From 93c12cf2595ac473061f83486139907d7c2c7bb0 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <c.oelckers@zdoom.fake>
Date: Thu, 12 Feb 2015 18:57:06 +0100
Subject: [PATCH] - addressed the problem that prompted setting NOGRAVITY for
 all floatbobbing items for real:

Hexen uses the spawn height value from the mapthing_t structure to offset the item when floatbobbing. With proper gravity handling enabled this method doesn't really work so as a workaround ZDoom will now enable a hidden compatibility option when playing any map with a Hexen format MAPINFO so that any positive value in this field will make P_ZMovement revert to the original method of setting the items height (excluding the floatbob offset, of course.)

This also removes some code from P_NightmareRespawn that originate from the original Hexen method for floatbobbing which aren't needed anymore
---
 src/compatibility.cpp |  6 ++++++
 src/doomdef.h         |  1 +
 src/p_mobj.cpp        | 24 +++++++++++++++++++++---
 3 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/src/compatibility.cpp b/src/compatibility.cpp
index 4ddc670e9..da4ab4945 100644
--- a/src/compatibility.cpp
+++ b/src/compatibility.cpp
@@ -109,6 +109,7 @@ static FCompatOption Options[] =
 	{ "rebuildnodes",			BCOMPATF_REBUILDNODES, SLOT_BCOMPAT },
 	{ "linkfrozenprops",		BCOMPATF_LINKFROZENPROPS, SLOT_BCOMPAT },
 	{ "disablepushwindowcheck",	BCOMPATF_NOWINDOWCHECK, SLOT_BCOMPAT },
+	{ "floatbob",				BCOMPATF_FLOATBOB, SLOT_BCOMPAT },
 
 	// list copied from g_mapinfo.cpp
 	{ "shorttex",				COMPATF_SHORTTEX, SLOT_COMPAT },
@@ -434,6 +435,11 @@ void CheckCompatibility(MapData *map)
 	// Reset i_compatflags
 	compatflags.Callback();
 	compatflags2.Callback();
+	// Set floatbob compatibility for all maps with an original Hexen MAPINFO.
+	if (level.flags2 & LEVEL2_HEXENHACK)
+	{
+		ib_compatflags |= BCOMPATF_FLOATBOB;
+	}
 }
 
 //==========================================================================
diff --git a/src/doomdef.h b/src/doomdef.h
index 767f97661..c8aa66c17 100644
--- a/src/doomdef.h
+++ b/src/doomdef.h
@@ -354,6 +354,7 @@ enum
 	BCOMPATF_REBUILDNODES		= 1 << 5,	// Force node rebuild
 	BCOMPATF_LINKFROZENPROPS	= 1 << 6,	// Clearing PROP_TOTALLYFROZEN or PROP_FROZEN also clears the other
 	BCOMPATF_NOWINDOWCHECK		= 1 << 7,	// Disable the window check in CheckForPushSpecial()
+	BCOMPATF_FLOATBOB			= 1 << 8,	// Use Hexen's original method of preventing floatbobbing items from falling down
 };
 
 // phares 3/20/98:
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index b27c79d91..2235c7820 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -2314,6 +2314,16 @@ void P_ZMovement (AActor *mo, fixed_t oldfloorz)
 		}
 	}
 
+	// Hexen compatibility handling for floatbobbing. Ugh...
+	// Hexen yanked all items to the floor, except those being spawned at map start in the air.
+	// Those were kept at their original height.
+	// Do this only if the item was actually spawned by the map above ground to avoid problems.
+	if (mo->special1 > 0 && (mo->flags2 & MF2_FLOATBOB) && (ib_compatflags & BCOMPATF_FLOATBOB))
+	{
+		mo->z = mo->floorz + mo->special1;
+	}
+
+
 //
 // adjust height
 //
@@ -2616,8 +2626,6 @@ void P_NightmareRespawn (AActor *mobj)
 		z = ONCEILINGZ;
 	else if (info->flags2 & MF2_SPAWNFLOAT)
 		z = FLOATRANDZ;
-	else if (info->flags2 & MF2_FLOATBOB)
-		z = mobj->SpawnPoint[2];
 	else
 		z = ONFLOORZ;
 
@@ -4869,7 +4877,13 @@ AActor *P_SpawnMapThing (FMapThing *mthing, int position)
 	mobj = AActor::StaticSpawn (i, x, y, z, NO_REPLACE, true);
 
 	if (z == ONFLOORZ)
+	{
 		mobj->z += mthing->z;
+		if ((mobj->flags2 & MF2_FLOATBOB) && (ib_compatflags & BCOMPATF_FLOATBOB))
+		{
+			mobj->special1 = mthing->z;
+		}
+	}
 	else if (z == ONCEILINGZ)
 		mobj->z -= mthing->z;
 
@@ -4882,7 +4896,11 @@ AActor *P_SpawnMapThing (FMapThing *mthing, int position)
 	else if (mthing->gravity > 0) mobj->gravity = FixedMul(mobj->gravity, mthing->gravity);
 	else mobj->flags &= ~MF_NOGRAVITY;
 
-	P_FindFloorCeiling(mobj, FFCF_SAMESECTOR | FFCF_ONLY3DFLOORS | FFCF_3DRESTRICT);
+	// For Hexen floatbob 'compatibility' we do not really want to alter the floorz.
+	if (mobj->special1 == 0 || !(mobj->flags2 & MF2_FLOATBOB) || !(ib_compatflags & BCOMPATF_FLOATBOB))
+	{
+		P_FindFloorCeiling(mobj, FFCF_SAMESECTOR | FFCF_ONLY3DFLOORS | FFCF_3DRESTRICT);
+	}
 
 	if (!(mobj->flags2 & MF2_ARGSDEFINED))
 	{