Audio: Add MIDI format playback support

This adds a new dependency with libfuildsynth. MIDI support
is built by default, but can be disabled if not desired.

All RTP songs should work well, but there are known problems
with other files (see README). Also, the pitch shift implementation
is somewhat poor and doesn't match RMXP (at least subjectively).

A soundfont is not included and must be provided by
the user themself.

src/sharedstate.cpp

@@ -37,6 +37,10 @@
 #include "binding.h"
 #include "exception.h"
 
+#ifdef MIDI
+#include "sharedmidistate.h"
+#endif
+
 #include <unistd.h>
 #include <stdio.h>
 #include <string>
@@ -58,6 +62,10 @@ struct SharedStatePrivate
 	RGSSThreadData &rtData;
 	Config &config;
 
+#ifdef MIDI
+	SharedMidiState midiState;
+#endif
+
 	Graphics graphics;
 	Input input;
 	Audio audio;
@@ -89,6 +97,9 @@ struct SharedStatePrivate
 	      eThread(*threadData->ethread),
 	      rtData(*threadData),
 	      config(threadData->config),
+#ifdef MIDI
+	      midiState(threadData->config),
+#endif
 	      graphics(threadData),
 	      fontState(threadData->config),
 	      stampCounter(0)
@@ -137,6 +148,12 @@ struct SharedStatePrivate
 		/* Reuse starting values */
 		TEXFBO::allocEmpty(gpTexFBO, globalTexW, globalTexH);
 		TEXFBO::linkFBO(gpTexFBO);
+
+		/* RGSS3 games will call setup_midi, so there's
+		 * no need to do it on startup */
+#if MIDI && !RGSS3
+		midiState.initDefaultSynths();
+#endif
 	}
 
 	~SharedStatePrivate()
@@ -212,6 +229,10 @@ GSATT(TexPool&, texPool)
 GSATT(Quad&, gpQuad)
 GSATT(SharedFontState&, fontState)
 
+#ifdef MIDI
+GSATT(SharedMidiState&, midiState)
+#endif
+
 void SharedState::setBindingData(void *data)
 {
 	p->bindingData = data;