SCUMM: (iMuse/Amiga) - improve accuracy

This fixes the issue that some rhythm instruments didn't receive correct notes. The changes have been limited to the Amiga versions.

engines/scumm/imuse/imuse.cpp

@@ -45,6 +45,7 @@ namespace Scumm {
 IMuseInternal::IMuseInternal() :
 	_native_mt32(false),
 	_enable_gs(false),
+	_isAmiga(false),
 	_midi_adlib(NULL),
 	_midi_native(NULL),
 	_sysex(NULL),
@@ -481,6 +482,10 @@ uint32 IMuseInternal::property(int prop, uint32 value) {
 		}
 		break;
 
+	case IMuse::PROP_AMIGA:
+		_isAmiga = (value > 0);
+		break;
+
 	case IMuse::PROP_LIMIT_PLAYERS:
 		if (value > 0 && value <= ARRAYSIZE(_players))
 			_player_limit = (int)value;

engines/scumm/imuse/imuse.h

@@ -53,6 +53,7 @@ public:
 		PROP_TEMPO_BASE,
 		PROP_NATIVE_MT32,
 		PROP_GS,
+		PROP_AMIGA,
 		PROP_LIMIT_PLAYERS,
 		PROP_RECYCLE_PLAYERS,
 		PROP_GAME_ID,

engines/scumm/imuse/imuse_internal.h

@@ -372,6 +372,7 @@ struct Part : public Common::Serializable {
 
 private:
 	void sendPitchBend();
+	void sendTranspose();
 	void sendPanPosition(uint8 value);
 	void sendEffectLevel(uint8 value);
 };
@@ -399,6 +400,7 @@ class IMuseInternal : public IMuse {
 protected:
 	bool _native_mt32;
 	bool _enable_gs;
+	bool _isAmiga;
 	MidiDriver *_midi_adlib;
 	MidiDriver *_midi_native;
 	TimerCallbackInfo _timer_info_adlib;

engines/scumm/imuse/imuse_part.cpp

@@ -145,9 +145,18 @@ void Part::set_pan(int8 pan) {
 
 void Part::set_transpose(int8 transpose) {
 	_transpose = transpose;
+	
+	if (_se->_isAmiga) {
+		// The Amiga version does a check like this. While this is probably a bug (a signed int8 can never be 128),
+		// the playback depends on this being implemented exactly like in the original driver. I found this bug with
+		// the WinUAE debugger. I don't know whether this is an Amiga only thing...
+		_transpose_eff = /*(_transpose == 128) ? 0 : */transpose_clamp(_transpose + _player->getTranspose(), -12, 12);
+		sendTranspose();
+	} else {
 		_transpose_eff = (_transpose == -128) ? 0 : transpose_clamp(_transpose + _player->getTranspose(), -24, 24);
 		sendPitchBend();
 	}	
+}
 
 void Part::sustain(bool value) {
 	_pedal = value;
@@ -332,6 +341,7 @@ void Part::sendAll() {
 		return;
 
 	_mc->pitchBendFactor(_pitchbend_factor);
+	sendTranspose();
 	sendPitchBend();
 	_mc->volume(_vol_eff);
 	_mc->sustain(_pedal);
@@ -358,7 +368,24 @@ void Part::sendPitchBend() {
 	// so we'll do the scaling ourselves.
 	if (_player->_se->isNativeMT32())
 		bend = bend * _pitchbend_factor / 12;
-	_mc->pitchBend(clamp(bend + (_detune_eff * 64 / 12) + (_transpose_eff * 8192 / 12), -8192, 8191));
+	
+	// We send the transpose value separately for Amiga (which is more like the original handles this).
+	// Some rhythm instruments depend on this. 
+	int8 transpose = _se->_isAmiga ? 0 : _transpose_eff;
+	_mc->pitchBend(clamp(bend + (_detune_eff * 64 / 12) + (transpose * 8192 / 12), -8192, 8191));
+}
+
+void Part::sendTranspose() {
+	if (!_mc)
+		return;
+
+	// See comment above. The transpose function was never implemented into our other drivers,
+	// since this seems to have been handled via pitchBend() instead. The original drivers do have
+	// such functions.
+	if (!_se->_isAmiga)
+		return;
+	
+	_mc->transpose(_transpose_eff);
 }
 
 void Part::programChange(byte value) {

engines/scumm/scumm.cpp

@@ -2039,6 +2039,8 @@ void ScummEngine::setupMusic(int midi) {
 			}
 			if (_sound->_musicType == MDT_PCSPK)
 				_imuse->property(IMuse::PROP_PC_SPEAKER, 1);
+			if (_sound->_musicType == MDT_AMIGA)
+				_imuse->property(IMuse::PROP_AMIGA, 1);
 		}
 	}
 }