SCI32: Fix bad interpolation of Robot audio samples

Previously, this code was interpolating samples if the previous
block had missing samples, instead of interpolating when samples
are missing in the upcoming block of samples.

1 files changed, 28 insertions, 33 deletions

diff --git a/engines/sci/video/robot_decoder.cpp b/engines/sci/video/robot_decoder.cpp
index d052929eeb..ba8a4683dd 100644
--- a/engines/sci/video/robot_decoder.cpp
+++ b/engines/sci/video/robot_decoder.cpp
@@ -65,36 +65,30 @@ static void interpolateChannel(int16 *buffer, int32 numSamples, const int8 buffe
 		return;
 	}
 
+	int16 *inBuffer, *outBuffer;
+	int16 sample, previousSample;
+
 	if (bufferIndex) {
-		int16 lastSample = *buffer;
-		int sample = lastSample;
-		int16 *target = buffer + 1;
-		const int16 *source = buffer + 2;
+		outBuffer = buffer + 1;
+		inBuffer = buffer + 2;
+		previousSample = sample = *buffer;
 		--numSamples;
+	} else {
+		outBuffer = buffer;
+		inBuffer = buffer + 1;
+		previousSample = sample = *inBuffer;
+	}
 
-		while (numSamples--) {
-			sample = *source + lastSample;
-			lastSample = *source;
-			sample /= 2;
-			*target = sample;
-			source += 2;
-			target += 2;
-		}
+	while (numSamples--) {
+		sample = (*inBuffer + previousSample) >> 1;
+		previousSample = *inBuffer;
+		*outBuffer = sample;
+		inBuffer += RobotAudioStream::kEOSExpansion;
+		outBuffer += RobotAudioStream::kEOSExpansion;
+	}
 
-		*target = sample;
-	} else {
-		int16 *target = buffer;
-		const int16 *source = buffer + 1;
-		int16 lastSample = *source;
-
-		while (numSamples--) {
-			int sample = *source + lastSample;
-			lastSample = *source;
-			sample /= 2;
-			*target = sample;
-			source += 2;
-			target += 2;
-		}
+	if (bufferIndex) {
+		*outBuffer = sample;
 	}
 }
 
@@ -254,9 +248,10 @@ void RobotAudioStream::fillRobotBuffer(const RobotAudioPacket &packet, const int
 void RobotAudioStream::interpolateMissingSamples(int32 numSamples) {
 	int32 numBytes = numSamples * (sizeof(int16) + kEOSExpansion);
 	int32 targetPosition = _readHead;
+	const int32 nextReadHeadPosition = _readHeadAbs + numBytes;
 
-	if (_readHeadAbs > _jointMin[1]) {
-		if (_readHeadAbs > _jointMin[0]) {
+	if (nextReadHeadPosition > _jointMin[1]) {
+		if (nextReadHeadPosition > _jointMin[0]) {
 			if (targetPosition + numBytes >= _loopBufferSize) {
 				const int32 numBytesToEdge = (_loopBufferSize - targetPosition);
 				memset(_loopBuffer + targetPosition, 0, numBytesToEdge);
@@ -264,8 +259,8 @@ void RobotAudioStream::interpolateMissingSamples(int32 numSamples) {
 				targetPosition = 0;
 			}
 			memset(_loopBuffer + targetPosition, 0, numBytes);
-			_jointMin[0] += numBytes;
-			_jointMin[1] += numBytes;
+			_jointMin[0] = nextReadHeadPosition;
+			_jointMin[1] = nextReadHeadPosition + sizeof(int16);
 		} else {
 			if (targetPosition + numBytes >= _loopBufferSize) {
 				const int32 numSamplesToEdge = (_loopBufferSize - targetPosition) / (sizeof(int16) + kEOSExpansion);
@@ -274,9 +269,9 @@ void RobotAudioStream::interpolateMissingSamples(int32 numSamples) {
 				targetPosition = 0;
 			}
 			interpolateChannel((int16 *)(_loopBuffer + targetPosition), numSamples, 1);
-			_jointMin[1] += numBytes;
+			_jointMin[1] = nextReadHeadPosition + sizeof(int16);
 		}
-	} else if (_readHeadAbs > _jointMin[0]) {
+	} else if (nextReadHeadPosition > _jointMin[0]) {
 		if (targetPosition + numBytes >= _loopBufferSize) {
 			const int32 numSamplesToEdge = (_loopBufferSize - targetPosition) / (sizeof(int16) + kEOSExpansion);
 			interpolateChannel((int16 *)(_loopBuffer + targetPosition), numSamplesToEdge, 0);
@@ -284,7 +279,7 @@ void RobotAudioStream::interpolateMissingSamples(int32 numSamples) {
 			targetPosition = 2;
 		}
 		interpolateChannel((int16 *)(_loopBuffer + targetPosition), numSamples, 0);
-		_jointMin[0] += numBytes;
+		_jointMin[0] = nextReadHeadPosition;
 	}
 }