diff --git a/src/farchive.h b/src/farchive.h
index 64c7cc9fe..b6a223bab 100644
--- a/src/farchive.h
+++ b/src/farchive.h
@@ -286,9 +286,11 @@ template<> inline FArchive &operator<< <FFont> (FArchive &arc, FFont* &font)
 struct FStrifeDialogueNode;
 struct FSwitchDef;
 struct FDoorAnimation;
+struct FLinePortal;
 template<> FArchive &operator<< (FArchive &arc, FStrifeDialogueNode *&node);
 template<> FArchive &operator<< (FArchive &arc, FSwitchDef* &sw);
 template<> FArchive &operator<< (FArchive &arc, FDoorAnimation* &da);
+FArchive &operator<< (FArchive &arc, FLinePortal &da);
 
 
 
diff --git a/src/p_saveg.cpp b/src/p_saveg.cpp
index 31eb76c7a..f0aedd5c6 100644
--- a/src/p_saveg.cpp
+++ b/src/p_saveg.cpp
@@ -53,6 +53,7 @@
 #include "p_lnspec.h"
 #include "p_acs.h"
 #include "p_terrain.h"
+#include "portal.h"
 
 static void CopyPlayer (player_t *dst, player_t *src, const char *name);
 static void ReadOnePlayer (FArchive &arc, bool skipload);
@@ -474,6 +475,12 @@ void P_SerializeWorld (FArchive &arc)
 		}
 		arc << li->args[1] << li->args[2] << li->args[3] << li->args[4];
 
+		if (SaveVersion >= 4532)
+		{
+			arc << li->portalindex;
+		}
+		else li->portalindex = UINT_MAX;
+
 		for (j = 0; j < 2; j++)
 		{
 			if (li->sidedef[j] == NULL)
@@ -508,6 +515,15 @@ void P_SerializeWorld (FArchive &arc)
 	{
 		arc << zn->Environment;
 	}
+
+	if (SaveVersion >= 4532)
+	{
+		arc << linePortals;
+	}
+	else
+	{
+		linePortals.Clear();
+	}
 }
 
 void extsector_t::Serialize(FArchive &arc)
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index 6229d811c..d1519d031 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -2156,6 +2156,7 @@ void P_LoadLineDefs (MapData * map)
 	for (i = 0; i < numlines; i++, mld++, ld++)
 	{
 		ld->Alpha = FRACUNIT;	// [RH] Opaque by default
+		ld->portalindex = UINT_MAX;
 
 		// [RH] Translate old linedef special and flags to be
 		//		compatible with the new format.
@@ -2236,6 +2237,8 @@ void P_LoadLineDefs2 (MapData * map)
 	{
 		int j;
 
+		ld->portalindex = UINT_MAX;
+
 		for (j = 0; j < 5; j++)
 			ld->args[j] = mld->args[j];
 
@@ -3365,6 +3368,7 @@ void P_FreeLevelData ()
 		level.killed_monsters = level.found_items = level.found_secrets =
 		wminfo.maxfrags = 0;
 		
+	linePortals.Clear();
 	FBehavior::StaticUnloadModules ();
 	if (vertexes != NULL)
 	{
diff --git a/src/p_spec.cpp b/src/p_spec.cpp
index 15182661b..833e3b632 100644
--- a/src/p_spec.cpp
+++ b/src/p_spec.cpp
@@ -1504,6 +1504,7 @@ void P_SpawnSpecials (void)
 	}
 	// [RH] Start running any open scripts on this map
 	FBehavior::StaticStartTypedScripts (SCRIPT_Open, NULL, false);
+	P_FinalizePortals();
 }
 
 // killough 2/28/98:
diff --git a/src/p_tags.cpp b/src/p_tags.cpp
index 15528378b..30b0db819 100644
--- a/src/p_tags.cpp
+++ b/src/p_tags.cpp
@@ -247,6 +247,18 @@ bool FTagManager::SectorHasTag(const sector_t *sector, int tag) const
 //
 //-----------------------------------------------------------------------------
 
+int FTagManager::GetFirstLineID(const line_t *line) const
+{
+	int i = lineindex(line);
+	return LineHasIDs(i) ? allIDs[startForLine[i]].tag : 0;
+}
+
+//-----------------------------------------------------------------------------
+//
+//
+//
+//-----------------------------------------------------------------------------
+
 bool FTagManager::LineHasID(int i, int tag) const
 {
 	if (LineHasIDs(i))
diff --git a/src/p_tags.h b/src/p_tags.h
index c3162d9b5..b351b04eb 100644
--- a/src/p_tags.h
+++ b/src/p_tags.h
@@ -57,6 +57,7 @@ public:
 	bool SectorHasTag(int sector, int tag) const;
 	bool SectorHasTag(const sector_t *sector, int tag) const;
 
+	int GetFirstLineID(const line_t *line) const;
 	bool LineHasID(int line, int id) const;
 	bool LineHasID(const line_t *line, int id) const;
 
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index 366a56dcf..118ee2d95 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -792,6 +792,7 @@ public:
 
 		memset(ld, 0, sizeof(*ld));
 		ld->Alpha = FRACUNIT;
+		ld->portalindex = UINT_MAX;
 		ld->sidedef[0] = ld->sidedef[1] = NULL;
 		if (level.flags2 & LEVEL2_CLIPMIDTEX) ld->flags |= ML_CLIP_MIDTEX;
 		if (level.flags2 & LEVEL2_WRAPMIDTEX) ld->flags |= ML_WRAP_MIDTEX;
diff --git a/src/portal.cpp b/src/portal.cpp
index 2d99a3df7..b49eb0d3a 100644
--- a/src/portal.cpp
+++ b/src/portal.cpp
@@ -6,10 +6,128 @@
 #include "c_cvars.h"
 #include "m_bbox.h"
 #include "p_tags.h"
+#include "farchive.h"
 
 // simulation recurions maximum
 CVAR(Int, sv_portal_recursions, 4, CVAR_ARCHIVE|CVAR_SERVERINFO)
 
+TArray<FLinePortal> linePortals;
+
+
+FArchive &operator<< (FArchive &arc, FLinePortal &port)
+{
+	arc << port.mOrigin
+		<< port.mDestination
+		<< port.mXDisplacement
+		<< port.mYDisplacement
+		<< port.mType
+		<< port.mFlags
+		<< port.mDefFlags
+		<< port.mAlign;
+	return arc;
+}
+
+
+void P_SpawnLinePortal(line_t* line)
+{
+	// portal destination is special argument #0
+	line_t* dst = NULL;
+
+	if (line->args[2] >= PORTT_VISUAL && line->args[2] <= PORTT_LINKED)
+	{
+		if (line->args[0] > 0)
+		{
+			int linenum = -1;
+
+			for (int i = 0; i < numlines; i++)
+			{
+				if (&lines[i] == line)
+					continue;
+				if (tagManager.LineHasID(&lines[i], line->args[0]))
+				{
+					dst = &lines[i];
+					break;
+				}
+			}
+		}
+
+		line->portalindex = linePortals.Reserve(1);
+		FLinePortal *port = &linePortals.Last();
+
+		memset(port, 0, sizeof(FLinePortal));
+		port->mOrigin = line;
+		port->mDestination = dst;
+		port->mType = BYTE(line->args[2]);	// range check is done above.
+		port->mAlign = BYTE(line->args[3] >= PORG_ABSOLUTE && line->args[3] <= PORG_CEILING ? line->args[3] : PORG_ABSOLUTE);
+		if (port->mDestination != NULL)
+		{
+			port->mDefFlags = port->mType == PORTT_VISUAL ? PORTF_VISIBLE : port->mType == PORTT_TELEPORT ? PORTF_TYPETELEPORT : PORTF_TYPEINTERACTIVE;
+
+
+		}
+	}
+	else if (line->args[2] == PORTT_LINKEDEE && line->args[0] == 0)
+	{
+		// EE-style portals require that the first line ID is identical and the first arg of the two linked linedefs are 0 and 1 respectively.
+
+		int mytag = tagManager.GetFirstLineID(line);
+
+		for (int i = 0; i < numlines; i++)
+		{
+			if (tagManager.GetFirstLineID(&lines[i]) == mytag && lines[i].args[0] == 1)
+			{
+				line->portalindex = linePortals.Reserve(1);
+				FLinePortal *port = &linePortals.Last();
+
+				memset(port, 0, sizeof(FLinePortal));
+				port->mOrigin = line;
+				port->mDestination = &lines[i];
+				port->mType = PORTT_LINKED;
+				port->mAlign = PORG_ABSOLUTE;
+				port->mDefFlags = PORTF_TYPEINTERACTIVE;
+			}
+		}
+	}
+	else
+	{
+		// undefined type
+		return;
+	}
+}
+
+void P_UpdatePortal(FLinePortal *port)
+{
+	if (port->mDestination == NULL)
+	{
+		// Portal has no destination: switch it off
+		port->mFlags = 0;
+	}
+	else if (port->mDestination->getPortalDestination() != port->mOrigin)
+	{
+		//portal doesn't link back. This will be a simple teleporter portal.
+		port->mFlags = port->mDefFlags & ~PORTF_INTERACTIVE;
+		if (port->mType == PORTT_LINKED)
+		{
+			// this is illegal. Demote the type to TELEPORT
+			port->mType = PORTT_TELEPORT;
+			port->mDefFlags &= ~PORTF_INTERACTIVE;
+		}
+	}
+	else
+	{
+		port->mFlags = port->mDefFlags;
+	}
+}
+
+void P_FinalizePortals()
+{
+	for (unsigned i = 0; i < linePortals.Size(); i++)
+	{
+		FLinePortal * port = &linePortals[i];
+		P_UpdatePortal(port);
+	}
+}
+
 // [ZZ] lots of floats here to avoid overflowing a lot
 bool P_IntersectLines(fixed_t o1x, fixed_t o1y, fixed_t p1x, fixed_t p1y,
 				      fixed_t o2x, fixed_t o2y, fixed_t p2x, fixed_t p2y,
@@ -78,41 +196,6 @@ bool P_ClipLineToPortal(line_t* line, line_t* portal, fixed_t viewx, fixed_t vie
 	return false;
 }
 
-void P_SpawnLinePortal(line_t* line)
-{
-	// portal destination is special argument #0
-	line_t* dst = NULL;
-
-	if (line->args[0] > 0)
-	{
-		int linenum = -1;
-
-		for (int i = 0; i < numlines; i++)
-		{
-			if (&lines[i] == line)
-				continue;
-			if (tagManager.LineHasID(&lines[i], line->args[0]))
-			{
-				dst = &lines[i];
-				break;
-			}
-		}
-	}
-
-	if (dst)
-	{
-		line->_portal = true;
-		//line->portal_passive = true;// !!(line->args[2] & PORTAL_VISUAL; (line->special == Line_SetVisualPortal);
-		line->_portal_dst = dst;
-	}
-	else
-	{
-		line->_portal = false;
-		//line->portal_passive = false;
-		line->_portal_dst = NULL;
-	}
-}
-
 void P_TranslatePortalXY(line_t* src, line_t* dst, fixed_t& x, fixed_t& y)
 {
 	if (!src || !dst)
@@ -185,17 +268,22 @@ void P_TranslatePortalAngle(line_t* src, line_t* dst, angle_t& angle)
 
 void P_TranslatePortalZ(line_t* src, line_t* dst, fixed_t& z)
 {
-	// args[2] = 0 - no teleport
+	// args[2] = 0 - no adjustment
 	// args[2] = 1 - adjust by floor difference
 	// args[2] = 2 - adjust by ceiling difference
 
-	if (src->args[2] == 1)
+	switch (src->getPortalAlignment())
 	{
+	case PORG_FLOOR:
 		z = z - src->frontsector->floorplane.ZatPoint(src->v1->x, src->v1->y) + dst->frontsector->floorplane.ZatPoint(dst->v2->x, dst->v2->y);
-	}
-	else if (src->args[2] == 2)
-	{
+		return;
+
+	case PORG_CEILING:
 		z = z - src->frontsector->ceilingplane.ZatPoint(src->v1->x, src->v1->y) + dst->frontsector->ceilingplane.ZatPoint(dst->v2->x, dst->v2->y);
+		return;
+
+	default:
+		return;
 	}
 }
 
diff --git a/src/portal.h b/src/portal.h
index 3b707f543..6a947fd0e 100644
--- a/src/portal.h
+++ b/src/portal.h
@@ -8,7 +8,50 @@
 #include "p_local.h"
 #include "m_bbox.h"
 
+
+enum
+{
+	PORTF_VISIBLE = 1,
+	PORTF_PASSABLE = 2,
+	PORTF_SOUNDTRAVERSE = 4,
+	PORTF_INTERACTIVE = 8,
+
+	PORTF_TYPETELEPORT = PORTF_VISIBLE | PORTF_PASSABLE | PORTF_SOUNDTRAVERSE,
+	PORTF_TYPEINTERACTIVE = PORTF_VISIBLE | PORTF_PASSABLE | PORTF_SOUNDTRAVERSE | PORTF_INTERACTIVE,
+};
+
+enum
+{
+	PORTT_VISUAL,
+	PORTT_TELEPORT,
+	PORTT_INTERACTIVE,
+	PORTT_LINKED,
+	PORTT_LINKEDEE	// Eternity compatible definition which uses only one line ID and a different anchor type to link to.
+};
+
+enum
+{
+	PORG_ABSOLUTE,	// does not align at all. z-ccoordinates must match.
+	PORG_FLOOR,
+	PORG_CEILING,
+};
+
+struct FLinePortal
+{
+	line_t *mOrigin;
+	line_t *mDestination;
+	fixed_t mXDisplacement;
+	fixed_t mYDisplacement;
+	BYTE mType;
+	BYTE mFlags;
+	BYTE mDefFlags;
+	BYTE mAlign;
+};
+
+extern TArray<FLinePortal> linePortals;
+
 void P_SpawnLinePortal(line_t* line);
+void P_FinalizePortals();
 
 
 /* code ported from prototype */
@@ -53,4 +96,27 @@ public:
 /* new code */
 fixed_t P_PointLineDistance(line_t* line, fixed_t x, fixed_t y);
 
+
+// returns true if the portal is crossable by actors
+inline bool line_t::isLinePortal() const
+{
+	return portalindex >= linePortals.Size() ? false : !!(linePortals[portalindex].mFlags & PORTF_PASSABLE);
+}
+
+// returns true if the portal needs to be handled by the renderer
+inline bool line_t::isVisualPortal() const
+{
+	return portalindex >= linePortals.Size() ? false : !!(linePortals[portalindex].mFlags & PORTF_VISIBLE);
+}
+
+inline line_t *line_t::getPortalDestination() const
+{
+	return portalindex >= linePortals.Size() ? (line_t*)NULL : linePortals[portalindex].mDestination;
+}
+
+inline int line_t::getPortalAlignment() const
+{
+	return portalindex >= linePortals.Size() ? 0 : linePortals[portalindex].mAlign;
+}
+
 #endif
\ No newline at end of file
diff --git a/src/r_bsp.cpp b/src/r_bsp.cpp
index a6dd7f61b..819bd9532 100644
--- a/src/r_bsp.cpp
+++ b/src/r_bsp.cpp
@@ -99,7 +99,7 @@ static BYTE		FakeSide;
 
 int WindowLeft, WindowRight;
 WORD MirrorFlags;
-TArray<PortalDrawseg> WallPortals;
+TArray<PortalDrawseg> WallPortals(1000);	// note: this array needs to go away as reallocation can cause crashes.
 
 
 static subsector_t *InSubsector;
diff --git a/src/r_defs.h b/src/r_defs.h
index 901dadcb0..a000fb8e3 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -988,26 +988,14 @@ struct line_t
 	sector_t	*frontsector, *backsector;
 	int 		validcount;	// if == validcount, already checked
 	int			locknumber;	// [Dusk] lock number for special
-
-	line_t		*_portal_dst;
-	bool		_portal;
+	unsigned	portalindex;
 
 	// returns true if the portal is crossable by actors
-	bool isLinePortal() const
-	{
-		return false;	// right now there are no crossable portals
-	}
-
+	bool isLinePortal() const;
 	// returns true if the portal needs to be handled by the renderer
-	bool isVisualPortal() const
-	{
-		return _portal;
-	}
-
-	line_t *getPortalDestination() const
-	{
-		return _portal_dst;
-	}
+	bool isVisualPortal() const;
+	line_t *getPortalDestination() const;
+	int getPortalAlignment() const;
 };
 
 // phares 3/14/98
diff --git a/src/r_utility.h b/src/r_utility.h
index 2d9aac086..10dcf5352 100644
--- a/src/r_utility.h
+++ b/src/r_utility.h
@@ -58,6 +58,11 @@ inline int R_PointOnSide (fixed_t x, fixed_t y, const node_t *node)
 
 angle_t R_PointToAngle2 (fixed_t x1, fixed_t y1, fixed_t x2, fixed_t y2);
 inline angle_t R_PointToAngle (fixed_t x, fixed_t y) { return R_PointToAngle2 (viewx, viewy, x, y); }
+inline angle_t R_PointToAnglePrecise (fixed_t viewx, fixed_t viewy, fixed_t x, fixed_t y)
+{
+	return xs_RoundToUInt(atan2(double(y-viewy), double(x-viewx)) * (ANGLE_180/M_PI));
+}
+
 subsector_t *R_PointInSubsector (fixed_t x, fixed_t y);
 fixed_t R_PointToDist2 (fixed_t dx, fixed_t dy);
 void R_ResetViewInterpolation ();
diff --git a/src/version.h b/src/version.h
index b4b3ace12..3af1c1b7f 100644
--- a/src/version.h
+++ b/src/version.h
@@ -76,7 +76,7 @@ const char *GetVersionString();
 
 // Use 4500 as the base git save version, since it's higher than the
 // SVN revision ever got.
-#define SAVEVER 4531
+#define SAVEVER 4532
 
 #define SAVEVERSTRINGIFY2(x) #x
 #define SAVEVERSTRINGIFY(x) SAVEVERSTRINGIFY2(x)