Source/WebCore/page/scrolling/ScrollingStateNode.h - external/github.com/WebKit/webkit - Git at Google

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  * THE POSSIBILITY OF SUCH DAMAGE.
  */

 #pragma once

 #if ENABLE(ASYNC_SCROLLING)

 #include <WebCore/GraphicsLayer.h>
 #include <WebCore/ScrollingCoordinator.h>
 #include <WebCore/ScrollingPlatformLayer.h>
 #include <stdint.h>
 #include <wtf/CheckedPtr.h>
 #include <wtf/TZoneMalloc.h>
 #include <wtf/ThreadSafeWeakPtr.h>
 #include <wtf/TypeCasts.h>
 #include <wtf/Vector.h>

 namespace WTF {
 class TextStream;
 }

 namespace WebCore {

 class GraphicsLayer;
 class ScrollingStateTree;

 // Used to allow ScrollingStateNodes to refer to layers in various contexts:
 // a) Async scrolling, main thread: ScrollingStateNode holds onto a GraphicsLayer, and uses m_layerID
 //    to detect whether that GraphicsLayer's underlying PlatformLayer changed.
 // b) Threaded scrolling, commit to scrolling thread: ScrollingStateNode wraps a PlatformLayer, which
 //    can be passed to the Scrolling Thread
 // c) Remote scrolling UI process, where LayerRepresentation wraps just a PlatformLayerID.
 class LayerRepresentation {
 public:
     enum Type {
         EmptyRepresentation,
         GraphicsLayerRepresentation,
         PlatformLayerRepresentation,
         PlatformLayerIDRepresentation
     };

     LayerRepresentation() = default;

     LayerRepresentation(GraphicsLayer* graphicsLayer)
         : m_graphicsLayer(graphicsLayer)
         , m_layerID(graphicsLayer ? std::optional { graphicsLayer->primaryLayerID() } : std::nullopt)
         , m_representation(GraphicsLayerRepresentation)
     { }

     LayerRepresentation(ScrollingPlatformLayer* platformLayer)
         : m_typelessPlatformLayer(makePlatformLayerTypeless(platformLayer))
         , m_representation(PlatformLayerRepresentation)
     {
         retainPlatformLayer(m_typelessPlatformLayer);
     }

     LayerRepresentation(std::optional<PlatformLayerIdentifier> layerID)
         : m_layerID(layerID)
         , m_representation(PlatformLayerIDRepresentation)
     {
     }

     LayerRepresentation(const LayerRepresentation& other)
         : m_typelessPlatformLayer(other.m_typelessPlatformLayer)
         , m_layerID(other.m_layerID)
         , m_representation(other.m_representation)
     {
         if (m_representation == PlatformLayerRepresentation)
             retainPlatformLayer(m_typelessPlatformLayer);
     }

     ~LayerRepresentation()
     {
         if (m_representation == PlatformLayerRepresentation)
             releasePlatformLayer(m_typelessPlatformLayer);
     }

     explicit operator GraphicsLayer*() const
     {
         ASSERT(m_representation == GraphicsLayerRepresentation);
         return m_graphicsLayer.get();
     }

     explicit operator ScrollingPlatformLayer*() const
     {
         ASSERT(m_representation == PlatformLayerRepresentation);
         return makePlatformLayerTyped(m_typelessPlatformLayer);
     }

     std::optional<PlatformLayerIdentifier> layerID() const
     {
         return m_layerID.asOptional();
     }

     LayerRepresentation& operator=(const LayerRepresentation& other)
     {
         m_graphicsLayer = other.m_graphicsLayer;
         m_typelessPlatformLayer = other.m_typelessPlatformLayer;
         m_layerID = other.m_layerID;
         m_representation = other.m_representation;

         if (m_representation == PlatformLayerRepresentation)
             retainPlatformLayer(m_typelessPlatformLayer);

         return *this;
     }

     explicit operator bool() const
     {
         switch (m_representation) {
         case EmptyRepresentation:
             return false;
         case GraphicsLayerRepresentation:
             return !!m_graphicsLayer;
         case PlatformLayerRepresentation:
             return !!m_typelessPlatformLayer;
         case PlatformLayerIDRepresentation:
             return !!m_layerID;
         }
         ASSERT_NOT_REACHED();
         return false;
     }

     bool operator==(const LayerRepresentation& other) const
     {
         if (m_representation != other.m_representation)
             return false;
         switch (m_representation) {
         case EmptyRepresentation:
             return true;
         case GraphicsLayerRepresentation:
             return m_graphicsLayer == other.m_graphicsLayer
                 && m_layerID == other.m_layerID;
         case PlatformLayerRepresentation:
             return m_typelessPlatformLayer == other.m_typelessPlatformLayer;
         case PlatformLayerIDRepresentation:
             return m_layerID == other.m_layerID;
         }
         ASSERT_NOT_REACHED();
         return true;
     }

     LayerRepresentation toRepresentation(Type representation) const
     {
         switch (representation) {
         case EmptyRepresentation:
             return LayerRepresentation();
         case GraphicsLayerRepresentation:
             ASSERT(m_representation == GraphicsLayerRepresentation);
             return LayerRepresentation(m_graphicsLayer.get());
         case PlatformLayerRepresentation:
             return m_graphicsLayer ? platformLayerFromGraphicsLayer(Ref { *m_graphicsLayer }) : nullptr;
         case PlatformLayerIDRepresentation:
             return LayerRepresentation(m_layerID);
         }
         ASSERT_NOT_REACHED();
         return LayerRepresentation();
     }

     bool representsGraphicsLayer() const { return m_representation == GraphicsLayerRepresentation; }
     bool representsPlatformLayerID() const { return m_representation == PlatformLayerIDRepresentation; }

 private:
     WEBCORE_EXPORT static void retainPlatformLayer(void* typelessPlatformLayer);
     WEBCORE_EXPORT static void releasePlatformLayer(void* typelessPlatformLayer);
     WEBCORE_EXPORT static ScrollingPlatformLayer* makePlatformLayerTyped(void* typelessPlatformLayer);
     WEBCORE_EXPORT static void* makePlatformLayerTypeless(ScrollingPlatformLayer*);
     WEBCORE_EXPORT static ScrollingPlatformLayer* platformLayerFromGraphicsLayer(GraphicsLayer&);

     RefPtr<GraphicsLayer> m_graphicsLayer;
     void* m_typelessPlatformLayer { nullptr };
     Markable<PlatformLayerIdentifier> m_layerID;
     Type m_representation { EmptyRepresentation };
 };

 enum class ScrollingStateNodeProperty : uint64_t {
     // ScrollingStateNode
     Layer                                       = 1LLU << 0,
     ChildNodes                                  = 1LLU << 45,
     // ScrollingStateScrollingNode
     ScrollableAreaSize                          = 1LLU << 1, // Same value as RelatedOverflowScrollingNodes, ViewportConstraints and OverflowScrollingNode
     TotalContentsSize                           = 1LLU << 2, // Same value as LayoutConstraintData
     ReachableContentsSize                       = 1LLU << 3,
     ScrollPosition                              = 1LLU << 4,
     ScrollOrigin                                = 1LLU << 5,
     ScrollableAreaParams                        = 1LLU << 6,
 #if ENABLE(SCROLLING_THREAD)
     ReasonsForSynchronousScrolling              = 1LLU << 7,
     RequestedScrollPosition                     = 1LLU << 8,
 #else
     RequestedScrollPosition                     = 1LLU << 7,
 #endif
     SnapOffsetsInfo                             = RequestedScrollPosition << 1,
     CurrentHorizontalSnapOffsetIndex            = SnapOffsetsInfo << 1,
     CurrentVerticalSnapOffsetIndex              = CurrentHorizontalSnapOffsetIndex << 1,
     IsMonitoringWheelEvents                     = CurrentVerticalSnapOffsetIndex << 1,
     ScrollContainerLayer                        = IsMonitoringWheelEvents << 1,
     ScrolledContentsLayer                       = ScrollContainerLayer << 1,
     HorizontalScrollbarLayer                    = ScrolledContentsLayer << 1,
     VerticalScrollbarLayer                      = HorizontalScrollbarLayer << 1,
     PainterForScrollbar                         = 1LLU << 44, // Not serialized
     ContentAreaHoverState                       = VerticalScrollbarLayer << 1,
     MouseActivityState                          = ContentAreaHoverState << 1,
     ScrollbarHoverState                         = MouseActivityState << 1,
     ScrollbarEnabledState                       = ScrollbarHoverState << 1,
     ScrollbarColor                              = ScrollbarEnabledState << 1,
     ScrollbarLayoutDirection                    = ScrollbarColor << 1,
     ScrollbarWidth                              = ScrollbarLayoutDirection << 1,
     UseDarkAppearanceForScrollbars              = ScrollbarWidth << 1,
 #if USE(COORDINATED_GRAPHICS_ASYNC_SCROLLBAR)
     ScrollbarOpacity                            = 1LLU << 51, // Not serialized
 #endif
     // ScrollingStateFrameScrollingNode
     KeyboardScrollData                          = UseDarkAppearanceForScrollbars << 1,
     FrameScaleFactor                            = KeyboardScrollData << 1,
     EventTrackingRegion                         = FrameScaleFactor << 1,
     RootContentsLayer                           = EventTrackingRegion << 1,
     CounterScrollingLayer                       = RootContentsLayer << 1,
     InsetClipLayer                              = CounterScrollingLayer << 1,
     ContentShadowLayer                          = InsetClipLayer << 1,
     HeaderHeight                                = ContentShadowLayer << 1,
     FooterHeight                                = HeaderHeight << 1,
     HeaderLayer                                 = 1LLU << 50, // Not serialized
     FooterLayer                                 = 1LLU << 43, // Not serialized
     BehaviorForFixedElements                    = FooterHeight << 1,
     ObscuredContentInsets                       = BehaviorForFixedElements << 1,
     VisualViewportIsSmallerThanLayoutViewport   = ObscuredContentInsets << 1,
     AsyncFrameOrOverflowScrollingEnabled        = VisualViewportIsSmallerThanLayoutViewport << 1,
     WheelEventGesturesBecomeNonBlocking         = AsyncFrameOrOverflowScrollingEnabled << 1,
     ScrollingPerformanceTestingEnabled          = WheelEventGesturesBecomeNonBlocking << 1,
     LayoutViewport                              = ScrollingPerformanceTestingEnabled << 1,
     SizeForVisibleContent                       = LayoutViewport << 1,
     MinLayoutViewportOrigin                     = SizeForVisibleContent << 1,
     MaxLayoutViewportOrigin                     = MinLayoutViewportOrigin << 1,
     OverrideVisualViewportSize                  = MaxLayoutViewportOrigin << 1,
     OverlayScrollbarsEnabled                    = OverrideVisualViewportSize << 1,
     // ScrollingStatePositionedNode
     RelatedOverflowScrollingNodes               = 1LLU << 1, // Same value as ScrollableAreaSize, ViewportConstraints and OverflowScrollingNode
     LayoutConstraintData                        = 1LLU << 2, // Same value as TotalContentsSize
     // ScrollingStateFixedNode, ScrollingStateStickyNode
     ViewportConstraints                         = 1LLU << 1, // Same value as ScrollableAreaSize, RelatedOverflowScrollingNodes and OverflowScrollingNode
     ViewportAnchorLayer                         = 1LLU << 2, // Same value as TotalContentsSize
     // ScrollingStateOverflowScrollProxyNode
     OverflowScrollingNode                       = 1LLU << 1, // Same value as ScrollableAreaSize, ViewportConstraints and RelatedOverflowScrollingNodes
     // ScrollingStateFrameHostingNode
     LayerHostingContextIdentifier               = 1LLU << 1,

 };

 class ScrollingStateNode : public ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr<ScrollingStateNode> {
     WTF_MAKE_TZONE_ALLOCATED_EXPORT(ScrollingStateNode, WEBCORE_EXPORT);
 public:
     virtual ~ScrollingStateNode();

     using Property = ScrollingStateNodeProperty;

     ScrollingNodeType nodeType() const { return m_nodeType; }

     bool isFixedNode() const { return m_nodeType == ScrollingNodeType::Fixed; }
     bool isStickyNode() const { return m_nodeType == ScrollingNodeType::Sticky; }
     bool isPositionedNode() const { return m_nodeType == ScrollingNodeType::Positioned; }
     bool isScrollingNode() const { return isFrameScrollingNode() || isOverflowScrollingNode() || isPluginScrollingNode(); }
     bool isFrameScrollingNode() const { return m_nodeType == ScrollingNodeType::MainFrame || m_nodeType == ScrollingNodeType::Subframe; }
     bool isFrameHostingNode() const { return m_nodeType == ScrollingNodeType::FrameHosting; }
     bool isPluginScrollingNode() const { return m_nodeType == ScrollingNodeType::PluginScrolling; }
     bool isPluginHostingNode() const { return m_nodeType == ScrollingNodeType::PluginHosting; }
     bool isOverflowScrollingNode() const { return m_nodeType == ScrollingNodeType::Overflow; }
     bool isOverflowScrollProxyNode() const { return m_nodeType == ScrollingNodeType::OverflowProxy; }

     virtual Ref<ScrollingStateNode> clone(ScrollingStateTree& adoptiveTree) = 0;
     Ref<ScrollingStateNode> cloneAndReset(ScrollingStateTree& adoptiveTree);
     void cloneAndResetChildren(ScrollingStateNode&, ScrollingStateTree& adoptiveTree);

     bool hasChangedProperties() const { return !m_changedProperties.isEmpty(); }
     bool hasChangedProperty(Property property) const { return m_changedProperties.contains(property); }
     void resetChangedProperties() { m_changedProperties = { }; }
     void setPropertyChanged(Property);

     void setPropertyChangesAfterReattach();

     OptionSet<Property> changedProperties() const { return m_changedProperties; }
     void setChangedProperties(OptionSet<Property> changedProperties) { m_changedProperties = changedProperties; }

     virtual void reconcileLayerPositionForViewportRect(const LayoutRect& /*viewportRect*/, ScrollingLayerPositionAction) { }

     const LayerRepresentation& layer() const { return m_layer; }
     WEBCORE_EXPORT void setLayer(const LayerRepresentation&);

     bool isAttachedToScrollingStateTree() const { return !!m_scrollingStateTree; }
     ScrollingStateTree& scrollingStateTree() const
     {
         ASSERT(m_scrollingStateTree);
         return *m_scrollingStateTree;
     }
     void attachAfterDeserialization(ScrollingStateTree&);

     ScrollingNodeID scrollingNodeID() const { return m_nodeID; }

     RefPtr<ScrollingStateNode> parent() const { return m_parent.get(); }
     void setParent(RefPtr<ScrollingStateNode>&& parent) { m_parent = parent; }
     std::optional<ScrollingNodeID> parentNodeID() const;

     Vector<Ref<ScrollingStateNode>>& children() { return m_children; }
     const Vector<Ref<ScrollingStateNode>>& children() const { return m_children; }
     Vector<Ref<ScrollingStateNode>> takeChildren() { return std::exchange(m_children, { }); }
     WEBCORE_EXPORT void setChildren(Vector<Ref<ScrollingStateNode>>&&);
     void traverse(NOESCAPE const Function<void(ScrollingStateNode&)>&);

     void appendChild(Ref<ScrollingStateNode>&&);
     void insertChild(Ref<ScrollingStateNode>&&, size_t index);

     // Note that node ownership is via the parent, so these functions can trigger node deletion.
     void removeFromParent();
     void removeChild(ScrollingStateNode&);

     RefPtr<ScrollingStateNode> childAtIndex(size_t) const;

     String scrollingStateTreeAsText(OptionSet<ScrollingStateTreeAsTextBehavior> = { }) const;
 #if ASSERT_ENABLED
     bool parentPointersAreCorrect() const;
 #endif

 protected:
     ScrollingStateNode(const ScrollingStateNode&, ScrollingStateTree&);
     ScrollingStateNode(ScrollingNodeType, ScrollingStateTree&, ScrollingNodeID);
     ScrollingStateNode(ScrollingNodeType, ScrollingNodeID, Vector<Ref<ScrollingStateNode>>&&, OptionSet<ScrollingStateNodeProperty>, std::optional<PlatformLayerIdentifier>);

     void setPropertyChangedInternal(Property property) { m_changedProperties.add(property); }
     void setPropertiesChangedInternal(OptionSet<Property> properties) { m_changedProperties.add(properties); }

     virtual void dumpProperties(WTF::TextStream&, OptionSet<ScrollingStateTreeAsTextBehavior>) const;
     virtual OptionSet<Property> applicableProperties() const;

 private:
     void dump(WTF::TextStream&, OptionSet<ScrollingStateTreeAsTextBehavior>) const;

     const ScrollingNodeType m_nodeType;
     const ScrollingNodeID m_nodeID;
     OptionSet<Property> m_changedProperties;

     CheckedPtr<ScrollingStateTree> m_scrollingStateTree; // Only null between deserialization and attachAfterDeserialization.

     ThreadSafeWeakPtr<ScrollingStateNode> m_parent;
     Vector<Ref<ScrollingStateNode>> m_children;

     LayerRepresentation m_layer;
 };

 inline std::optional<ScrollingNodeID> ScrollingStateNode::parentNodeID() const
 {
     auto parent = m_parent.get();
     if (!parent)
         return std::nullopt;
     return parent->scrollingNodeID();
 }

 } // namespace WebCore

 #define SPECIALIZE_TYPE_TRAITS_SCROLLING_STATE_NODE(ToValueTypeName, predicate) \
 SPECIALIZE_TYPE_TRAITS_BEGIN(WebCore::ToValueTypeName) \
     static bool isType(const WebCore::ScrollingStateNode& node) { return node.predicate; } \
 SPECIALIZE_TYPE_TRAITS_END()

 #endif // ENABLE(ASYNC_SCROLLING)
	/*
	* Copyright (C) 2012 Apple Inc. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
	* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
	* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
	* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
	* THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#pragma once

	#if ENABLE(ASYNC_SCROLLING)

	#include <WebCore/GraphicsLayer.h>
	#include <WebCore/ScrollingCoordinator.h>
	#include <WebCore/ScrollingPlatformLayer.h>
	#include <stdint.h>
	#include <wtf/CheckedPtr.h>
	#include <wtf/TZoneMalloc.h>
	#include <wtf/ThreadSafeWeakPtr.h>
	#include <wtf/TypeCasts.h>
	#include <wtf/Vector.h>

	namespace WTF {
	class TextStream;
	}

	namespace WebCore {

	class GraphicsLayer;
	class ScrollingStateTree;

	// Used to allow ScrollingStateNodes to refer to layers in various contexts:
	// a) Async scrolling, main thread: ScrollingStateNode holds onto a GraphicsLayer, and uses m_layerID
	// to detect whether that GraphicsLayer's underlying PlatformLayer changed.
	// b) Threaded scrolling, commit to scrolling thread: ScrollingStateNode wraps a PlatformLayer, which
	// can be passed to the Scrolling Thread
	// c) Remote scrolling UI process, where LayerRepresentation wraps just a PlatformLayerID.
	class LayerRepresentation {
	public:
	enum Type {
	EmptyRepresentation,
	GraphicsLayerRepresentation,
	PlatformLayerRepresentation,
	PlatformLayerIDRepresentation
	};

	LayerRepresentation() = default;

	LayerRepresentation(GraphicsLayer* graphicsLayer)
	: m_graphicsLayer(graphicsLayer)
	, m_layerID(graphicsLayer ? std::optional { graphicsLayer->primaryLayerID() } : std::nullopt)
	, m_representation(GraphicsLayerRepresentation)
	{ }

	LayerRepresentation(ScrollingPlatformLayer* platformLayer)
	: m_typelessPlatformLayer(makePlatformLayerTypeless(platformLayer))
	, m_representation(PlatformLayerRepresentation)
	{
	retainPlatformLayer(m_typelessPlatformLayer);
	}

	LayerRepresentation(std::optional<PlatformLayerIdentifier> layerID)
	: m_layerID(layerID)
	, m_representation(PlatformLayerIDRepresentation)
	{
	}

	LayerRepresentation(const LayerRepresentation& other)
	: m_typelessPlatformLayer(other.m_typelessPlatformLayer)
	, m_layerID(other.m_layerID)
	, m_representation(other.m_representation)
	{
	if (m_representation == PlatformLayerRepresentation)
	retainPlatformLayer(m_typelessPlatformLayer);
	}

	~LayerRepresentation()
	{
	if (m_representation == PlatformLayerRepresentation)
	releasePlatformLayer(m_typelessPlatformLayer);
	}

	explicit operator GraphicsLayer*() const
	{
	ASSERT(m_representation == GraphicsLayerRepresentation);
	return m_graphicsLayer.get();
	}

	explicit operator ScrollingPlatformLayer*() const
	{
	ASSERT(m_representation == PlatformLayerRepresentation);
	return makePlatformLayerTyped(m_typelessPlatformLayer);
	}

	std::optional<PlatformLayerIdentifier> layerID() const
	{
	return m_layerID.asOptional();
	}

	LayerRepresentation& operator=(const LayerRepresentation& other)
	{
	m_graphicsLayer = other.m_graphicsLayer;
	m_typelessPlatformLayer = other.m_typelessPlatformLayer;
	m_layerID = other.m_layerID;
	m_representation = other.m_representation;

	if (m_representation == PlatformLayerRepresentation)
	retainPlatformLayer(m_typelessPlatformLayer);

	return *this;
	}

	explicit operator bool() const
	{
	switch (m_representation) {
	case EmptyRepresentation:
	return false;
	case GraphicsLayerRepresentation:
	return !!m_graphicsLayer;
	case PlatformLayerRepresentation:
	return !!m_typelessPlatformLayer;
	case PlatformLayerIDRepresentation:
	return !!m_layerID;
	}
	ASSERT_NOT_REACHED();
	return false;
	}

	bool operator==(const LayerRepresentation& other) const
	{
	if (m_representation != other.m_representation)
	return false;
	switch (m_representation) {
	case EmptyRepresentation:
	return true;
	case GraphicsLayerRepresentation:
	return m_graphicsLayer == other.m_graphicsLayer
	&& m_layerID == other.m_layerID;
	case PlatformLayerRepresentation:
	return m_typelessPlatformLayer == other.m_typelessPlatformLayer;
	case PlatformLayerIDRepresentation:
	return m_layerID == other.m_layerID;
	}
	ASSERT_NOT_REACHED();
	return true;
	}

	LayerRepresentation toRepresentation(Type representation) const
	{
	switch (representation) {
	case EmptyRepresentation:
	return LayerRepresentation();
	case GraphicsLayerRepresentation:
	ASSERT(m_representation == GraphicsLayerRepresentation);
	return LayerRepresentation(m_graphicsLayer.get());
	case PlatformLayerRepresentation:
	return m_graphicsLayer ? platformLayerFromGraphicsLayer(Ref { *m_graphicsLayer }) : nullptr;
	case PlatformLayerIDRepresentation:
	return LayerRepresentation(m_layerID);
	}
	ASSERT_NOT_REACHED();
	return LayerRepresentation();
	}

	bool representsGraphicsLayer() const { return m_representation == GraphicsLayerRepresentation; }
	bool representsPlatformLayerID() const { return m_representation == PlatformLayerIDRepresentation; }

	private:
	WEBCORE_EXPORT static void retainPlatformLayer(void* typelessPlatformLayer);
	WEBCORE_EXPORT static void releasePlatformLayer(void* typelessPlatformLayer);
	WEBCORE_EXPORT static ScrollingPlatformLayer* makePlatformLayerTyped(void* typelessPlatformLayer);
	WEBCORE_EXPORT static void* makePlatformLayerTypeless(ScrollingPlatformLayer*);
	WEBCORE_EXPORT static ScrollingPlatformLayer* platformLayerFromGraphicsLayer(GraphicsLayer&);

	RefPtr<GraphicsLayer> m_graphicsLayer;
	void* m_typelessPlatformLayer { nullptr };
	Markable<PlatformLayerIdentifier> m_layerID;
	Type m_representation { EmptyRepresentation };
	};

	enum class ScrollingStateNodeProperty : uint64_t {
	// ScrollingStateNode
	Layer = 1LLU << 0,
	ChildNodes = 1LLU << 45,
	// ScrollingStateScrollingNode
	ScrollableAreaSize = 1LLU << 1, // Same value as RelatedOverflowScrollingNodes, ViewportConstraints and OverflowScrollingNode
	TotalContentsSize = 1LLU << 2, // Same value as LayoutConstraintData
	ReachableContentsSize = 1LLU << 3,
	ScrollPosition = 1LLU << 4,
	ScrollOrigin = 1LLU << 5,
	ScrollableAreaParams = 1LLU << 6,
	#if ENABLE(SCROLLING_THREAD)
	ReasonsForSynchronousScrolling = 1LLU << 7,
	RequestedScrollPosition = 1LLU << 8,
	#else
	RequestedScrollPosition = 1LLU << 7,
	#endif
	SnapOffsetsInfo = RequestedScrollPosition << 1,
	CurrentHorizontalSnapOffsetIndex = SnapOffsetsInfo << 1,
	CurrentVerticalSnapOffsetIndex = CurrentHorizontalSnapOffsetIndex << 1,
	IsMonitoringWheelEvents = CurrentVerticalSnapOffsetIndex << 1,
	ScrollContainerLayer = IsMonitoringWheelEvents << 1,
	ScrolledContentsLayer = ScrollContainerLayer << 1,
	HorizontalScrollbarLayer = ScrolledContentsLayer << 1,
	VerticalScrollbarLayer = HorizontalScrollbarLayer << 1,
	PainterForScrollbar = 1LLU << 44, // Not serialized
	ContentAreaHoverState = VerticalScrollbarLayer << 1,
	MouseActivityState = ContentAreaHoverState << 1,
	ScrollbarHoverState = MouseActivityState << 1,
	ScrollbarEnabledState = ScrollbarHoverState << 1,
	ScrollbarColor = ScrollbarEnabledState << 1,
	ScrollbarLayoutDirection = ScrollbarColor << 1,
	ScrollbarWidth = ScrollbarLayoutDirection << 1,
	UseDarkAppearanceForScrollbars = ScrollbarWidth << 1,
	#if USE(COORDINATED_GRAPHICS_ASYNC_SCROLLBAR)
	ScrollbarOpacity = 1LLU << 51, // Not serialized
	#endif
	// ScrollingStateFrameScrollingNode
	KeyboardScrollData = UseDarkAppearanceForScrollbars << 1,
	FrameScaleFactor = KeyboardScrollData << 1,
	EventTrackingRegion = FrameScaleFactor << 1,
	RootContentsLayer = EventTrackingRegion << 1,
	CounterScrollingLayer = RootContentsLayer << 1,
	InsetClipLayer = CounterScrollingLayer << 1,
	ContentShadowLayer = InsetClipLayer << 1,
	HeaderHeight = ContentShadowLayer << 1,
	FooterHeight = HeaderHeight << 1,
	HeaderLayer = 1LLU << 50, // Not serialized
	FooterLayer = 1LLU << 43, // Not serialized
	BehaviorForFixedElements = FooterHeight << 1,
	ObscuredContentInsets = BehaviorForFixedElements << 1,
	VisualViewportIsSmallerThanLayoutViewport = ObscuredContentInsets << 1,
	AsyncFrameOrOverflowScrollingEnabled = VisualViewportIsSmallerThanLayoutViewport << 1,
	WheelEventGesturesBecomeNonBlocking = AsyncFrameOrOverflowScrollingEnabled << 1,
	ScrollingPerformanceTestingEnabled = WheelEventGesturesBecomeNonBlocking << 1,
	LayoutViewport = ScrollingPerformanceTestingEnabled << 1,
	SizeForVisibleContent = LayoutViewport << 1,
	MinLayoutViewportOrigin = SizeForVisibleContent << 1,
	MaxLayoutViewportOrigin = MinLayoutViewportOrigin << 1,
	OverrideVisualViewportSize = MaxLayoutViewportOrigin << 1,
	OverlayScrollbarsEnabled = OverrideVisualViewportSize << 1,
	// ScrollingStatePositionedNode
	RelatedOverflowScrollingNodes = 1LLU << 1, // Same value as ScrollableAreaSize, ViewportConstraints and OverflowScrollingNode
	LayoutConstraintData = 1LLU << 2, // Same value as TotalContentsSize
	// ScrollingStateFixedNode, ScrollingStateStickyNode
	ViewportConstraints = 1LLU << 1, // Same value as ScrollableAreaSize, RelatedOverflowScrollingNodes and OverflowScrollingNode
	ViewportAnchorLayer = 1LLU << 2, // Same value as TotalContentsSize
	// ScrollingStateOverflowScrollProxyNode
	OverflowScrollingNode = 1LLU << 1, // Same value as ScrollableAreaSize, ViewportConstraints and RelatedOverflowScrollingNodes
	// ScrollingStateFrameHostingNode
	LayerHostingContextIdentifier = 1LLU << 1,

	};

	class ScrollingStateNode : public ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr<ScrollingStateNode> {
	WTF_MAKE_TZONE_ALLOCATED_EXPORT(ScrollingStateNode, WEBCORE_EXPORT);
	public:
	virtual ~ScrollingStateNode();

	using Property = ScrollingStateNodeProperty;

	ScrollingNodeType nodeType() const { return m_nodeType; }

	bool isFixedNode() const { return m_nodeType == ScrollingNodeType::Fixed; }
	bool isStickyNode() const { return m_nodeType == ScrollingNodeType::Sticky; }
	bool isPositionedNode() const { return m_nodeType == ScrollingNodeType::Positioned; }
	bool isScrollingNode() const { return isFrameScrollingNode() \|\| isOverflowScrollingNode() \|\| isPluginScrollingNode(); }
	bool isFrameScrollingNode() const { return m_nodeType == ScrollingNodeType::MainFrame \|\| m_nodeType == ScrollingNodeType::Subframe; }
	bool isFrameHostingNode() const { return m_nodeType == ScrollingNodeType::FrameHosting; }
	bool isPluginScrollingNode() const { return m_nodeType == ScrollingNodeType::PluginScrolling; }
	bool isPluginHostingNode() const { return m_nodeType == ScrollingNodeType::PluginHosting; }
	bool isOverflowScrollingNode() const { return m_nodeType == ScrollingNodeType::Overflow; }
	bool isOverflowScrollProxyNode() const { return m_nodeType == ScrollingNodeType::OverflowProxy; }

	virtual Ref<ScrollingStateNode> clone(ScrollingStateTree& adoptiveTree) = 0;
	Ref<ScrollingStateNode> cloneAndReset(ScrollingStateTree& adoptiveTree);
	void cloneAndResetChildren(ScrollingStateNode&, ScrollingStateTree& adoptiveTree);

	bool hasChangedProperties() const { return !m_changedProperties.isEmpty(); }
	bool hasChangedProperty(Property property) const { return m_changedProperties.contains(property); }
	void resetChangedProperties() { m_changedProperties = { }; }
	void setPropertyChanged(Property);

	void setPropertyChangesAfterReattach();

	OptionSet<Property> changedProperties() const { return m_changedProperties; }
	void setChangedProperties(OptionSet<Property> changedProperties) { m_changedProperties = changedProperties; }

	virtual void reconcileLayerPositionForViewportRect(const LayoutRect& /viewportRect/, ScrollingLayerPositionAction) { }

	const LayerRepresentation& layer() const { return m_layer; }
	WEBCORE_EXPORT void setLayer(const LayerRepresentation&);

	bool isAttachedToScrollingStateTree() const { return !!m_scrollingStateTree; }
	ScrollingStateTree& scrollingStateTree() const
	{
	ASSERT(m_scrollingStateTree);
	return *m_scrollingStateTree;
	}
	void attachAfterDeserialization(ScrollingStateTree&);

	ScrollingNodeID scrollingNodeID() const { return m_nodeID; }

	RefPtr<ScrollingStateNode> parent() const { return m_parent.get(); }
	void setParent(RefPtr<ScrollingStateNode>&& parent) { m_parent = parent; }
	std::optional<ScrollingNodeID> parentNodeID() const;

	Vector<Ref<ScrollingStateNode>>& children() { return m_children; }
	const Vector<Ref<ScrollingStateNode>>& children() const { return m_children; }
	Vector<Ref<ScrollingStateNode>> takeChildren() { return std::exchange(m_children, { }); }
	WEBCORE_EXPORT void setChildren(Vector<Ref<ScrollingStateNode>>&&);
	void traverse(NOESCAPE const Function<void(ScrollingStateNode&)>&);

	void appendChild(Ref<ScrollingStateNode>&&);
	void insertChild(Ref<ScrollingStateNode>&&, size_t index);

	// Note that node ownership is via the parent, so these functions can trigger node deletion.
	void removeFromParent();
	void removeChild(ScrollingStateNode&);

	RefPtr<ScrollingStateNode> childAtIndex(size_t) const;

	String scrollingStateTreeAsText(OptionSet<ScrollingStateTreeAsTextBehavior> = { }) const;
	#if ASSERT_ENABLED
	bool parentPointersAreCorrect() const;
	#endif

	protected:
	ScrollingStateNode(const ScrollingStateNode&, ScrollingStateTree&);
	ScrollingStateNode(ScrollingNodeType, ScrollingStateTree&, ScrollingNodeID);
	ScrollingStateNode(ScrollingNodeType, ScrollingNodeID, Vector<Ref<ScrollingStateNode>>&&, OptionSet<ScrollingStateNodeProperty>, std::optional<PlatformLayerIdentifier>);

	void setPropertyChangedInternal(Property property) { m_changedProperties.add(property); }
	void setPropertiesChangedInternal(OptionSet<Property> properties) { m_changedProperties.add(properties); }

	virtual void dumpProperties(WTF::TextStream&, OptionSet<ScrollingStateTreeAsTextBehavior>) const;
	virtual OptionSet<Property> applicableProperties() const;

	private:
	void dump(WTF::TextStream&, OptionSet<ScrollingStateTreeAsTextBehavior>) const;

	const ScrollingNodeType m_nodeType;
	const ScrollingNodeID m_nodeID;
	OptionSet<Property> m_changedProperties;

	CheckedPtr<ScrollingStateTree> m_scrollingStateTree; // Only null between deserialization and attachAfterDeserialization.

	ThreadSafeWeakPtr<ScrollingStateNode> m_parent;
	Vector<Ref<ScrollingStateNode>> m_children;

	LayerRepresentation m_layer;
	};

	inline std::optional<ScrollingNodeID> ScrollingStateNode::parentNodeID() const
	{
	auto parent = m_parent.get();
	if (!parent)
	return std::nullopt;
	return parent->scrollingNodeID();
	}

	} // namespace WebCore

	#define SPECIALIZE_TYPE_TRAITS_SCROLLING_STATE_NODE(ToValueTypeName, predicate) \
	SPECIALIZE_TYPE_TRAITS_BEGIN(WebCore::ToValueTypeName) \
	static bool isType(const WebCore::ScrollingStateNode& node) { return node.predicate; } \
	SPECIALIZE_TYPE_TRAITS_END()

	#endif // ENABLE(ASYNC_SCROLLING)