Changed interface to register ImGui debug delegates:

- Added new FImGuiDelegates interface for ImGui debug delegates.
- Added FImGuiDelegatesContainer for ImGui delegates.
- Added code preserving delegates during hot-reloading and moving them to a new module.
- Depreciated old FImGuiModule delegates interface and FImGuiDelegateHandle.
- Delegates registered with depreciated interface are redirected and get benefit of being preserved during hot-reloading. This can be controlled with IMGUI_REDIRECT_OBSOLETE_DELEGATES.
- Added IMGUI_WITH_OBSOLETE_DELEGATES allowing to strip depreciated interface from builds.
- Modified context manager and context proxy to work with FImGuiDelegatesContainer.

CHANGES.md

@@ -5,6 +5,13 @@ Versions marked as 'unofficial' are labelled only for the needs of this changelo
 Change History
 --------------
 
+Version: 1.15 (2019/04)
+- Added new FImGuiDelegates interface for ImGui debug delegates.
+- Added code preserving delegates during hot-reloading and moving them to a new module.
+- DEPRECIATED old FImGuiModule delegates interface and FImGuiDelegateHandle.
+- Delegates registered with depreciated interface are redirected and get benefit of being preserved during hot-reloading. This can be controlled with IMGUI_REDIRECT_OBSOLETE_DELEGATES.
+- Added IMGUI_WITH_OBSOLETE_DELEGATES allowing to strip depreciated interface from builds (that interface will be officially removed in one of later releases).
+
 Version: 1.14 (2019/03)
 - Added SImGuiLayout to resets layout for SImGuiWidget.
 - Refactored rendering in SImGuiWidget to take advantage of layout reset.

ImGui.uplugin

@@ -1,7 +1,7 @@
 {
 	"FileVersion": 3,
 	"Version": 1,
-	"VersionName": "1.14",
+	"VersionName": "1.15",
 	"FriendlyName": "ImGui",
 	"Description": "",
 	"Category": "Debug",

Source/ImGui/Private/ImGuiContextManager.cpp

@@ -4,6 +4,7 @@
 
 #include "ImGuiContextManager.h"
 
+#include "ImGuiDelegatesContainer.h"
 #include "ImGuiImplementation.h"
 #include "Utilities/ScopeGuards.h"
 #include "Utilities/WorldContext.h"
@@ -89,6 +90,11 @@ void FImGuiContextManager::Tick(float DeltaSeconds)
 		{
 			ContextData.ContextProxy.Tick(DeltaSeconds);
 		}
+		else
+		{
+			// Clear to make sure that we don't store objects registered for world that is no longer valid.
+			FImGuiDelegatesContainer::Get().OnWorldDebug(Pair.Key).Clear();
+		}
 	}
 }
 

Source/ImGui/Private/ImGuiContextManager.h

@@ -72,7 +72,7 @@ private:
 	{
 		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, ImFontAtlas& FontAtlas, int32 InPIEInstance = -1)
 			: PIEInstance(InPIEInstance)
-			, ContextProxy(ContextName, &SharedDrawEvent, &FontAtlas)
+			, ContextProxy(ContextName, ContextIndex, &SharedDrawEvent, &FontAtlas)
 		{
 		}
 
@@ -87,7 +87,7 @@ private:
 	struct FContextData
 	{
 		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, ImFontAtlas& FontAtlas)
-			: ContextProxy(ContextName, &SharedDrawEvent, &FontAtlas)
+			: ContextProxy(ContextName, ContextIndex, &SharedDrawEvent, &FontAtlas)
 		{
 		}
 

Source/ImGui/Private/ImGuiContextProxy.cpp

@@ -4,6 +4,7 @@
 
 #include "ImGuiContextProxy.h"
 
+#include "ImGuiDelegatesContainer.h"
 #include "ImGuiImplementation.h"
 #include "ImGuiInteroperability.h"
 
@@ -52,8 +53,9 @@ FImGuiContextProxy::FImGuiContextPtr::~FImGuiContextPtr()
 	}
 }
 
-FImGuiContextProxy::FImGuiContextProxy(const FString& InName, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas)
+FImGuiContextProxy::FImGuiContextProxy(const FString& InName, int32 InContextIndex, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas)
 	: Name(InName)
+	, ContextIndex(InContextIndex)
 	, SharedDrawEvent(InSharedDrawEvent)
 	, IniFilename(TCHAR_TO_ANSI(*GetIniFile(InName)))
 {
@@ -91,22 +93,13 @@ void FImGuiContextProxy::Draw()
 
 		// Broadcast draw event to allow listeners to draw their controls to this context.
 #if DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT
-		if (DrawEvent.IsBound())
-		{
-			DrawEvent.Broadcast();
-		}
+		BroadcastWorldTick();
 #endif // DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT
 
-		if (SharedDrawEvent && SharedDrawEvent->IsBound())
-		{
-			SharedDrawEvent->Broadcast();
-		}
+		BroadcastMultiContextTick();
 
 #if !DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT
-		if (DrawEvent.IsBound())
-		{
-			DrawEvent.Broadcast();
-		}
+		BroadcastWorldTick();
 #endif // !DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT
 	}
 }
@@ -192,3 +185,34 @@ void FImGuiContextProxy::UpdateDrawData(ImDrawData* DrawData)
 		DrawLists.Empty();
 	}
 }
+
+void FImGuiContextProxy::BroadcastWorldTick()
+{
+	if (DrawEvent.IsBound())
+	{
+		DrawEvent.Broadcast();
+	}
+
+	if (ContextIndex != Utilities::INVALID_CONTEXT_INDEX)
+	{
+		FSimpleMulticastDelegate& WorldDebugEvent = FImGuiDelegatesContainer::Get().OnWorldDebug(ContextIndex);
+		if (WorldDebugEvent.IsBound())
+		{
+			WorldDebugEvent.Broadcast();
+		}
+	}
+}
+
+void FImGuiContextProxy::BroadcastMultiContextTick()
+{
+	if (SharedDrawEvent && SharedDrawEvent->IsBound())
+	{
+		SharedDrawEvent->Broadcast();
+	}
+
+	FSimpleMulticastDelegate& MultiContextDebugEvent = FImGuiDelegatesContainer::Get().OnMultiContextDebug();
+	if (MultiContextDebugEvent.IsBound())
+	{
+		MultiContextDebugEvent.Broadcast();
+	}
+}

Source/ImGui/Private/ImGuiContextProxy.h

@@ -4,6 +4,8 @@
 
 #include "ImGuiDrawData.h"
 
+#include "Utilities/WorldContextIndex.h"
+
 #include <ICursor.h>
 
 #include <imgui.h>
@@ -41,7 +43,7 @@ class FImGuiContextProxy
 
 public:
 
-	FImGuiContextProxy(const FString& Name, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas);
+	FImGuiContextProxy(const FString& Name, int32 InContextIndex, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas);
 
 	FImGuiContextProxy(const FImGuiContextProxy&) = delete;
 	FImGuiContextProxy& operator=(const FImGuiContextProxy&) = delete;
@@ -96,6 +98,9 @@ private:
 
 	void UpdateDrawData(ImDrawData* DrawData);
 
+	void BroadcastWorldTick();
+	void BroadcastMultiContextTick();
+
 	FImGuiContextPtr Context;
 
 	FVector2D DisplaySize = FVector2D::ZeroVector;
@@ -115,6 +120,8 @@ private:
 
 	TArray<FImGuiDrawList> DrawLists;
 
+	int32 ContextIndex = Utilities::INVALID_CONTEXT_INDEX;
+
 	FString Name;
 	std::string IniFilename;
 };

Source/ImGui/Private/ImGuiDelegates.cpp

@@ -0,0 +1,22 @@
+// Distributed under the MIT License (MIT) (see accompanying LICENSE file)
+
+#include "ImGuiPrivatePCH.h"
+
+#include "ImGuiDelegates.h"
+#include "ImGuiDelegatesContainer.h"
+
+
+FSimpleMulticastDelegate& FImGuiDelegates::OnWorldDebug()
+{
+	return OnWorldDebug(GWorld);
+}
+
+FSimpleMulticastDelegate& FImGuiDelegates::OnWorldDebug(UWorld* World)
+{
+	return FImGuiDelegatesContainer::Get().OnWorldDebug(World);
+}
+
+FSimpleMulticastDelegate& FImGuiDelegates::OnMultiContextDebug()
+{
+	return FImGuiDelegatesContainer::Get().OnMultiContextDebug();
+}

Source/ImGui/Private/ImGuiDelegatesContainer.cpp

@@ -0,0 +1,37 @@
+// Distributed under the MIT License (MIT) (see accompanying LICENSE file)
+
+#include "ImGuiPrivatePCH.h"
+
+#include "ImGuiDelegatesContainer.h"
+
+#include "Utilities/WorldContextIndex.h"
+
+
+FImGuiDelegatesContainer FImGuiDelegatesContainer::DefaultInstance;
+
+FImGuiDelegatesContainer* FImGuiDelegatesContainer::InstancePtr = &FImGuiDelegatesContainer::DefaultInstance;
+
+void FImGuiDelegatesContainer::MoveContainer(FImGuiDelegatesContainer& Dst)
+{
+	// Only move data if pointer points to default instance, otherwise our data has already been moved and we only
+	// keep pointer to a more recent version.
+	if (InstancePtr == &DefaultInstance)
+	{
+		Dst = MoveTemp(DefaultInstance);
+		DefaultInstance.Clear();
+	}
+
+	// Update pointer to the most recent version.
+	InstancePtr = &Dst;
+}
+
+FSimpleMulticastDelegate& FImGuiDelegatesContainer::OnWorldDebug(UWorld* World)
+{
+	return OnWorldDebug(Utilities::GetWorldContextIndex(*World));
+}
+
+void FImGuiDelegatesContainer::Clear()
+{
+	WorldDelegates.Empty();
+	MultiContextDelegate.Clear();
+}

Source/ImGui/Private/ImGuiDelegatesContainer.h

@@ -0,0 +1,40 @@
+// Distributed under the MIT License (MIT) (see accompanying LICENSE file)
+
+#pragma once
+
+#include <Containers/Map.h>
+#include <Delegates/Delegate.h>
+
+
+struct FImGuiDelegatesContainer
+{
+public:
+
+	// Get the current instance (can change during hot-reloading).
+	static FImGuiDelegatesContainer& Get() { return *InstancePtr; }
+
+	// If this is an active container move its data to a destination and redirect all future calls to that instance.
+	static void MoveContainer(FImGuiDelegatesContainer& Dst);
+
+	// Get delegate to ImGui world debug event from known world instance.
+	FSimpleMulticastDelegate& OnWorldDebug(UWorld* World);
+
+	// Get delegate to ImGui world debug event from known context index.
+	FSimpleMulticastDelegate& OnWorldDebug(int32 ContextIndex) { return WorldDelegates.FindOrAdd(ContextIndex); }
+
+	// Get delegate to ImGui multi-context debug event.
+	FSimpleMulticastDelegate& OnMultiContextDebug() { return MultiContextDelegate; }
+
+private:
+
+	void Clear();
+
+	TMap<int32, FSimpleMulticastDelegate> WorldDelegates;
+	FSimpleMulticastDelegate MultiContextDelegate;
+
+	// Default container instance.
+	static FImGuiDelegatesContainer DefaultInstance;
+
+	// Pointer to the container instance that can be overwritten during hot-reloading.
+	static FImGuiDelegatesContainer* InstancePtr;
+};

Source/ImGui/Private/ImGuiModule.cpp

@@ -4,6 +4,7 @@
 
 #include "ImGuiModuleManager.h"
 
+#include "ImGuiDelegatesContainer.h"
 #include "ImGuiTextureHandle.h"
 #include "TextureManager.h"
 #include "Utilities/WorldContext.h"
@@ -16,6 +17,8 @@
 
 #include <IPluginManager.h>
 
+#define IMGUI_REDIRECT_OBSOLETE_DELEGATES 1
+
 
 #define LOCTEXT_NAMESPACE "FImGuiModule"
 
@@ -38,18 +41,29 @@ static FImGuiModuleManager* ImGuiModuleManager = nullptr;
 static FImGuiEditor* ImGuiEditor = nullptr;
 #endif
 
+#if IMGUI_WITH_OBSOLETE_DELEGATES
+
 #if WITH_EDITOR
 FImGuiDelegateHandle FImGuiModule::AddEditorImGuiDelegate(const FImGuiDelegate& Delegate)
 {
+#if IMGUI_REDIRECT_OBSOLETE_DELEGATES
+	return { FImGuiDelegatesContainer::Get().OnWorldDebug(Utilities::EDITOR_CONTEXT_INDEX).Add(Delegate),
+		EDelegateCategory::Default, Utilities::EDITOR_CONTEXT_INDEX };
+#else
 	checkf(ImGuiModuleManager, TEXT("Null pointer to internal module implementation. Is module available?"));
 
 	return { ImGuiModuleManager->GetContextManager().GetEditorContextProxy().OnDraw().Add(Delegate),
 		EDelegateCategory::Default, Utilities::EDITOR_CONTEXT_INDEX };
+#endif // IMGUI_REDIRECT_OBSOLETE_DELEGATES
 }
 #endif
 
 FImGuiDelegateHandle FImGuiModule::AddWorldImGuiDelegate(const FImGuiDelegate& Delegate)
 {
+#if IMGUI_REDIRECT_OBSOLETE_DELEGATES
+	const int32 ContextIndex = Utilities::GetWorldContextIndex((UWorld*)GWorld);
+	return { FImGuiDelegatesContainer::Get().OnWorldDebug(ContextIndex).Add(Delegate), EDelegateCategory::Default, ContextIndex };
+#else
 	checkf(ImGuiModuleManager, TEXT("Null pointer to internal module implementation. Is module available?"));
 
 #if WITH_EDITOR
@@ -71,17 +85,32 @@ FImGuiDelegateHandle FImGuiModule::AddWorldImGuiDelegate(const FImGuiDelegate& D
 #endif
 
 	return{ Proxy.OnDraw().Add(Delegate), EDelegateCategory::Default, Index };
+#endif // IMGUI_REDIRECT_OBSOLETE_DELEGATES
 }
 
 FImGuiDelegateHandle FImGuiModule::AddMultiContextImGuiDelegate(const FImGuiDelegate& Delegate)
 {
+#if IMGUI_REDIRECT_OBSOLETE_DELEGATES
+	return { FImGuiDelegatesContainer::Get().OnMultiContextDebug().Add(Delegate), EDelegateCategory::MultiContext };
+#else
 	checkf(ImGuiModuleManager, TEXT("Null pointer to internal module implementation. Is module available?"));
 
 	return { ImGuiModuleManager->GetContextManager().OnDrawMultiContext().Add(Delegate), EDelegateCategory::MultiContext };
+#endif
 }
 
 void FImGuiModule::RemoveImGuiDelegate(const FImGuiDelegateHandle& Handle)
 {
+#if IMGUI_REDIRECT_OBSOLETE_DELEGATES
+	if (Handle.Category == EDelegateCategory::MultiContext)
+	{
+		FImGuiDelegatesContainer::Get().OnMultiContextDebug().Remove(Handle.Handle);
+	}
+	else
+	{
+		FImGuiDelegatesContainer::Get().OnWorldDebug(Handle.Index).Remove(Handle.Handle);
+	}
+#else
 	if (ImGuiModuleManager)
 	{
 		if (Handle.Category == EDelegateCategory::MultiContext)
@@ -93,8 +122,11 @@ void FImGuiModule::RemoveImGuiDelegate(const FImGuiDelegateHandle& Handle)
 			Proxy->OnDraw().Remove(Handle.Handle);
 		}
 	}
+#endif
 }
 
+#endif // IMGUI_WITH_OBSOLETE_DELEGATES
+
 FImGuiTextureHandle FImGuiModule::FindTextureHandle(const FName& Name)
 {
 	const TextureIndex Index = ImGuiModuleManager->GetTextureManager().FindTextureIndex(Name);
@@ -154,6 +186,10 @@ void FImGuiModule::ShutdownModule()
 	// deleted. This can cause troubles after hot-reload when code in other modules calls ImGui interface functions
 	// which are statically bound to the obsolete module. To keep ImGui code functional we can redirect context handle
 	// to point to the new module.
+
+	// When shutting down during hot-reloading, we might want to rewire handles used in statically bound functions
+	// or move data to a new module.
+
 	FModuleManager::Get().OnModulesChanged().AddLambda([this] (FName Name, EModuleChangeReason Reason)
 	{
 		if (Reason == EModuleChangeReason::ModuleLoaded && Name == "ImGui")
@@ -161,8 +197,11 @@ void FImGuiModule::ShutdownModule()
 			FImGuiModule& LoadedModule = FImGuiModule::Get();
 			if (&LoadedModule != this)
 			{
+				// Statically bound functions will be still made to the obsolete module so we need to  
 				ImGuiImplementation::SetImGuiContextHandle(LoadedModule.GetImGuiContextHandle());
 
+				FImGuiDelegatesContainer::MoveContainer(LoadedModule.GetDelegatesContainer());
+
 				if (bMoveProperties)
 				{
 					bMoveProperties = false;
@@ -184,6 +223,11 @@ ImGuiContext** FImGuiModule::GetImGuiContextHandle()
 {
 	return ImGuiImplementation::GetImGuiContextHandle();
 }
+
+FImGuiDelegatesContainer& FImGuiModule::GetDelegatesContainer()
+{
+	return FImGuiDelegatesContainer::Get();
+}
 #endif
 
 FImGuiModuleProperties& FImGuiModule::GetProperties()

Source/ImGui/Private/Utilities/WorldContextIndex.h

@@ -56,6 +56,11 @@ namespace Utilities
 		return (World.WorldType == EWorldType::Editor) ? EDITOR_CONTEXT_INDEX : GetWorldContextIndex(World.GetGameInstance());
 	}
 
+	FORCEINLINE int32 GetWorldContextIndex(const UWorld* World)
+	{
+		return World ? GetWorldContextIndex(*World) : INVALID_CONTEXT_INDEX;
+	}
+
 #else
 
 	template<typename T>

Source/ImGui/Public/ImGuiDelegates.h

@@ -5,6 +5,43 @@
 #include <Core.h>
 
 
+/**
+ * Delegates to ImGui debug events called. World delegates are called once per frame to draw debug for owning world
+ * and are automatically cleared when that world becomes invalid. Multi-context delegates are called once for every
+ * world that needs to be debugged.
+ * In engine version 4.18 or later delegates are called during OnWorldPostActorTick event while in older versions
+ * 4.18 during OnWorldTickStart event. Calling behaviours can be changed in build configuration.
+ */
+class IMGUI_API FImGuiDelegates
+{
+public:
+
+	/**
+	 * Get a delegate to ImGui world debug event for current world (GWorld).
+	 * @returns Simple multicast delegate to debug events called once per frame to debug current world
+	 */
+	static FSimpleMulticastDelegate& OnWorldDebug();
+
+	/**
+	 * Get a delegate to ImGui world debug event for given world.
+	 * @param World - World for which we need a delegate
+	 * @returns Simple multicast delegate to debug events called once per frame to debug given world
+	 */
+	static FSimpleMulticastDelegate& OnWorldDebug(UWorld* World);
+
+	/**
+	 * Get a delegate to ImGui multi-context debug event.
+	 * @returns Simple multicast delegate to debug events called once per frame for every world to debug
+	 */
+	static FSimpleMulticastDelegate& OnMultiContextDebug();
+};
+
+
+/** Enable to support legacy ImGui delegates API. */
+#define IMGUI_WITH_OBSOLETE_DELEGATES 1
+
+#if IMGUI_WITH_OBSOLETE_DELEGATES
+
 /** Delegate that allows to subscribe for ImGui events.  */
 typedef FSimpleMulticastDelegate::FDelegate FImGuiDelegate;
 
@@ -53,3 +90,5 @@ private:
 
 	friend class FImGuiModule;
 };
+
+#endif // IMGUI_WITH_OBSOLETE_DELEGATES

Source/ImGui/Public/ImGuiModule.h

@@ -34,6 +34,8 @@ public:
 		return FModuleManager::Get().IsModuleLoaded("ImGui");
 	}
 
+#if IMGUI_WITH_OBSOLETE_DELEGATES
+
 #if WITH_EDITOR
 	/**
 	 * Add a delegate called at the end of editor debug frame to draw debug controls in its ImGui context, creating
@@ -71,6 +73,8 @@ public:
 	 */
 	virtual void RemoveImGuiDelegate(const FImGuiDelegateHandle& Handle);
 
+#endif // #if IMGUI_WITH_OBSOLETE_DELEGATES
+
 	/**
 	 * If it exists, get a handle to the texture with given resource name.
 	 *
@@ -165,5 +169,6 @@ public:
 #if WITH_EDITOR
 	virtual void SetProperties(const FImGuiModuleProperties& Properties);
 	virtual struct ImGuiContext** GetImGuiContextHandle();
+	virtual struct FImGuiDelegatesContainer& GetDelegatesContainer();
 #endif
 };