Changed FImGuiContextManager to prevent moving created context proxies and to allow other objects with the same or shorter lifespan safely use cached pointers to those resources.

- Disabled move semantics in FImGuiContextProxy and removed code related to moving ImGui context.
- Changed FImGuiContextManager to store proxies as unique pointers.

Source/ImGui/Private/ImGuiContextManager.cpp

@@ -88,7 +88,7 @@ void FImGuiContextManager::Tick(float DeltaSeconds)
 		auto& ContextData = Pair.Value;
 		if (ContextData.CanTick())
 		{
-			ContextData.ContextProxy.Tick(DeltaSeconds);
+			ContextData.ContextProxy->Tick(DeltaSeconds);
 		}
 		else
 		{
@@ -129,7 +129,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetEditorContextData()
 	if (UNLIKELY(!Data))
 	{
 		Data = &Contexts.Emplace(Utilities::EDITOR_CONTEXT_INDEX, FContextData{ GetEditorContextName(), Utilities::EDITOR_CONTEXT_INDEX, DrawMultiContextEvent, FontAtlas, -1 });
-		ContextProxyCreatedEvent.Broadcast(Utilities::EDITOR_CONTEXT_INDEX, Data->ContextProxy);
+		ContextProxyCreatedEvent.Broadcast(Utilities::EDITOR_CONTEXT_INDEX, *Data->ContextProxy);
 	}
 
 	return *Data;
@@ -144,7 +144,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetStandaloneWorldCont
 	if (UNLIKELY(!Data))
 	{
 		Data = &Contexts.Emplace(Utilities::STANDALONE_GAME_CONTEXT_INDEX, FContextData{ GetWorldContextName(), Utilities::STANDALONE_GAME_CONTEXT_INDEX, DrawMultiContextEvent, FontAtlas });
-		ContextProxyCreatedEvent.Broadcast(Utilities::STANDALONE_GAME_CONTEXT_INDEX, Data->ContextProxy);
+		ContextProxyCreatedEvent.Broadcast(Utilities::STANDALONE_GAME_CONTEXT_INDEX, *Data->ContextProxy);
 	}
 
 	return *Data;
@@ -185,7 +185,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetWorldContextData(co
 	if (UNLIKELY(!Data))
 	{
 		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, DrawMultiContextEvent, FontAtlas, WorldContext->PIEInstance });
-		ContextProxyCreatedEvent.Broadcast(Index, Data->ContextProxy);
+		ContextProxyCreatedEvent.Broadcast(Index, *Data->ContextProxy);
 	}
 	else
 	{
@@ -196,7 +196,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetWorldContextData(co
 	if (UNLIKELY(!Data))
 	{
 		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, DrawMultiContextEvent, FontAtlas });
-		ContextProxyCreatedEvent.Broadcast(Index, Data->ContextProxy);
+		ContextProxyCreatedEvent.Broadcast(Index, *Data->ContextProxy);
 	}
 #endif
 

Source/ImGui/Private/ImGuiContextManager.h

@@ -34,25 +34,25 @@ public:
 
 #if WITH_EDITOR
 	// Get or create editor ImGui context proxy.
-	FORCEINLINE FImGuiContextProxy& GetEditorContextProxy() { return GetEditorContextData().ContextProxy; }
+	FORCEINLINE FImGuiContextProxy& GetEditorContextProxy() { return *GetEditorContextData().ContextProxy; }
 #endif
 
 #if !WITH_EDITOR
 	// Get or create standalone game ImGui context proxy.
-	FORCEINLINE FImGuiContextProxy& GetWorldContextProxy() { return GetStandaloneWorldContextData().ContextProxy; }
+	FORCEINLINE FImGuiContextProxy& GetWorldContextProxy() { return *GetStandaloneWorldContextData().ContextProxy; }
 #endif
 
 	// Get or create ImGui context proxy for given world.
-	FORCEINLINE FImGuiContextProxy& GetWorldContextProxy(const UWorld& World) { return GetWorldContextData(World).ContextProxy; }
+	FORCEINLINE FImGuiContextProxy& GetWorldContextProxy(const UWorld& World) { return *GetWorldContextData(World).ContextProxy; }
 
 	// Get or create ImGui context proxy for given world. Additionally get context index for that proxy.
-	FORCEINLINE FImGuiContextProxy& GetWorldContextProxy(const UWorld& World, int32& OutContextIndex) { return GetWorldContextData(World, &OutContextIndex).ContextProxy; }
+	FORCEINLINE FImGuiContextProxy& GetWorldContextProxy(const UWorld& World, int32& OutContextIndex) { return *GetWorldContextData(World, &OutContextIndex).ContextProxy; }
 
 	// Get context proxy by index, or null if context with that index doesn't exist.
 	FORCEINLINE FImGuiContextProxy* GetContextProxy(int32 ContextIndex)
 	{
 		FContextData* Data = Contexts.Find(ContextIndex);
-		return Data ? &(Data->ContextProxy) : nullptr;
+		return Data ? Data->ContextProxy.Get() : nullptr;
 	}
 
 	// Delegate called for all contexts in manager, right after calling context specific draw event. Allows listeners
@@ -66,38 +66,20 @@ public:
 
 private:
 
-#if WITH_EDITOR
-
 	struct FContextData
 	{
 		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, ImFontAtlas& FontAtlas, int32 InPIEInstance = -1)
 			: PIEInstance(InPIEInstance)
-			, ContextProxy(ContextName, ContextIndex, &SharedDrawEvent, &FontAtlas)
+			, ContextProxy(new FImGuiContextProxy(ContextName, ContextIndex, &SharedDrawEvent, &FontAtlas))
 		{
 		}
 
 		FORCEINLINE bool CanTick() const { return PIEInstance < 0 || GEngine->GetWorldContextFromPIEInstance(PIEInstance); }
 
 		int32 PIEInstance = -1;
-		FImGuiContextProxy ContextProxy;
+		TUniquePtr<FImGuiContextProxy> ContextProxy;
 	};
 
-#else
-
-	struct FContextData
-	{
-		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, ImFontAtlas& FontAtlas)
-			: ContextProxy(ContextName, ContextIndex, &SharedDrawEvent, &FontAtlas)
-		{
-		}
-
-		FORCEINLINE bool CanTick() const { return true; }
-
-		FImGuiContextProxy ContextProxy;
-	};
-
-#endif // WITH_EDITOR
-
 	void OnWorldTickStart(ELevelTick TickType, float DeltaSeconds);
 
 #if ENGINE_COMPATIBILITY_WITH_WORLD_POST_ACTOR_TICK

Source/ImGui/Private/ImGuiContextProxy.cpp

@@ -41,19 +41,6 @@ namespace
 	}
 }
 
-FImGuiContextProxy::FImGuiContextPtr::~FImGuiContextPtr()
-{
-	if (Context)
-	{
-		// Setting this as a current context. is still required in the current framework version to properly shutdown
-		// and save data.
-		ImGui::SetCurrentContext(Context);
-
-		// Save context data and destroy.
-		ImGui::DestroyContext(Context);
-	}
-}
-
 FImGuiContextProxy::FImGuiContextProxy(const FString& InName, int32 InContextIndex, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas)
 	: Name(InName)
 	, ContextIndex(InContextIndex)
@@ -61,7 +48,7 @@ FImGuiContextProxy::FImGuiContextProxy(const FString& InName, int32 InContextInd
 	, IniFilename(TCHAR_TO_ANSI(*GetIniFile(InName)))
 {
 	// Create context.
-	Context = FImGuiContextPtr(ImGui::CreateContext(InFontAtlas));
+	Context = ImGui::CreateContext(InFontAtlas);
 
 	// Set this context in ImGui for initialization (any allocations will be tracked in this context).
 	SetAsCurrent();
@@ -84,6 +71,19 @@ FImGuiContextProxy::FImGuiContextProxy(const FString& InName, int32 InContextInd
 	BeginFrame();
 }
 
+FImGuiContextProxy::~FImGuiContextProxy()
+{
+	if (Context)
+	{
+		// It seems that to properly shutdown context we need to set it as the current one (at least in this framework
+		// version), even though we can pass it to the destroy function.
+		SetAsCurrent();
+
+		// Save context data and destroy.
+		ImGui::DestroyContext(Context);
+	}
+}
+
 void FImGuiContextProxy::DrawEarlyDebug()
 {
 	if (bIsFrameStarted && !bIsDrawEarlyDebugCalled)

Source/ImGui/Private/ImGuiContextProxy.h

@@ -17,37 +17,16 @@
 // broadcasts draw events to allow listeners draw their controls. After update it stores draw data.
 class FImGuiContextProxy
 {
-	class FImGuiContextPtr
-	{
-	public:
-
-		FImGuiContextPtr() = default;
-		FImGuiContextPtr(ImGuiContext* InContext) : Context(InContext) {}
-
-		FImGuiContextPtr(const FImGuiContextPtr&) = delete;
-		FImGuiContextPtr& operator=(const FImGuiContextPtr&) = delete;
-
-		FImGuiContextPtr(FImGuiContextPtr&& Other) : Context(Other.Context) { Other.Context = nullptr; }
-		FImGuiContextPtr& operator=(FImGuiContextPtr&& Other) { std::swap(Context, Other.Context); return *this; }
-
-		~FImGuiContextPtr();
-
-		ImGuiContext* Get() const { return Context; }
-
-	private:
-
-		ImGuiContext* Context = nullptr;
-	};
-
 public:
 
 	FImGuiContextProxy(const FString& Name, int32 InContextIndex, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas);
+	~FImGuiContextProxy();
 
 	FImGuiContextProxy(const FImGuiContextProxy&) = delete;
 	FImGuiContextProxy& operator=(const FImGuiContextProxy&) = delete;
 
-	FImGuiContextProxy(FImGuiContextProxy&&) = default;
+	FImGuiContextProxy(FImGuiContextProxy&&) = delete;
-	FImGuiContextProxy& operator=(FImGuiContextProxy&&) = default;
+	FImGuiContextProxy& operator=(FImGuiContextProxy&&) = delete;
 
 	// Get the name of this context.
 	const FString& GetName() const { return Name; }
@@ -60,10 +39,10 @@ public:
 	const FImGuiInputState& GetInputState() const { return InputState; }
 
 	// Is this context the current ImGui context.
-	bool IsCurrentContext() const { return ImGui::GetCurrentContext() == Context.Get(); }
+	bool IsCurrentContext() const { return ImGui::GetCurrentContext() == Context; }
 
 	// Set this context as current ImGui context.
-	void SetAsCurrent() { ImGui::SetCurrentContext(Context.Get()); }
+	void SetAsCurrent() { ImGui::SetCurrentContext(Context); }
 
 	// Context display size (read once per frame during context update).
 	const FVector2D& GetDisplaySize() const { return DisplaySize; }
@@ -102,7 +81,7 @@ private:
 	void BroadcastWorldDebug();
 	void BroadcastMultiContextDebug();
 
-	FImGuiContextPtr Context;
+	ImGuiContext* Context;
 
 	FVector2D DisplaySize = FVector2D::ZeroVector;