if (_sampleBufferCnt > 0) {
-		memmove(&_sampleBuffer[0],
-			&_sampleBuffer[_samplesPerPeriod - _sampleBufferCnt],
+		memmove(_sampleBuffer,
+			sampleBufferPtr,
 			_sampleBufferCnt * sizeof(int16));
 	}