SCUMM: Add hack to preserve savegame compatibility with Mac MI1

For old savegames, we now use a "dummy" iMUSE objet to skip the old
iMUSE save state. I had hoped to be able to do this without making
any changes to the iMUSE code itself, but I was unable to.

Also added note about how the save state for the new music will not
quite work if the mixer output rate changes. Personally, I'm not
too worried about that. It breaks, but it shouldn't break badly.

engines/scumm/imuse/imuse.cpp

@@ -363,7 +363,7 @@ void IMuseInternal::pause(bool paused) {
 	_paused = paused;
 }
 
-int IMuseInternal::save_or_load(Serializer *ser, ScummEngine *scumm) {
+int IMuseInternal::save_or_load(Serializer *ser, ScummEngine *scumm, bool fixAfterLoad) {
 	Common::StackLock lock(_mutex, "IMuseInternal::save_or_load()");
 	const SaveLoadEntry mainEntries[] = {
 		MKLINE(IMuseInternal, _queue_end, sleUint8, VER(8)),
@@ -440,7 +440,16 @@ int IMuseInternal::save_or_load(Serializer *ser, ScummEngine *scumm) {
 	for (i = 0; i < 8; ++i)
 		ser->saveLoadEntries(0, volumeFaderEntries);
 
-	if (ser->isLoading()) {
+	// Normally, we have to fix up the data structures after loading a
+	// saved game. But there are cases where we don't. For instance, The
+	// Macintosh version of Monkey Island 1 used to convert the Mac0 music
+	// resources to General MIDI and play it through iMUSE as a rough
+	// approximation. Now it has its own player, but old savegame still
+	// have the iMUSE data in them. We have to skip that data, using a
+	// dummy iMUSE object, but since the resource is no longer recognizable
+	// to iMUSE, the fixup fails hard. So yes, this is a bit of a hack.
+
+	if (ser->isLoading() && fixAfterLoad) {
 		// Load all sounds that we need
 		fix_players_after_load(scumm);
 		fix_parts_after_load();

engines/scumm/imuse/imuse.h

@@ -62,7 +62,7 @@ class IMuse : public MusicEngine {
 public:
 	virtual void on_timer(MidiDriver *midi) = 0;
 	virtual void pause(bool paused) = 0;
-	virtual int save_or_load(Serializer *ser, ScummEngine *scumm) = 0;
+	virtual int save_or_load(Serializer *ser, ScummEngine *scumm, bool fixAfterLoad = true) = 0;
 	virtual bool get_sound_active(int sound) const = 0;
 	virtual int32 doCommand(int numargs, int args[]) = 0;
 	virtual int clear_queue() = 0;

engines/scumm/imuse/imuse_internal.h

@@ -518,7 +518,7 @@ class IMuseInternal : public IMuse {
 public:
 	// IMuse interface
 	void pause(bool paused);
-	int save_or_load(Serializer *ser, ScummEngine *scumm);
+	int save_or_load(Serializer *ser, ScummEngine *scumm, bool fixAfterLoad = true);
 	bool get_sound_active(int sound) const;
 	int32 doCommand(int numargs, int args[]);
 	uint32 property(int prop, uint32 value);

engines/scumm/player_mac.cpp

@@ -26,6 +26,7 @@
 #include "gui/message.h"
 #include "scumm/player_mac.h"
 #include "scumm/scumm.h"
+#include "scumm/imuse/imuse.h"
 
 namespace Scumm {
 
@@ -101,14 +102,21 @@ void Player_Mac::saveLoadWithSerializer(Serializer *ser) {
 	Common::StackLock lock(_mutex);
 	if (ser->getVersion() < VER(94)) {
 		if (_vm->_game.id == GID_MONKEY && ser->isLoading()) {
-			// TODO: Skip old iMUSE save/load information
+			IMuse *dummyImuse = IMuse::create(_vm->_system, NULL, NULL);
+			dummyImuse->save_or_load(ser, _vm, false);
 		}
 	} else {
 		static const SaveLoadEntry musicEntries[] = {
 			MKLINE(Player_Mac, _soundPlaying, sleInt16, VER(94)),
 			MKEND()
 		};
 
+		// Note: This will fail slightly when loading a savegame if
+		// the mixer output rate has changed, because the pitch
+		// modifier and remaining samples were calculated from it. As
+		// a result, the first note to be played will be out of tune,
+		// and the channels will probably be slightly out of sync.
+
 		static const SaveLoadEntry channelEntries[] = {
 			MKLINE(Channel, _pos, sleUint16, VER(94)),
 			MKLINE(Channel, _pitchModifier, sleInt32, VER(94)),