- added a 'no MBF21' compatibility flag.

Turns out that there's a few old maps that have the extended line flags set but not the guard bit that forces their clearance.
Astrostein 1's first map is an example for this.

src/d_main.cpp

@@ -588,7 +588,7 @@ CUSTOM_CVAR(Int, compatmode, 0, CVAR_ARCHIVE|CVAR_NOINITCALL)
 		v = COMPATF_SHORTTEX | COMPATF_STAIRINDEX | COMPATF_USEBLOCKING | COMPATF_NODOORLIGHT | COMPATF_SPRITESORT |
 			COMPATF_TRACE | COMPATF_MISSILECLIP | COMPATF_SOUNDTARGET | COMPATF_DEHHEALTH | COMPATF_CROSSDROPOFF |
 			COMPATF_LIGHT | COMPATF_MASKEDMIDTEX;
-		w = COMPATF2_FLOORMOVE | COMPATF2_EXPLODE1;
+		w = COMPATF2_FLOORMOVE | COMPATF2_EXPLODE1 | COMPATF2_NOMBF21;
 		break;
 
 	case 2:	// same as 1 but stricter (NO_PASSMOBJ and INVISIBILITY are also set)
@@ -596,36 +596,36 @@ CUSTOM_CVAR(Int, compatmode, 0, CVAR_ARCHIVE|CVAR_NOINITCALL)
 			COMPATF_TRACE | COMPATF_MISSILECLIP | COMPATF_SOUNDTARGET | COMPATF_NO_PASSMOBJ | COMPATF_LIMITPAIN |
 			COMPATF_DEHHEALTH | COMPATF_INVISIBILITY | COMPATF_CROSSDROPOFF | COMPATF_CORPSEGIBS | COMPATF_HITSCAN |
 			COMPATF_WALLRUN | COMPATF_NOTOSSDROPS | COMPATF_LIGHT | COMPATF_MASKEDMIDTEX;
-		w = COMPATF2_BADANGLES | COMPATF2_FLOORMOVE | COMPATF2_POINTONLINE | COMPATF2_EXPLODE2;
+		w = COMPATF2_BADANGLES | COMPATF2_FLOORMOVE | COMPATF2_POINTONLINE | COMPATF2_EXPLODE2 | COMPATF2_NOMBF21;
 		break;
 
 	case 3: // Boom compat mode
 		v = COMPATF_TRACE|COMPATF_SOUNDTARGET|COMPATF_BOOMSCROLL|COMPATF_MISSILECLIP|COMPATF_MASKEDMIDTEX;
-		w = COMPATF2_EXPLODE1;
+		w = COMPATF2_EXPLODE1 | COMPATF2_NOMBF21;
 		break;
 
 	case 4: // Old ZDoom compat mode
 		v = COMPATF_SOUNDTARGET | COMPATF_LIGHT;
-		w = COMPATF2_MULTIEXIT | COMPATF2_TELEPORT | COMPATF2_PUSHWINDOW | COMPATF2_CHECKSWITCHRANGE;
+		w = COMPATF2_MULTIEXIT | COMPATF2_TELEPORT | COMPATF2_PUSHWINDOW | COMPATF2_CHECKSWITCHRANGE | COMPATF2_NOMBF21;
 		break;
 
 	case 5: // MBF compat mode
 		v = COMPATF_TRACE | COMPATF_SOUNDTARGET | COMPATF_BOOMSCROLL | COMPATF_MISSILECLIP | COMPATF_MUSHROOM |
 			COMPATF_MBFMONSTERMOVE | COMPATF_NOBLOCKFRIENDS | COMPATF_MASKEDMIDTEX;
-		w = COMPATF2_EXPLODE1 | COMPATF2_AVOID_HAZARDS | COMPATF2_STAYONLIFT;
+		w = COMPATF2_EXPLODE1 | COMPATF2_AVOID_HAZARDS | COMPATF2_STAYONLIFT | COMPATF2_NOMBF21;
 		break;
 
 	case 6:	// Boom with some added settings to reenable some 'broken' behavior
 		v = COMPATF_TRACE | COMPATF_SOUNDTARGET | COMPATF_BOOMSCROLL | COMPATF_MISSILECLIP | COMPATF_NO_PASSMOBJ |
 			COMPATF_INVISIBILITY | COMPATF_CORPSEGIBS | COMPATF_HITSCAN | COMPATF_WALLRUN | COMPATF_NOTOSSDROPS | COMPATF_MASKEDMIDTEX;
-		w = COMPATF2_POINTONLINE | COMPATF2_EXPLODE2;
+		w = COMPATF2_POINTONLINE | COMPATF2_EXPLODE2 | COMPATF2_NOMBF21;
 		break;
 
 	case 7: // Stricter MBF compatibility
 		v = COMPATF_CORPSEGIBS | COMPATF_NOBLOCKFRIENDS | COMPATF_MBFMONSTERMOVE | COMPATF_INVISIBILITY |
 			COMPATF_NOTOSSDROPS | COMPATF_MUSHROOM | COMPATF_NO_PASSMOBJ | COMPATF_BOOMSCROLL | COMPATF_WALLRUN |
 			COMPATF_TRACE | COMPATF_HITSCAN | COMPATF_MISSILECLIP | COMPATF_MASKEDMIDTEX | COMPATF_SOUNDTARGET;
-		w = COMPATF2_POINTONLINE | COMPATF2_EXPLODE1 | COMPATF2_EXPLODE2 | COMPATF2_AVOID_HAZARDS | COMPATF2_STAYONLIFT;
+		w = COMPATF2_POINTONLINE | COMPATF2_EXPLODE1 | COMPATF2_EXPLODE2 | COMPATF2_AVOID_HAZARDS | COMPATF2_STAYONLIFT | COMPATF2_NOMBF21;
 		break;
 	}
 	compatflags = v;
@@ -677,6 +677,7 @@ CVAR (Flag, compat_explode2,			compatflags2, COMPATF2_EXPLODE2);
 CVAR (Flag, compat_railing,				compatflags2, COMPATF2_RAILING);
 CVAR (Flag, compat_avoidhazard,			compatflags2, COMPATF2_AVOID_HAZARDS);
 CVAR (Flag, compat_stayonlift,			compatflags2, COMPATF2_STAYONLIFT);
+CVAR (Flag, compat_nombf21,				compatflags2, COMPATF2_NOMBF21);
 
 CVAR(Bool, vid_activeinbackground, false, CVAR_ARCHIVE | CVAR_GLOBALCONFIG)
 

src/doomdef.h

@@ -224,6 +224,7 @@ enum : unsigned int
 	COMPATF2_SCRIPTWAIT		= 1 << 11,	// Use old scriptwait implementation where it doesn't wait on a non-running script.
 	COMPATF2_AVOID_HAZARDS	= 1 << 12,	// another MBF thing.
 	COMPATF2_STAYONLIFT		= 1 << 13,	// yet another MBF thing.
+	COMPATF2_NOMBF21		= 1 << 14,	// disable MBF21 features that may clash with certain maps
 
 };
 

src/g_levellocals.h

@@ -597,6 +597,12 @@ public:
 		return p->camera == mo;
 	}
 
+	bool MBF21Enabled() const
+	{
+		// The affected features only are a problem with Doom format maps - the flag should have no effect in Hexen and UDMF format.
+		return !(i_compatflags2 & COMPATF2_NOMBF21) || maptype != MAPTYPE_DOOM;
+	}
+
 	int NumMapSections;
 
 	uint32_t		flags;

src/gamedata/g_mapinfo.cpp

@@ -1706,6 +1706,7 @@ MapFlagHandlers[] =
 	{ "compat_scriptwait",				MITYPE_COMPATFLAG, 0, COMPATF2_SCRIPTWAIT },
 	{ "compat_avoidhazards",			MITYPE_COMPATFLAG, 0, COMPATF2_AVOID_HAZARDS },
 	{ "compat_stayonlift",				MITYPE_COMPATFLAG, 0, COMPATF2_STAYONLIFT },
+	{ "compat_nombf21",					MITYPE_COMPATFLAG, 0, COMPATF2_NOMBF21 },
 	{ "cd_start_track",					MITYPE_EATNEXT,	0, 0 },
 	{ "cd_end1_track",					MITYPE_EATNEXT,	0, 0 },
 	{ "cd_end2_track",					MITYPE_EATNEXT,	0, 0 },

src/maploader/compatibility.cpp

@@ -169,6 +169,7 @@ static FCompatOption Options[] =
 	{ "explode2",				COMPATF2_EXPLODE2, SLOT_COMPAT2 },
 	{ "railing",				COMPATF2_RAILING, SLOT_COMPAT2 },
 	{ "scriptwait",				COMPATF2_SCRIPTWAIT, SLOT_COMPAT2 },
+	{ "nombf21",				COMPATF2_NOMBF21, SLOT_COMPAT2 },
 	{ NULL, 0, 0 }
 };
 

src/maploader/specials.cpp

@@ -484,11 +484,12 @@ void MapLoader::InitSectorSpecial(sector_t *sector, int special)
 	{
 		sector->Flags |= SECF_PUSH;
 	}
-	if (sector->special & KILL_MONSTERS_MASK)
+	// Nom MBF21 compatibility needs to be checked here, because after this point there is no longer any context in which it can be done.
+	if ((sector->special & KILL_MONSTERS_MASK) && Level->MBF21Enabled())
 	{
 		sector->Flags |= SECF_KILLMONSTERS;
 	}
-	if (!(sector->special & DEATH_MASK))
+	if (!(sector->special & DEATH_MASK) || !Level->MBF21Enabled())
 	{
 		if ((sector->special & DAMAGE_MASK) == 0x100)
 		{

src/playsim/actorinlines.h

@@ -197,11 +197,11 @@ inline bool P_IsBlockedByLine(AActor* actor, line_t* line)
 		// the regular 'blockmonsters' flag.
 		if (line->flags & ML_BLOCKMONSTERS) return true;
 		// MBF21's flag for walking monsters
-		if ((line->flags2 & ML2_BLOCKLANDMONSTERS) && !(actor->flags & MF_FLOAT)) return true;
+		if ((line->flags2 & ML2_BLOCKLANDMONSTERS) && actor->Level->MBF21Enabled() && !(actor->flags & MF_FLOAT)) return true;
 	}
 
 	// Blocking players
-	if (((actor->player != nullptr) || (actor->flags8 & MF8_BLOCKASPLAYER)) && (line->flags & ML_BLOCK_PLAYERS)) return true;
+	if ((((actor->player != nullptr) || (actor->flags8 & MF8_BLOCKASPLAYER)) && (line->flags & ML_BLOCK_PLAYERS)) && actor->Level->MBF21Enabled()) return true;
 
 	// Blocking floaters.
 	if ((actor->flags & MF_FLOAT) && (line->flags & ML_BLOCK_FLOATERS)) return true;

wadsrc/static/compatibility.txt

@@ -105,6 +105,10 @@ A81E2734F735A82720D8E0F1442BA0C9 // Imp's [sic] are Ghost Gods map01
 
 // invert the sorting order of overlapping sprites at the same spot
 551D6B416EB3324790BC0F0F74B49600 // Strain map13
+{
+	spritesort
+}
+
 2F49C29691F8565F0B99B27FCF2627E6 // Astrostein 1 MAP01
 55A741F9C2955C2B06F2387E45ED6C62 // MAP02
 4E7286B735671A942C54FAC6CB52A8C3 // MAP03
@@ -133,6 +137,7 @@ AB1A6C1D3898D4259C0645306939374C // map15
 CA267398C9B3A8F79349D3394F8B2106 // map20
 {
 	spritesort
+	nombf21
 }
 
 1D9E43988940CCD3555724E15DD8B1AB // Happy Time Circus map01 has bad teleporters

wadsrc/static/menudef.txt

@@ -1776,6 +1776,7 @@ OptionMenu "CompatMapMenu" protected
 	Option "$CMPTMNU_PUSHWINDOW",					"compat_pushwindow", "YesNo"
 	Option "$CMPTMNU_CHECKSWITCHRANGE",				"compat_checkswitchrange", "YesNo"
 	Option "$CMPTMNU_RAILINGHACK",					"compat_railing", "YesNo"
+	Option "$CMPTMNU_NOMBF21",						"compat_nombf21", "YeaNo"
 	Class "CompatibilityMenu"
 }