Replaced 'ImGui.DebugDrawOnWorldTick' console variable with conditional compilation switches and extended support to post actor tick event:

- Replaced 'ImGui.DebugDrawOnWorldTick' with DRAW_EVENTS_ON_WORLD_TICK_START switch to enforce consistency in project setup.
- Added DRAW_EVENTS_ON_POST_ACTOR_TICK to support post actor tick events (only for UE 4.18 or later).
- Added DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT to allow explicitly define order between multi-context and world-context draw events.
- Rules can be configured in ImGui.Build.cs file.

Source/ImGui/ImGui.Build.cs

@@ -1,11 +1,45 @@
 // Distributed under the MIT License (MIT) (see accompanying LICENSE file)
 
+#if UE_4_18_OR_LATER
+#define WITH_POST_ACTOR_TICK
+#endif
+
 using System.Collections.Generic;
 using System.IO;
 using UnrealBuildTool;
 
 public class ImGui : ModuleRules
 {
+	// Defines when events should be broadcast. Note that at the end of the ImGui frame some global variables might be
+	// not set and so it seems preferable to use post actor tick (not available in older engine versions) or world tick
+	// start events. If more control is required Late mode with manually calling events may be used (as in practice
+	// events are guaranteed to be raised only once per frame).
+	enum EEventsBroadcastMode
+	{
+		OnWorldTickStart,   // Broadcast during world tick start event.
+#if WITH_POST_ACTOR_TICK
+		OnPostActorTick,    // Broadcast during post actor tick event.
+#endif
+		Late,               // Broadcast at the end of the ImGui frame.
+	}
+
+	// Defines order in which multi-context and world-context events are called.
+	enum EEventsOrder
+	{
+		MultiBeforeWorldContext,
+		WorldBeforeMultiContext,
+	}
+
+#if WITH_POST_ACTOR_TICK
+	EEventsBroadcastMode DrawEventsBroadcastMode = EEventsBroadcastMode.OnPostActorTick;
+	EEventsOrder DrawEventsOrder = EEventsOrder.WorldBeforeMultiContext;
+#else
+	EEventsBroadcastMode DrawEventsBroadcastMode = EEventsBroadcastMode.OnWorldTickStart;
+	EEventsOrder DrawEventsOrder = EEventsOrder.MultiBeforeWorldContext;
+#endif // WITH_POST_ACTOR_TICK
+
+
+
 #if WITH_FORWARDED_MODULE_RULES_CTOR
 	public ImGui(ReadOnlyTargetRules Target) : base(Target)
 #else
@@ -89,6 +123,19 @@ public class ImGui : ModuleRules
 #if !UE_4_19_OR_LATER
 		List<string> PrivateDefinitions = Definitions;
 #endif
+
 		PrivateDefinitions.Add(string.Format("RUNTIME_LOADER_ENABLED = {0}", bEnableRuntimeLoader ? 1 : 0));
+
+		bool bDrawOnWorldTickStart = (DrawEventsBroadcastMode == EEventsBroadcastMode.OnWorldTickStart);
+#if WITH_POST_ACTOR_TICK
+		bool bDrawOnPostActorTick = (DrawEventsBroadcastMode == EEventsBroadcastMode.OnPostActorTick);
+#else
+		bool bDrawOnPostActorTick = false;
+#endif
+
+		PrivateDefinitions.Add(string.Format("DRAW_EVENTS_ON_WORLD_TICK_START = {0}", bDrawOnWorldTickStart ? 1 : 0));
+		PrivateDefinitions.Add(string.Format("DRAW_EVENTS_ON_POST_ACTOR_TICK = {0}", bDrawOnPostActorTick ? 1 : 0));
+		PrivateDefinitions.Add(string.Format("DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT = {0}",
+			(DrawEventsOrder == EEventsOrder.WorldBeforeMultiContext) ? 1 : 0));
 	}
 }

Source/ImGui/Private/ImGuiContextManager.cpp

@@ -12,20 +12,6 @@
 #include <imgui.h>
 
 
-namespace CVars
-{
-	TAutoConsoleVariable<int> DebugDrawOnWorldTick(TEXT("ImGui.DebugDrawOnWorldTick"), 1,
-		TEXT("If this is enabled then all the ImGui debug draw events will be called during World Tick Start.\n")
-		TEXT("This has an advantage that all the global variables like GWorld are set to correct values.\n")
-		TEXT("A disadvantage is that objects are not yet updated. That can be changed by disabling this feature,")
-		TEXT("but preferable solution is to call debug code from object's own Tick function.\n")
-		TEXT("NOTE: Order of multi-context and world draw events depends on this value and is arranged in a way ")
-		TEXT("that world draw events and objects updates are closer together.\n")
-		TEXT("0: disabled, ImGui Debug Draw is called during Post-Tick\n")
-		TEXT("1: enabled (default), ImGui Debug Draw is called during World Tick Start"),
-		ECVF_Default);
-}
-
 namespace
 {
 #if WITH_EDITOR
@@ -77,12 +63,18 @@ FImGuiContextManager::FImGuiContextManager()
 	FontAtlas.GetTexDataAsRGBA32(&Pixels, &Width, &Height, &Bpp);
 
 	FWorldDelegates::OnWorldTickStart.AddRaw(this, &FImGuiContextManager::OnWorldTickStart);
+#if DRAW_EVENTS_ON_POST_ACTOR_TICK
+	FWorldDelegates::OnWorldPostActorTick.AddRaw(this, &FImGuiContextManager::OnWorldPostActorTick);
+#endif
 }
 
 FImGuiContextManager::~FImGuiContextManager()
 {
 	// Order matters because contexts can be created during World Tick Start events.
 	FWorldDelegates::OnWorldTickStart.RemoveAll(this);
+#if DRAW_EVENTS_ON_POST_ACTOR_TICK
+	FWorldDelegates::OnWorldPostActorTick.RemoveAll(this);
+#endif
 }
 
 void FImGuiContextManager::Tick(float DeltaSeconds)
@@ -106,12 +98,21 @@ void FImGuiContextManager::OnWorldTickStart(ELevelTick TickType, float DeltaSeco
 	{
 		FImGuiContextProxy& ContextProxy = GetWorldContextProxy(*GWorld);
 		ContextProxy.SetAsCurrent();
-		if (CVars::DebugDrawOnWorldTick.GetValueOnGameThread() > 0)
+
+#if DRAW_EVENTS_ON_WORLD_TICK_START
+		ContextProxy.Draw();
+#endif
+	}
+}
+
+#if DRAW_EVENTS_ON_POST_ACTOR_TICK
+void FImGuiContextManager::OnWorldPostActorTick(UWorld* World, ELevelTick TickType, float DeltaSeconds)
 {
+	FImGuiContextProxy& ContextProxy = GetWorldContextProxy(*GWorld);
+	ContextProxy.SetAsCurrent();
 	ContextProxy.Draw();
 }
-	}
+#endif // DRAW_EVENTS_ON_POST_ACTOR_TICK
-}
 
 #if WITH_EDITOR
 FImGuiContextManager::FContextData& FImGuiContextManager::GetEditorContextData()

Source/ImGui/Private/ImGuiContextManager.h

@@ -92,6 +92,10 @@ private:
 
 	void OnWorldTickStart(ELevelTick TickType, float DeltaSeconds);
 
+#if DRAW_EVENTS_ON_POST_ACTOR_TICK
+	void OnWorldPostActorTick(UWorld* World, ELevelTick TickType, float DeltaSeconds);
+#endif
+
 #if WITH_EDITOR
 	FContextData& GetEditorContextData();
 #endif

Source/ImGui/Private/ImGuiContextProxy.cpp

@@ -14,11 +14,6 @@ static constexpr float DEFAULT_CANVAS_WIDTH = 3840.f;
 static constexpr float DEFAULT_CANVAS_HEIGHT = 2160.f;
 
 
-namespace CVars
-{
-	extern TAutoConsoleVariable<int> DebugDrawOnWorldTick;
-}
-
 namespace
 {
 	FString GetSaveDirectory()
@@ -94,21 +89,25 @@ void FImGuiContextProxy::Draw()
 
 		SetAsCurrent();
 
-		const bool bSharedFirst = (CVars::DebugDrawOnWorldTick.GetValueOnGameThread() > 0);
-
 		// Broadcast draw event to allow listeners to draw their controls to this context.
-		if (bSharedFirst && SharedDrawEvent && SharedDrawEvent->IsBound())
+#if DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT
-		{
-			SharedDrawEvent->Broadcast();
-		}
 		if (DrawEvent.IsBound())
 		{
 			DrawEvent.Broadcast();
 		}
-		if (!bSharedFirst && SharedDrawEvent && SharedDrawEvent->IsBound())
+#endif // DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT
+
+		if (SharedDrawEvent && SharedDrawEvent->IsBound())
 		{
 			SharedDrawEvent->Broadcast();
 		}
+
+#if !DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT
+		if (DrawEvent.IsBound())
+		{
+			DrawEvent.Broadcast();
+		}
+#endif // !DRAW_EVENTS_ORDER_WORLD_BEFORE_MULTI_CONTEXT
 	}
 }