From 6107f36ad225890d9c4da0369bd4c557fb40e3e4 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@users.noreply.github.com>
Date: Mon, 29 Jan 2018 18:00:55 +0100
Subject: [PATCH] - iterating through portal groups must check for situations
 where badly constructed maps let items end up in another portal group.

---
 src/p_maputl.cpp | 27 ++++++++++++++++++---------
 src/p_maputl.h   |  2 +-
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/p_maputl.cpp b/src/p_maputl.cpp
index 24c30375e..6b19942e0 100644
--- a/src/p_maputl.cpp
+++ b/src/p_maputl.cpp
@@ -809,11 +809,13 @@ bool FMultiBlockLinesIterator::GoUp(double x, double y)
 	{
 		if (!cursector->PortalBlocksMovement(sector_t::ceiling))
 		{
-			startIteratorForGroup(cursector->GetOppositePortalGroup(sector_t::ceiling));
-			portalflags = FFCF_NOFLOOR;
-			return true;
+			if (startIteratorForGroup(cursector->GetOppositePortalGroup(sector_t::ceiling)))
+			{
+				portalflags = FFCF_NOFLOOR;
+				return true;
+			}
 		}
-		else continueup = false;
+		continueup = false;
 	}
 	return false;
 }
@@ -830,11 +832,13 @@ bool FMultiBlockLinesIterator::GoDown(double x, double y)
 	{
 		if (!cursector->PortalBlocksMovement(sector_t::floor))
 		{
-			startIteratorForGroup(cursector->GetOppositePortalGroup(sector_t::floor));
-			portalflags = FFCF_NOCEILING;
-			return true;
+			if (startIteratorForGroup(cursector->GetOppositePortalGroup(sector_t::floor)))
+			{
+				portalflags = FFCF_NOCEILING;
+				return true;
+			}
 		}
-		else continuedown = false;
+		continuedown = false;
 	}
 	return false;
 }
@@ -906,14 +910,19 @@ bool FMultiBlockLinesIterator::Next(FMultiBlockLinesIterator::CheckResult *item)
 //
 //===========================================================================
 
-void FMultiBlockLinesIterator::startIteratorForGroup(int group)
+bool FMultiBlockLinesIterator::startIteratorForGroup(int group)
 {
 	offset = Displacements.getOffset(basegroup, group);
 	offset.X += checkpoint.X;
 	offset.Y += checkpoint.Y;
 	cursector = group == startsector->PortalGroup ? startsector : P_PointInSector(offset);
+	// If we ended up in a different group, 
+	// presumably because the spot to be checked is too far outside the actual portal group,
+	// the search needs to abort.
+	if (cursector->PortalGroup != group) return false;
 	bbox.setBox(offset.X, offset.Y, checkpoint.Z);
 	blockIterator.init(bbox);
+	return true;
 }
 
 //===========================================================================
diff --git a/src/p_maputl.h b/src/p_maputl.h
index 8ac3ea76a..4dfa99e0f 100644
--- a/src/p_maputl.h
+++ b/src/p_maputl.h
@@ -240,7 +240,7 @@ class FMultiBlockLinesIterator
 
 	bool GoUp(double x, double y);
 	bool GoDown(double x, double y);
-	void startIteratorForGroup(int group);
+	bool startIteratorForGroup(int group);
 
 public: