From 3923039a1bbda2f910ba7af11a74b79b514ac623 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <c.oelckers@zdoom.fake>
Date: Thu, 7 Apr 2016 01:16:07 +0200
Subject: [PATCH] - fixed: a sight check that starts right on a linedef should
 ignore that linedef.

Trying to calculate a slope to the target from this linedef's opening will always result in failure because it'd involve a division by zero.
---
 src/p_sight.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/p_sight.cpp b/src/p_sight.cpp
index f8d2043fd..847448185 100644
--- a/src/p_sight.cpp
+++ b/src/p_sight.cpp
@@ -216,6 +216,9 @@ bool SightCheck::PTR_SightTraverse (intercept_t *in)
 	if (open.range == 0 && open.portalflags == 0 && (lport == NULL || lport->mType != PORTT_LINKED))		// quick test for totally closed doors (must be delayed if portal checks are needed, though)
 		return false;		// stop
 
+	if (in->frac == 0)
+		return true;
+
 	// check bottom
 	if (open.bottom > LINEOPEN_MIN)
 	{