Added multi-PIE support to adaptive canvas size:

- Adaptive size is controlled by the ImGui Widget, which passes it from the view-port to the context proxy.
- Context only copies display size that is set from the outside.
- Removed feature dependency from the manager.

Source/ImGui/Private/ImGuiContextProxy.cpp

@@ -59,9 +59,9 @@ FImGuiContextProxy::FImGuiContextProxy(const FString& InName, int32 InContextInd
 	// Set session data storage.
 	IO.IniFilename = IniFilename.c_str();
 
-	// Use pre-defined canvas size.
-	IO.DisplaySize = { DEFAULT_CANVAS_WIDTH, DEFAULT_CANVAS_HEIGHT };
-	DisplaySize = ImGuiInterops::ToVector2D(IO.DisplaySize);
+	// Start with the default canvas size.
+	ResetDisplaySize();
+	IO.DisplaySize = { DisplaySize.X, DisplaySize.Y };
 
 	// Initialize key mapping, so context can correctly interpret input state.
 	ImGuiInterops::SetUnrealKeyMap(IO);
@@ -84,6 +84,11 @@ FImGuiContextProxy::~FImGuiContextProxy()
 	}
 }
 
+void FImGuiContextProxy::ResetDisplaySize()
+{
+	DisplaySize = { DEFAULT_CANVAS_WIDTH, DEFAULT_CANVAS_HEIGHT };
+}
+
 void FImGuiContextProxy::DrawEarlyDebug()
 {
 	if (bIsFrameStarted && !bIsDrawEarlyDebugCalled)
@@ -147,11 +152,6 @@ void FImGuiContextProxy::Tick(float DeltaSeconds)
 	}
 }
 
-void FImGuiContextProxy::SetAdaptiveCanvasSize(bool bAdaptive)
-{
-    bAdaptiveCanvasSize = bAdaptive;
-}
-
 void FImGuiContextProxy::BeginFrame(float DeltaTime)
 {
 	if (!bIsFrameStarted)
@@ -162,16 +162,7 @@ void FImGuiContextProxy::BeginFrame(float DeltaTime)
 		ImGuiInterops::CopyInput(IO, InputState);
 		InputState.ClearUpdateState();
 
-		if (bAdaptiveCanvasSize) {
-			if (GEngine && GEngine->GameViewport)
-			{
-				GEngine->GameViewport->GetViewportSize(DisplaySize);
-				IO.DisplaySize = ImVec2(DisplaySize.X, DisplaySize.Y);
-			}
-		} else {
-			IO.DisplaySize = { DEFAULT_CANVAS_WIDTH, DEFAULT_CANVAS_HEIGHT };
-			DisplaySize = ImGuiInterops::ToVector2D(IO.DisplaySize);
-		}
+		IO.DisplaySize = { DisplaySize.X, DisplaySize.Y };
 
 		ImGui::NewFrame();
 

Source/ImGui/Private/ImGuiContextProxy.h

@@ -44,9 +44,15 @@ public:
 	// Set this context as current ImGui context.
 	void SetAsCurrent() { ImGui::SetCurrentContext(Context); }
 
-	// Context display size (read once per frame during context update).
+	// Get the desired context display size.
 	const FVector2D& GetDisplaySize() const { return DisplaySize; }
 
+	// Set the desired context display size.
+	void SetDisplaySize(const FVector2D& Size) { DisplaySize = Size; }
+
+	// Reset the desired context display size to default size.
+	void ResetDisplaySize();
+
 	// Whether this context has an active item (read once per frame during context update).
 	bool HasActiveItem() const { return bHasActiveItem; }
 
@@ -68,9 +74,6 @@ public:
 	// Tick to advance context to the next frame. Only one call per frame will be processed.
 	void Tick(float DeltaSeconds);
 
-	// Set the adaptive canvas size configuration.
-	void SetAdaptiveCanvasSize(bool);
-
 private:
 
 	void BeginFrame(float DeltaTime = 1.f / 60.f);
@@ -109,6 +112,4 @@ private:
 	FSimpleMulticastDelegate* SharedDrawEvent = nullptr;
 
 	std::string IniFilename;
-
-	bool bAdaptiveCanvasSize = false;
 };

Source/ImGui/Private/ImGuiModuleManager.cpp

@@ -175,7 +175,6 @@ void FImGuiModuleManager::AddWidgetToViewport(UGameViewportClient* GameViewport)
 	// Make sure that we have a context for this viewport's world and get its index.
 	int32 ContextIndex;
 	auto& ContextProxy = ContextManager.GetWorldContextProxy(*GameViewport->GetWorld(), ContextIndex);
-	ContextProxy.SetAdaptiveCanvasSize(Settings.AdaptiveCanvasSize());
 
 	// Make sure that textures are loaded before the first Slate widget is created.
 	LoadTextures();

Source/ImGui/Private/Widgets/SImGuiWidget.cpp

@@ -84,6 +84,7 @@ void SImGuiWidget::Construct(const FArguments& InArgs)
 	const auto& Settings = ModuleManager->GetSettings();
 	SetHideMouseCursor(Settings.UseSoftwareCursor());
 	CreateInputHandler(Settings.GetImGuiInputHandlerClass());
+	SetAdaptiveCanvasSize(Settings.AdaptiveCanvasSize());
 
 	// Initialize state.
 	UpdateVisibility();
@@ -125,6 +126,7 @@ void SImGuiWidget::Tick(const FGeometry& AllottedGeometry, const double InCurren
 	UpdateInputState();
 	UpdateTransparentMouseInput(AllottedGeometry);
 	HandleWindowFocusLost();
+	UpdateCanvasSize();
 }
 
 FReply SImGuiWidget::OnKeyChar(const FGeometry& MyGeometry, const FCharacterEvent& CharacterEvent)
@@ -496,9 +498,44 @@ void SImGuiWidget::HandleWindowFocusLost()
 	}
 }
 
+void SImGuiWidget::SetAdaptiveCanvasSize(bool bEnabled)
+{
+	if (bAdaptiveCanvasSize != bEnabled)
+	{
+		bAdaptiveCanvasSize = bEnabled;
+		bUpdateCanvasSize = true;
+		UpdateCanvasSize();
+	}
+}
+
+void SImGuiWidget::UpdateCanvasSize()
+{
+	if (bUpdateCanvasSize)
+	{
+		if (auto* ContextProxy = ModuleManager->GetContextManager().GetContextProxy(ContextIndex))
+		{
+			if (bAdaptiveCanvasSize)
+			{
+				if (GameViewport.IsValid())
+				{
+					FVector2D DisplaySize;
+					GameViewport->GetViewportSize(DisplaySize);
+					ContextProxy->SetDisplaySize(DisplaySize);
+				}
+			}
+			else
+			{
+				ContextProxy->ResetDisplaySize();
+				// No need for more updates, if we successfully processed fixed-canvas mode.
+				bUpdateCanvasSize = false;
+			}
+		}
+	}
+}
+
 void SImGuiWidget::UpdateCanvasControlMode(const FInputEvent& InputEvent)
 {
-	CanvasControlWidget->SetActive(InputEvent.IsLeftAltDown() && InputEvent.IsLeftShiftDown());
+	CanvasControlWidget->SetActive(!bAdaptiveCanvasSize && InputEvent.IsLeftAltDown() && InputEvent.IsLeftShiftDown());
 }
 
 void SImGuiWidget::OnPostImGuiUpdate()

Source/ImGui/Private/Widgets/SImGuiWidget.h

@@ -103,6 +103,9 @@ private:
 	void UpdateTransparentMouseInput(const FGeometry& AllottedGeometry);
 	void HandleWindowFocusLost();
 
+	void SetAdaptiveCanvasSize(bool bEnabled);
+	void UpdateCanvasSize();
+
 	void UpdateCanvasControlMode(const FInputEvent& InputEvent);
 
 	void OnPostImGuiUpdate();
@@ -135,6 +138,8 @@ private:
 	bool bForegroundWindow = false;
 	bool bHideMouseCursor = true;
 	bool bTransparentMouseInput = false;
+	bool bAdaptiveCanvasSize = false;
+	bool bUpdateCanvasSize = false;
 
 	TSharedPtr<SImGuiCanvasControl> CanvasControlWidget;
 	TWeakPtr<SWidget> PreviousUserFocusedWidget;