SScrollBarTrack.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "Layout/Visibility.h"
#include "Widgets/DeclarativeSyntaxSupport.h"
#include "SlotBase.h"
#include "Layout/Children.h"
#include "Widgets/SPanel.h"
 
class FArrangedChildren;
 
template <>
struct TWidgetTypeTraits<class SScrollBarTrack>
{
    static constexpr bool SupportsInvalidation() { return true; }
};
 
class SScrollBarTrack : public SPanel
{
public:
    class FSlot : public TSlotBase<FSlot>
    {
    public:
        FSlot()
            : TSlotBase<FSlot>()
        {}
    };
 
    SLATE_BEGIN_ARGS(SScrollBarTrack)
        : _TopSlot()
        , _ThumbSlot()
        , _BottomSlot()
        , _Orientation(Orient_Vertical)
    {
        _Visibility = EVisibility::SelfHitTestInvisible;
    }
 
    SLATE_NAMED_SLOT(FArguments, TopSlot)
        SLATE_NAMED_SLOT(FArguments, ThumbSlot)
        SLATE_NAMED_SLOT(FArguments, BottomSlot)
        SLATE_ARGUMENT(EOrientation, Orientation)
 
    SLATE_END_ARGS()
 
    SScrollBarTrack()
        : Children(this)
    {
    }
 
    SLATE_API void Construct(const FArguments& InArgs);
 
    struct FTrackSizeInfo
    {
        FTrackSizeInfo(const FGeometry& TrackGeometry, EOrientation InOrientation, float InMinThumbSize, float ThumbSizeAsFractionOfTrack, float ThumbOffsetAsFractionOfTrack)
        {
            BiasedTrackSize = ((InOrientation == Orient_Horizontal) ? TrackGeometry.GetLocalSize().X : TrackGeometry.GetLocalSize().Y) - InMinThumbSize;
            const float AccurateThumbSize = ThumbSizeAsFractionOfTrack * (BiasedTrackSize);
            ThumbStart = BiasedTrackSize * ThumbOffsetAsFractionOfTrack;
            ThumbSize = InMinThumbSize + AccurateThumbSize;
 
        }
 
        float BiasedTrackSize;
        float ThumbStart;
        float ThumbSize;
        float GetThumbEnd()
        {
            return ThumbStart + ThumbSize;
        }
    };
 
    SLATE_API FTrackSizeInfo GetTrackSizeInfo(const FGeometry& InTrackGeometry) const;
 
    SLATE_API virtual void OnArrangeChildren(const FGeometry& AllottedGeometry, FArrangedChildren& ArrangedChildren) const;
 
    SLATE_API virtual FVector2D ComputeDesiredSize(float) const;
 
    SLATE_API virtual FChildren* GetChildren();
 
    SLATE_API void SetSizes(float InThumbOffsetFraction, float InThumbSizeFraction);
 
    SLATE_API bool IsNeeded() const;
 
    SLATE_API float DistanceFromTop() const;
 
    SLATE_API float DistanceFromBottom() const;
 
    SLATE_API float GetMinThumbSize() const;
 
    SLATE_API float GetThumbSizeFraction() const;
 
    SLATE_API void SetIsAlwaysVisible(bool InIsAlwaysVisible);
 
protected:
 
    static const int32 TOP_SLOT_INDEX = 0;
    static const int32 BOTTOM_SLOT_INDEX = 1;
    static const int32 THUMB_SLOT_INDEX = 2;
 
    TPanelChildren< FSlot > Children;
 
    float OffsetFraction;
    float ThumbSizeFraction;
    float MinThumbSize;
    bool bIsAlwaysVisible = false;
    EOrientation Orientation;
};