diff --git a/src/portal.cpp b/src/portal.cpp
index 3b17eb74a..02ff5e7fd 100644
--- a/src/portal.cpp
+++ b/src/portal.cpp
@@ -80,14 +80,7 @@ bool P_ClipLineToPortal(line_t* line, line_t* portal, fixed_t viewx, fixed_t vie
 
 bool P_CheckPortal(line_t* line)
 {
-	if (line->special == Line_Mirror)
-	{
-		line->portal = true;
-		line->portal_mirror = true;
-		line->portal_passive = true;
-		line->portal_dst = line;
-	}
-	else if (line->special == Line_SetPortal)
+	if (line->special == Line_SetPortal)
 	{
 		// portal destination is special argument #0
 		line_t* dst = NULL;
@@ -110,28 +103,18 @@ bool P_CheckPortal(line_t* line)
 
 		if (dst)
 		{
-			line->portal = true;
-			line->portal_mirror = false;
-			line->portal_passive = true;// !!(line->args[2] & PORTAL_VISUAL; (line->special == Line_SetVisualPortal);
-			line->portal_dst = 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_mirror = false;
-			line->portal_passive = false;
-			line->portal_dst = NULL;
+			line->_portal = false;
+			//line->portal_passive = false;
+			line->_portal_dst = NULL;
 		}
 	}
-	else
-	{
-		line->portal = false;
-		line->portal_mirror = false;
-		line->portal_passive = false;
-		line->portal_dst = NULL;
-	}
-
-	return (line->portal);
+	return (line->_portal);
 }
 
 void P_TranslatePortalXY(line_t* src, line_t* dst, fixed_t& x, fixed_t& y)
@@ -297,12 +280,12 @@ bool PortalTracer::TraceStep()
 		{
 			li = in->d.line;
 
-			if (li->portal && !li->portal_passive)
+			if (li->isLinePortal())
 			{
 				if (P_PointOnLineSide(startx-dirx, starty-diry, li))
 					continue; // we're at the back side of this line
 
-				line_t* out = li->portal_dst;
+				line_t* out = li->getPortalDestination();
 
 				this->in = li;
 				this->out = out;
diff --git a/src/r_bsp.cpp b/src/r_bsp.cpp
index e9802e5b1..a6dd7f61b 100644
--- a/src/r_bsp.cpp
+++ b/src/r_bsp.cpp
@@ -590,7 +590,7 @@ void R_AddLine (seg_t *line)
 	rw_havehigh = rw_havelow = false;
 
 	// Single sided line?
-	if (backsector == NULL || (line->linedef->portal && line->sidedef == line->linedef->sidedef[0]))
+	if (backsector == NULL || (line->linedef->isVisualPortal() && line->sidedef == line->linedef->sidedef[0]))
 	{
 		solid = true;
 	}
diff --git a/src/r_defs.h b/src/r_defs.h
index fb40a2bd1..901dadcb0 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -988,14 +988,25 @@ 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;
-	bool		portal_mirror;
-	bool		portal_passive;
 
+	line_t		*_portal_dst;
+	bool		_portal;
+
+	// returns true if the portal is crossable by actors
 	bool isLinePortal() const
 	{
-		return portal;
+		return false;	// right now there are no crossable portals
+	}
+
+	// returns true if the portal needs to be handled by the renderer
+	bool isVisualPortal() const
+	{
+		return _portal;
+	}
+
+	line_t *getPortalDestination() const
+	{
+		return _portal_dst;
 	}
 };
 
diff --git a/src/r_segs.cpp b/src/r_segs.cpp
index 79b5251c4..59bf12b39 100644
--- a/src/r_segs.cpp
+++ b/src/r_segs.cpp
@@ -2004,8 +2004,7 @@ void R_NewWall (bool needlights)
 	midtexture = toptexture = bottomtexture = 0;
 
 	if (sidedef == linedef->sidedef[0] &&
-		linedef->portal &&
-		(!linedef->portal_mirror || r_drawmirrors)) // [ZZ] compatibility with r_drawmirrors cvar that existed way before portals
+		(linedef->isVisualPortal() || (linedef->special == Line_Mirror && r_drawmirrors))) // [ZZ] compatibility with r_drawmirrors cvar that existed way before portals
 	{
 		markfloor = markceiling = true; // act like an one-sided wall here (todo: check how does this work with transparency)
 		rw_markportal = true;
@@ -2632,7 +2631,7 @@ void R_StoreWallRange (int start, int stop)
 	{
 		PortalDrawseg pds;
 		pds.src = curline->linedef;
-		pds.dst = curline->linedef->portal_dst;
+		pds.dst = curline->linedef->special == Line_Mirror? curline->linedef : curline->linedef->getPortalDestination();
 		pds.x1 = ds_p->x1;
 		pds.x2 = ds_p->x2;
 		pds.len = pds.x2 - pds.x1;
@@ -2653,7 +2652,7 @@ void R_StoreWallRange (int start, int stop)
 				pds.floorclip[i] = RenderTarget->GetHeight()-1;
 		}
 
-		pds.mirror = curline->linedef->portal_mirror;
+		pds.mirror = curline->linedef->special == Line_Mirror;
 		WallPortals.Push(pds);
 	}
 
diff --git a/src/r_things.cpp b/src/r_things.cpp
index 003e3a758..682ad5f35 100644
--- a/src/r_things.cpp
+++ b/src/r_things.cpp
@@ -31,6 +31,7 @@
 #include <stdlib.h>
 #include <algorithm>
 
+#include "p_lnspec.h"
 #include "templates.h"
 #include "doomdef.h"
 #include "m_swap.h"
@@ -339,11 +340,11 @@ static inline bool R_ClipSpriteColumnWithPortals (fixed_t x, fixed_t y, vissprit
 		if (!seg->curline) continue;
 
 		line_t* line = seg->curline->linedef;
-		// divline? wtf, anyway, divlines aren't supposed to be drawn. But I definitely saw NULL linedefs in drawsegs.
+		// ignore minisegs from GL nodes.
 		if (!line) continue;
 
 		// check if this line will clip sprites to itself
-		if (!line->portal)
+		if (!line->isVisualPortal() && line->special != Line_Mirror)
 			continue;
 
 		// don't clip sprites with portal's back side (it's transparent)
@@ -739,7 +740,7 @@ void R_ProjectSprite (AActor *thing, int fakeside, F3DFloor *fakefloor, F3DFloor
 
 	// [ZZ] Or less definitely not visible (hue)
 	// [ZZ] 10.01.2016: don't try to clip stuff inside a skybox against the current portal.
-	if (!CurrentPortalInSkybox && CurrentPortal && !!P_PointOnLineSide(thing->X(), thing->Y(), CurrentPortal->dst))
+	if (!CurrentPortalInSkybox && CurrentPortal && !!P_PointOnLineSidePrecise(thing->X(), thing->Y(), CurrentPortal->dst))
 		return;
 
 	// [RH] Interpolate the sprite's position to make it look smooth