From 047384cb5a485f3b640a2c58b632146b8b748ce4 Mon Sep 17 00:00:00 2001
From: Major Cooke <majorcooke22@gmail.com>
Date: Sat, 19 Dec 2020 11:00:57 -0600
Subject: [PATCH] Merged https://github.com/coelckers/gzdoom/pull/1192
 (CanCrossLine)

---
 src/playsim/p_map.cpp                 | 39 +++++++++++++++++++++++++++
 wadsrc/static/zscript/actors/actor.zs |  6 +++++
 2 files changed, 45 insertions(+)

diff --git a/src/playsim/p_map.cpp b/src/playsim/p_map.cpp
index 9ba6dd8e1..151953d07 100644
--- a/src/playsim/p_map.cpp
+++ b/src/playsim/p_map.cpp
@@ -155,6 +155,38 @@ bool P_CanCollideWith(AActor *tmthing, AActor *thing)
 	return true;
 }
 
+//==========================================================================
+// 
+// CanCrossLine
+//
+// Checks if an actor can cross a line after all checks are processed.
+// If false, the line blocks them.
+//==========================================================================
+
+bool P_CanCrossLine(AActor *mo, line_t *line, int side, DVector3 next)
+{
+	static unsigned VIndex = ~0u;
+	if (VIndex == ~0u)
+	{
+		VIndex = GetVirtualIndex(RUNTIME_CLASS(AActor), "CanCrossLine");
+		assert(VIndex != ~0u);
+	}
+
+	VMValue params[] = { mo, line, side, next.X, next.Y, next.Z, false };
+	VMReturn ret;
+	int retval;
+	ret.IntAt(&retval);
+
+	auto clss = mo->GetClass();
+	VMFunction *func = clss->Virtuals.Size() > VIndex ? clss->Virtuals[VIndex] : nullptr;
+	if (func != nullptr)
+	{
+		VMCall(func, params, countof(params), &ret, 1);
+		return retval;
+	}
+	return true;
+}
+
 //==========================================================================
 //
 // FindRefPoint
@@ -962,6 +994,13 @@ bool PIT_CheckLine(FMultiBlockLinesIterator &mit, FMultiBlockLinesIterator::Chec
 		}
 	}
 
+	if (!P_CanCrossLine(tm.thing, ld, P_PointOnLineSide(cres.Position, ld), tm.pos))
+	{
+		if (wasfit)
+			tm.thing->BlockingLine = ld;
+		
+		return false;
+	}
 	// If the floor planes on both sides match we should recalculate open.bottom at the actual position we are checking
 	// This is to avoid bumpy movement when crossing a linedef with the same slope on both sides.
 	// This should never narrow down the opening, though, only widen it.
diff --git a/wadsrc/static/zscript/actors/actor.zs b/wadsrc/static/zscript/actors/actor.zs
index 45662bdce..7cc252c7f 100644
--- a/wadsrc/static/zscript/actors/actor.zs
+++ b/wadsrc/static/zscript/actors/actor.zs
@@ -485,6 +485,12 @@ class Actor : Thinker native
 		return true;
 	}
 
+	// Called by PIT_CheckLine to check if an actor can cross a line.
+	virtual bool CanCrossLine(Line crossing, int side, Vector3 next)
+	{
+		return true;
+	}
+
 	// Called by revival/resurrection to check if one can resurrect the other.
 	// "other" can be null when not passive.
 	virtual bool CanResurrect(Actor other, bool passive)