UnrealEngineUWP/Engine/Source/Editor/GraphEditor/Private/SNodePanel.cpp

// Copyright 1998-2014 Epic Games, Inc. All Rights Reserved.


#include "GraphEditorCommon.h"
#include "ScopedTransaction.h"

struct FZoomLevelEntry
{
public:
	FZoomLevelEntry(float InZoomAmount, const FText& InDisplayText, EGraphRenderingLOD::Type InLOD)
		: DisplayText(FText::Format(NSLOCTEXT("GraphEditor", "Zoom", "Zoom {0}"), InDisplayText))
	 , ZoomAmount(InZoomAmount)
	 , LOD(InLOD)
	{
	}

public:
	FText DisplayText;
	float ZoomAmount;
	EGraphRenderingLOD::Type LOD;
};

struct FFixedZoomLevelsContainer : public FZoomLevelsContainer
{
	FFixedZoomLevelsContainer()
	{
		// Initialize zoom levels if not done already
		if (ZoomLevels.Num() == 0)
		{
			ZoomLevels.Reserve(20);
			ZoomLevels.Add(FZoomLevelEntry(0.100f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-12"), EGraphRenderingLOD::LowestDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.125f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-11"), EGraphRenderingLOD::LowestDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.150f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-10"), EGraphRenderingLOD::LowestDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.175f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-9"), EGraphRenderingLOD::LowestDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.200f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-8"), EGraphRenderingLOD::LowestDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.225f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-7"), EGraphRenderingLOD::LowDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.250f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-6"), EGraphRenderingLOD::LowDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.375f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-5"), EGraphRenderingLOD::MediumDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.500f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-4"), EGraphRenderingLOD::MediumDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.675f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-3"), EGraphRenderingLOD::MediumDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.750f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-2"), EGraphRenderingLOD::DefaultDetail));
			ZoomLevels.Add(FZoomLevelEntry(0.875f, NSLOCTEXT("GraphEditor", "ZoomLevel", "-1"), EGraphRenderingLOD::DefaultDetail));
			ZoomLevels.Add(FZoomLevelEntry(1.000f, NSLOCTEXT("GraphEditor", "ZoomLevel", "1:1"), EGraphRenderingLOD::DefaultDetail));
			ZoomLevels.Add(FZoomLevelEntry(1.250f, NSLOCTEXT("GraphEditor", "ZoomLevel", "+1"), EGraphRenderingLOD::DefaultDetail));
			ZoomLevels.Add(FZoomLevelEntry(1.375f, NSLOCTEXT("GraphEditor", "ZoomLevel", "+2"), EGraphRenderingLOD::DefaultDetail));
			ZoomLevels.Add(FZoomLevelEntry(1.500f, NSLOCTEXT("GraphEditor", "ZoomLevel", "+3"), EGraphRenderingLOD::FullyZoomedIn));
			ZoomLevels.Add(FZoomLevelEntry(1.675f, NSLOCTEXT("GraphEditor", "ZoomLevel", "+4"), EGraphRenderingLOD::FullyZoomedIn));
			ZoomLevels.Add(FZoomLevelEntry(1.750f, NSLOCTEXT("GraphEditor", "ZoomLevel", "+5"), EGraphRenderingLOD::FullyZoomedIn));
			ZoomLevels.Add(FZoomLevelEntry(1.875f, NSLOCTEXT("GraphEditor", "ZoomLevel", "+6"), EGraphRenderingLOD::FullyZoomedIn));
			ZoomLevels.Add(FZoomLevelEntry(2.000f, NSLOCTEXT("GraphEditor", "ZoomLevel", "+7"), EGraphRenderingLOD::FullyZoomedIn));
		}
	}

	float GetZoomAmount(int32 InZoomLevel) const override
	{
		checkSlow(ZoomLevels.IsValidIndex(InZoomLevel));
		return ZoomLevels[InZoomLevel].ZoomAmount;
	}

	int32 GetNearestZoomLevel(float InZoomAmount) const override
	{
		for (int32 ZoomLevelIndex=0; ZoomLevelIndex < GetNumZoomLevels(); ++ZoomLevelIndex)
		{
			if (InZoomAmount <= GetZoomAmount(ZoomLevelIndex))
			{
				return ZoomLevelIndex;
			}
		}

		return GetDefaultZoomLevel();
	}
	
	FText GetZoomText(int32 InZoomLevel) const override
	{
		checkSlow(ZoomLevels.IsValidIndex(InZoomLevel));
		return ZoomLevels[InZoomLevel].DisplayText;
	}
	
	int32 GetNumZoomLevels() const override
	{
		return ZoomLevels.Num();
	}
	
	int32 GetDefaultZoomLevel() const override
	{
		return 12;
	}

	EGraphRenderingLOD::Type GetLOD(int32 InZoomLevel) const override
	{
		checkSlow(ZoomLevels.IsValidIndex(InZoomLevel));
		return ZoomLevels[InZoomLevel].LOD;
	}

	static TArray<FZoomLevelEntry> ZoomLevels;
};

const TCHAR* XSymbol=TEXT("\xD7");
TArray<FZoomLevelEntry> FFixedZoomLevelsContainer::ZoomLevels;

//////////////////////////////////////////////////////////////////////////
// FGraphSelectionManager

const FGraphPanelSelectionSet& FGraphSelectionManager::GetSelectedNodes() const
{
	return SelectedNodes;
}

void FGraphSelectionManager::SelectSingleNode(SelectedItemType Node)
{
	SelectedNodes.Empty();
	SetNodeSelection(Node, true);
}

// Reset the selection state of all nodes
void FGraphSelectionManager::ClearSelectionSet()
{
	if (SelectedNodes.Num())
	{
		SelectedNodes.Empty();
		OnSelectionChanged.ExecuteIfBound(SelectedNodes);
	}
}

// Changes the selection set to contain exactly all of the passed in nodes
void FGraphSelectionManager::SetSelectionSet(FGraphPanelSelectionSet& NewSet)
{
	SelectedNodes = NewSet;
	OnSelectionChanged.ExecuteIfBound(SelectedNodes);
}

void FGraphSelectionManager::SetNodeSelection(SelectedItemType Node, bool bSelect)
{
	ensureMsg(Node != NULL, TEXT("Node is invalid"));
	if (bSelect)
	{
		SelectedNodes.Add(Node);
		OnSelectionChanged.ExecuteIfBound(SelectedNodes);
	}
	else
	{
		SelectedNodes.Remove(Node);
		OnSelectionChanged.ExecuteIfBound(SelectedNodes);
	}
}

bool FGraphSelectionManager::IsNodeSelected(SelectedItemType Node) const
{
	return SelectedNodes.Contains(Node);
}


void FGraphSelectionManager::StartDraggingNode(SelectedItemType NodeBeingDragged, const FPointerEvent& MouseEvent)
{
	if (!IsNodeSelected(NodeBeingDragged))
	{
		if (MouseEvent.IsControlDown() || MouseEvent.IsShiftDown())
		{
			// Control and shift do not clear existing selection.
			SetNodeSelection(NodeBeingDragged, true);
		}
		else
		{
			SelectSingleNode(NodeBeingDragged);
		}
	}
}

void FGraphSelectionManager::ClickedOnNode(SelectedItemType Node, const FPointerEvent& MouseEvent)
{
	if (MouseEvent.IsShiftDown())
	{
		// Shift always adds to selection
		SetNodeSelection(Node, true);
	}
	else if (MouseEvent.IsControlDown())
	{
		// Control toggles selection
		SetNodeSelection(Node, !IsNodeSelected(Node));
	}				
	else
	{
		// No modifiers sets selection
		SelectSingleNode(Node);
	}
}

//////////////////////////////////////////////////////////////////////////
// SNodePanel

namespace NodePanelDefs
{
	// Default Zoom Padding Value
	static const float DefaultZoomPadding = 25.f;
	// Node Culling Guardband Area
	static const float GuardBandArea = 0.5f;
	// Scaling factor to reduce speed of mouse zooming
	static const float MouseZoomScaling = 0.05f;
};

void SNodePanel::OnArrangeChildren(const FGeometry& AllottedGeometry, FArrangedChildren& ArrangedChildren) const
{
	const TSlotlessChildren<SNode>& ChildrenToArrange = ArrangedChildren.Accepts(EVisibility::Hidden) ? Children : VisibleChildren;
	// First pass nodes
	for (int32 ChildIndex = 0; ChildIndex < ChildrenToArrange.Num(); ++ChildIndex)
	{
		const TSharedRef<SNode>& SomeChild = ChildrenToArrange[ChildIndex];
		if (!SomeChild->RequiresSecondPassLayout())
		{
			ArrangedChildren.AddWidget( AllottedGeometry.MakeChild( SomeChild, SomeChild->GetPosition() - ViewOffset, SomeChild->GetDesiredSize(), GetZoomAmount() ) );
		}
	}

	// Second pass nodes
	for (int32 ChildIndex = 0; ChildIndex < ChildrenToArrange.Num(); ++ChildIndex)
	{
		const TSharedRef<SNode>& SomeChild = ChildrenToArrange[ChildIndex];
		if (SomeChild->RequiresSecondPassLayout())
		{
			SomeChild->PerformSecondPassLayout(NodeToWidgetLookup);
			ArrangedChildren.AddWidget( AllottedGeometry.MakeChild( SomeChild, SomeChild->GetPosition() - ViewOffset, SomeChild->GetDesiredSize(), GetZoomAmount() ) );
		}
	}
}

FVector2D SNodePanel::ComputeDesiredSize() const
{	
	// In this case, it would be an expensive computation that is not worth performing.
	// Users prefer to explicitly size canvases just like they do with text documents, browser pages, etc.
	return FVector2D(160.0f, 120.0f);
}

FChildren* SNodePanel::GetChildren()
{
	return &VisibleChildren;
}

float SNodePanel::GetZoomAmount() const
{
	if (bAllowContinousZoomInterpolation)
	{
		return FMath::Lerp(ZoomLevels->GetZoomAmount(PreviousZoomLevel), ZoomLevels->GetZoomAmount(ZoomLevel), ZoomLevelGraphFade.GetLerp());
	}
	else
	{
		return ZoomLevels->GetZoomAmount(ZoomLevel);
	}
}

FText SNodePanel::GetZoomText() const
{
	return ZoomLevels->GetZoomText(ZoomLevel);
}

FSlateColor SNodePanel::GetZoomTextColorAndOpacity() const
{
	return FLinearColor( 1, 1, 1, 1.25f - ZoomLevelFade.GetLerp() );
}

FVector2D SNodePanel::GetViewOffset() const
{
	return ViewOffset;
}

void SNodePanel::Construct()
{
	if (!ZoomLevels.IsValid())
	{
		ZoomLevels = new FFixedZoomLevelsContainer();
	}
	ZoomLevel = ZoomLevels->GetDefaultZoomLevel();
	PreviousZoomLevel = ZoomLevels->GetDefaultZoomLevel();
	PostChangedZoom();

	ViewOffset = FVector2D::ZeroVector;
	TotalMouseDelta = 0;
	TotalMouseDeltaY = 0;
	bDeferredZoomToSelection = false;
	bDeferredZoomingToFit = false;
	bDeferredZoomToNodeExtents = false;

	ZoomTargetTopLeft = FVector2D::ZeroVector;
	ZoomTargetBottomRight = FVector2D::ZeroVector;
	ZoomPadding = NodePanelDefs::DefaultZoomPadding;

	bAllowContinousZoomInterpolation = false;
	bTeleportInsteadOfScrollingWhenZoomingToFit = false;

	DeferredSelectionTargetObject = NULL;
	DeferredMovementTargetObject = NULL;

	bIsPanning = false;
	IsEditable.Set(true);

	ZoomLevelFade = FCurveSequence( 0.0f, 1.0f );
	ZoomLevelFade.Play();

	ZoomLevelGraphFade = FCurveSequence( 0.0f, 0.5f );
	ZoomLevelGraphFade.Play();

	PastePosition = FVector2D::ZeroVector;

	DeferredPanPosition = FVector2D::ZeroVector;
	bRequestDeferredPan = false;

	OldViewOffset = ViewOffset;
	OldZoomAmount = GetZoomAmount();
	ZoomStartOffset = FVector2D::ZeroVector;

	ScopedTransactionPtr.Reset();
}

FVector2D SNodePanel::ComputeEdgePanAmount(const FGeometry& MyGeometry, const FVector2D& TargetPosition)
{
	// How quickly to ramp up the pan speed as the user moves the mouse further past the edge of the graph panel.
	static const float EdgePanSpeedCoefficient = 2.f, EdgePanSpeedPower = 0.6f;

	// Never pan faster than this - probably not really required since we raise to a power of 0.6
	static const float MaxPanSpeed = 200.0f;

	// Start panning before we reach the edge of the graph panel.
	static const float EdgePanForgivenessZone = 30.0f;

	const FVector2D LocalCursorPos = MyGeometry.AbsoluteToLocal( TargetPosition );

	// If the mouse is outside of the graph area, then we want to pan in that direction.
	// The farther out the mouse is, the more we want to pan.

	FVector2D EdgePanThisTick(0,0);
	if ( LocalCursorPos.X <= EdgePanForgivenessZone )
	{
		EdgePanThisTick.X += FMath::Max( -MaxPanSpeed, EdgePanSpeedCoefficient * -FMath::Pow(EdgePanForgivenessZone - LocalCursorPos.X, EdgePanSpeedPower) );
	}
	else if( LocalCursorPos.X >= MyGeometry.Size.X - EdgePanForgivenessZone )
	{
		EdgePanThisTick.X = FMath::Min( MaxPanSpeed, EdgePanSpeedCoefficient * FMath::Pow(LocalCursorPos.X - MyGeometry.Size.X + EdgePanForgivenessZone, EdgePanSpeedPower) );
	}

	if ( LocalCursorPos.Y <= EdgePanForgivenessZone )
	{
		EdgePanThisTick.Y += FMath::Max( -MaxPanSpeed, EdgePanSpeedCoefficient * -FMath::Pow(EdgePanForgivenessZone - LocalCursorPos.Y, EdgePanSpeedPower) );
	}
	else if( LocalCursorPos.Y >= MyGeometry.Size.Y - EdgePanForgivenessZone )
	{
		EdgePanThisTick.Y = FMath::Min( MaxPanSpeed, EdgePanSpeedCoefficient * FMath::Pow(LocalCursorPos.Y - MyGeometry.Size.Y + EdgePanForgivenessZone, EdgePanSpeedPower) );
	}

	return EdgePanThisTick;
}

void SNodePanel::UpdateViewOffset (const FGeometry& MyGeometry, const FVector2D& TargetPosition)
{
	const FVector2D PanAmount = ComputeEdgePanAmount( MyGeometry, TargetPosition ) / GetZoomAmount();
	ViewOffset += PanAmount;
}

void SNodePanel::RequestDeferredPan(const FVector2D& UpdatePosition)
{
	bRequestDeferredPan = true;
	DeferredPanPosition = UpdatePosition;
}

FVector2D SNodePanel::GraphCoordToPanelCoord( const FVector2D& GraphSpaceCoordinate ) const
{
	return (GraphSpaceCoordinate - GetViewOffset()) * GetZoomAmount();
}

FVector2D SNodePanel::PanelCoordToGraphCoord( const FVector2D& PanelSpaceCoordinate ) const
{
	return PanelSpaceCoordinate / GetZoomAmount() + GetViewOffset();
}

FSlateRect SNodePanel::PanelRectToGraphRect( const FSlateRect& PanelSpaceRect ) const
{
	FVector2D UpperLeft = PanelCoordToGraphCoord( FVector2D(PanelSpaceRect.Left, PanelSpaceRect.Top) );
	FVector2D LowerRight = PanelCoordToGraphCoord(  FVector2D(PanelSpaceRect.Right, PanelSpaceRect.Bottom) );

	return FSlateRect(
		UpperLeft.X, UpperLeft.Y,
		LowerRight.X, LowerRight.Y );
}

void SNodePanel::OnBeginNodeInteraction(const TSharedRef<SNode>& InNodeToDrag, const FVector2D& GrabOffset)
{
	NodeUnderMousePtr = InNodeToDrag;
	NodeGrabOffset = GrabOffset;
}

void SNodePanel::OnEndNodeInteraction(const TSharedRef<SNode>& InNodeToDrag)
{
}

// Ticks this widget.  Override in derived classes, but always call the parent implementation.
void SNodePanel::Tick(const FGeometry& AllottedGeometry, const double InCurrentTime, const float InDeltaTime)
{
	if(DeferredSelectionTargetObject != NULL)
	{
		TSharedRef<SNode>* pWidget = NodeToWidgetLookup.Find(DeferredSelectionTargetObject);
		if (pWidget != NULL)
		{
			SelectionManager.SelectSingleNode(const_cast<SelectedItemType>(DeferredSelectionTargetObject));
			DeferredSelectionTargetObject = NULL;
		}
		else
		{
			// The selection target does not have a corresponding widget. Just end the selection.
			DeferredSelectionTargetObject = NULL;
		}

		// Since we want to move to a target object, do not zoom to extent. Panning and zoom will not begin until next tick however due to the nodes potentially not having a size yet.
		if( DeferredMovementTargetObject )
		{
			bDeferredZoomToNodeExtents = false;
		}
	}
	else if(DeferredMovementTargetObject != NULL && GetBoundsForNodes(true, ZoomTargetTopLeft, ZoomTargetBottomRight, ZoomPadding))
	{
		// Zoom to fit the target node
		bDeferredZoomingToFit = true;
		DeferredMovementTargetObject = NULL;
	}
	
	// Zoom to node extents
	if( bDeferredZoomToNodeExtents )
	{
		bDeferredZoomToNodeExtents = false;
		ZoomPadding = NodePanelDefs::DefaultZoomPadding;
		if( GetBoundsForNodes(bDeferredZoomToSelection, ZoomTargetTopLeft, ZoomTargetBottomRight, ZoomPadding))
		{
			bDeferredZoomToSelection = false;
			bDeferredZoomingToFit = true;
		}
	}

	if (bDeferredZoomingToFit)
	{
		const FVector2D DesiredViewCenter = (ZoomTargetTopLeft + ZoomTargetBottomRight) * 0.5f;
		const bool bDoneScrolling = ScrollToLocation(AllottedGeometry, DesiredViewCenter, bTeleportInsteadOfScrollingWhenZoomingToFit ? 1000.0f : InDeltaTime);
		bool bDoneZooming = ZoomToLocation(AllottedGeometry.Size, ZoomTargetBottomRight - ZoomTargetTopLeft, bDoneScrolling);

		if (bDoneZooming && bDoneScrolling)
		{	
			// One final push to make sure we centered in the end
			ViewOffset = DesiredViewCenter - (0.5f * AllottedGeometry.Scale * AllottedGeometry.Size / GetZoomAmount());
			// Reset ZoomPadding
			ZoomPadding = NodePanelDefs::DefaultZoomPadding;
			ZoomTargetTopLeft = FVector2D::ZeroVector;
			ZoomTargetBottomRight = FVector2D::ZeroVector;

			bDeferredZoomingToFit = false;
			DeferredMovementTargetObject = NULL;
		}
	}

	// Handle any deferred panning
	if (bRequestDeferredPan)
	{
		bRequestDeferredPan = false;
		UpdateViewOffset(AllottedGeometry, DeferredPanPosition);
	}

	if ( !HasMouseCapture() )
	{
		bShowSoftwareCursor = false;
		bIsPanning = false;
	}

	PopulateVisibleChildren(AllottedGeometry);

	OldZoomAmount = GetZoomAmount();
	OldViewOffset = ViewOffset;

	SPanel::Tick(AllottedGeometry, InCurrentTime, InDeltaTime);
}

// The system calls this method to notify the widget that a mouse button was pressed within it. This event is bubbled.
FReply SNodePanel::OnMouseButtonDown( const FGeometry& MyGeometry, const FPointerEvent& MouseEvent )
{
	const bool bIsLeftMouseButtonEffecting = MouseEvent.GetEffectingButton() == EKeys::LeftMouseButton;
	const bool bIsRightMouseButtonEffecting = MouseEvent.GetEffectingButton() == EKeys::RightMouseButton;
	const bool bIsRightMouseButtonDown = MouseEvent.IsMouseButtonDown( EKeys::RightMouseButton );
	const bool bIsLeftMouseButtonDown = MouseEvent.IsMouseButtonDown( EKeys::LeftMouseButton );

	TotalMouseDelta = 0;

	if ((bIsLeftMouseButtonEffecting && bIsRightMouseButtonDown)
	||  (bIsRightMouseButtonEffecting && bIsLeftMouseButtonDown))
	{
		// Starting zoom by holding LMB+RMB
		FReply ReplyState = FReply::Handled();
		ReplyState.CaptureMouse( SharedThis(this) );
		ReplyState.UseHighPrecisionMouseMovement( SharedThis(this) );

		DeferredMovementTargetObject = NULL; // clear any interpolation when you manually zoom
		TotalMouseDeltaY = 0;
		bShowSoftwareCursor = true;

		if (bIsLeftMouseButtonEffecting)
		{
			// Got here from panning mode (with RMB held) - clear panning mode, but use cached software cursor position
			const FVector2D WidgetSpaceCursorPos = GraphCoordToPanelCoord( SoftwareCursorPosition );
			ZoomStartOffset = WidgetSpaceCursorPos;
			this->bIsPanning = false;
		}
		else
		{
			// Cache current cursor position as zoom origin and software cursor position
			ZoomStartOffset = MyGeometry.AbsoluteToLocal( MouseEvent.GetLastScreenSpacePosition() );
			SoftwareCursorPosition = PanelCoordToGraphCoord( ZoomStartOffset );

			if (bIsRightMouseButtonEffecting)
			{
				// Clear things that may be set when left clicking
				if (NodeUnderMousePtr.IsValid())
				{
					OnEndNodeInteraction(NodeUnderMousePtr.Pin().ToSharedRef());
				}

				if ( Marquee.IsValid() )
				{
					auto PreviouslySelectedNodes = SelectionManager.SelectedNodes;
					ApplyMarqueeSelection(Marquee, PreviouslySelectedNodes, SelectionManager.SelectedNodes);
					if (SelectionManager.SelectedNodes.Num() > 0 || PreviouslySelectedNodes.Num() > 0)
					{
						SelectionManager.OnSelectionChanged.ExecuteIfBound(SelectionManager.SelectedNodes);
					}
				}

				Marquee = FMarqueeOperation();
			}
		}

		return ReplyState;
	}
	else if ( bIsRightMouseButtonEffecting )
	{
		FReply ReplyState = FReply::Handled();
		ReplyState.CaptureMouse( SharedThis(this) );
		ReplyState.UseHighPrecisionMouseMovement( SharedThis(this) );

		SoftwareCursorPosition = PanelCoordToGraphCoord( MyGeometry.AbsoluteToLocal( MouseEvent.GetScreenSpacePosition() ) );

		DeferredMovementTargetObject = NULL; // clear any interpolation when you manually pan

		// RIGHT BUTTON is for dragging and Context Menu.
		return ReplyState;
	}
	else if ( bIsLeftMouseButtonEffecting )
	{
		// LEFT BUTTON is for selecting nodes and manipulating pins.
		FArrangedChildren ArrangedChildren(EVisibility::Visible);
		ArrangeChildren(MyGeometry, ArrangedChildren);

		const int32 NodeUnderMouseIndex = SWidget::FindChildUnderMouse( ArrangedChildren, MouseEvent );
		if ( NodeUnderMouseIndex != INDEX_NONE )
		{
			// PRESSING ON A NODE!

			// This changes selection and starts dragging it.
			const FArrangedWidget& NodeGeometry = ArrangedChildren(NodeUnderMouseIndex);
			const FVector2D MousePositionInNode = NodeGeometry.Geometry.AbsoluteToLocal(MouseEvent.GetScreenSpacePosition());
			TSharedRef<SNode> NodeWidgetUnderMouse = StaticCastSharedRef<SNode>( NodeGeometry.Widget );

			if( NodeWidgetUnderMouse->CanBeSelected(MousePositionInNode) )
			{
				// Track the node that we're dragging; we will move it in OnMouseMove.
				this->OnBeginNodeInteraction(NodeWidgetUnderMouse, MousePositionInNode);
				return FReply::Handled().CaptureMouse( SharedThis(this) );
			}
		}

		// START MARQUEE SELECTION.
		const FVector2D GraphMousePos = PanelCoordToGraphCoord( MyGeometry.AbsoluteToLocal( MouseEvent.GetScreenSpacePosition() ) );
		Marquee.Start( GraphMousePos, FMarqueeOperation::OperationTypeFromMouseEvent(MouseEvent) );

		// If we're marquee selecting, then we're not clicking on a node!
		NodeUnderMousePtr.Reset();

		return FReply::Handled().CaptureMouse( SharedThis(this) );
	}
	else
	{
		return FReply::Unhandled();
	}
}

// The system calls this method to notify the widget that a mouse moved within it. This event is bubbled.
FReply SNodePanel::OnMouseMove(const FGeometry& MyGeometry, const FPointerEvent& MouseEvent)
{
	const bool bIsRightMouseButtonDown = MouseEvent.IsMouseButtonDown( EKeys::RightMouseButton );
	const bool bIsLeftMouseButtonDown = MouseEvent.IsMouseButtonDown( EKeys::LeftMouseButton );
	const FModifierKeysState ModifierKeysState = FSlateApplication::Get().GetModifierKeys();

	PastePosition = PanelCoordToGraphCoord( MyGeometry.AbsoluteToLocal( MouseEvent.GetScreenSpacePosition() ) );

	if ( this->HasMouseCapture() )
	{
		const FVector2D CursorDelta = MouseEvent.GetCursorDelta();
		// Track how much the mouse moved since the mouse down.
		TotalMouseDelta += CursorDelta.Size();

		const bool bShouldZoom = bIsRightMouseButtonDown && (bIsLeftMouseButtonDown || ModifierKeysState.IsAltDown() || FSlateApplication::Get().IsUsingTrackpad());
		if (bShouldZoom)
		{
			FReply ReplyState = FReply::Handled();

			TotalMouseDeltaY += CursorDelta.Y;

			const int32 ZoomLevelDelta = FMath::FloorToInt(TotalMouseDeltaY * NodePanelDefs::MouseZoomScaling);

			// Get rid of mouse movement that's been 'used up' by zooming
			if (ZoomLevelDelta != 0)
			{
				TotalMouseDeltaY -= (ZoomLevelDelta / NodePanelDefs::MouseZoomScaling);
			}

			// Perform zoom centered on the cached start offset
			ChangeZoomLevel(ZoomLevelDelta, ZoomStartOffset, MouseEvent.IsControlDown());

			this->bIsPanning = false;
			return ReplyState;
		}
		else if (bIsRightMouseButtonDown)
		{
			FReply ReplyState = FReply::Handled();

			if( !CursorDelta.IsZero() )
			{
				bShowSoftwareCursor = true;
			}

			// Panning and mouse is outside of panel? Pasting should just go to the screen center.
			PastePosition = PanelCoordToGraphCoord( 0.5f * MyGeometry.Size );

			this->bIsPanning = true;
			ViewOffset -= CursorDelta / GetZoomAmount();

			return ReplyState;
		}
		else if (bIsLeftMouseButtonDown)
		{
			TSharedPtr<SNode> NodeBeingDragged = NodeUnderMousePtr.Pin();

			if ( IsEditable.Get() )
			{
				// Update the amount to pan panel
				UpdateViewOffset(MyGeometry, MouseEvent.GetScreenSpacePosition());

				const bool bCursorInDeadZone = TotalMouseDelta <= SlatePanTriggerDistance;

				if ( NodeBeingDragged.IsValid() )
				{
					if ( !bCursorInDeadZone )
					{
						// Note, NodeGrabOffset() comes from the node itself, so it's already scaled correctly.
						FVector2D AnchorNodeNewPos = PanelCoordToGraphCoord( MyGeometry.AbsoluteToLocal( MouseEvent.GetScreenSpacePosition() ) ) - NodeGrabOffset;

						// Snap to grid
						const float SnapSize = GetSnapGridSize();
						AnchorNodeNewPos.X = SnapSize * FMath::RoundToFloat(AnchorNodeNewPos.X/SnapSize);
						AnchorNodeNewPos.Y = SnapSize * FMath::RoundToFloat(AnchorNodeNewPos.Y/SnapSize);

						// Dragging an unselected node automatically selects it.
						SelectionManager.StartDraggingNode(NodeBeingDragged->GetObjectBeingDisplayed(), MouseEvent);

						// Move all the selected nodes.
						{
							const FVector2D AnchorNodeOldPos = NodeBeingDragged->GetPosition();
							const FVector2D DeltaPos = AnchorNodeNewPos - AnchorNodeOldPos;

							// Perform movement in 2 passes:
							// 1. Gather all selected nodes positions and calculate new positions
							struct FDefferedNodePosition 
							{ 
								SNode*		Node; 
								FVector2D	NewPosition; 
							};
							TArray<FDefferedNodePosition> DefferedNodesToMove;
							
							for (FGraphPanelSelectionSet::TIterator NodeIt(SelectionManager.SelectedNodes); NodeIt; ++NodeIt)
							{
								TSharedRef<SNode>* pWidget = NodeToWidgetLookup.Find(*NodeIt);
								if (pWidget != NULL)
								{
									SNode& Widget = pWidget->Get();
									FDefferedNodePosition NodePosition = { &Widget, Widget.GetPosition() + DeltaPos };
									DefferedNodesToMove.Add(NodePosition);
								}
							}

							// Create a new transaction record
							if(!ScopedTransactionPtr.IsValid())
							{
								if(DefferedNodesToMove.Num() > 1)
								{
									ScopedTransactionPtr = MakeShareable(new FScopedTransaction(NSLOCTEXT("GraphEditor", "MoveNodesAction", "Move Nodes")));
								}
								else if(DefferedNodesToMove.Num() > 0)
								{
									ScopedTransactionPtr = MakeShareable(new FScopedTransaction(NSLOCTEXT("GraphEditor", "MoveNodeAction", "Move Node")));
								}
							}

							// 2. Move selected nodes to new positions
							SNode::FNodeSet NodeFilter;

							for (int32 NodeIdx = 0; NodeIdx < DefferedNodesToMove.Num(); ++NodeIdx)
							{
								DefferedNodesToMove[NodeIdx].Node->MoveTo( DefferedNodesToMove[NodeIdx].NewPosition, NodeFilter );
							}
						}
					}

					return FReply::Handled();
				}
			}

			if ( !NodeBeingDragged.IsValid() )
			{
				// We are marquee selecting
				const FVector2D GraphMousePos = PanelCoordToGraphCoord( MyGeometry.AbsoluteToLocal( MouseEvent.GetScreenSpacePosition() ) );
				Marquee.Rect.UpdateEndPoint(GraphMousePos);

				FindNodesAffectedByMarquee( /*out*/ Marquee.AffectedNodes );
				return FReply::Handled();
			}
		}
	}

	return FReply::Unhandled();
}

// The system calls this method to notify the widget that a mouse button was release within it. This event is bubbled.
FReply SNodePanel::OnMouseButtonUp( const FGeometry& MyGeometry, const FPointerEvent& MouseEvent )
{
	FReply ReplyState = FReply::Unhandled();

	const bool bIsLeftMouseButtonEffecting = MouseEvent.GetEffectingButton() == EKeys::LeftMouseButton;
	const bool bIsRightMouseButtonEffecting = MouseEvent.GetEffectingButton() == EKeys::RightMouseButton;
	const bool bIsRightMouseButtonDown = MouseEvent.IsMouseButtonDown( EKeys::RightMouseButton );
	const bool bIsLeftMouseButtonDown = MouseEvent.IsMouseButtonDown( EKeys::LeftMouseButton );

	// Did the user move the cursor sufficiently far, or is it in a dead zone?
	// In Dead zone     - implies actions like summoning context menus and general clicking.
	// Out of Dead Zone - implies dragging actions like moving nodes and marquee selection.
	const bool bCursorInDeadZone = TotalMouseDelta <= SlatePanTriggerDistance;

	// Set to true later if we need to finish with the software cursor
	bool bRemoveSoftwareCursor = false;

	if ((bIsLeftMouseButtonEffecting && bIsRightMouseButtonDown)
	||  (bIsRightMouseButtonEffecting && bIsLeftMouseButtonDown))
	{
		// Ending zoom by releasing LMB or RMB
		ReplyState = FReply::Handled();

		if (bIsLeftMouseButtonDown)
		{
			// If we released the right mouse button first, we need to cancel the software cursor display
			bRemoveSoftwareCursor = true;
			ReplyState.ReleaseMouseCapture();
		}
	}
	else if ( bIsRightMouseButtonEffecting )
	{
		ReplyState = FReply::Handled().ReleaseMouseCapture();

		bRemoveSoftwareCursor = true;

		TSharedPtr<SWidget> WidgetToFocus;
		if (bCursorInDeadZone)
		{
			WidgetToFocus = OnSummonContextMenu(MyGeometry, MouseEvent);
		}

		this->bIsPanning = false;

		if (WidgetToFocus.IsValid())
		{
			ReplyState.SetKeyboardFocus( WidgetToFocus.ToSharedRef(), EKeyboardFocusCause::SetDirectly );
		}
	}
	else if ( bIsLeftMouseButtonEffecting )
	{
		if (NodeUnderMousePtr.IsValid())
		{
			OnEndNodeInteraction(NodeUnderMousePtr.Pin().ToSharedRef());

			ScopedTransactionPtr.Reset();
		}
				
		if (OnHandleLeftMouseRelease(MyGeometry, MouseEvent))
		{

		}
		else if ( bCursorInDeadZone )
		{
			//@TODO: Move to selection manager
			if ( NodeUnderMousePtr.IsValid() )
			{
				// We clicked on a node!
				TSharedRef<SNode> NodeWidgetUnderMouse = NodeUnderMousePtr.Pin().ToSharedRef();

				SelectionManager.ClickedOnNode(NodeWidgetUnderMouse->GetObjectBeingDisplayed(), MouseEvent);

				// We're done interacting with this node.
				NodeUnderMousePtr.Reset();
			}
			else if (this->HasMouseCapture())
			{
				// We clicked on the panel background
				this->SelectionManager.ClearSelectionSet();

				if(OnSpawnNodeByShortcut.IsBound())
				{
					OnSpawnNodeByShortcut.Execute(LastKeyGestureDetected, PanelCoordToGraphCoord(  MyGeometry.AbsoluteToLocal( MouseEvent.GetScreenSpacePosition() ) ));
				}

				LastKeyGestureDetected.Key = EKeys::Invalid;
				LastKeyGestureDetected.bAlt = false;
				LastKeyGestureDetected.bCtrl = false;
				LastKeyGestureDetected.bShift = false;
			}
		}
		else if ( Marquee.IsValid() )
		{
			auto PreviouslySelectedNodes = SelectionManager.SelectedNodes;
			ApplyMarqueeSelection(Marquee, PreviouslySelectedNodes, SelectionManager.SelectedNodes);
			if (SelectionManager.SelectedNodes.Num() > 0 || PreviouslySelectedNodes.Num() > 0)
			{
				SelectionManager.OnSelectionChanged.ExecuteIfBound(SelectionManager.SelectedNodes);
			}
		}

		// The existing marquee operation ended; reset it.
		Marquee = FMarqueeOperation();

		ReplyState = FReply::Handled().ReleaseMouseCapture();
	}

	if (bRemoveSoftwareCursor)
	{
		// If we released the right mouse button first, we need to cancel the software cursor display
		if ( this->HasMouseCapture() )
		{
			FSlateRect ThisPanelScreenSpaceRect = MyGeometry.GetClippingRect();
			const FVector2D ScreenSpaceCursorPos = MyGeometry.LocalToAbsolute( GraphCoordToPanelCoord( SoftwareCursorPosition ) );

			FIntPoint BestPositionInViewport(
				FMath::RoundToInt( FMath::Clamp( ScreenSpaceCursorPos.X, ThisPanelScreenSpaceRect.Left, ThisPanelScreenSpaceRect.Right ) ),
				FMath::RoundToInt( FMath::Clamp( ScreenSpaceCursorPos.Y, ThisPanelScreenSpaceRect.Top, ThisPanelScreenSpaceRect.Bottom ) )
				);

			if (!bCursorInDeadZone)
			{
				ReplyState.SetMousePos(BestPositionInViewport);
			}
		}

		bShowSoftwareCursor = false;
	}

	return ReplyState;	
}

FReply SNodePanel::OnMouseWheel(const FGeometry& MyGeometry, const FPointerEvent& MouseEvent)
{
	// We want to zoom into this point; i.e. keep it the same fraction offset into the panel
	const FVector2D WidgetSpaceCursorPos = MyGeometry.AbsoluteToLocal( MouseEvent.GetScreenSpacePosition() );
	const int32 ZoomLevelDelta = FMath::FloorToInt( MouseEvent.GetWheelDelta() );
	ChangeZoomLevel(ZoomLevelDelta, WidgetSpaceCursorPos, MouseEvent.IsControlDown());

	return FReply::Handled();
}

FCursorReply SNodePanel::OnCursorQuery( const FGeometry& MyGeometry, const FPointerEvent& CursorEvent ) const
{
	return bShowSoftwareCursor ? 
		FCursorReply::Cursor( EMouseCursor::None ) :
		FCursorReply::Cursor( EMouseCursor::Default );
}

FReply SNodePanel::OnKeyDown( const FGeometry& MyGeometry, const FKeyboardEvent& InKeyboardEvent )
{
	if( IsEditable.Get() )
	{
		LastKeyGestureDetected.Key = InKeyboardEvent.GetKey();
		LastKeyGestureDetected.bAlt = InKeyboardEvent.IsAltDown();
		LastKeyGestureDetected.bCtrl = InKeyboardEvent.IsControlDown();
		LastKeyGestureDetected.bShift = InKeyboardEvent.IsShiftDown();
	}

	return FReply::Unhandled();
}

FReply SNodePanel::OnKeyUp( const FGeometry& MyGeometry, const FKeyboardEvent& InKeyboardEvent )
{
	if(LastKeyGestureDetected.Key == InKeyboardEvent.GetKey())
	{
		LastKeyGestureDetected.Key = EKeys::Invalid;
		LastKeyGestureDetected.bAlt = false;
		LastKeyGestureDetected.bCtrl = false;
		LastKeyGestureDetected.bShift = false;
	}

	return FReply::Unhandled();
}

void SNodePanel::OnKeyboardFocusLost( const FKeyboardFocusEvent& InKeyboardFocusEvent )
{
	LastKeyGestureDetected.Key = EKeys::Invalid;
	LastKeyGestureDetected.bAlt = false;
	LastKeyGestureDetected.bCtrl = false;
	LastKeyGestureDetected.bShift = false;
}

FReply SNodePanel::OnTouchGesture( const FGeometry& MyGeometry, const FPointerEvent& GestureEvent )
{
	const EGestureEvent::Type GestureType = GestureEvent.GetGestureType();
	const FVector2D& GestureDelta = GestureEvent.GetGestureDelta();
	if (GestureType == EGestureEvent::Magnify)
	{
		// We want to zoom into this point; i.e. keep it the same fraction offset into the panel
		const FVector2D WidgetSpaceCursorPos = MyGeometry.AbsoluteToLocal(GestureEvent.GetScreenSpacePosition());
		const int32 ZoomLevelDelta = FMath::FloorToInt(GestureDelta.X * 10);
		ChangeZoomLevel(ZoomLevelDelta, WidgetSpaceCursorPos, GestureEvent.IsControlDown());
		return FReply::Handled();
	}
	else if (GestureType == EGestureEvent::Scroll)
	{
		this->bIsPanning = true;
		ViewOffset -= GestureDelta / GetZoomAmount();
		return FReply::Handled();
	}
	return FReply::Unhandled();
}

void SNodePanel::FindNodesAffectedByMarquee( FGraphPanelSelectionSet& OutAffectedNodes ) const
{
	OutAffectedNodes.Empty();

	FSlateRect MarqueeSlateRect = Marquee.Rect.ToSlateRect();

	for ( int32 NodeIndex=0; NodeIndex < Children.Num(); ++NodeIndex )
	{
		const TSharedRef<SNode>& SomeNodeWidget = Children[NodeIndex];
		const FVector2D NodePosition = SomeNodeWidget->GetPosition();
		const FVector2D NodeSize = SomeNodeWidget->GetDesiredSizeForMarquee();

		if (NodeSize.X > 0.f && NodeSize.Y > 0.f)
		{
			const FSlateRect NodeGeometryGraphSpace( NodePosition.X, NodePosition.Y, NodePosition.X + NodeSize.X, NodePosition.Y + NodeSize.Y );
			const bool bIsInMarqueeRect = FSlateRect::DoRectanglesIntersect( MarqueeSlateRect, NodeGeometryGraphSpace );
			if (bIsInMarqueeRect)
			{
				// This node is affected by the marquee rect
				OutAffectedNodes.Add(SomeNodeWidget->GetObjectBeingDisplayed());
			}
		}
	}	
}

void SNodePanel::ApplyMarqueeSelection( const FMarqueeOperation& InMarquee, const FGraphPanelSelectionSet& CurrentSelection, FGraphPanelSelectionSet& OutNewSelection )
{
	switch (InMarquee.Operation )
	{
	default:
	case FMarqueeOperation::Replace:
		{
			OutNewSelection = InMarquee.AffectedNodes;
		}
		break;

	case FMarqueeOperation::Remove:
		{
			OutNewSelection = CurrentSelection.Difference(InMarquee.AffectedNodes);
		}
		break;

	case FMarqueeOperation::Add:
		{
			OutNewSelection = CurrentSelection.Union(InMarquee.AffectedNodes);
		}
		break;
	}
}

FSlateRect SNodePanel::ComputeSensibleGraphBounds() const
{
	float Left = 0.0f;
	float Top = 0.0f;
	float Right = 0.0f;
	float Bottom = 0.0f;

	// Find the bounds of the node positions
	for (int32 ChildIndex = 0; ChildIndex < Children.Num(); ++ChildIndex)
	{
		const TSharedRef<SNode>& SomeChild = Children[ChildIndex];

		FVector2D ChildPos = SomeChild->GetPosition();

		Left = FMath::Min( Left, ChildPos.X );
		Right = FMath::Max( Right, ChildPos.X );
		Top = FMath::Min( Top, ChildPos.Y );
		Bottom = FMath::Max( Bottom, ChildPos.Y );
	}

	// Pad it out in every direction, to roughly account for nodes being of non-zero extent
	const float Padding = 100.0f;

	return FSlateRect( Left - Padding, Top - Padding, Right + Padding, Bottom + Padding );
}

void SNodePanel::SelectAndCenterObject(const UObject* ObjectToSelect, bool bCenter)
{
	DeferredSelectionTargetObject = ObjectToSelect;

	if( bCenter )
	{
		DeferredMovementTargetObject = ObjectToSelect;
	}
}

/** Add a slot to the CanvasPanel dynamically */
void SNodePanel::AddGraphNode( const TSharedRef<SNodePanel::SNode>& NodeToAdd )
{
	Children.Add( NodeToAdd );
	NodeToWidgetLookup.Add( NodeToAdd->GetObjectBeingDisplayed(), NodeToAdd );
}

/** Add a node in the 'back plane' of the panel */
void SNodePanel::AddGraphNodeToBack( const TSharedRef<SNodePanel::SNode>& NodeToAdd )
{
	// add into the back plane
	Children.Insert( NodeToAdd, 0 );
	NodeToWidgetLookup.Add( NodeToAdd->GetObjectBeingDisplayed(), NodeToAdd );
}

/** Remove all nodes from the panel */
void SNodePanel::RemoveAllNodes()
{
	Children.Empty();
	NodeToWidgetLookup.Empty();
	VisibleChildren.Empty();
}

void SNodePanel::PopulateVisibleChildren(const FGeometry& AllottedGeometry)
{
	VisibleChildren.Empty();

	for (int32 ChildIndex = 0; ChildIndex < Children.Num(); ++ChildIndex)
	{
		const TSharedRef<SNode>& SomeChild = Children[ChildIndex];
		if ( !IsNodeCulled(SomeChild, AllottedGeometry) )
		{
			VisibleChildren.Add(SomeChild);
		}
	}
}

// Is the given node being observed by a widget in this panel?
bool SNodePanel::Contains(UObject* Node) const
{
	return NodeToWidgetLookup.Find(Node) != NULL;
}

void SNodePanel::RestoreViewSettings(const FVector2D& InViewOffset, float InZoomAmount)
{
	ViewOffset = InViewOffset;

	if (InZoomAmount <= 0.0f)
	{
		// Zoom into the graph; it's the first time it's ever been displayed
		ZoomLevel = ZoomLevels->GetDefaultZoomLevel();
		bDeferredZoomToNodeExtents = true;
	}
	else
	{
		ZoomLevel = ZoomLevels->GetNearestZoomLevel(InZoomAmount);
		bDeferredZoomingToFit = false;
		bDeferredZoomToNodeExtents = false;
	}

	PostChangedZoom();

	// If we have been forced to a specific position, set the old values equal to the new ones.
	// This is so our locked window isn't forced to update according to this movement.
	OldViewOffset = ViewOffset;
	OldZoomAmount = GetZoomAmount();
}

inline float FancyMod(float Value, float Size)
{
	return ((Value >= 0) ? 0.0f : Size) + FMath::Fmod(Value, Size);
}

void SNodePanel::PaintBackgroundAsLines(const FSlateBrush* BackgroundImage, const FGeometry& AllottedGeometry, const FSlateRect& MyClippingRect, FSlateWindowElementList& OutDrawElements, int32& DrawLayerId) const
{
	const bool bAntialias = false;

	const int32 RulePeriod = (int32)FEditorStyle::GetFloat("Graph.Panel.GridRulePeriod");
	check(RulePeriod > 0);

	const FLinearColor RegularColor(FEditorStyle::GetColor("Graph.Panel.GridLineColor"));
	const FLinearColor RuleColor(FEditorStyle::GetColor("Graph.Panel.GridRuleColor"));
	const FLinearColor CenterColor(FEditorStyle::GetColor("Graph.Panel.GridCenterColor"));
	const float GraphSmallestGridSize = 8.0f;
	const float RawZoomFactor = GetZoomAmount();
	const float NominalGridSize = GetSnapGridSize();

	float ZoomFactor = RawZoomFactor;
	float Inflation = 1.0f;
	while (ZoomFactor*Inflation*NominalGridSize <= GraphSmallestGridSize)
	{
		Inflation *= 2.0f;
	}
	
	const float GridCellSize = NominalGridSize * ZoomFactor * Inflation;

	const float GraphSpaceGridX0 = FancyMod(ViewOffset.X, Inflation * NominalGridSize * RulePeriod);
	const float GraphSpaceGridY0 = FancyMod(ViewOffset.Y, Inflation * NominalGridSize * RulePeriod);

	float ImageOffsetX = GraphSpaceGridX0 * -ZoomFactor;
	float ImageOffsetY = GraphSpaceGridY0 * -ZoomFactor;

	const FVector2D ZeroSpace = GraphCoordToPanelCoord(FVector2D::ZeroVector);
	
	// Fill the background
	FSlateDrawElement::MakeBox(
		OutDrawElements,
		DrawLayerId,
		AllottedGeometry.ToPaintGeometry(),
		BackgroundImage,
		MyClippingRect
	);

	TArray<FVector2D> LinePoints;
	new (LinePoints) FVector2D(0.0f, 0.0f);
	new (LinePoints) FVector2D(0.0f, 0.0f);

	// Horizontal bars
	for (int32 GridIndex = 0; ImageOffsetY < AllottedGeometry.Size.Y; ImageOffsetY += GridCellSize, ++GridIndex)
	{
		if (ImageOffsetY >= 0.0f)
		{
			const bool bIsRuleLine = (GridIndex % RulePeriod) == 0;
			const int32 Layer = bIsRuleLine ? (DrawLayerId+1) : DrawLayerId;

			const FLinearColor* Color = bIsRuleLine ? &RuleColor : &RegularColor;
			if (FMath::IsNearlyEqual(ZeroSpace.Y, ImageOffsetY, 1.0f))
			{
				Color = &CenterColor;
			}

			LinePoints[0] = FVector2D(0.0f, ImageOffsetY);
			LinePoints[1] = FVector2D(AllottedGeometry.Size.X, ImageOffsetY);

			FSlateDrawElement::MakeLines(
				OutDrawElements,
				Layer,
				AllottedGeometry.ToPaintGeometry(),
				LinePoints,
				MyClippingRect,
				ESlateDrawEffect::None,
				*Color,
				bAntialias);
		}
	}

	// Vertical bars
	for (int32 GridIndex = 0; ImageOffsetX < AllottedGeometry.Size.X; ImageOffsetX += GridCellSize, ++GridIndex)
	{
		if (ImageOffsetX >= 0.0f)
		{
			const bool bIsRuleLine = (GridIndex % RulePeriod) == 0;
			const int32 Layer = bIsRuleLine ? (DrawLayerId+1) : DrawLayerId;

			const FLinearColor* Color = bIsRuleLine ? &RuleColor : &RegularColor;
			if (FMath::IsNearlyEqual(ZeroSpace.X, ImageOffsetX, 1.0f))
			{
				Color = &CenterColor;
			}

			LinePoints[0] = FVector2D(ImageOffsetX, 0.0f);
			LinePoints[1] = FVector2D(ImageOffsetX, AllottedGeometry.Size.Y);

			FSlateDrawElement::MakeLines(
				OutDrawElements,
				Layer,
				AllottedGeometry.ToPaintGeometry(),
				LinePoints,
				MyClippingRect,
				ESlateDrawEffect::None,
				*Color,
				bAntialias);
		}
	}

	DrawLayerId += 2;
}

void SNodePanel::PaintSurroundSunkenShadow(const FSlateBrush* ShadowImage, const FGeometry& AllottedGeometry, const FSlateRect& MyClippingRect, FSlateWindowElementList& OutDrawElements, int32 DrawLayerId) const
{
	FSlateDrawElement::MakeBox(
		OutDrawElements,
		DrawLayerId,
		AllottedGeometry.ToPaintGeometry(),
		ShadowImage,
		MyClippingRect
	);
}

void SNodePanel::PaintMarquee(const FGeometry& AllottedGeometry, const FSlateRect& MyClippingRect, FSlateWindowElementList& OutDrawElements, int32 DrawLayerId) const
{
	if (Marquee.IsValid())
	{
		FSlateDrawElement::MakeBox(
			OutDrawElements,
			DrawLayerId,
			AllottedGeometry.ToPaintGeometry( GraphCoordToPanelCoord(Marquee.Rect.GetUpperLeft()), Marquee.Rect.GetSize()*GetZoomAmount() ),
			FEditorStyle::GetBrush(TEXT("MarqueeSelection")),
			MyClippingRect
		);
	}
}

void SNodePanel::PaintSoftwareCursor(const FGeometry& AllottedGeometry, const FSlateRect& MyClippingRect, FSlateWindowElementList& OutDrawElements, int32 DrawLayerId) const
{
	if( !bShowSoftwareCursor )
	{
		return;
	}

	// Get appropriate software cursor, depending on whether we're panning or zooming
	const FSlateBrush* Brush = FEditorStyle::GetBrush(bIsPanning ? TEXT("SoftwareCursor_Grab") : TEXT("SoftwareCursor_UpDown"));

	FSlateDrawElement::MakeBox(
		OutDrawElements,
		DrawLayerId,
		AllottedGeometry.ToPaintGeometry( GraphCoordToPanelCoord( SoftwareCursorPosition ) - ( Brush->ImageSize / 2 ), Brush->ImageSize ),
		Brush,
		MyClippingRect
	);
}

void SNodePanel::PaintComment(const FString& CommentText, const FGeometry& AllottedGeometry, const FSlateRect& MyClippingRect, FSlateWindowElementList& OutDrawElements, int32 DrawLayerId, const FLinearColor& CommentTinting, float& HeightAboveNode, const FWidgetStyle& InWidgetStyle) const
{
	//@TODO: Ideally we don't need to grab these resources for every comment being drawn
	// Get resources/settings for drawing comment bubbles
	const FSlateBrush* CommentCalloutArrow = FEditorStyle::GetBrush(TEXT("Graph.Node.CommentArrow"));
	const FSlateBrush* CommentCalloutBubble = FEditorStyle::GetBrush(TEXT("Graph.Node.CommentBubble"));
	const FSlateFontInfo CommentFont = FEditorStyle::GetFontStyle( TEXT("Graph.Node.CommentFont") );
	const FSlateColor CommentTextColor = FEditorStyle::GetColor( TEXT("Graph.Node.Comment.TextColor") );
	const FVector2D CommentBubblePadding = FEditorStyle::GetVector( TEXT("Graph.Node.Comment.BubblePadding") );

	const TSharedRef< FSlateFontMeasure > FontMeasureService = FSlateApplication::Get().GetRenderer()->GetFontMeasureService();
	FVector2D CommentTextSize = FontMeasureService->Measure( CommentText, CommentFont ) + (CommentBubblePadding * 2);

	const float PositionBias = HeightAboveNode;
	HeightAboveNode += CommentTextSize.Y + 8.0f;

	const FVector2D CommentBubbleOffset = FVector2D(0, -(CommentTextSize.Y + CommentCalloutArrow->ImageSize.Y) - PositionBias);
	const FVector2D CommentBubbleArrowOffset = FVector2D( CommentCalloutArrow->ImageSize.X, -CommentCalloutArrow->ImageSize.Y - PositionBias);

	// Draw a comment bubble
	FSlateDrawElement::MakeBox(
		OutDrawElements,
		DrawLayerId-1,
		AllottedGeometry.ToPaintGeometry(CommentBubbleOffset, CommentTextSize),
		CommentCalloutBubble,
		MyClippingRect,
		ESlateDrawEffect::None,
		CommentTinting
		);

	FSlateDrawElement::MakeBox(
		OutDrawElements,
		DrawLayerId-1,
		AllottedGeometry.ToPaintGeometry( CommentBubbleArrowOffset, CommentCalloutArrow->ImageSize ),
		CommentCalloutArrow,
		MyClippingRect,
		ESlateDrawEffect::None,
		CommentTinting
		);

	// Draw the comment text itself
	FSlateDrawElement::MakeText(
		OutDrawElements,
		DrawLayerId,
		AllottedGeometry.ToPaintGeometry( CommentBubbleOffset + CommentBubblePadding, CommentTextSize ),
		CommentText,
		CommentFont,
		MyClippingRect,
		ESlateDrawEffect::None,
		CommentTextColor.GetColor( InWidgetStyle )
		);

}

bool SNodePanel::IsNodeCulled(const TSharedRef<SNode>& Node, const FGeometry& AllottedGeometry) const
{
	if ( Node->ShouldAllowCulling() )
	{
		const FVector2D MinClipArea = AllottedGeometry.GetDrawSize() * -NodePanelDefs::GuardBandArea;
		const FVector2D MaxClipArea = AllottedGeometry.GetDrawSize() * ( 1.f + NodePanelDefs::GuardBandArea );
		const FVector2D NodeTopLeft = GraphCoordToPanelCoord( Node->GetPosition() );
		const FVector2D NodeBottomRight = GraphCoordToPanelCoord( Node->GetPosition() + Node->GetDesiredSize() );

		return 
			NodeBottomRight.X < MinClipArea.X ||
			NodeBottomRight.Y < MinClipArea.Y ||
			NodeTopLeft.X > MaxClipArea.X ||
			NodeTopLeft.Y > MaxClipArea.Y;
	}
	else
	{
		return false;
	}

}

bool SNodePanel::GetBoundsForNodes(bool bSelectionSetOnly, FVector2D& MinCorner, FVector2D& MaxCorner, float Padding)
{
	MinCorner = FVector2D(MAX_FLT, MAX_FLT);
	MaxCorner = FVector2D(-MAX_FLT, -MAX_FLT);

	bool bValid = false;

	if (bSelectionSetOnly && (SelectionManager.GetSelectedNodes().Num() > 0))
	{
		for (FGraphPanelSelectionSet::TConstIterator NodeIt(SelectionManager.GetSelectedNodes()); NodeIt; ++NodeIt)
		{
			TSharedRef<SNode>* pWidget = NodeToWidgetLookup.Find(*NodeIt);
			if (pWidget != NULL)
			{
				SNode& Widget = pWidget->Get();
				const FVector2D Lower = Widget.GetPosition();
				const FVector2D Upper = Lower + Widget.GetDesiredSize();

				MinCorner.X = FMath::Min(MinCorner.X, Lower.X);
				MinCorner.Y = FMath::Min(MinCorner.Y, Lower.Y);
				MaxCorner.X = FMath::Max(MaxCorner.X, Upper.X);
				MaxCorner.Y = FMath::Max(MaxCorner.Y, Upper.Y);
				bValid = true;
			}
		}
	}
	else
	{
		bValid = NodeToWidgetLookup.Num() > 0;
		for (auto NodeIt = NodeToWidgetLookup.CreateConstIterator(); NodeIt; ++NodeIt)
		{
			SNode& Widget = NodeIt.Value().Get();

			const FVector2D Lower = Widget.GetPosition();
			const FVector2D Upper = Lower + Widget.GetDesiredSize();

			MinCorner.X = FMath::Min(MinCorner.X, Lower.X);
			MinCorner.Y = FMath::Min(MinCorner.Y, Lower.Y);
			MaxCorner.X = FMath::Max(MaxCorner.X, Upper.X);
			MaxCorner.Y = FMath::Max(MaxCorner.Y, Upper.Y);
		}
	}

	if (bValid)
	{
		MinCorner.X -= Padding;
		MinCorner.Y -= Padding;
		MaxCorner.X += Padding;
		MaxCorner.Y += Padding;
	}

	return bValid;
}

bool SNodePanel::ScrollToLocation(const FGeometry& MyGeometry, FVector2D DesiredCenterPosition, const float InDeltaTime)
{
	const FVector2D HalfOFScreenInGraphSpace = 0.5f * MyGeometry.Size / GetZoomAmount();
	FVector2D CurrentPosition = ViewOffset + HalfOFScreenInGraphSpace;

	FVector2D NewPosition = FMath::Vector2DInterpTo(CurrentPosition, DesiredCenterPosition, InDeltaTime, 10.f);
	ViewOffset = NewPosition - HalfOFScreenInGraphSpace;

	// If within 1 pixel of target, stop interpolating
	return ((NewPosition - DesiredCenterPosition).Size() < 1.f);
}

bool SNodePanel::ZoomToLocation(const FVector2D& CurrentSizeWithoutZoom, const FVector2D& DesiredSize, bool bDoneScrolling)
{
	if (bAllowContinousZoomInterpolation && ZoomLevelGraphFade.IsPlaying())
	{
		return false;
	}

	const int32 DefaultZoomLevel = ZoomLevels->GetDefaultZoomLevel();
	const int32 NumZoomLevels = ZoomLevels->GetNumZoomLevels();
	int32 DesiredZoom = DefaultZoomLevel;

	// Find lowest zoom level that will display all nodes
	for (int32 Zoom = 0; Zoom < DefaultZoomLevel; ++Zoom)
	{
		const FVector2D SizeWithZoom = CurrentSizeWithoutZoom / ZoomLevels->GetZoomAmount(Zoom);
		const FVector2D LeftOverSize = SizeWithZoom - DesiredSize;
		
		if ((DesiredSize.X > SizeWithZoom.X) || (DesiredSize.Y > SizeWithZoom.Y))
		{
			// Use the previous zoom level, this one is too tight
			DesiredZoom = FMath::Max<int32>(0, Zoom - 1);
			break; 
		}
	}

	if (DesiredZoom != ZoomLevel)
	{
		if (bAllowContinousZoomInterpolation)
		{
			// Animate to it
			PreviousZoomLevel = ZoomLevel;
			ZoomLevel = FMath::Clamp(DesiredZoom, 0, NumZoomLevels-1);
			ZoomLevelGraphFade.Play();
			return false;
		}
		else
		{
			// Do it instantly, either first or last
			if (DesiredZoom < ZoomLevel)
			{
				// Zooming out; do it instantly
				ZoomLevel = PreviousZoomLevel = DesiredZoom;
				ZoomLevelFade.Play();
			}
			else
			{
				// Zooming in; do it last
				if (bDoneScrolling)
				{
					ZoomLevel = PreviousZoomLevel = DesiredZoom;
					ZoomLevelFade.Play();
				}
			}
		}

		PostChangedZoom();
	}

	return true;
}

void SNodePanel::ZoomToFit(bool bOnlySelection)
{
	// Deferred zoom/pan action
	bDeferredZoomingToFit = true;
	bDeferredZoomToNodeExtents = true;
	bDeferredZoomToSelection = bOnlySelection;
	ZoomPadding = NodePanelDefs::DefaultZoomPadding;
}

void SNodePanel::ChangeZoomLevel(int32 ZoomLevelDelta, const FVector2D& WidgetSpaceZoomOrigin, bool bOverrideZoomLimiting)
{
	// We want to zoom into this point; i.e. keep it the same fraction offset into the panel
	const FVector2D PointToMaintainGraphSpace = PanelCoordToGraphCoord( WidgetSpaceZoomOrigin );

	const int32 DefaultZoomLevel = ZoomLevels->GetDefaultZoomLevel();
	const int32 NumZoomLevels = ZoomLevels->GetNumZoomLevels();

	const bool bAllowFullZoomRange =
		// To zoom in past 1:1 the user must press control
		(ZoomLevel == DefaultZoomLevel && ZoomLevelDelta > 0 && bOverrideZoomLimiting) ||
		// If they are already zoomed in past 1:1, user may zoom freely
		(ZoomLevel > DefaultZoomLevel);

	const float OldZoomLevel = ZoomLevel;

	if ( bAllowFullZoomRange )
	{
		ZoomLevel = FMath::Clamp( ZoomLevel + ZoomLevelDelta, 0, NumZoomLevels-1 );
	}
	else
	{
		// Without control, we do not allow zooming in past 1:1.
		ZoomLevel = FMath::Clamp( ZoomLevel + ZoomLevelDelta, 0, DefaultZoomLevel );
	}

	if (OldZoomLevel != ZoomLevel)
	{
		PostChangedZoom();
	}

	// Note: This happens even when maxed out at a stop; so the user sees the animation and knows that they're at max zoom in/out
	ZoomLevelFade.Play();

	// Re-center the screen so that it feels like zooming around the cursor.
	{
		FSlateRect GraphBounds = ComputeSensibleGraphBounds();

		// Make sure we are not zooming into/out into emptiness; otherwise the user will get lost..
		const FVector2D ClampedPointToMaintainGraphSpace(
			FMath::Clamp(PointToMaintainGraphSpace.X, GraphBounds.Left, GraphBounds.Right),
			FMath::Clamp(PointToMaintainGraphSpace.Y, GraphBounds.Top, GraphBounds.Bottom)
			);

		this->ViewOffset = ClampedPointToMaintainGraphSpace - WidgetSpaceZoomOrigin / GetZoomAmount();
	}

}

bool SNodePanel::GetBoundsForSelectedNodes( class FSlateRect& Rect, float Padding )
{
	bool Result = false;
	if(SelectionManager.GetSelectedNodes().Num()  > 0)
	{
		FVector2D MinCorner, MaxCorner;
		Result =  GetBoundsForNodes(true, MinCorner, MaxCorner,Padding);

		Rect = FSlateRect(MinCorner.X, MinCorner.Y, MaxCorner.X, MaxCorner.Y);
	}
	return Result;
}

FVector2D SNodePanel::GetPastePosition() const
{
	return PastePosition;
}

bool SNodePanel::HasDeferredObjectFocus() const
{
	return DeferredMovementTargetObject != NULL;
}

void SNodePanel::PostChangedZoom()
{
	CurrentLOD = ZoomLevels->GetLOD(ZoomLevel);
}

bool SNodePanel::HasMoved() const
{
	return (!FMath::IsNearlyEqual(GetZoomAmount(), OldZoomAmount) || !ViewOffset.Equals(OldViewOffset, SMALL_NUMBER));
}