Making sure that the DPI scale is set new contexts:

- Moved implementation of the DPI scale from context manager to context proxy.
- Passing the DPI scale to the context proxy constructor for the initial setup.

Source/ImGui/Private/ImGuiContextManager.cpp

@@ -152,7 +152,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetEditorContextData()
 
 	if (UNLIKELY(!Data))
 	{
-		Data = &Contexts.Emplace(Utilities::EDITOR_CONTEXT_INDEX, FContextData{ GetEditorContextName(), Utilities::EDITOR_CONTEXT_INDEX, OnDrawMultiContext, FontAtlas, -1 });
+		Data = &Contexts.Emplace(Utilities::EDITOR_CONTEXT_INDEX, FContextData{ GetEditorContextName(), Utilities::EDITOR_CONTEXT_INDEX, OnDrawMultiContext, FontAtlas, DPIScale, -1 });
 		OnContextProxyCreated.Broadcast(Utilities::EDITOR_CONTEXT_INDEX, *Data->ContextProxy);
 	}
 
@@ -167,7 +167,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetStandaloneWorldCont
 
 	if (UNLIKELY(!Data))
 	{
-		Data = &Contexts.Emplace(Utilities::STANDALONE_GAME_CONTEXT_INDEX, FContextData{ GetWorldContextName(), Utilities::STANDALONE_GAME_CONTEXT_INDEX, OnDrawMultiContext, FontAtlas });
+		Data = &Contexts.Emplace(Utilities::STANDALONE_GAME_CONTEXT_INDEX, FContextData{ GetWorldContextName(), Utilities::STANDALONE_GAME_CONTEXT_INDEX, OnDrawMultiContext, FontAtlas, DPIScale });
 		OnContextProxyCreated.Broadcast(Utilities::STANDALONE_GAME_CONTEXT_INDEX, *Data->ContextProxy);
 	}
 
@@ -209,7 +209,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetWorldContextData(co
 #if WITH_EDITOR
 	if (UNLIKELY(!Data))
 	{
-		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, OnDrawMultiContext, FontAtlas, WorldContext->PIEInstance });
+		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, OnDrawMultiContext, FontAtlas, DPIScale, WorldContext->PIEInstance });
 		OnContextProxyCreated.Broadcast(Index, *Data->ContextProxy);
 	}
 	else
@@ -220,7 +220,7 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetWorldContextData(co
 #else
 	if (UNLIKELY(!Data))
 	{
-		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, OnDrawMultiContext, FontAtlas });
+		Data = &Contexts.Emplace(Index, FContextData{ GetWorldContextName(World), Index, OnDrawMultiContext, FontAtlas, DPIScale });
 		OnContextProxyCreated.Broadcast(Index, *Data->ContextProxy);
 	}
 #endif
@@ -232,38 +232,6 @@ FImGuiContextManager::FContextData& FImGuiContextManager::GetWorldContextData(co
 	return *Data;
 }
 
-struct FGuardContext
-{
-	FGuardContext()
-		: OldContext(ImGui::GetCurrentContext())
-	{
-	}
-
-	~FGuardContext()
-	{
-		if (bRestore)
-		{
-			ImGui::SetCurrentContext(OldContext);
-		}
-	}
-
-	FGuardContext(FGuardContext&& Other)
-		: OldContext(MoveTemp(Other.OldContext))
-	{
-		Other.bRestore = false;
-	}
-
-	FGuardContext& operator=(FGuardContext&&) = delete;
-
-	FGuardContext(const FGuardContext&) = delete;
-	FGuardContext& operator=(const FGuardContext&) = delete;
-
-private:
-
-	ImGuiContext* OldContext = nullptr;
-	bool bRestore = true;
-};
-
 void FImGuiContextManager::SetDPIScale(const FImGuiDPIScaleInfo& ScaleInfo)
 {
 	const float Scale = ScaleInfo.GetImGuiScale();
@@ -281,12 +249,7 @@ void FImGuiContextManager::SetDPIScale(const FImGuiDPIScaleInfo& ScaleInfo)
 		{
 			if (Pair.Value.ContextProxy)
 			{
-				ImGuiStyle NewStyle = ImGuiStyle();
+				Pair.Value.ContextProxy->SetDPIScale(DPIScale);
-				NewStyle.ScaleAllSizes(DPIScale);
-
-				FGuardContext GuardContext;
-				Pair.Value.ContextProxy->SetAsCurrent();
-				ImGui::GetStyle() = MoveTemp(NewStyle);
 			}
 		}
 	}

Source/ImGui/Private/ImGuiContextManager.h

@@ -74,9 +74,9 @@ private:
 
 	struct FContextData
 	{
-		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, ImFontAtlas& FontAtlas, int32 InPIEInstance = -1)
+		FContextData(const FString& ContextName, int32 ContextIndex, FSimpleMulticastDelegate& SharedDrawEvent, ImFontAtlas& FontAtlas, float DPIScale, int32 InPIEInstance = -1)
 			: PIEInstance(InPIEInstance)
-			, ContextProxy(new FImGuiContextProxy(ContextName, ContextIndex, &SharedDrawEvent, &FontAtlas))
+			, ContextProxy(new FImGuiContextProxy(ContextName, ContextIndex, &SharedDrawEvent, &FontAtlas, DPIScale))
 		{
 		}
 

Source/ImGui/Private/ImGuiContextProxy.cpp

@@ -39,9 +39,41 @@ namespace
 		static FString SaveDirectory = GetSaveDirectory();
 		return FPaths::Combine(SaveDirectory, Name + TEXT(".ini"));
 	}
+
+	struct FGuardCurrentContext
+	{
+		FGuardCurrentContext()
+			: OldContext(ImGui::GetCurrentContext())
+		{
+		}
+
+		~FGuardCurrentContext()
+		{
+			if (bRestore)
+			{
+				ImGui::SetCurrentContext(OldContext);
+			}
+		}
+
+		FGuardCurrentContext(FGuardCurrentContext&& Other)
+			: OldContext(MoveTemp(Other.OldContext))
+		{
+			Other.bRestore = false;
+		}
+
+		FGuardCurrentContext& operator=(FGuardCurrentContext&&) = delete;
+
+		FGuardCurrentContext(const FGuardCurrentContext&) = delete;
+		FGuardCurrentContext& operator=(const FGuardCurrentContext&) = delete;
+
+	private:
+
+		ImGuiContext* OldContext = nullptr;
+		bool bRestore = true;
+	};
 }
 
-FImGuiContextProxy::FImGuiContextProxy(const FString& InName, int32 InContextIndex, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas)
+FImGuiContextProxy::FImGuiContextProxy(const FString& InName, int32 InContextIndex, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas, float InDPIScale)
 	: Name(InName)
 	, ContextIndex(InContextIndex)
 	, SharedDrawEvent(InSharedDrawEvent)
@@ -63,6 +95,9 @@ FImGuiContextProxy::FImGuiContextProxy(const FString& InName, int32 InContextInd
 	ResetDisplaySize();
 	IO.DisplaySize = { DisplaySize.X, DisplaySize.Y };
 
+	// Set the initial DPI scale.
+	SetDPIScale(InDPIScale);
+
 	// Initialize key mapping, so context can correctly interpret input state.
 	ImGuiInterops::SetUnrealKeyMap(IO);
 
@@ -89,6 +124,21 @@ void FImGuiContextProxy::ResetDisplaySize()
 	DisplaySize = { DEFAULT_CANVAS_WIDTH, DEFAULT_CANVAS_HEIGHT };
 }
 
+void FImGuiContextProxy::SetDPIScale(float Scale)
+{
+	if (DPIScale != Scale)
+	{
+		DPIScale = Scale;
+
+		ImGuiStyle NewStyle = ImGuiStyle();
+		NewStyle.ScaleAllSizes(Scale);
+
+		FGuardCurrentContext GuardContext;
+		SetAsCurrent();
+		ImGui::GetStyle() = MoveTemp(NewStyle);
+	}
+}
+
 void FImGuiContextProxy::DrawEarlyDebug()
 {
 	if (bIsFrameStarted && !bIsDrawEarlyDebugCalled)

Source/ImGui/Private/ImGuiContextProxy.h

@@ -19,7 +19,7 @@ class FImGuiContextProxy
 {
 public:
 
-	FImGuiContextProxy(const FString& Name, int32 InContextIndex, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas);
+	FImGuiContextProxy(const FString& Name, int32 InContextIndex, FSimpleMulticastDelegate* InSharedDrawEvent, ImFontAtlas* InFontAtlas, float InDPIScale);
 	~FImGuiContextProxy();
 
 	FImGuiContextProxy(const FImGuiContextProxy&) = delete;
@@ -53,6 +53,12 @@ public:
 	// Reset the desired context display size to default size.
 	void ResetDisplaySize();
 
+	// Get the DPI scale set for this context.
+	float GetDPIScale() const { return DPIScale; }
+
+	// Set the DPI scale for this context.
+	void SetDPIScale(float Scale);
+
 	// Whether this context has an active item (read once per frame during context update).
 	bool HasActiveItem() const { return bHasActiveItem; }
 
@@ -90,6 +96,7 @@ private:
 	ImGuiContext* Context;
 
 	FVector2D DisplaySize = FVector2D::ZeroVector;
+	float DPIScale = 1.f;
 
 	EMouseCursor::Type MouseCursor = EMouseCursor::None;
 	bool bHasActiveItem = false;