UnrealEngine/Engine/Source/Runtime/UMG/Private/Slate/SRetainerWidget.cpp

// Copyright Epic Games, Inc. All Rights Reserved.

#include "Slate/SRetainerWidget.h"
#include "Misc/App.h"
#include "UObject/Package.h"
#include "Framework/Application/SlateApplication.h"
#include "Materials/MaterialInstanceDynamic.h"
#include "RenderDeferredCleanup.h"
#include "RHI.h"
#include "Engine/TextureRenderTarget2D.h"
#include "Engine/World.h"
#include "UMGPrivate.h"
#include "Widgets/SNullWidget.h"

DECLARE_CYCLE_STAT(TEXT("Retainer Widget Tick"), STAT_SlateRetainerWidgetTick, STATGROUP_Slate);
DECLARE_CYCLE_STAT(TEXT("Retainer Widget Paint"), STAT_SlateRetainerWidgetPaint, STATGROUP_Slate);

#if !UE_BUILD_SHIPPING
FOnRetainedModeChanged SRetainerWidget::OnRetainerModeChangedDelegate;
#endif

static void HandleDesignerRetainedRenderingToggled(IConsoleVariable* CVar)
{
	FSlateApplication::Get().InvalidateAllWidgets(false);
}

/** True if we should do retained rendering in designer. */
bool GEnableDesignerRetainedRendering = true;
FAutoConsoleVariableRef EnableDesignerRetainedRendering(
	TEXT("Slate.EnableDesignerRetainedRendering"),
	GEnableDesignerRetainedRendering,
	TEXT("Controls if retainer renders in designer; 0 - Never; 1 - Per Widget Properties"),
	FConsoleVariableDelegate::CreateStatic(&HandleDesignerRetainedRenderingToggled)
);

/** True if we should allow widgets to be cached in the UI at all. */
int32 GEnableRetainedRendering = 1;
FAutoConsoleVariableRef EnableRetainedRendering(
	TEXT("Slate.EnableRetainedRendering"),
	GEnableRetainedRendering,
	TEXT("Whether to attempt to render things in SRetainerWidgets to render targets first.") 
);

/** True if we allow the transform to be modify to render in local space. */
bool GSlateEnableRenderWithLocalTransform = true;
FAutoConsoleVariableRef CVarGlateEnableRenderWithLocalTransform(
	TEXT("Slate.EnableRetainedRenderingWithLocalTransform"),
	GSlateEnableRenderWithLocalTransform,
	TEXT("This console variable is no longer useful, as the SRetainerWidget render bugs workedaround by it have been fixed. It will be removed.")
);

static bool IsRetainedRenderingEnabled()
{
	return GEnableRetainedRendering != 0;
}

/** Whether or not the platform should have deferred retainer widget render target updating enabled by default */
#define PLATFORM_REQUIRES_DEFERRED_RETAINER_UPDATE PLATFORM_IOS || PLATFORM_ANDROID;

/**
 * If this is true the retained rendering render thread work will happen during normal slate render thread rendering after the back buffer has been presented
 * in order to avoid extra render target switching in the middle of the frame. The downside is that the UI update will be a frame late
 */
int32 GDeferRetainedRenderingRenderThread = PLATFORM_REQUIRES_DEFERRED_RETAINER_UPDATE;
FAutoConsoleVariableRef DeferRetainedRenderingRT(
	TEXT("Slate.DeferRetainedRenderingRenderThread"),
	GDeferRetainedRenderingRenderThread,
	TEXT("Whether or not to defer retained rendering to happen at the same time as the rest of slate render thread work"));


class FRetainerWidgetRenderingResources : public FDeferredCleanupInterface, public FGCObject
{
public:
	FRetainerWidgetRenderingResources()
		: WidgetRenderer(nullptr)
		, RenderTarget(nullptr)
		, DynamicEffect(nullptr)
	{}

	~FRetainerWidgetRenderingResources()
	{
		// Note not using deferred cleanup for widget renderer here as it is already in deferred cleanup
		if (WidgetRenderer)
		{
			delete WidgetRenderer;
		}
	}

	/** FGCObject interface */
	virtual void AddReferencedObjects(FReferenceCollector& Collector) override
	{
		Collector.AddReferencedObject(RenderTarget);
		Collector.AddReferencedObject(DynamicEffect);
	}

	virtual FString GetReferencerName() const override
	{
		return TEXT("FRetainerWidgetRenderingResources");
	}
	
public:
	FWidgetRenderer* WidgetRenderer;
	TObjectPtr<UTextureRenderTarget2D> RenderTarget;
	TObjectPtr<UMaterialInstanceDynamic> DynamicEffect;
};

TArray<SRetainerWidget*, TInlineAllocator<3>> SRetainerWidget::Shared_WaitingToRender;
int32 SRetainerWidget::Shared_MaxRetainerWorkPerFrame(0);
TFrameValue<int32> SRetainerWidget::Shared_RetainerWorkThisFrame(0);


SRetainerWidget::SRetainerWidget()
	: PreviousRenderSize(FIntPoint::NoneValue)
	, PreviousClipRectSize(FIntPoint::NoneValue)
	, PreviousColorAndOpacity(FColor::Transparent)
	, LastIncomingLayerId(0)
	, VirtualWindow(SNew(SVirtualWindow))
	, HittestGrid(MakeShared<FHittestGrid>())
	, RenderingResources(new FRetainerWidgetRenderingResources)
{
	FSlateApplicationBase::Get().OnGlobalInvalidationToggled().AddRaw(this, &SRetainerWidget::OnGlobalInvalidationToggled);
	if (FSlateApplication::IsInitialized())
	{
#if !UE_BUILD_SHIPPING
		OnRetainerModeChangedDelegate.RemoveAll(this);
#endif
	}
	bHasCustomPrepass = true;
	SetInvalidationRootWidget(*this);
	SetInvalidationRootHittestGrid(HittestGrid.Get());
	SetCanTick(false);
}

SRetainerWidget::~SRetainerWidget()
{
	if( FSlateApplication::IsInitialized() )
	{
		FSlateApplicationBase::Get().OnGlobalInvalidationToggled().RemoveAll(this);
#if !UE_BUILD_SHIPPING
		OnRetainerModeChangedDelegate.RemoveAll( this );
#endif
	}

	// Begin deferred cleanup of rendering resources.  DO NOT delete here.  Will be deleted when safe
	BeginCleanup(RenderingResources);

	Shared_WaitingToRender.Remove(this);
}

void SRetainerWidget::UpdateWidgetRenderer()
{
	// We can't write out linear.  If we write out linear, then we end up with premultiplied alpha
	// in linear space, which blending with gamma space later is difficult...impossible? to get right
	// since the rest of slate does blending in gamma space.
	const bool bWriteContentInGammaSpace = true;

	if (!RenderingResources->WidgetRenderer)
	{
		RenderingResources->WidgetRenderer = new FWidgetRenderer(bWriteContentInGammaSpace);
	}

	UTextureRenderTarget2D* RenderTarget = RenderingResources->RenderTarget;
	FWidgetRenderer* WidgetRenderer = RenderingResources->WidgetRenderer;

	WidgetRenderer->SetUseGammaCorrection(bWriteContentInGammaSpace);

	// This will be handled by the main slate rendering pass
	WidgetRenderer->SetApplyColorDeficiencyCorrection(false);

	WidgetRenderer->SetIsPrepassNeeded(false);
	WidgetRenderer->SetClearHitTestGrid(false);

	// Update the render target to match the current gamma rendering preferences.
	if (RenderTarget && RenderTarget->SRGB != !bWriteContentInGammaSpace)
	{
		// Note, we do the opposite here of whatever write is, if we we're writing out gamma,
		// then sRGB writes were not supported, so it won't be an sRGB texture.
		RenderTarget->TargetGamma = !bWriteContentInGammaSpace ? 0.0f : 1.0;
		RenderTarget->SRGB = !bWriteContentInGammaSpace;

		RenderTarget->UpdateResource();
	}
}

void SRetainerWidget::Construct(const FArguments& InArgs)
{
	STAT(MyStatId = FDynamicStats::CreateStatId<FStatGroup_STATGROUP_Slate>(InArgs._StatId);)

	UTextureRenderTarget2D* RenderTarget = NewObject<UTextureRenderTarget2D>();
	RenderTarget->ClearColor = FLinearColor::Transparent;
	RenderTarget->RenderTargetFormat = RTF_RGBA8_SRGB;

	RenderingResources->RenderTarget = RenderTarget;
	SurfaceBrush.SetResourceObject(RenderTarget);

	VirtualWindow->SetVisibility(EVisibility::SelfHitTestInvisible);  // deubanks: We don't want Retainer Widgets blocking hit testing for tooltips
	VirtualWindow->SetShouldResolveDeferred(false);

	UpdateWidgetRenderer();

	MyWidget = InArgs._Content.Widget;

	RenderOnPhase = InArgs._RenderOnPhase;
	RenderOnInvalidation = InArgs._RenderOnInvalidation;

	Phase = InArgs._Phase;
	PhaseCount = InArgs._PhaseCount;

	LastDrawTime = FApp::GetCurrentTime();
	LastTickedFrame = 0;

	bEnableRetainedRenderingDesire = true;
	bEnableRetainedRendering = false;
	SetVolatilePrepass(bEnableRetainedRendering);

#if WITH_EDITOR
	bIsDesignTime = false;
	bShowEffectsInDesigner = true;
	bWarnOnInvalidSize = InArgs._bWarnOnInvalidSize;
#endif // WITH_EDITOR

	RefreshRenderingMode();
	bRenderRequested = true;
	bInvalidSizeLogged = false;

	ChildSlot
	[
		MyWidget.ToSharedRef()
	];

	if ( FSlateApplication::IsInitialized() )
	{
#if !UE_BUILD_SHIPPING
		OnRetainerModeChangedDelegate.AddRaw(this, &SRetainerWidget::OnRetainerModeChanged);

		static bool bStaticInit = false;

		if ( !bStaticInit )
		{
			bStaticInit = true;
			EnableRetainedRendering->SetOnChangedCallback(FConsoleVariableDelegate::CreateStatic(&SRetainerWidget::OnRetainerModeCVarChanged));
		}
#endif
	}
}

bool SRetainerWidget::ShouldBeRenderingOffscreen() const
{
	return bEnableRetainedRenderingDesire && IsRetainedRenderingEnabled();
}

bool SRetainerWidget::IsAnythingVisibleToRender() const
{
	return MyWidget.IsValid() && MyWidget->GetVisibility().IsVisible();
}

void SRetainerWidget::OnRetainerModeChanged()
{
	if (MyWidget.IsValid())
	{
		InvalidateChildRemovedFromTree(*MyWidget.Get());
	}

	// Invalidate myself
	Advanced_ResetInvalidation(true);

	// Invalidate my invalidation root, since all my children were once it's children
	// it needs to force a generation bump just like me.
	if (FSlateInvalidationRoot* MyInvalidationRoot = GetProxyHandle().GetInvalidationRootHandle().GetInvalidationRoot())
	{
		MyInvalidationRoot->Advanced_ResetInvalidation(true);
	}

	RefreshRenderingMode();

	bRenderRequested = true;
}

void SRetainerWidget::OnRootInvalidated()
{
	RequestRender();
}

#if !UE_BUILD_SHIPPING

void SRetainerWidget::OnRetainerModeCVarChanged( IConsoleVariable* CVar )
{
	OnRetainerModeChangedDelegate.Broadcast();
}

#endif

void SRetainerWidget::SetRetainedRendering(bool bRetainRendering)
{
	if (bEnableRetainedRenderingDesire != bRetainRendering)
	{
		bEnableRetainedRenderingDesire = bRetainRendering;
		OnRetainerModeChanged();
	}
}

void SRetainerWidget::RefreshRenderingMode()
{
	const bool bShouldBeRenderingOffscreen = ShouldBeRenderingOffscreen();

	if ( bEnableRetainedRendering != bShouldBeRenderingOffscreen )
	{
		bEnableRetainedRendering = bShouldBeRenderingOffscreen;
		SetVolatilePrepass(bEnableRetainedRendering);
		InvalidateRootChildOrder();
	}
}

void SRetainerWidget::SetContent(const TSharedRef< SWidget >& InContent)
{
	MyWidget = InContent;
	ChildSlot
	[
		InContent
	];
}

UMaterialInstanceDynamic* SRetainerWidget::GetEffectMaterial() const
{
	return RenderingResources->DynamicEffect;
}

void SRetainerWidget::SetEffectMaterial(UMaterialInterface* EffectMaterial)
{
	if ( EffectMaterial )
	{
		UMaterialInstanceDynamic* DynamicEffect = Cast<UMaterialInstanceDynamic>(EffectMaterial);
		if ( !DynamicEffect )
		{
			DynamicEffect = UMaterialInstanceDynamic::Create(EffectMaterial, GetTransientPackage());
		}
		RenderingResources->DynamicEffect = DynamicEffect;

		SurfaceBrush.SetResourceObject(RenderingResources->DynamicEffect);
	}
	else
	{
		RenderingResources->DynamicEffect = nullptr;
		SurfaceBrush.SetResourceObject(RenderingResources->RenderTarget);
	}

	UpdateWidgetRenderer();
}

void SRetainerWidget::SetTextureParameter(FName TextureParameter)
{
	DynamicEffectTextureParameter = TextureParameter;
}
 
void SRetainerWidget::SetWorld(UWorld* World)
{
	OuterWorld = World;
}

FChildren* SRetainerWidget::GetChildren()
{
	if (bEnableRetainedRendering)
	{
		return &FNoChildren::NoChildrenInstance;
	}
	else
	{
		return SCompoundWidget::GetChildren();
	}
}

#if WITH_SLATE_DEBUGGING
FChildren* SRetainerWidget::Debug_GetChildrenForReflector()
{
	return SCompoundWidget::GetChildren();
}
#endif

void SRetainerWidget::SetRenderingPhase(int32 InPhase, int32 InPhaseCount)
{
	Phase = InPhase;
	PhaseCount = InPhaseCount;
}

void SRetainerWidget::RequestRender()
{
	bRenderRequested = true;
	InvalidateRootChildOrder();
}

#if WITH_EDITOR
void SRetainerWidget::SetIsDesignTime(bool bInIsDesignTime)
{
	bIsDesignTime = bInIsDesignTime;
}

void SRetainerWidget::SetShowEffectsInDesigner(bool bInShowEffectsInDesigner)
{
	bShowEffectsInDesigner = bInShowEffectsInDesigner;
}
#endif // WITH_EDITOR

SRetainerWidget::EPaintRetainedContentResult SRetainerWidget::PaintRetainedContentImpl(const FSlateInvalidationContext& Context, const FGeometry& AllottedGeometry, int32 LayerId)
{
	if (RenderOnPhase)
	{
		if (LastTickedFrame != GFrameCounter && (GFrameCounter % PhaseCount) == Phase)
		{
			// If doing some phase based invalidation, just redraw everything again
			bRenderRequested = true;
			InvalidateRootLayout();
		}
	}

	const FPaintGeometry PaintGeometry = AllottedGeometry.ToPaintGeometry();
	FSlateRenderTransform AccumulatedRenderTransform = PaintGeometry.GetAccumulatedRenderTransform();
	const FVector2f RenderSize = FVector2f(PaintGeometry.GetLocalSize()) * AccumulatedRenderTransform.GetMatrix().GetScale().GetVector();
	const FIntPoint RoundedRenderSize = RenderSize.IntPoint();

	if (RenderOnInvalidation)
	{
		// the invalidation root will take care of whether or not we actually rendered
		bRenderRequested = true;

		const FIntPoint ClipRectSize = Context.CullingRect.GetSize().IntPoint();
		const TOptional<FSlateClippingState> ClippingState = Context.WindowElementList->GetClippingState();
		const FColor ColorAndOpacityTint = Context.WidgetStyle.GetColorAndOpacityTint().ToFColor(false);


		// Aggressively re-layout when a base state changes.
		if (RoundedRenderSize != PreviousRenderSize
			|| AllottedGeometry != PreviousAllottedGeometry
			|| AllottedGeometry.GetAccumulatedRenderTransform() != PreviousAllottedGeometry.GetAccumulatedRenderTransform()
			|| ClipRectSize != PreviousClipRectSize
			|| ClippingState != PreviousClippingState)
		{
			PreviousRenderSize = RoundedRenderSize;
			PreviousAllottedGeometry = AllottedGeometry;
			PreviousClipRectSize = ClipRectSize;
			PreviousClippingState = ClippingState;

			InvalidateRootLayout();
		}

		// Aggressively repaint when a base state changes.
		if (LayerId != LastIncomingLayerId
			|| ColorAndOpacityTint != PreviousColorAndOpacity)
		{
			LastIncomingLayerId = LayerId;
			PreviousColorAndOpacity = ColorAndOpacityTint;

			GetRootWidget()->Invalidate(EInvalidateWidgetReason::Paint);
		}
	}
	else if (RoundedRenderSize != PreviousRenderSize)
	{
		bRenderRequested = true;
		InvalidateRootLayout();
		PreviousRenderSize = RoundedRenderSize;
	}

	if (Shared_MaxRetainerWorkPerFrame > 0)
	{
		if (Shared_RetainerWorkThisFrame.TryGetValue(0) > Shared_MaxRetainerWorkPerFrame)
		{
			Shared_WaitingToRender.AddUnique(this);
			return EPaintRetainedContentResult::Queued;
		}
	}

	if (bRenderRequested)
	{
		// In order to get material parameter collections to function properly, we need the current world's Scene
		// properly propagated through to any widgets that depend on that functionality. The SceneViewport and RetainerWidget the 
		// only location where this information exists in Slate, so we push the current scene onto the current
		// Slate application so that we can leverage it in later calls.
		UWorld* TickWorld = OuterWorld.Get();
		if (TickWorld && TickWorld->Scene && IsInGameThread())
		{
			FSlateApplication::Get().GetRenderer()->RegisterCurrentScene(TickWorld->Scene);
		}
		else if (IsInGameThread())
		{
			FSlateApplication::Get().GetRenderer()->RegisterCurrentScene(nullptr);
		}

		// Update the number of retainers we've drawn this frame.
		Shared_RetainerWorkThisFrame = Shared_RetainerWorkThisFrame.TryGetValue(0) + 1;

		LastTickedFrame = GFrameCounter;
		const double TimeSinceLastDraw = FApp::GetCurrentTime() - LastDrawTime;

		// Size must be a positive integer to allocate the RenderTarget
		const uint32 RenderTargetWidth  = FMath::RoundToInt(FMath::Abs(RenderSize.X));
		const uint32 RenderTargetHeight = FMath::RoundToInt(FMath::Abs(RenderSize.Y));
		const bool bTextureIsTooLarge = FMath::Max(RenderTargetWidth, RenderTargetHeight) > GetMax2DTextureDimension();
		const bool bTextureSizeZero = (RenderTargetWidth == 0 || RenderTargetHeight == 0);

		if (bTextureIsTooLarge || bTextureSizeZero)
		{
			// if bTextureTooLarge then the user probably have a layout issue. Warn the user.
			if (!bInvalidSizeLogged)
			{
				bInvalidSizeLogged = true;

				const bool bEnableWarnOnInvalidSize =
#if WITH_EDITOR
					bWarnOnInvalidSize;
#else
					true;
#endif
				if (bTextureIsTooLarge)
				{
					if (bEnableWarnOnInvalidSize)
					{
						UE_LOG(LogUMG, Warning, TEXT("The requested size for SRetainerWidget is too large. W:%i H:%i"), RenderTargetWidth, RenderTargetHeight);
					}
				}
				else
				{
					if (bEnableWarnOnInvalidSize)
					{
						UE_LOG(LogUMG, Warning, TEXT("The requested size for SRetainerWidget is 0. W:%i H:%i"), RenderTargetWidth, RenderTargetHeight);
					}
				}
			}
			return bTextureIsTooLarge ? EPaintRetainedContentResult::TextureSizeTooBig : EPaintRetainedContentResult::TextureSizeZero;
		}
		bInvalidSizeLogged = false;

		if (RenderTargetWidth >= 1 && RenderTargetHeight >= 1)
		{
			const FVector2D ViewOffset = PaintGeometry.GetAccumulatedRenderTransform().GetTranslation();

			UTextureRenderTarget2D* RenderTarget = RenderingResources->RenderTarget;
			FWidgetRenderer* WidgetRenderer = RenderingResources->WidgetRenderer;

			if ( MyWidget->GetVisibility().IsVisible() )
			{
				if ( (int32)RenderTarget->GetSurfaceWidth() != (int32)RenderTargetWidth ||
					 (int32)RenderTarget->GetSurfaceHeight() != (int32)RenderTargetHeight )
				{
					
					// If the render target resource already exists just resize it.  Calling InitCustomFormat flushes render commands which could result in a huge hitch
					if(RenderTarget->GameThread_GetRenderTargetResource() && RenderTarget->OverrideFormat == PF_B8G8R8A8)
					{
						RenderTarget->ResizeTarget(RenderTargetWidth, RenderTargetHeight);
					}
					else
					{
						const bool bForceLinearGamma = false;
						RenderTarget->InitCustomFormat(RenderTargetWidth, RenderTargetHeight, PF_B8G8R8A8, bForceLinearGamma);
						RenderTarget->UpdateResourceImmediate();
					}
				}

				const float Scale = AllottedGeometry.Scale;

				const FVector2D DrawSize = FVector2D(RenderTargetWidth, RenderTargetHeight);
				//const FGeometry WindowGeometry = FGeometry::MakeRoot(DrawSize * ( 1 / Scale ), FSlateLayoutTransform(Scale, PaintGeometry.DrawPosition));

				// Update the surface brush to match the latest size.
				SurfaceBrush.ImageSize = DrawSize;

				WidgetRenderer->ViewOffset = -ViewOffset;
				WidgetRenderer->SetIsPrepassNeeded(false);

				FVector2f WindowSize(RenderSize);
				SWindow* PaintWindow = Context.WindowElementList->GetPaintWindow();
				if (PaintWindow)
				{
					const FVector2f ViewportSize = PaintWindow->GetViewportSize();
					WindowSize.X = FMath::Max(WindowSize.X, ViewportSize.X);
					WindowSize.Y = FMath::Max(WindowSize.Y, ViewportSize.Y);
				}
				VirtualWindow->Resize(WindowSize);

				bool bRepaintedWidgets = WidgetRenderer->DrawInvalidationRoot(VirtualWindow, RenderTarget, *this, Context, GDeferRetainedRenderingRenderThread != 0);
				bRenderRequested = false;
				Shared_WaitingToRender.Remove(this);

				LastDrawTime = FApp::GetCurrentTime();

				return bRepaintedWidgets ? EPaintRetainedContentResult::Painted : EPaintRetainedContentResult::NotPainted;
			}
		}
	}

	return EPaintRetainedContentResult::NotPainted;
}

int32 SRetainerWidget::OnPaint(const FPaintArgs& Args, const FGeometry& AllottedGeometry, const FSlateRect& MyCullingRect, FSlateWindowElementList& OutDrawElements, int32 LayerId, const FWidgetStyle& InWidgetStyle, bool bParentEnabled) const
{
	STAT(FScopeCycleCounter PaintCycleCounter(MyStatId););

	SRetainerWidget* MutableThis = const_cast<SRetainerWidget*>(this);

	bool bShouldRetainRendering = bEnableRetainedRendering;

#if WITH_EDITOR
	bool bShouldSkipDesignerRendering = bIsDesignTime && (!bShowEffectsInDesigner || !GEnableDesignerRetainedRendering);
	bShouldRetainRendering = bEnableRetainedRendering && !bShouldSkipDesignerRendering;
#endif // WITH_EDITOR

	if (bShouldRetainRendering && IsAnythingVisibleToRender())
	{
		SCOPE_CYCLE_COUNTER(STAT_SlateRetainerWidgetPaint);

		// Copy hit test grid settings from the root
		const bool bHittestCleared = HittestGrid->SetHittestArea(Args.RootGrid.GetGridOrigin(), Args.RootGrid.GetGridSize(), Args.RootGrid.GetGridWindowOrigin());
		if (bHittestCleared)
		{
			MutableThis->RequestRender();
		}
		HittestGrid->SetOwner(this);
		HittestGrid->SetCullingRect(MyCullingRect);

		FPaintArgs NewArgs = Args.WithNewHitTestGrid(HittestGrid.Get());

		// Copy the current user index into the new grid since nested hittest grids should inherit their parents user id
		NewArgs.GetHittestGrid().SetUserIndex(Args.RootGrid.GetUserIndex());

		FSlateInvalidationContext Context(OutDrawElements, InWidgetStyle);
		Context.bParentEnabled = bParentEnabled;
		Context.bAllowFastPathUpdate = true;
		Context.LayoutScaleMultiplier = GetPrepassLayoutScaleMultiplier();
		Context.PaintArgs = &NewArgs;
		Context.IncomingLayerId = LayerId;
		Context.CullingRect = MyCullingRect;

		EPaintRetainedContentResult PaintResult = MutableThis->PaintRetainedContentImpl(Context, AllottedGeometry, LayerId);

#if WITH_SLATE_DEBUGGING
		if (PaintResult == EPaintRetainedContentResult::NotPainted
			|| PaintResult == EPaintRetainedContentResult::TextureSizeZero
			|| PaintResult == EPaintRetainedContentResult::TextureSizeTooBig)
		{
			MutableThis->SetLastPaintType(ESlateInvalidationPaintType::None);
		}
#endif

		if (PaintResult == EPaintRetainedContentResult::TextureSizeTooBig)
		{
			return SCompoundWidget::OnPaint(Args, AllottedGeometry, MyCullingRect, OutDrawElements, LayerId, InWidgetStyle, bParentEnabled);
		}
		else if (PaintResult == EPaintRetainedContentResult::TextureSizeZero)
		{
			return GetCachedMaxLayerId();
		}
		else
		{
			UTextureRenderTarget2D* RenderTarget = RenderingResources->RenderTarget;
			check(RenderTarget);

			if (RenderTarget->GetSurfaceWidth() >= 1 && RenderTarget->GetSurfaceHeight() >= 1)
			{
				const FLinearColor ComputedColorAndOpacity(Context.WidgetStyle.GetColorAndOpacityTint() * GetColorAndOpacity() * SurfaceBrush.GetTint(Context.WidgetStyle));
				// Retainer widget uses pre-multiplied alpha, so pre-multiply the color by the alpha to respect opacity.
				const FLinearColor PremultipliedColorAndOpacity(ComputedColorAndOpacity * ComputedColorAndOpacity.A);

				FWidgetRenderer* WidgetRenderer = RenderingResources->WidgetRenderer;
				UMaterialInstanceDynamic* DynamicEffect = RenderingResources->DynamicEffect;

				const bool bDynamicMaterialInUse = (DynamicEffect != nullptr);
				if (bDynamicMaterialInUse)
				{
					DynamicEffect->SetTextureParameterValue(DynamicEffectTextureParameter, RenderTarget);
				}

				FSlateDrawElement::MakeBox(
					*Context.WindowElementList,
					Context.IncomingLayerId,
					AllottedGeometry.ToPaintGeometry(),
					&SurfaceBrush,
					// We always write out the content in gamma space, so when we render the final version we need to
					// render without gamma correction enabled.
					ESlateDrawEffect::PreMultipliedAlpha | ESlateDrawEffect::NoGamma,
					FLinearColor(PremultipliedColorAndOpacity.R, PremultipliedColorAndOpacity.G, PremultipliedColorAndOpacity.B, PremultipliedColorAndOpacity.A)
				);
			}

			const bool bInheritedHittestability = Args.GetInheritedHittestability();
			const bool bOutgoingHittestability = bInheritedHittestability && GetVisibility().AreChildrenHitTestVisible();

			// add our widgets to the root hit test grid
			if (bOutgoingHittestability)
			{
				Args.GetHittestGrid().AddGrid(HittestGrid);
			}

			return GetCachedMaxLayerId();
		}
	}
	else
	{
		return SCompoundWidget::OnPaint(Args, AllottedGeometry, MyCullingRect, OutDrawElements, LayerId, InWidgetStyle, bParentEnabled);
	}
}

FVector2D SRetainerWidget::ComputeDesiredSize(float LayoutScaleMuliplier) const
{
	if ( bEnableRetainedRendering )
	{
		return MyWidget->GetDesiredSize();
	}
	else
	{
		return SCompoundWidget::ComputeDesiredSize(LayoutScaleMuliplier);
	}
}

void SRetainerWidget::OnGlobalInvalidationToggled(bool bGlobalInvalidationEnabled)
{
	InvalidateRootChildOrder();

	ClearAllFastPathData(true);
}

bool SRetainerWidget::CustomPrepass(float LayoutScaleMultiplier)
{
	if (bEnableRetainedRendering)
	{
		if (NeedsPrepass())
		{
			SetNeedsSlowPath(true);
		}
		ProcessInvalidation();
		if (NeedsSlowPath())
		{
			FChildren* Children = SCompoundWidget::GetChildren();
			Prepass_ChildLoop(LayoutScaleMultiplier, Children);
		}
		return false;
	}
	else
	{
		return true;
	}
}

TSharedRef<SWidget> SRetainerWidget::GetRootWidget()
{
	return bEnableRetainedRendering ? SCompoundWidget::GetChildren()->GetChildAt(0) : SNullWidget::NullWidget;
}

int32 SRetainerWidget::PaintSlowPath(const FSlateInvalidationContext& Context)
{
	HittestGrid->Clear();

	const FGeometry& OriginalPaintSpaceGeometry = GetPaintSpaceGeometry();
	FSlateRenderTransform SimplifiedRenderTransform(OriginalPaintSpaceGeometry.GetAccumulatedRenderTransform().GetMatrix().GetScale(), OriginalPaintSpaceGeometry.GetAccumulatedRenderTransform().GetTranslation());
	FTransform2D ScalePosTransform(OriginalPaintSpaceGeometry.Scale, OriginalPaintSpaceGeometry.AbsolutePosition);
	SimplifiedRenderTransform = Concatenate(SimplifiedRenderTransform, Inverse(ScalePosTransform));
	const FGeometry NewPaintSpaceGeometry = FGeometry::MakeRoot(OriginalPaintSpaceGeometry.GetLocalSize(), FSlateLayoutTransform(OriginalPaintSpaceGeometry.Scale, OriginalPaintSpaceGeometry.AbsolutePosition)).MakeChild(SimplifiedRenderTransform, FVector2D::ZeroVector);
	return SCompoundWidget::OnPaint(*Context.PaintArgs, NewPaintSpaceGeometry, Context.CullingRect, *Context.WindowElementList, Context.IncomingLayerId, Context.WidgetStyle, Context.bParentEnabled);
}