Added more options to control the canvas size:

- Canvas size can be set to custom width and height, desktop size or viewport size.
- The old Adaptive Canvas Size is replaced by the viewport size type.
- Custom and desktop size types can be also extended to the viewport size but they will never be smaller than their base sizes.

Source/ImGui/Private/Editor/ImGuiCanvasSizeInfoCustomization.cpp

@@ -0,0 +1,160 @@
+// Distributed under the MIT License (MIT) (see accompanying LICENSE file)
+
+#include "ImGuiPrivatePCH.h"
+
+#if WITH_EDITOR
+
+#include "ImGuiCanvasSizeInfoCustomization.h"
+
+#include "ImGuiModuleSettings.h"
+
+#include <PropertyCustomizationHelpers.h>
+
+
+#define LOCTEXT_NAMESPACE "ImGuiEditor"
+
+
+namespace
+{
+	EImGuiCanvasSizeType GetCanvasSizeTypeEnumValue(const TSharedPtr<IPropertyHandle>& TypeHandle)
+	{
+		uint8 ValueAsByte = 0;
+		if (TypeHandle.IsValid())
+		{
+			TypeHandle->GetValue(ValueAsByte);
+		}
+		return static_cast<EImGuiCanvasSizeType>(ValueAsByte);
+	}
+
+	bool IsAny(const TSharedPtr<IPropertyHandle>& TypeHandle, EImGuiCanvasSizeType Value)
+	{
+		return GetCanvasSizeTypeEnumValue(TypeHandle) == Value;
+	}
+
+	template<typename... TRest>
+	bool IsAny(const TSharedPtr<IPropertyHandle>& TypeHandle, EImGuiCanvasSizeType First, TRest... Rest)
+	{
+		return IsAny(TypeHandle, First) || IsAny(TypeHandle, Rest...);
+	}
+
+	float ShowToHeight(bool bShow)
+	{
+		return bShow ? 0.f /* Infinity */ : SMALL_NUMBER;
+	}
+
+	EVisibility ShowToVisibility(bool bShow)
+	{
+		return bShow ? EVisibility::SelfHitTestInvisible : EVisibility::Hidden;
+	}
+}
+
+//----------------------------------------------------------------------------------------------------
+// FImGuiKeyInfoCustomization implementation
+//----------------------------------------------------------------------------------------------------
+
+TSharedRef<IPropertyTypeCustomization> FImGuiCanvasSizeInfoCustomization::MakeInstance()
+{
+	return MakeShareable(new FImGuiCanvasSizeInfoCustomization);
+}
+
+void FImGuiCanvasSizeInfoCustomization::CustomizeHeader(TSharedRef<IPropertyHandle> InStructPropertyHandle, FDetailWidgetRow& HeaderRow, IPropertyTypeCustomizationUtils& StructCustomizationUtils)
+{
+	TSharedPtr<IPropertyHandle> TypeHandle = InStructPropertyHandle->GetChildHandle(GET_MEMBER_NAME_CHECKED(FImGuiCanvasSizeInfo, SizeType));
+	TSharedPtr<IPropertyHandle> WidthHandle = InStructPropertyHandle->GetChildHandle(GET_MEMBER_NAME_CHECKED(FImGuiCanvasSizeInfo, Width));
+	TSharedPtr<IPropertyHandle> HeightHandle = InStructPropertyHandle->GetChildHandle(GET_MEMBER_NAME_CHECKED(FImGuiCanvasSizeInfo, Height));
+	TSharedPtr<IPropertyHandle> ExtendToViewportHandle = InStructPropertyHandle->GetChildHandle(GET_MEMBER_NAME_CHECKED(FImGuiCanvasSizeInfo, bExtendToViewport));
+
+#define ADD_DIMENSION_SLOT(Handle, LPadding) \
+	+ SHorizontalBox::Slot()\
+	.Padding(LPadding, 0.f, 0.f, 0.f)\
+	.HAlign(HAlign_Fill)\
+	.MaxWidth(80.f)\
+	[\
+		SNew(SVerticalBox)\
+		+ SVerticalBox::Slot()\
+		.AutoHeight()\
+		[\
+			Handle->CreatePropertyNameWidget()\
+		]\
+		+ SVerticalBox::Slot()\
+		.HAlign(HAlign_Fill)\
+		.AutoHeight()\
+		[\
+			Handle->CreatePropertyValueWidget()\
+		]\
+	]
+
+	auto SizeRowHeight = TAttribute<float>::Create([TypeHandle]()
+	{
+		return ShowToHeight(IsAny(TypeHandle, EImGuiCanvasSizeType::Custom));
+	});
+
+	auto SizeRowVisibility = TAttribute<EVisibility>::Create([TypeHandle]()
+	{
+		return ShowToVisibility(IsAny(TypeHandle, EImGuiCanvasSizeType::Custom));
+	});
+
+	auto ExtendRowHeight = TAttribute<float>::Create([TypeHandle]()
+	{
+		return ShowToHeight(IsAny(TypeHandle, EImGuiCanvasSizeType::Custom, EImGuiCanvasSizeType::Desktop));
+	});
+
+	auto ExtendRowVisibility = TAttribute<EVisibility>::Create([TypeHandle]()
+	{
+		return ShowToVisibility(IsAny(TypeHandle, EImGuiCanvasSizeType::Custom, EImGuiCanvasSizeType::Desktop));
+	});
+
+	HeaderRow
+	.NameContent()
+	[
+		InStructPropertyHandle->CreatePropertyNameWidget()
+	]
+	.ValueContent()
+	.MinDesiredWidth(168.f)
+	[
+		SNew(SVerticalBox)
+		+ SVerticalBox::Slot()
+		.AutoHeight()
+		[
+			TypeHandle->CreatePropertyValueWidget()
+		]
+		+ SVerticalBox::Slot()
+		.AutoHeight()
+		.MaxHeight(SizeRowHeight)
+		[
+			SNew(SHorizontalBox)
+			.Visibility(SizeRowVisibility)
+			ADD_DIMENSION_SLOT(WidthHandle, 0.f)
+			ADD_DIMENSION_SLOT(HeightHandle, 6.f)
+		]
+		+ SVerticalBox::Slot()
+		.AutoHeight()
+		.MaxHeight(ExtendRowHeight)
+		[
+			SNew(SHorizontalBox)
+			.Visibility(ExtendRowVisibility)
+			+ SHorizontalBox::Slot()
+			.AutoWidth()
+			[
+				ExtendToViewportHandle->CreatePropertyValueWidget()
+			]
+			+ SHorizontalBox::Slot()
+			.Padding(4.f, 0.f, 0.f, 0.f)
+			.AutoWidth()
+			[
+				ExtendToViewportHandle->CreatePropertyNameWidget()
+			]
+		]
+	];
+
+#undef ADD_DIMENSION_SLOT
+}
+
+void FImGuiCanvasSizeInfoCustomization::CustomizeChildren(TSharedRef<IPropertyHandle> InStructPropertyHandle, IDetailChildrenBuilder& StructBuilder, IPropertyTypeCustomizationUtils& StructCustomizationUtils)
+{
+}
+
+
+#undef LOCTEXT_NAMESPACE
+
+#endif // WITH_EDITOR

Source/ImGui/Private/Editor/ImGuiCanvasSizeInfoCustomization.h

@@ -0,0 +1,22 @@
+// Copyright 1998-2018 Epic Games, Inc. All Rights Reserved.
+
+#pragma once
+
+#if WITH_EDITOR
+
+#include <IPropertyTypeCustomization.h>
+#include <PropertyHandle.h>
+
+
+// Property type customization for FImGuiCanvasSizeInfo.
+class FImGuiCanvasSizeInfoCustomization : public IPropertyTypeCustomization
+{
+public:
+	static TSharedRef<IPropertyTypeCustomization> MakeInstance();
+
+	// IPropertyTypeCustomization interface
+	virtual void CustomizeHeader(TSharedRef<IPropertyHandle> InStructPropertyHandle, FDetailWidgetRow& HeaderRow, IPropertyTypeCustomizationUtils& StructCustomizationUtils) override;
+	virtual void CustomizeChildren(TSharedRef<IPropertyHandle> InStructPropertyHandle, IDetailChildrenBuilder& StructBuilder, IPropertyTypeCustomizationUtils& StructCustomizationUtils) override;
+};
+
+#endif // WITH_EDITOR

Source/ImGui/Private/Editor/ImGuiEditor.cpp

@@ -6,6 +6,7 @@
 
 #include "ImGuiEditor.h"
 
+#include "ImGuiCanvasSizeInfoCustomization.h"
 #include "ImGuiKeyInfoCustomization.h"
 #include "ImGuiModuleSettings.h"
 
@@ -69,6 +70,8 @@ void FImGuiEditor::Register()
 		{
 			bCustomPropertyTypeLayoutsRegistered = true;
 
+			PropertyModule->RegisterCustomPropertyTypeLayout("ImGuiCanvasSizeInfo",
+				FOnGetPropertyTypeCustomizationInstance::CreateStatic(&FImGuiCanvasSizeInfoCustomization::MakeInstance));
 			PropertyModule->RegisterCustomPropertyTypeLayout("ImGuiKeyInfo",
 				FOnGetPropertyTypeCustomizationInstance::CreateStatic(&FImGuiKeyInfoCustomization::MakeInstance));
 		}
@@ -93,6 +96,7 @@ void FImGuiEditor::Unregister()
 
 		if (FPropertyEditorModule* PropertyModule = GetPropertyEditorModule())
 		{
+			PropertyModule->UnregisterCustomPropertyTypeLayout("ImGuiCanvasSizeInfo");
 			PropertyModule->UnregisterCustomPropertyTypeLayout("ImGuiKeyInfo");
 		}
 	}

Source/ImGui/Private/ImGuiModuleSettings.cpp

@@ -103,7 +103,7 @@ void FImGuiModuleSettings::UpdateSettings()
 		SetShareMouseInput(SettingsObject->bShareMouseInput);
 		SetUseSoftwareCursor(SettingsObject->bUseSoftwareCursor);
 		SetToggleInputKey(SettingsObject->ToggleInput);
-		SetAdaptiveCanvasSize(SettingsObject->bAdaptiveCanvasSize);
+		SetCanvasSizeInfo(SettingsObject->CanvasSize);
 	}
 }
 
@@ -161,11 +161,11 @@ void FImGuiModuleSettings::SetToggleInputKey(const FImGuiKeyInfo& KeyInfo)
 	}
 }
 
-void FImGuiModuleSettings::SetAdaptiveCanvasSize(bool bAdaptive)
+void FImGuiModuleSettings::SetCanvasSizeInfo(const FImGuiCanvasSizeInfo& CanvasSizeInfo)
 {
-	if (bAdaptiveCanvasSize != bAdaptive)
+	if (CanvasSize != CanvasSizeInfo)
 	{
-		bAdaptiveCanvasSize = bAdaptive;
+		CanvasSize = CanvasSizeInfo;
 	}
 }
 

Source/ImGui/Private/ImGuiModuleSettings.h

@@ -47,6 +47,47 @@ struct FImGuiKeyInfo
 	}
 };
 
+UENUM(BlueprintType)
+enum class EImGuiCanvasSizeType : uint8
+{
+	Custom UMETA(ToolTip = "Canvas will have a custom width and height."),
+	Desktop UMETA(ToolTip = "Canvas will have the same width and height as the desktop."),
+	Viewport UMETA(ToolTip = "Canvas will always have the same width and height as the viewport."),
+};
+
+/**
+ * Struct with information how to calculate canvas size. 
+ */
+USTRUCT()
+struct FImGuiCanvasSizeInfo
+{
+	GENERATED_BODY()
+
+	// Select how to specify canvas size.
+	UPROPERTY(EditAnywhere, Category = "Canvas Size")
+	EImGuiCanvasSizeType SizeType = EImGuiCanvasSizeType::Desktop;
+
+	// Custom canvas width.
+	UPROPERTY(EditAnywhere, Category = "Canvas Size", meta = (ClampMin = 0, UIMin = 0))
+	int32 Width = 3840;
+
+	// Custom canvas height.
+	UPROPERTY(EditAnywhere, Category = "Canvas Size", meta = (ClampMin = 0, UIMin = 0))
+	int32 Height = 2160;
+
+	// If this is true, canvas width or height may be extended, if the viewport size is larger.
+	UPROPERTY(EditAnywhere, Category = "Canvas Size", meta = (ClampMin = 0, UIMin = 0))
+	bool bExtendToViewport = true;
+
+	bool operator==(const FImGuiCanvasSizeInfo& Other) const
+	{
+		return (SizeType == Other.SizeType) && (Width == Other.Width)
+			&& (Height == Other.Height) && (bExtendToViewport == Other.bExtendToViewport);
+	}
+
+	bool operator!=(const FImGuiCanvasSizeInfo& Other) const { return !(*this == Other); }
+};
+
 // UObject used for loading and saving ImGui settings. To access actual settings use FImGuiModuleSettings interface.
 UCLASS(config=ImGui, defaultconfig)
 class UImGuiSettings : public UObject
@@ -103,9 +144,9 @@ protected:
 	UPROPERTY(EditAnywhere, config, Category = "Keyboard Shortcuts")
 	FImGuiKeyInfo ToggleInput;
 
-	// If true, the size of ImGui canvas will be adaptive to game viewport.
+	// Chose how to define the ImGui canvas size. Select between custom, desktop and viewport.
 	UPROPERTY(EditAnywhere, config, Category = "Canvas Size")
-	bool bAdaptiveCanvasSize = false;
+	FImGuiCanvasSizeInfo CanvasSize;
 
 	// Deprecated name for ToggleInput. Kept temporarily to automatically move old configuration.
 	UPROPERTY(config)
@@ -152,8 +193,8 @@ public:
 	// Get the shortcut configuration for 'ImGui.ToggleInput' command.
 	const FImGuiKeyInfo& GetToggleInputKey() const { return ToggleInputKey; }
 
-	// Get the adaptive canvas size configuration.
-	bool AdaptiveCanvasSize() const { return bAdaptiveCanvasSize; }
+	// Get the information how to calculate the canvas size.
+	const FImGuiCanvasSizeInfo& GetCanvasSizeInfo() const { return CanvasSize; }
 
 	// Delegate raised when ImGui Input Handle is changed.
 	FStringClassReferenceChangeDelegate OnImGuiInputHandlerClassChanged;
@@ -171,7 +212,7 @@ private:
 	void SetShareMouseInput(bool bShare);
 	void SetUseSoftwareCursor(bool bUse);
 	void SetToggleInputKey(const FImGuiKeyInfo& KeyInfo);
-	void SetAdaptiveCanvasSize(bool bAdaptive);
+	void SetCanvasSizeInfo(const FImGuiCanvasSizeInfo& CanvasSizeInfo);
 
 #if WITH_EDITOR
 	void OnPropertyChanged(class UObject* ObjectBeingModified, struct FPropertyChangedEvent& PropertyChangedEvent);
@@ -182,9 +223,9 @@ private:
 
 	FStringClassReference ImGuiInputHandlerClass;
 	FImGuiKeyInfo ToggleInputKey;
+	FImGuiCanvasSizeInfo CanvasSize;
 	bool bShareKeyboardInput = false;
 	bool bShareGamepadInput = false;
 	bool bShareMouseInput = false;
 	bool bUseSoftwareCursor = false;
-	bool bAdaptiveCanvasSize = false;
 };

Source/ImGui/Private/Widgets/SImGuiWidget.cpp

@@ -84,7 +84,7 @@ void SImGuiWidget::Construct(const FArguments& InArgs)
 	const auto& Settings = ModuleManager->GetSettings();
 	SetHideMouseCursor(Settings.UseSoftwareCursor());
 	CreateInputHandler(Settings.GetImGuiInputHandlerClass());
-	SetAdaptiveCanvasSize(Settings.AdaptiveCanvasSize());
+	SetCanvasSizeInfo(Settings.GetCanvasSizeInfo());
 
 	// Initialize state.
 	UpdateVisibility();
@@ -498,15 +498,40 @@ void SImGuiWidget::HandleWindowFocusLost()
 	}
 }
 
-void SImGuiWidget::SetAdaptiveCanvasSize(bool bEnabled)
+void SImGuiWidget::SetCanvasSizeInfo(const FImGuiCanvasSizeInfo& CanvasSizeInfo)
 {
-	if (bAdaptiveCanvasSize != bEnabled)
+	switch (CanvasSizeInfo.SizeType)
 	{
-		bAdaptiveCanvasSize = bEnabled;
+		case EImGuiCanvasSizeType::Custom:
+			MinCanvasSize = { static_cast<float>(CanvasSizeInfo.Width), static_cast<float>(CanvasSizeInfo.Height) };
+			bAdaptiveCanvasSize = CanvasSizeInfo.bExtendToViewport;
+			bCanvasControlEnabled = true;
+			break;
+
+		case EImGuiCanvasSizeType::Desktop:
+			MinCanvasSize = (GEngine && GEngine->GameUserSettings)
+				? GEngine->GameUserSettings->GetDesktopResolution() : FVector2D::ZeroVector;
+			bAdaptiveCanvasSize = CanvasSizeInfo.bExtendToViewport;
+			bCanvasControlEnabled = true;
+			break;
+
+		case EImGuiCanvasSizeType::Viewport:
+		default:
+			MinCanvasSize = FVector2D::ZeroVector;
+			bAdaptiveCanvasSize = true;
+			bCanvasControlEnabled = false;
+	}
+
+	// We only update canvas control widget when canvas control is enabled. Make sure that we will not leave
+	// that widget active after disabling canvas control.
+	if (CanvasControlWidget && !bCanvasControlEnabled)
+	{
+		CanvasControlWidget->SetActive(false);
+	}
+
 	bUpdateCanvasSize = true;
 	UpdateCanvasSize();
 }
-}
 
 void SImGuiWidget::UpdateCanvasSize()
 {
@@ -514,28 +539,30 @@ void SImGuiWidget::UpdateCanvasSize()
 	{
 		if (auto* ContextProxy = ModuleManager->GetContextManager().GetContextProxy(ContextIndex))
 		{
-			if (bAdaptiveCanvasSize)
+			CanvasSize = MinCanvasSize;
+			if (bAdaptiveCanvasSize && GameViewport.IsValid())
 			{
-				if (GameViewport.IsValid())
-				{
-					FVector2D DisplaySize;
-					GameViewport->GetViewportSize(DisplaySize);
-					ContextProxy->SetDisplaySize(DisplaySize);
-				}
+				FVector2D ViewportSize;
+				GameViewport->GetViewportSize(ViewportSize);
+				CanvasSize = FVector2D::Max(CanvasSize, ViewportSize);
 			}
 			else
 			{
-				ContextProxy->ResetDisplaySize();
-				// No need for more updates, if we successfully processed fixed-canvas mode.
+				// No need for more updates, if we successfully processed fixed-canvas size.
 				bUpdateCanvasSize = false;
 			}
+
+			ContextProxy->SetDisplaySize(CanvasSize);
 		}
 	}
 }
 
 void SImGuiWidget::UpdateCanvasControlMode(const FInputEvent& InputEvent)
 {
-	CanvasControlWidget->SetActive(!bAdaptiveCanvasSize && InputEvent.IsLeftAltDown() && InputEvent.IsLeftShiftDown());
+	if (bCanvasControlEnabled)
+	{
+		CanvasControlWidget->SetActive(InputEvent.IsLeftAltDown() && InputEvent.IsLeftShiftDown());
+	}
 }
 
 void SImGuiWidget::OnPostImGuiUpdate()
@@ -628,7 +655,7 @@ int32 SImGuiWidget::OnPaint(const FPaintArgs& Args, const FGeometry& AllottedGeo
 
 FVector2D SImGuiWidget::ComputeDesiredSize(float Scale) const
 {
-	return FVector2D{ 3840.f, 2160.f } * Scale;
+	return CanvasSize * Scale;
 }
 
 #if IMGUI_WIDGET_DEBUG
@@ -744,6 +771,13 @@ namespace TwoColumns
 		LabelText(Label); ImGui::NextColumn();
 		ImGui::Text("%ls", Value); ImGui::NextColumn();
 	}
+
+	template<typename LabelType>
+	static void ValueWidthHeight(LabelType&& Label, const FVector2D& Value)
+	{
+		LabelText(Label); ImGui::NextColumn();
+		ImGui::Text("Width = %.0f, Height = %.0f", Value.X, Value.Y); ImGui::NextColumn();
+	}
 }
 
 namespace Styles
@@ -770,11 +804,19 @@ void SImGuiWidget::OnDebugDraw()
 	if (CVars::DebugWidget.GetValueOnGameThread() > 0)
 	{
 		bool bDebug = true;
-		ImGui::SetNextWindowSize(ImVec2(380, 480), ImGuiSetCond_Once);
+		ImGui::SetNextWindowSize(ImVec2(380, 480), ImGuiCond_Once);
 		if (ImGui::Begin("ImGui Widget Debug", &bDebug))
 		{
 			ImGui::Spacing();
 
+			TwoColumns::CollapsingGroup("Canvas Size", [&]()
+			{
+				TwoColumns::Value("Is Adaptive", bAdaptiveCanvasSize);
+				TwoColumns::Value("Is Updating", bUpdateCanvasSize);
+				TwoColumns::ValueWidthHeight("Min Canvas Size", MinCanvasSize);
+				TwoColumns::ValueWidthHeight("Canvas Size", CanvasSize);
+			});
+
 			TwoColumns::CollapsingGroup("Context", [&]()
 			{
 				TwoColumns::Value("Context Index", ContextIndex);
@@ -821,7 +863,7 @@ void SImGuiWidget::OnDebugDraw()
 		FImGuiInputState& InputState = ContextProxy->GetInputState();
 
 		bool bDebug = true;
-		ImGui::SetNextWindowSize(ImVec2(460, 480), ImGuiSetCond_Once);
+		ImGui::SetNextWindowSize(ImVec2(460, 480), ImGuiCond_Once);
 		if (ImGui::Begin("ImGui Input State", &bDebug))
 		{
 			const ImVec4 HiglightColor{ 1.f, 1.f, 0.5f, 1.f };

Source/ImGui/Private/Widgets/SImGuiWidget.h

@@ -103,7 +103,7 @@ private:
 	void UpdateTransparentMouseInput(const FGeometry& AllottedGeometry);
 	void HandleWindowFocusLost();
 
-	void SetAdaptiveCanvasSize(bool bEnabled);
+	void SetCanvasSizeInfo(const FImGuiCanvasSizeInfo& CanvasSizeInfo);
 	void UpdateCanvasSize();
 
 	void UpdateCanvasControlMode(const FInputEvent& InputEvent);
@@ -134,12 +134,16 @@ private:
 
 	int32 ContextIndex = 0;
 
+	FVector2D MinCanvasSize = FVector2D::ZeroVector;
+	FVector2D CanvasSize = FVector2D::ZeroVector;
+
 	bool bInputEnabled = false;
 	bool bForegroundWindow = false;
 	bool bHideMouseCursor = true;
 	bool bTransparentMouseInput = false;
 	bool bAdaptiveCanvasSize = false;
 	bool bUpdateCanvasSize = false;
+	bool bCanvasControlEnabled = false;
 
 	TSharedPtr<SImGuiCanvasControl> CanvasControlWidget;
 	TWeakPtr<SWidget> PreviousUserFocusedWidget;