From 40359929757fa9d142de41ff4735dc429bd8dea1 Mon Sep 17 00:00:00 2001
From: Jonathan Campbell <jonathan@castus.tv>
Date: Fri, 10 Jan 2025 18:35:31 -0800
Subject: [PATCH] MIDI synth (Fluidsynth): Add code to recognize Roland GS
 MASTER VOLUME sysex. Now PC-98 games can "fade out" the MIDI music using GS
 commands (Seiyoku Gakuen Seraphita)

---
 include/midi.h       |  1 +
 src/gui/midi_synth.h | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/midi.h b/include/midi.h
index 13c648fee..85a48cc03 100644
--- a/include/midi.h
+++ b/include/midi.h
@@ -58,6 +58,7 @@ struct DB_Midi {
 	DB_Midi() {}
 };
 
+extern bool roland_gs_sysex;
 extern DB_Midi midi;
 
 #endif
diff --git a/src/gui/midi_synth.h b/src/gui/midi_synth.h
index dd5f945a6..0a7c4a78e 100644
--- a/src/gui/midi_synth.h
+++ b/src/gui/midi_synth.h
@@ -33,6 +33,7 @@
 static MixerChannel *synthchan = NULL;
 static fluid_synth_t *synth_soft = NULL;
 static int synthsamplerate = 0;
+static uint8_t master_volume = 128;
 
 static void synth_log(int level,
 #if !defined (FLUIDSYNTH_VERSION_MAJOR) || FLUIDSYNTH_VERSION_MAJOR >= 2 // Let version 2.x be the default
@@ -61,6 +62,11 @@ static void synth_log(int level,
 static void synth_CallBack(Bitu len) {
 	if (synth_soft != NULL) {
 		fluid_synth_write_s16(synth_soft, (int)len, MixTemp, 0, 2, MixTemp, 1, 2);
+		if (master_volume < 128) {
+			for (unsigned int i=0;i < (len*2);i++) {
+				((int16_t*)MixTemp)[i] = (int16_t)(((((int16_t*)MixTemp)[i]) * master_volume) >> 7);
+			}
+		}
 		synthchan->AddSamples_s16(len,(int16_t *)MixTemp);
 	}
 }
@@ -82,6 +88,23 @@ private:
 	void PlayEvent(uint8_t *msg, Bitu len) {
 		uint8_t event = msg[0], channel, p1, p2;
 
+		if (roland_gs_sysex) {
+			if (msg[1] == 0x41/*Roland*/ && msg[3] == 0x42/*GS*/ && msg[4] == 0x12/*Send*/ && len >= 9) {
+				const uint32_t addr =
+					((uint32_t)msg[5] << 16) +
+					((uint32_t)msg[6] <<  8) +
+					(uint32_t)msg[7];
+
+				if (addr == 0x400004) { /* MASTER VOLUME */
+					/* Fluidsynth doesn't appear to support this message, so we have to handle it ourself. */
+					master_volume = msg[8];
+					if (master_volume >= 127) master_volume = 128;
+					LOG_MSG("MIDI synth: MASTER VOLUME %u",master_volume);
+					return;
+				}
+			}
+		}
+
 		switch (event) {
 		case 0xf0:
 		case 0xf7:
@@ -92,6 +115,7 @@ private:
 			LOG(LOG_MISC,LOG_DEBUG)("SYNTH: midi tick");
 			return;
 		case 0xff:
+			master_volume = 128;
 			LOG(LOG_MISC,LOG_DEBUG)("SYNTH: system reset");
 			fluid_synth_system_reset(synth_soft);
 			return;
@@ -224,6 +248,7 @@ public:
 		sffile=sf;
         fsinfo="Sound font: "+sf;
 
+		master_volume = 128;
 		synthchan = MIXER_AddChannel(synth_CallBack, (unsigned int)synthsamplerate, "SYNTH");
 		synthchan->Enable(false);
 		isOpen = true;