Merged https://github.com/coelckers/gzdoom/pull/1561

src/playsim/actor.h

@@ -425,6 +425,7 @@ enum ActorFlag8
 	MF8_STAYONLIFT		= 0x02000000,	// MBF AI enhancement.
 	MF8_DONTFOLLOWPLAYERS	= 0x04000000,	// [inkoalawetrust] Friendly monster will not follow players.
 	MF8_SEEFRIENDLYMONSTERS	= 0X08000000,	// [inkoalawetrust] Hostile monster can see friendly monsters.
+	MF8_CROSSLINECHECK	= 0x10000000,	// [MC]Enables CanCrossLine virtual
 };
 
 // --- mobj.renderflags ---

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, DVector3 next)
+{
+	static unsigned VIndex = ~0u;
+	if (VIndex == ~0u)
+	{
+		VIndex = GetVirtualIndex(RUNTIME_CLASS(AActor), "CanCrossLine");
+		assert(VIndex != ~0u);
+	}
+
+	VMValue params[] = { mo, line, 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
@@ -953,6 +985,13 @@ bool PIT_CheckLine(FMultiBlockLinesIterator &mit, FMultiBlockLinesIterator::Chec
 		}
 	}
 
+	if ((tm.thing->flags8 & MF8_CROSSLINECHECK) && !P_CanCrossLine(tm.thing, 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.

src/scripting/thingdef_data.cpp

@@ -340,6 +340,7 @@ static FFlagDef ActorFlagDefs[]=
 	DEFINE_FLAG(MF8, STAYONLIFT, AActor, flags8),
 	DEFINE_FLAG(MF8, DONTFOLLOWPLAYERS, AActor, flags8),
 	DEFINE_FLAG(MF8, SEEFRIENDLYMONSTERS, AActor, flags8),
+	DEFINE_FLAG(MF8, CROSSLINECHECK, AActor, flags8),
 
 	// Effect flags
 	DEFINE_FLAG(FX, VISIBILITYPULSE, AActor, effects),

wadsrc/static/zscript/actors/actor.zs

@@ -506,6 +506,12 @@ class Actor : Thinker native
 		return true;
 	}
 
+	// Called by PIT_CheckLine to check if an actor can cross a line.
+	virtual bool CanCrossLine(Line crossing, 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)