From bb862098ea4ae72b21f9ea0c2a8d8c7a83aa2357 Mon Sep 17 00:00:00 2001
From: Major Cooke <majorcooke22@gmail.com>
Date: Sun, 27 Sep 2020 16:15:58 -0500
Subject: [PATCH] Added CanCrossLine virtual for actors.

- Called last after all other line checks occur. Returning false means the actor cannot cross that line.
---
 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 1dd5d55781..5d0017bffa 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)
+{
+	static unsigned VIndex = ~0u;
+	if (VIndex == ~0u)
+	{
+		VIndex = GetVirtualIndex(RUNTIME_CLASS(AActor), "CanCrossLine");
+		assert(VIndex != ~0u);
+	}
+
+	VMValue params[4] = { mo, line, side, 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, 4, &ret, 1);
+		return retval;
+	}
+	return true;
+}
+
 //==========================================================================
 //
 // FindRefPoint
@@ -953,6 +985,13 @@ bool PIT_CheckLine(FMultiBlockLinesIterator &mit, FMultiBlockLinesIterator::Chec
 		}
 	}
 
+	if (!P_CanCrossLine(tm.thing, ld, P_PointOnLineSide(cres.Position, ld)))
+	{
+		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 96d60b7616..2972055989 100644
--- a/wadsrc/static/zscript/actors/actor.zs
+++ b/wadsrc/static/zscript/actors/actor.zs
@@ -501,6 +501,12 @@ 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)
+	{
+		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)