Credit system BP: make the BP loader an UEngineSubsystem

so that we don't have to manage its lifecycle and especially not
CesiumCreditSystemBP's lifecycle either, which was causing issues
when unloading then reloading levels in-game (Shipping).

Author: GhisBntly

Diff for: Source/CesiumRuntime/Private/CesiumCreditSystem.cpp

@@ -21,7 +21,6 @@
 #include "Modules/ModuleManager.h"
 #endif
 
-/*static*/ UObject* ACesiumCreditSystem::CesiumCreditSystemBP = nullptr;
 namespace {
 
 /**
@@ -89,22 +88,6 @@ FName ACesiumCreditSystem::DEFAULT_CREDITSYSTEM_TAG =
 
 /*static*/ ACesiumCreditSystem*
 ACesiumCreditSystem::GetDefaultCreditSystem(const UObject* WorldContextObject) {
-  // Blueprint loading can only happen in a constructor, so we instantiate a
-  // loader object that retrieves the blueprint class in its constructor. We can
-  // destroy the loader immediately once it's done since it will have already
-  // set CesiumCreditSystemBP.
-  if (!IsValid(CesiumCreditSystemBP)) {
-    UCesiumCreditSystemBPLoader* bpLoader =
-        NewObject<UCesiumCreditSystemBPLoader>();
-    CesiumCreditSystemBP = bpLoader->CesiumCreditSystemBP.LoadSynchronous();
-    // Prevent the GC from destroying the object when unloading a level, as it will be reused
-    // if one subsequently loads another level. This kind of static object should probably be
-    // replaced by a "subsystem"
-    // (https://dev.epicgames.com/documentation/en-us/unreal-engine/programming-subsystems-in-unreal-engine)
-    CesiumCreditSystemBP->AddToRoot();
-    bpLoader->ConditionalBeginDestroy();
-  }
-
   UWorld* world = WorldContextObject->GetWorld();
   // This method can be called by actors even when opening the content browser.
   if (!IsValid(world)) {
@@ -159,8 +142,11 @@ ACesiumCreditSystem::GetDefaultCreditSystem(const UObject* WorldContextObject) {
     spawnParameters.SpawnCollisionHandlingOverride =
         ESpawnActorCollisionHandlingMethod::AlwaysSpawn;
     spawnParameters.OverrideLevel = world->PersistentLevel;
-    pCreditSystem = world->SpawnActor<ACesiumCreditSystem>(
-        Cast<UClass>(CesiumCreditSystemBP),
+    UCesiumCreditSystemBPLoader* bpLoader =
+      GEngine->GetEngineSubsystem<UCesiumCreditSystemBPLoader>();
+    UClass* CesiumCreditSystemBP =
+        Cast<UClass>(bpLoader->CesiumCreditSystemBP.LoadSynchronous());
+        CesiumCreditSystemBP,
         spawnParameters);
     // Null check so the editor doesn't crash when it makes arbitrary calls to
     // this function without a valid world context object.

Diff for: Source/CesiumRuntime/Private/CesiumCreditSystemBPLoader.h

@@ -2,10 +2,12 @@
 
 #pragma once
 
+#include <Subsystems/EngineSubsystem.h>
+
 #include "CesiumCreditSystemBPLoader.generated.h"
 
 UCLASS()
-class UCesiumCreditSystemBPLoader : public UObject {
+class UCesiumCreditSystemBPLoader : public UEngineSubsystem {
   GENERATED_BODY()
 
 public:

Diff for: Source/CesiumRuntime/Public/CesiumCreditSystem.h

@@ -75,8 +75,6 @@ class CESIUMRUNTIME_API ACesiumCreditSystem : public AActor {
 #endif
 
 private:
-  static UObject* CesiumCreditSystemBP;
-
   /**
    * A tag that is assigned to Credit Systems when they are created
    * as the "default" Credit System for a certain world.