From e18b17217fbcb35e9670b3fae2f39bfcb0715ecf Mon Sep 17 00:00:00 2001
From: Marisa Kirisame <marisa@sayachan.org>
Date: Wed, 15 Aug 2018 17:46:03 +0200
Subject: [PATCH] Added CheckReplacement to event handlers, a function inspired
 by its namesake in Unreal's Mutator class. Performs runtime replacement of
 actor classes. Takes priority over the "replaces" keyword in both DECORATE
 and ZScript.

---
 src/events.cpp                   | 27 +++++++++++++++++++++++++++
 src/events.h                     | 12 ++++++++++++
 src/info.cpp                     |  4 +++-
 wadsrc/static/zscript/events.txt |  9 +++++++++
 4 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/src/events.cpp b/src/events.cpp
index eabf1b9313..11766f6c90 100755
--- a/src/events.cpp
+++ b/src/events.cpp
@@ -38,6 +38,7 @@
 #include "actor.h"
 #include "c_dispatch.h"
 #include "d_net.h"
+#include "info.h"
 
 DStaticEventHandler* E_FirstEventHandler = nullptr;
 DStaticEventHandler* E_LastEventHandler = nullptr;
@@ -506,6 +507,12 @@ bool E_CheckRequireMouse()
 	return false;
 }
 
+void E_CheckReplacement( PClassActor *replacee, PClassActor **replacement )
+{
+	for (DStaticEventHandler *handler = E_FirstEventHandler; handler; handler = handler->next)
+		handler->CheckReplacement(replacee,replacement);
+}
+
 // normal event loopers (non-special, argument-less)
 DEFINE_EVENT_LOOPER(RenderFrame)
 DEFINE_EVENT_LOOPER(WorldLightning)
@@ -571,6 +578,9 @@ DEFINE_FIELD_X(ConsoleEvent, FConsoleEvent, Name)
 DEFINE_FIELD_X(ConsoleEvent, FConsoleEvent, Args)
 DEFINE_FIELD_X(ConsoleEvent, FConsoleEvent, IsManual)
 
+DEFINE_FIELD_X(ReplaceEvent, FReplaceEvent, Replacee)
+DEFINE_FIELD_X(ReplaceEvent, FReplaceEvent, Replacement)
+
 DEFINE_ACTION_FUNCTION(DStaticEventHandler, SetOrder)
 {
 	PARAM_SELF_PROLOGUE(DStaticEventHandler);
@@ -653,6 +663,8 @@ DEFINE_EMPTY_HANDLER(DStaticEventHandler, PostUiTick);
 DEFINE_EMPTY_HANDLER(DStaticEventHandler, ConsoleProcess);
 DEFINE_EMPTY_HANDLER(DStaticEventHandler, NetworkProcess);
 
+DEFINE_EMPTY_HANDLER(DStaticEventHandler, CheckReplacement);
+
 // ===========================================
 //
 //  Event handlers
@@ -1123,6 +1135,21 @@ void DStaticEventHandler::ConsoleProcess(int player, FString name, int arg1, int
 	}
 }
 
+void DStaticEventHandler::CheckReplacement( PClassActor *replacee, PClassActor **replacement )
+{
+	IFVIRTUAL(DStaticEventHandler, CheckReplacement)
+	{
+		// don't create excessive DObjects if not going to be processed anyway
+		if (func == DStaticEventHandler_CheckReplacement_VMPtr)
+			return;
+		FReplaceEvent e = { replacee, *replacement };
+		VMValue params[2] = { (DStaticEventHandler*)this, &e };
+		VMCall(func, params, 2, nullptr, 0);
+		if ( e.Replacement != replacee ) // prevent infinite recursion
+			*replacement = e.Replacement;
+	}
+}
+
 //
 void DStaticEventHandler::OnDestroy()
 {
diff --git a/src/events.h b/src/events.h
index 072502501b..4359178ceb 100755
--- a/src/events.h
+++ b/src/events.h
@@ -69,6 +69,9 @@ bool E_Responder(const event_t* ev); // splits events into InputProcess and UiPr
 // this executes on console/net events.
 void E_Console(int player, FString name, int arg1, int arg2, int arg3, bool manual);
 
+// called when looking up the replacement for an actor class
+void E_CheckReplacement(PClassActor* replacee, PClassActor** replacement);
+
 // send networked event. unified function.
 bool E_SendNetworkEvent(FString name, int arg1, int arg2, int arg3, bool manual);
 
@@ -166,6 +169,9 @@ public:
 	
 	// 
 	void ConsoleProcess(int player, FString name, int arg1, int arg2, int arg3, bool manual);
+
+	//
+	void CheckReplacement(PClassActor* replacee, PClassActor** replacement);
 };
 class DEventHandler : public DStaticEventHandler
 {
@@ -262,4 +268,10 @@ struct FConsoleEvent
 	bool IsManual;
 };
 
+struct FReplaceEvent
+{
+	PClassActor* Replacee;
+	PClassActor* Replacement;
+};
+
 #endif
diff --git a/src/info.cpp b/src/info.cpp
index 4022e8b2ab..480c358145 100644
--- a/src/info.cpp
+++ b/src/info.cpp
@@ -425,7 +425,9 @@ PClassActor *PClassActor::GetReplacement(bool lookskill)
 			lookskill = false; skillrepname = NAME_None;
 		}
 	}
-	auto Replacement = ActorInfo()->Replacement;
+	// [MK] ZScript replacement through Event Handlers, has priority over others
+	PClassActor *Replacement = ActorInfo()->Replacement;
+	E_CheckReplacement(this,&Replacement);
 	if (Replacement == nullptr && (!lookskill || skillrepname == NAME_None))
 	{
 		return this;
diff --git a/wadsrc/static/zscript/events.txt b/wadsrc/static/zscript/events.txt
index fc8b82721a..038e84515c 100755
--- a/wadsrc/static/zscript/events.txt
+++ b/wadsrc/static/zscript/events.txt
@@ -285,6 +285,12 @@ struct ConsoleEvent native version("2.4")
     native readonly bool IsManual;
 }
 
+struct ReplaceEvent native version("2.4")
+{
+	native readonly Class<Actor> Replacee;
+	native Class<Actor> Replacement;
+}
+
 class StaticEventHandler : Object native play version("2.4")
 {
     // static event handlers CAN register other static event handlers.
@@ -329,6 +335,9 @@ class StaticEventHandler : Object native play version("2.4")
     virtual native ui void ConsoleProcess(ConsoleEvent e);
     virtual native void NetworkProcess(ConsoleEvent e);
     
+    //
+    virtual native void CheckReplacement(ReplaceEvent e);
+
     // this value will be queried on Register() to decide the relative order of this handler to every other.
     // this is most useful in UI systems.
     // default is 0.