Add g_musicfade, generic system to fade out the level music for a brief period

src/doomstat.h

@@ -811,6 +811,12 @@ extern struct darkness_t
 	fixed_t value[MAXSPLITSCREENPLAYERS];
 } g_darkness;
 
+extern struct musicfade_t
+{
+	tic_t start, end, fade;
+	boolean ticked;
+} g_musicfade;
+
 #define DEFAULT_GRAVITY (4*FRACUNIT/5)
 extern fixed_t gravity;
 extern fixed_t mapobjectscale;

src/g_game.c

@@ -279,6 +279,7 @@ tic_t racecountdown, exitcountdown, musiccountdown; // for racing
 exitcondition_t g_exit;
 
 darkness_t g_darkness;
+musicfade_t g_musicfade;
 
 fixed_t gravity;
 fixed_t mapobjectscale;

src/k_kart.c

@@ -118,6 +118,7 @@ void K_TimerReset(void)
 {
 	starttime = introtime = 0;
 	memset(&g_darkness, 0, sizeof g_darkness);
+	memset(&g_musicfade, 0, sizeof g_musicfade);
 	numbulbs = 1;
 	inDuel = rainbowstartavailable = false;
 	linecrossed = 0;

src/p_saveg.c

@@ -6567,6 +6567,11 @@ static void P_NetArchiveMisc(savebuffer_t *save, boolean resending)
 	WRITEUINT32(save->p, g_darkness.start);
 	WRITEUINT32(save->p, g_darkness.end);
 
+	WRITEUINT32(save->p, g_musicfade.start);
+	WRITEUINT32(save->p, g_musicfade.end);
+	WRITEUINT32(save->p, g_musicfade.fade);
+	WRITEUINT8(save->p, g_musicfade.ticked);
+
 	WRITEUINT16(save->p, numchallengedestructibles);
 
 	// Is it paused?
@@ -6753,6 +6758,11 @@ static boolean P_NetUnArchiveMisc(savebuffer_t *save, boolean reloading)
 	g_darkness.start = READUINT32(save->p);
 	g_darkness.end = READUINT32(save->p);
 
+	g_musicfade.start = READUINT32(save->p);
+	g_musicfade.end = READUINT32(save->p);
+	g_musicfade.fade = READUINT32(save->p);
+	g_musicfade.ticked = READUINT8(save->p);
+
 	numchallengedestructibles = READUINT16(save->p);
 
 	// Is it paused?

src/p_tick.c

@@ -808,6 +808,22 @@ static void P_TickDarkness(void)
 	}
 }
 
+static void P_TickMusicFade(void)
+{
+	if (leveltime >= g_musicfade.start && leveltime <= g_musicfade.end)
+	{
+		INT32 half = (g_musicfade.end - g_musicfade.start) / 2;
+		INT32 fade = max(1, g_musicfade.fade);
+		INT32 mid = half - fade;
+		INT32 t = abs((INT32)leveltime - (INT32)(g_musicfade.start + half));
+		Music_LevelVolume((max(t, mid) - mid) * 100 / fade);
+	}
+	else if (!g_musicfade.ticked)
+		Music_LevelVolume(100);
+
+	g_musicfade.ticked = true;
+}
+
 //
 // P_Ticker
 //
@@ -1102,6 +1118,7 @@ void P_Ticker(boolean run)
 			racecountdown--;
 
 		P_TickDarkness();
+		P_TickMusicFade();
 
 		if (exitcountdown >= 1)
 		{

src/typedef.h

@@ -143,6 +143,7 @@ TYPEDEF (cupheader_t);
 TYPEDEF (unloaded_cupheader_t);
 TYPEDEF (exitcondition_t);
 TYPEDEF (darkness_t);
+TYPEDEF (musicfade_t);
 
 // font.h
 TYPEDEF (font_t);