Since updateAndOutput2() is the only function that sets up wave forms and

stuff, it pretty much has to be our "set instrument" function. Also, while I'm
not entirely sure of the implications, "unk23" is the Algorithm bit for the
Feedback / Algorithm register, so I've renamed it "algorithm".

svn-id: r21197

1 files changed, 31 insertions, 21 deletions

diff --git a/engines/kyra/sound_adlib.cpp b/engines/kyra/sound_adlib.cpp
index dda58f9353..767d4330a6 100644
--- a/engines/kyra/sound_adlib.cpp
+++ b/engines/kyra/sound_adlib.cpp
@@ -127,7 +127,7 @@ private:
 		uint8 unk24;
 		uint8 unk25;
 		uint8 unk28;
-		uint8 unk23;
+		uint8 algorithm;
 		uint8 unk39;	
 		uint8 unk40;
 		uint8 unk3;
@@ -157,7 +157,7 @@ private:
 	void update1(uint8 unk1, OutputState &state);
 
 	void updateAndOutput1(uint8 rawNote, OutputState &state, bool flag = false);
-	void updateAndOutput2(uint8 unk1, uint8 *dataptr, OutputState &state);
+	void setInstrument(uint8 regOffset, uint8 *dataptr, OutputState &state);
 	void updateAndOutput3(OutputState &state);
 
 	void adjustVolume(OutputState &state);
@@ -771,38 +771,48 @@ void AdlibDriver::updateAndOutput1(uint8 rawNote, OutputState &state, bool flag)
 	writeOPL(0xB0 + _curTable, state.regBx);
 }
 
-void AdlibDriver::updateAndOutput2(uint8 unk1, uint8 *dataptr, OutputState &state) {
-	debugC(9, kDebugLevelSound, "updateAndOutput2(%d, %p, %d)", unk1, (const void *)dataptr, &state - _outputTables);
+void AdlibDriver::setInstrument(uint8 regOffset, uint8 *dataptr, OutputState &state) {
+	debugC(9, kDebugLevelSound, "setInstrument(%d, %p, %d)", regOffset, (const void *)dataptr, &state - _outputTables);
 	// Amplitude Modulation / Vibrato / Envelope Generator Type /
 	// Keyboard Scaling Rate / Modulator Frequency Multiple
-	writeOPL(0x20 + unk1, *dataptr++);
-	writeOPL(0x23 + unk1, *dataptr++);
+	writeOPL(0x20 + regOffset, *dataptr++);
+	writeOPL(0x23 + regOffset, *dataptr++);
 
 	uint8 temp = *dataptr++;
 
 	// Feedback / Algorithm
+
+	// It is very likely that _curTable really does refer to the same
+	// channel as regOffset, but there's only one Cx register per channel.
+
 	writeOPL(0xC0 + _curTable, temp);
 
-	state.unk23 = temp & 1;
+	// The algorithm bit. I don't pretend to understand this fully, but
+	// "If set to 0, operator 1 modulates operator 2. In this case,
+	// operator 2 is the only one producing sound. If set to 1, both
+	// operators produce sound directly. Complex sounds are more easily
+	// created if the algorithm is set to 0."
+
+	state.algorithm = temp & 1;
 
 	// Waveform Select
-	writeOPL(0xE0 + unk1, *dataptr++);
-	writeOPL(0xE3 + unk1, *dataptr++);
+	writeOPL(0xE0 + regOffset, *dataptr++);
+	writeOPL(0xE3 + regOffset, *dataptr++);
 
 	state.unk24 = *dataptr++;
 	state.unk25 = *dataptr++;
 
 	// Level Key Scaling / Total Level
-	writeOPL(0x40 + unk1, calculateLowByte1(state));
-	writeOPL(0x43 + unk1, calculateLowByte2(state));
+	writeOPL(0x40 + regOffset, calculateLowByte1(state));
+	writeOPL(0x43 + regOffset, calculateLowByte2(state));
 
 	// Attack Rate / Decay Rate
-	writeOPL(0x60 + unk1, *dataptr++);
-	writeOPL(0x63 + unk1, *dataptr++);
+	writeOPL(0x60 + regOffset, *dataptr++);
+	writeOPL(0x63 + regOffset, *dataptr++);
 
 	// Sustain Level / Release Rate
-	writeOPL(0x80 + unk1, *dataptr++);
-	writeOPL(0x83 + unk1, *dataptr++);
+	writeOPL(0x80 + regOffset, *dataptr++);
+	writeOPL(0x83 + regOffset, *dataptr++);
 }
 
 void AdlibDriver::updateAndOutput3(OutputState &state) {
@@ -825,7 +835,7 @@ void AdlibDriver::adjustVolume(OutputState &state) {
 
 	// Level Key Scaling / Total Level
 	writeOPL(0x43 + _outputTable[_curTable], lowByte);
-	if (state.unk23) {
+	if (state.algorithm) {
 		lowByte = calculateLowByte1(state);
 
 		// Level Key Scaling / Total Level
@@ -916,7 +926,7 @@ void AdlibDriver::stateCallback2_1(OutputState &state) {
 
 uint8 AdlibDriver::calculateLowByte1(OutputState &state) {
 	int8 value = state.unk24 & 0x3F;
-	if (state.unk23) {
+	if (state.algorithm) {
 		value += state.unk26;
 		value += state.unk27;
 		value += state.unk28;
@@ -1077,7 +1087,7 @@ int AdlibDriver::updateCallback16(uint8 *&dataptr, OutputState &state, uint8 val
 int AdlibDriver::updateCallback17(uint8 *&dataptr, OutputState &state, uint8 value) {
 	uint8 *ptr = _soundData;
 	ptr += READ_LE_UINT16(_soundData + (value << 1) + 0x1F4);
-	updateAndOutput2(_unkOutputByte1, ptr, state);
+	setInstrument(_unkOutputByte1, ptr, state);
 	return 0;
 }
 
@@ -1353,7 +1363,7 @@ int AdlibDriver::updateCallback48(uint8 *&dataptr, OutputState &state, uint8 val
 	_unkOutputByte1 = _outputTable[6];
 
 	_unkValue6 = *(ptr + 6);
-	updateAndOutput2(_unkOutputByte1, ptr, state);
+	setInstrument(_unkOutputByte1, ptr, state);
 
 	entry = *dataptr++ << 1;
 	ptr = _soundData + READ_LE_UINT16(_soundData + entry + 0x1F4);
@@ -1363,7 +1373,7 @@ int AdlibDriver::updateCallback48(uint8 *&dataptr, OutputState &state, uint8 val
 
 	_unkValue7 = entry = *(ptr + 5);
 	_unkValue8 = entry = *(ptr + 6);
-	updateAndOutput2(_unkOutputByte1, ptr, state);
+	setInstrument(_unkOutputByte1, ptr, state);
 
 	entry = *dataptr++ << 1;
 	ptr = _soundData + READ_LE_UINT16(_soundData + entry + 0x1F4);
@@ -1373,7 +1383,7 @@ int AdlibDriver::updateCallback48(uint8 *&dataptr, OutputState &state, uint8 val
 
 	_unkValue9 = entry = *(ptr + 5);
 	_unkValue10 = entry = *(ptr + 6);
-	updateAndOutput2(_unkOutputByte1, ptr, state);
+	setInstrument(_unkOutputByte1, ptr, state);
 
 	// Octave / F-Number / Key-On for channels 6, 7 and 8