diff --git a/src/p_map.cpp b/src/p_map.cpp
index 5d5777d6f..61e651ce6 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -4463,10 +4463,17 @@ struct SRailHit
 	DVector3 HitPos;
 	DAngle HitAngle;
 };
+struct SPortalHit
+{
+	DVector3 HitPos;
+	DVector3 ContPos;
+	DVector3 OutDir;
+};
 struct RailData
 {
 	AActor *Caller;
 	TArray<SRailHit> RailHits;
+	TArray<SPortalHit> PortalHits;
 	bool StopAtOne;
 	bool StopAtInvul;
 	bool ThruSpecies;
@@ -4475,6 +4482,16 @@ struct RailData
 static ETraceStatus ProcessRailHit(FTraceResults &res, void *userdata)
 {
 	RailData *data = (RailData *)userdata;
+	if (res.HitType == TRACE_CrossingPortal)
+	{
+		SPortalHit newhit;
+		newhit.HitPos = res.HitPos;
+		newhit.ContPos = res.SrcFromTarget;
+		newhit.OutDir = res.HitVector;
+		data->PortalHits.Push(newhit);
+		return TRACE_Continue;
+	}
+
 	if (res.HitType != TRACE_HitActor)
 	{
 		return TRACE_Stop;
@@ -4559,7 +4576,8 @@ void P_RailAttack(FRailParams *p)
 	assert(puffclass != NULL);		// Because we set it to a default above
 	AActor *puffDefaults = GetDefaultByType(puffclass->GetReplacement()); //Contains all the flags such as FOILINVUL, etc.
 
-	flags = (puffDefaults->flags6 & MF6_NOTRIGGER) ? 0 : TRACE_PCross | TRACE_Impact;
+	// disabled because not complete yet.
+	flags = (puffDefaults->flags6 & MF6_NOTRIGGER) ? 0/*TRACE_ReportPortals*/ : TRACE_PCross | TRACE_Impact /*| TRACE_ReportPortals*/;
 	rail_data.StopAtInvul = (puffDefaults->flags3 & MF3_FOILINVUL) ? false : true;
 	rail_data.ThruSpecies = (puffDefaults->flags6 & MF6_MTHRUSPECIES) ? true : false;
 	Trace(start, source->Sector, vec, p->distance, MF_SHOOTABLE, ML_BLOCKEVERYTHING, source, trace,	flags, ProcessRailHit, &rail_data);
diff --git a/src/p_trace.cpp b/src/p_trace.cpp
index dabc92110..7526456e1 100644
--- a/src/p_trace.cpp
+++ b/src/p_trace.cpp
@@ -66,6 +66,8 @@ struct FTraceInfo
 	double startfrac;
 	int aimdir;
 	double limitz;
+	double lastfloorportalheight;
+	double lastceilingportalheight;
 
 	// These are required for 3D-floor checking
 	// to create a fake sector with a floor 
@@ -141,6 +143,7 @@ bool Trace(const DVector3 &start, sector_t *sector, const DVector3 &direction, d
 	inf.sectorsel=0;
 	inf.aimdir = -1;
 	inf.startfrac = 0;
+	inf.lastfloorportalheight = inf.lastceilingportalheight = start.Z;
 	memset(&res, 0, sizeof(res));
 
 	if (inf.TraceTraverse (ptflags))
@@ -196,6 +199,7 @@ void FTraceInfo::EnterSectorPortal(int position, double frac, sector_t *entersec
 	newtrace.aimdir = position;
 	newtrace.limitz = portal->specialf1;
 	newtrace.sectorsel = 0;
+	newtrace.lastfloorportalheight = newtrace.lastceilingportalheight = limitz;
 
 	if (newtrace.TraceTraverse(ActorMask ? PT_ADDLINES | PT_ADDTHINGS | PT_COMPATIBLE : PT_ADDLINES))
 	{
@@ -227,7 +231,7 @@ int FTraceInfo::EnterLinePortal(line_t *li, double frac)
 
 	frac += 1 / MaxDist;
 	double enterdist = MaxDist / frac;
-	DVector2 enter = newtrace.Start.XY() + enterdist * Vec.XY();
+	DVector2 enter = newtrace.Start + enterdist * Vec;
 
 	newtrace.ActorMask = ActorMask;
 	newtrace.WallMask = WallMask;
@@ -244,7 +248,9 @@ int FTraceInfo::EnterLinePortal(line_t *li, double frac)
 	newtrace.startfrac = frac;
 	newtrace.aimdir = aimdir;
 	newtrace.limitz = limitz;
+
 	P_TranslatePortalZ(li, newtrace.limitz);
+	newtrace.lastfloorportalheight = newtrace.lastceilingportalheight = newtrace.limitz;
 	newtrace.sectorsel = 0;
 	Results->unlinked = true;
 	return newtrace.TraceTraverse(ActorMask ? PT_ADDLINES | PT_ADDTHINGS | PT_COMPATIBLE : PT_ADDLINES);
@@ -442,11 +448,24 @@ bool FTraceInfo::LineCheck(intercept_t *in)
 			Results->HitType = TRACE_HitFloor;
 			Results->HitTexture = CurSector->GetTexture(sector_t::floor);
 		}
-		else if (entersector == NULL || entersector->PortalBlocksMovement(sector_t::floor))
+		else
 		{
-			// hit beyond a portal plane. This needs to be taken care of by the trace spawned on the other side.
-			Results->HitType = TRACE_HitNone;
-			return false;
+			if ((TraceFlags & TRACE_ReportPortals) && lastfloorportalheight > fc)
+			{
+				lastfloorportalheight = fc;
+				if (TraceCallback != NULL)
+				{
+					// Todo: calculate the intersection point.
+					Results->HitType = TRACE_CrossingPortal;
+					TraceCallback(*Results, TraceCallbackData);
+				}
+			}
+			if (entersector == NULL || entersector->PortalBlocksMovement(sector_t::floor))
+			{
+				// hit beyond a portal plane. This needs to be taken care of by the trace spawned on the other side.
+				Results->HitType = TRACE_HitNone;
+				return false;
+			}
 		}
 	}
 	else if (hit.Z >= fc)
@@ -457,11 +476,24 @@ bool FTraceInfo::LineCheck(intercept_t *in)
 			Results->HitType = TRACE_HitCeiling;
 			Results->HitTexture = CurSector->GetTexture(sector_t::ceiling);
 		}
-		else if (entersector == NULL || entersector->PortalBlocksMovement(sector_t::ceiling))
+		else
 		{
-			// hit beyond a portal plane. This needs to be taken care of by the trace spawned on the other side.
-			Results->HitType = TRACE_HitNone;
-			return false;
+			if ((TraceFlags & TRACE_ReportPortals) && lastceilingportalheight < fc)
+			{
+				lastceilingportalheight = fc;
+				if (TraceCallback != NULL)
+				{
+					// Todo: calculate the intersection point.
+					Results->HitType = TRACE_CrossingPortal;
+					TraceCallback(*Results, TraceCallbackData);
+				}
+			}
+			if (entersector == NULL || entersector->PortalBlocksMovement(sector_t::ceiling))
+			{
+				// hit beyond a portal plane. This needs to be taken care of by the trace spawned on the other side.
+				Results->HitType = TRACE_HitNone;
+				return false;
+			}
 		}
 	}
 	else if (in->d.line->isLinePortal())
diff --git a/src/p_trace.h b/src/p_trace.h
index 2c817816e..7eaf50ce5 100644
--- a/src/p_trace.h
+++ b/src/p_trace.h
@@ -50,7 +50,8 @@ enum ETraceResult
 	TRACE_HitFloor,
 	TRACE_HitCeiling,
 	TRACE_HitWall,
-	TRACE_HitActor
+	TRACE_HitActor,
+	TRACE_CrossingPortal,
 };
 
 enum
@@ -113,6 +114,7 @@ enum
 	TRACE_PCross		= 2,	// Trigger SPAC_PCROSS lines
 	TRACE_Impact		= 4,	// Trigger SPAC_IMPACT lines
 	TRACE_PortalRestrict= 8,	// Cannot go through portals without a static link offset.
+	TRACE_ReportPortals = 16,	// Report any portal crossing to the TraceCallback
 };
 
 // return values from callback