Attachment 356505 Details for Bug 176454 – Patch (applies on top of bug 192358)

[patch] Patch (applies on top of bug 192358)

0002-Bug-176454-Implement-CSS-overscroll-behavior.patch (text/plain), 52.88 KB, created by Frédéric Wang (:fredw) on 2018-12-04 09:16:44 PST

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Creator: Frédéric Wang (:fredw)

Created: 2018-12-04 09:16:44 PST

Size: 52.88 KB

patch

obsolete

>From 88022f89c684dfed1f6a49de5c501673f4347eda Mon Sep 17 00:00:00 2001
>From: Frederic Wang <fwang@igalia.com>
>Date: Thu, 29 Nov 2018 15:09:13 +0100
>Subject: [PATCH xserver 2/2] Bug 176454 - Implement CSS overscroll-behavior
>
>---
> .../css/CSSComputedStyleDeclaration.cpp       |  8 ++++
> .../WebCore/css/CSSPrimitiveValueMappings.h   | 37 ++++++++++++++++
> Source/WebCore/css/CSSProperties.json         | 40 +++++++++++++++++
> Source/WebCore/css/CSSValueKeywords.in        |  3 ++
> Source/WebCore/css/StyleProperties.cpp        |  6 +++
> .../WebCore/css/parser/CSSParserContext.cpp   |  2 +
> Source/WebCore/css/parser/CSSParserContext.h  |  4 +-
> .../WebCore/css/parser/CSSPropertyParser.cpp  | 44 +++++++++++++++++++
> Source/WebCore/css/parser/CSSPropertyParser.h |  2 +
> Source/WebCore/page/EventHandler.cpp          | 31 +++++++++----
> Source/WebCore/page/Settings.yaml             |  2 +
> .../scrolling/AsyncScrollingCoordinator.cpp   |  4 ++
> .../page/scrolling/ScrollingCoordinator.h     |  2 +
> .../scrolling/ScrollingStateScrollingNode.cpp | 26 +++++++++++
> .../scrolling/ScrollingStateScrollingNode.h   | 10 +++++
> .../scrolling/ScrollingTreeScrollingNode.cpp  | 13 ++++++
> .../scrolling/ScrollingTreeScrollingNode.h    |  4 ++
> Source/WebCore/platform/ScrollTypes.h         |  6 +++
> .../rendering/RenderLayerCompositor.cpp       |  4 ++
> Source/WebCore/rendering/style/RenderStyle.h  |  9 ++++
> .../style/StyleRareNonInheritedData.cpp       |  6 +++
> .../style/StyleRareNonInheritedData.h         |  3 ++
> .../RemoteScrollingCoordinatorTransaction.cpp | 10 +++++
> Source/WebKit/Shared/WebCoreArgumentCoders.h  | 10 +++++
> Source/WebKit/Shared/WebPreferences.yaml      |  7 +++
> .../ScrollingTreeScrollingNodeDelegateIOS.mm  | 20 +++++++++
> .../mac/WebView/WebPreferenceKeysPrivate.h    |  1 +
> .../mac/WebView/WebPreferences.mm             | 11 +++++
> .../mac/WebView/WebPreferencesPrivate.h       |  1 +
> Source/WebKitLegacy/mac/WebView/WebView.mm    |  1 +
> .../win/Interfaces/IWebPreferencesPrivate.idl |  2 +
> .../win/WebPreferenceKeysPrivate.h            |  1 +
> Source/WebKitLegacy/win/WebPreferences.cpp    | 16 +++++++
> Source/WebKitLegacy/win/WebPreferences.h      |  2 +
> Source/WebKitLegacy/win/WebView.cpp           |  5 +++
> Tools/DumpRenderTree/TestOptions.cpp          |  2 +
> Tools/DumpRenderTree/TestOptions.h            |  1 +
> Tools/DumpRenderTree/mac/DumpRenderTree.mm    |  1 +
> 38 files changed, 347 insertions(+), 10 deletions(-)
>
>diff --git a/Source/WebCore/css/CSSComputedStyleDeclaration.cpp b/Source/WebCore/css/CSSComputedStyleDeclaration.cpp
>index f1b50fba6d9..850a978d71a 100644
>--- a/Source/WebCore/css/CSSComputedStyleDeclaration.cpp
>+++ b/Source/WebCore/css/CSSComputedStyleDeclaration.cpp
>@@ -190,6 +190,8 @@ static const CSSPropertyID computedProperties[] = {
>     CSSPropertyOutlineWidth,
>     CSSPropertyOverflowWrap,
>     CSSPropertyOverflowX,
>+    CSSPropertyOverscrollBehaviorX,
>+    CSSPropertyOverscrollBehaviorY,
>     CSSPropertyOverflowY,
>     CSSPropertyPaddingBottom,
>     CSSPropertyPaddingLeft,
>@@ -3301,6 +3303,12 @@ RefPtr<CSSValue> ComputedStyleExtractor::valueForPropertyinStyle(const RenderSty
>             return cssValuePool.createValue(style.overflowX());
>         case CSSPropertyOverflowY:
>             return cssValuePool.createValue(style.overflowY());
>+        case CSSPropertyOverscrollBehavior:
>+            return cssValuePool.createValue(std::max(style.overscrollBehaviorX(), style.overscrollBehaviorY()));
>+        case CSSPropertyOverscrollBehaviorX:
>+            return cssValuePool.createValue(style.overscrollBehaviorX());
>+        case CSSPropertyOverscrollBehaviorY:
>+            return cssValuePool.createValue(style.overscrollBehaviorY());
>         case CSSPropertyPaddingTop:
>             return zoomAdjustedPaddingOrMarginPixelValue<&RenderStyle::paddingTop, &RenderBoxModelObject::computedCSSPaddingTop>(style, renderer);
>         case CSSPropertyPaddingRight:
>diff --git a/Source/WebCore/css/CSSPrimitiveValueMappings.h b/Source/WebCore/css/CSSPrimitiveValueMappings.h
>index c95ff65a835..07df8a072a0 100644
>--- a/Source/WebCore/css/CSSPrimitiveValueMappings.h
>+++ b/Source/WebCore/css/CSSPrimitiveValueMappings.h
>@@ -40,6 +40,7 @@
> #include "LineClampValue.h"
> #include "RenderStyleConstants.h"
> #include "SVGRenderStyleDefs.h"
>+#include "ScrollTypes.h"
> #include "TextFlags.h"
> #include "ThemeTypes.h"
> #include "UnicodeBidi.h"
>@@ -2204,6 +2205,42 @@ template<> inline CSSPrimitiveValue::operator Overflow() const
>     return Overflow::Visible;
> }
> 
>+template<> inline CSSPrimitiveValue::CSSPrimitiveValue(OverscrollBehavior e)
>+    : CSSValue(PrimitiveClass)
>+{
>+    m_primitiveUnitType = CSS_VALUE_ID;
>+    switch (e) {
>+    case OverscrollBehavior::Contain:
>+        m_value.valueID = CSSValueContain;
>+        break;
>+    case OverscrollBehavior::None:
>+        m_value.valueID = CSSValueNone;
>+        break;
>+    case OverscrollBehavior::Auto:
>+        m_value.valueID = CSSValueAuto;
>+        break;
>+    }
>+}
>+
>+template<> inline CSSPrimitiveValue::operator OverscrollBehavior() const
>+{
>+    ASSERT(isValueID());
>+
>+    switch (m_value.valueID) {
>+    case CSSValueContain:
>+        return OverscrollBehavior::Contain;
>+    case CSSValueNone:
>+        return OverscrollBehavior::None;
>+    case CSSValueAuto:
>+        return OverscrollBehavior::Auto;
>+    default:
>+        break;
>+    }
>+
>+    ASSERT_NOT_REACHED();
>+    return OverscrollBehavior::Auto;
>+}
>+
> template<> inline CSSPrimitiveValue::CSSPrimitiveValue(BreakBetween e)
>     : CSSValue(PrimitiveClass)
> {
>diff --git a/Source/WebCore/css/CSSProperties.json b/Source/WebCore/css/CSSProperties.json
>index fe012ba4b22..3bab9b87a50 100644
>--- a/Source/WebCore/css/CSSProperties.json
>+++ b/Source/WebCore/css/CSSProperties.json
>@@ -3053,6 +3053,46 @@
>                 "url": "https://www.w3.org/TR/css-overflow-3/#propdef-overflow-y"
>             }
>         },
>+        "overscroll-behavior": {
>+            "codegen-properties": {
>+                "longhands": [
>+                    "overscroll-behavior-x",
>+                    "overscroll-behavior-y"
>+                ]
>+            },
>+            "status": {
>+                "status": "in development"
>+            },
>+            "specification": {
>+                "url": "https://wicg.github.io/overscroll-behavior/#propdef-overscroll-behavior"
>+            }
>+        },
>+        "overscroll-behavior-x": {
>+            "values": [
>+                "contain",
>+                "none",
>+                "auto"
>+            ],
>+            "status": {
>+                "status": "in development"
>+            },
>+            "specification": {
>+                "url": "https://wicg.github.io/overscroll-behavior/#propdef-overscroll-behavior-x"
>+            }
>+        },
>+        "overscroll-behavior-y": {
>+            "values": [
>+                "contain",
>+                "none",
>+                "auto"
>+            ],
>+            "status": {
>+                "status": "in development"
>+            },
>+            "specification": {
>+                "url": "https://wicg.github.io/overscroll-behavior/#propdef-overscroll-behavior-y"
>+            }
>+        },
>         "padding": {
>             "codegen-properties": {
>                 "longhands": [
>diff --git a/Source/WebCore/css/CSSValueKeywords.in b/Source/WebCore/css/CSSValueKeywords.in
>index 86b5e5914f4..162216731ca 100644
>--- a/Source/WebCore/css/CSSValueKeywords.in
>+++ b/Source/WebCore/css/CSSValueKeywords.in
>@@ -1357,6 +1357,9 @@ scroll-position
> manipulation
> #endif
> 
>+// overscroll-behavior
>+// contain
>+
> // hanging-punctuation
> allow-end
> first
>diff --git a/Source/WebCore/css/StyleProperties.cpp b/Source/WebCore/css/StyleProperties.cpp
>index 5acb48f911a..a17907fdb91 100644
>--- a/Source/WebCore/css/StyleProperties.cpp
>+++ b/Source/WebCore/css/StyleProperties.cpp
>@@ -207,6 +207,8 @@ String StyleProperties::getPropertyValue(CSSPropertyID propertyID) const
>         return getShorthandValue(webkitMarginCollapseShorthand());
>     case CSSPropertyOverflow:
>         return getCommonValue(overflowShorthand());
>+    case CSSPropertyOverscrollBehavior:
>+        return getCommonValue(overscrollBehaviorShorthand());
>     case CSSPropertyPadding:
>         return get4Values(paddingShorthand());
>     case CSSPropertyTransition:
>@@ -1005,6 +1007,10 @@ String StyleProperties::asText() const
>             case CSSPropertyOverflowY:
>                 shorthandPropertyID = CSSPropertyOverflow;
>                 break;
>+            case CSSPropertyOverscrollBehaviorX:
>+            case CSSPropertyOverscrollBehaviorY:
>+                shorthandPropertyID = CSSPropertyOverscrollBehavior;
>+                break;
>             case CSSPropertyPaddingTop:
>             case CSSPropertyPaddingRight:
>             case CSSPropertyPaddingBottom:
>diff --git a/Source/WebCore/css/parser/CSSParserContext.cpp b/Source/WebCore/css/parser/CSSParserContext.cpp
>index 06c702a0db4..2065d30877d 100644
>--- a/Source/WebCore/css/parser/CSSParserContext.cpp
>+++ b/Source/WebCore/css/parser/CSSParserContext.cpp
>@@ -73,6 +73,7 @@ CSSParserContext::CSSParserContext(const Document& document, const URL& sheetBas
>     attachmentEnabled = RuntimeEnabledFeatures::sharedFeatures().attachmentElementEnabled();
> #endif
>     deferredCSSParserEnabled = document.settings().deferredCSSParserEnabled();
>+    overscrollBehaviorEnabled = document.settings().overscrollBehaviorEnabled();
>     useSystemAppearance = document.page() ? document.page()->useSystemAppearance() : false;
> 
> #if PLATFORM(IOS_FAMILY)
>@@ -102,6 +103,7 @@ bool operator==(const CSSParserContext& a, const CSSParserContext& b)
>         && a.attachmentEnabled == b.attachmentEnabled
> #endif
>         && a.deferredCSSParserEnabled == b.deferredCSSParserEnabled
>+        && a.overscrollBehaviorEnabled == b.overscrollBehaviorEnabled
>         && a.hasDocumentSecurityOrigin == b.hasDocumentSecurityOrigin
>         && a.useSystemAppearance == b.useSystemAppearance;
> }
>diff --git a/Source/WebCore/css/parser/CSSParserContext.h b/Source/WebCore/css/parser/CSSParserContext.h
>index 758b6eeb3af..9e97b0e7209 100644
>--- a/Source/WebCore/css/parser/CSSParserContext.h
>+++ b/Source/WebCore/css/parser/CSSParserContext.h
>@@ -59,6 +59,7 @@ public:
>     bool attachmentEnabled { false };
> #endif
>     bool deferredCSSParserEnabled { false };
>+    bool overscrollBehaviorEnabled { false };
>     
>     // This is only needed to support getMatchedCSSRules.
>     bool hasDocumentSecurityOrigin { false };
>@@ -106,7 +107,8 @@ struct CSSParserContextHash {
> #if ENABLE(ATTACHMENT_ELEMENT)
>             & key.attachmentEnabled                         << 11
> #endif
>-            & key.mode                                      << 12; // Keep this last.
>+            & key.overscrollBehaviorEnabled                 << 12
>+            & key.mode                                      << 13; // Keep this last.
>         hash ^= WTF::intHash(bits);
>         return hash;
>     }
>diff --git a/Source/WebCore/css/parser/CSSPropertyParser.cpp b/Source/WebCore/css/parser/CSSPropertyParser.cpp
>index 5cb8945b38f..5efe80818f5 100644
>--- a/Source/WebCore/css/parser/CSSPropertyParser.cpp
>+++ b/Source/WebCore/css/parser/CSSPropertyParser.cpp
>@@ -2326,6 +2326,14 @@ static RefPtr<CSSValueList> consumeScrollSnapType(CSSParserTokenRange& range)
> 
> #endif
> 
>+static RefPtr<CSSValue> consumeOverscrollBehavior(CSSParserTokenRange& range)
>+{
>+    auto valueID = range.peek().id();
>+    if (valueID != CSSValueAuto && valueID != CSSValueNone && valueID != CSSValueContain)
>+        return nullptr;
>+    return consumeIdent(range);
>+}
>+
> static RefPtr<CSSValue> consumeBorderRadiusCorner(CSSParserTokenRange& range, CSSParserMode cssParserMode)
> {
>     RefPtr<CSSPrimitiveValue> parsedValue1 = consumeLengthOrPercent(range, cssParserMode, ValueRangeNonNegative);
>@@ -4015,6 +4023,11 @@ RefPtr<CSSValue> CSSPropertyParser::parseSingleValue(CSSPropertyID property, CSS
>     case CSSPropertyScrollSnapType:
>         return consumeScrollSnapType(m_range);
> #endif
>+    case CSSPropertyOverscrollBehaviorX:
>+    case CSSPropertyOverscrollBehaviorY:
>+        if (!m_context.overscrollBehaviorEnabled)
>+            return nullptr;
>+        return consumeOverscrollBehavior(m_range);
>     case CSSPropertyClip:
>         return consumeClip(m_range, m_context.mode);
> #if ENABLE(TOUCH_EVENTS)
>@@ -5658,6 +5671,35 @@ bool CSSPropertyParser::consumePlaceSelfShorthand(bool important)
>     return true;
> }
> 
>+bool CSSPropertyParser::consumeOverscrollBehaviorShorthand(bool important)
>+{
>+    ASSERT(shorthandForProperty(CSSPropertyOverscrollBehavior).length() == 2);
>+    if (!m_context.overscrollBehaviorEnabled)
>+        return false;
>+
>+    if (m_range.atEnd())
>+        return false;
>+
>+    RefPtr<CSSValue> overscrollBehaviorX = consumeOverscrollBehavior(m_range);
>+    if (!overscrollBehaviorX)
>+        return false;
>+
>+    RefPtr<CSSValue> overscrollBehaviorY;
>+    m_range.consumeWhitespace();
>+    if (m_range.atEnd())
>+        overscrollBehaviorY = overscrollBehaviorX;
>+    else {
>+        overscrollBehaviorY = consumeOverscrollBehavior(m_range);
>+        m_range.consumeWhitespace();
>+        if (!m_range.atEnd())
>+            return false;
>+    }
>+
>+    addProperty(CSSPropertyOverscrollBehaviorX, CSSPropertyOverscrollBehavior, *overscrollBehaviorX, important);
>+    addProperty(CSSPropertyOverscrollBehaviorY, CSSPropertyOverscrollBehavior, *overscrollBehaviorY, important);
>+    return true;
>+}
>+
> bool CSSPropertyParser::parseShorthand(CSSPropertyID property, bool important)
> {
>     switch (property) {
>@@ -5697,6 +5739,8 @@ bool CSSPropertyParser::parseShorthand(CSSPropertyID property, bool important)
>         addProperty(CSSPropertyOverflowY, CSSPropertyOverflow, *overflowYValue, important);
>         return true;
>     }
>+    case CSSPropertyOverscrollBehavior:
>+        return consumeOverscrollBehaviorShorthand(important);
>     case CSSPropertyFont: {
>         const CSSParserToken& token = m_range.peek();
>         if (token.id() >= CSSValueCaption && token.id() <= CSSValueStatusBar)
>diff --git a/Source/WebCore/css/parser/CSSPropertyParser.h b/Source/WebCore/css/parser/CSSPropertyParser.h
>index 1dc05ef88da..3fc16653560 100644
>--- a/Source/WebCore/css/parser/CSSPropertyParser.h
>+++ b/Source/WebCore/css/parser/CSSPropertyParser.h
>@@ -107,6 +107,8 @@ private:
>     bool consumeTransformOrigin(bool important);
>     bool consumePerspectiveOrigin(bool important);
> 
>+    bool consumeOverscrollBehaviorShorthand(bool important);
>+
> private:
>     // Inputs:
>     CSSParserTokenRange m_range;
>diff --git a/Source/WebCore/page/EventHandler.cpp b/Source/WebCore/page/EventHandler.cpp
>index 6d141eafdaf..6f511b9f5b0 100644
>--- a/Source/WebCore/page/EventHandler.cpp
>+++ b/Source/WebCore/page/EventHandler.cpp
>@@ -283,15 +283,15 @@ static inline ScrollGranularity wheelGranularityToScrollGranularity(unsigned del
>     }
> }
> 
>-static inline bool didScrollInScrollableArea(ScrollableArea* scrollableArea, WheelEvent& wheelEvent)
>+static inline bool didScrollInScrollableArea(ScrollableArea* scrollableArea, double deltaX, double deltaY, unsigned deltaMode)
> {
>-    ScrollGranularity scrollGranularity = wheelGranularityToScrollGranularity(wheelEvent.deltaMode());
>+    ScrollGranularity scrollGranularity = wheelGranularityToScrollGranularity(deltaMode);
>     bool didHandleWheelEvent = false;
>-    if (float absoluteDelta = std::abs(wheelEvent.deltaX()))
>-        didHandleWheelEvent |= scrollableArea->scroll(wheelEvent.deltaX() > 0 ? ScrollRight : ScrollLeft, scrollGranularity, absoluteDelta);
>+    if (float absoluteDelta = std::abs(deltaX))
>+        didHandleWheelEvent |= scrollableArea->scroll(deltaX > 0 ? ScrollRight : ScrollLeft, scrollGranularity, absoluteDelta);
>     
>-    if (float absoluteDelta = std::abs(wheelEvent.deltaY()))
>-        didHandleWheelEvent |= scrollableArea->scroll(wheelEvent.deltaY() > 0 ? ScrollDown : ScrollUp, scrollGranularity, absoluteDelta);
>+    if (float absoluteDelta = std::abs(deltaY))
>+        didHandleWheelEvent |= scrollableArea->scroll(deltaY > 0 ? ScrollDown : ScrollUp, scrollGranularity, absoluteDelta);
>     
>     return didHandleWheelEvent;
> }
>@@ -310,18 +310,20 @@ static inline bool handleWheelEventInAppropriateEnclosingBox(Node* startNode, Wh
> 
>     RenderBox& initialEnclosingBox = startNode->renderer()->enclosingBox();
>     if (initialEnclosingBox.isListBox())
>-        return didScrollInScrollableArea(static_cast<RenderListBox*>(&initialEnclosingBox), wheelEvent);
>+        return didScrollInScrollableArea(static_cast<RenderListBox*>(&initialEnclosingBox), wheelEvent.deltaX(), wheelEvent.deltaY(), wheelEvent.deltaMode());
> 
>     RenderBox* currentEnclosingBox = &initialEnclosingBox;
>+    bool ignoreDeltaX = false;
>+    bool ignoreDeltaY = false;
>     while (currentEnclosingBox) {
>         if (RenderLayer* boxLayer = currentEnclosingBox->layer()) {
>             auto platformEvent = wheelEvent.underlyingPlatformEvent();
>             bool scrollingWasHandled;
>             if (platformEvent) {
>-                auto copiedEvent = platformEvent->copyWithDeltasAndVelocity(filteredPlatformDelta.width(), filteredPlatformDelta.height(), filteredVelocity);
>+                auto copiedEvent = platformEvent->copyWithDeltasAndVelocity(ignoreDeltaX ? 0 : filteredPlatformDelta.width(), ignoreDeltaY ? 0 : filteredPlatformDelta.height(), filteredVelocity);
>                 scrollingWasHandled = boxLayer->handleWheelEvent(copiedEvent);
>             } else
>-                scrollingWasHandled = didScrollInScrollableArea(boxLayer, wheelEvent);
>+                scrollingWasHandled = didScrollInScrollableArea(boxLayer, ignoreDeltaX ? 0 : wheelEvent.deltaX(), ignoreDeltaY ? 0 : wheelEvent.deltaY(), wheelEvent.deltaMode());
> 
>             if (scrollingWasHandled) {
>                 if (stopElement)
>@@ -333,6 +335,17 @@ static inline bool handleWheelEventInAppropriateEnclosingBox(Node* startNode, Wh
>         if (stopElement && *stopElement && *stopElement == currentEnclosingBox->element())
>             return true;
> 
>+        if (!ignoreDeltaX && currentEnclosingBox->style().overscrollBehaviorX() != OverscrollBehavior::Auto)
>+            ignoreDeltaX = true;
>+        if (!ignoreDeltaY && currentEnclosingBox->style().overscrollBehaviorY() != OverscrollBehavior::Auto)
>+            ignoreDeltaY = true;
>+        if (ignoreDeltaX && ignoreDeltaY) {
>+            // We claim that the event was handled so that it is not propagated to the ancestor frames.
>+            if (stopElement)
>+                *stopElement = currentEnclosingBox->element();
>+            return true;
>+        }
>+
>         currentEnclosingBox = currentEnclosingBox->containingBlock();
>         if (!currentEnclosingBox || currentEnclosingBox->isRenderView())
>             return false;
>diff --git a/Source/WebCore/page/Settings.yaml b/Source/WebCore/page/Settings.yaml
>index 6daec2ae5b7..7f673bccc70 100644
>--- a/Source/WebCore/page/Settings.yaml
>+++ b/Source/WebCore/page/Settings.yaml
>@@ -372,6 +372,8 @@ frameFlattening:
> asyncFrameScrollingEnabled:
>   initial: false
>   onChange: setNeedsRelayoutAllFrames
>+overscrollBehaviorEnabled:
>+  initial: false
> 
> asyncOverflowScrollingEnabled:
>   initial: false
>diff --git a/Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp b/Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp
>index 2638826b507..530032e5571 100644
>--- a/Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp
>+++ b/Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp
>@@ -523,6 +523,8 @@ void AsyncScrollingCoordinator::updateFrameScrollingNode(ScrollingNodeID nodeID,
>     node->setInsetClipLayer(insetClipLayer);
>     node->setScrolledContentsLayer(scrolledContentsLayer);
>     node->setCounterScrollingLayer(counterScrollingLayer);
>+    node->setHorizontalOverscrollBehavior(scrollingGeometry.horizontalOverscrollBehavior);
>+    node->setVerticalOverscrollBehavior(scrollingGeometry.verticalOverscrollBehavior);
>     node->setParentRelativeScrollableRect(scrollingGeometry.parentRelativeScrollableRect);
>     node->setScrollOrigin(scrollingGeometry.scrollOrigin);
>     node->setScrollPosition(scrollingGeometry.scrollPosition);
>@@ -540,6 +542,8 @@ void AsyncScrollingCoordinator::updateOverflowScrollingNode(ScrollingNodeID node
> 
>     node->setLayer(layer);
>     node->setScrolledContentsLayer(scrolledContentsLayer);
>+    node->setHorizontalOverscrollBehavior(scrollingGeometry.horizontalOverscrollBehavior);
>+    node->setVerticalOverscrollBehavior(scrollingGeometry.verticalOverscrollBehavior);
>     node->setParentRelativeScrollableRect(scrollingGeometry.parentRelativeScrollableRect);
>     node->setScrollOrigin(scrollingGeometry.scrollOrigin);
>     node->setScrollPosition(scrollingGeometry.scrollPosition);
>diff --git a/Source/WebCore/page/scrolling/ScrollingCoordinator.h b/Source/WebCore/page/scrolling/ScrollingCoordinator.h
>index f917089a5af..b2020997894 100644
>--- a/Source/WebCore/page/scrolling/ScrollingCoordinator.h
>+++ b/Source/WebCore/page/scrolling/ScrollingCoordinator.h
>@@ -173,6 +173,8 @@ public:
>     virtual void updateNodeViewportConstraints(ScrollingNodeID, const ViewportConstraints&) { }
> 
>     struct ScrollingGeometry {
>+        OverscrollBehavior horizontalOverscrollBehavior { OverscrollBehavior:: Auto };
>+        OverscrollBehavior verticalOverscrollBehavior { OverscrollBehavior:: Auto };
>         LayoutRect parentRelativeScrollableRect;
>         FloatSize scrollableAreaSize;
>         FloatSize contentSize;
>diff --git a/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp b/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp
>index 153362bb198..9728ccab826 100644
>--- a/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp
>+++ b/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp
>@@ -51,6 +51,8 @@ ScrollingStateScrollingNode::ScrollingStateScrollingNode(const ScrollingStateScr
>     , m_snapOffsetsInfo(stateNode.m_snapOffsetsInfo)
> #endif
>     , m_scrollableAreaParameters(stateNode.scrollableAreaParameters())
>+    , m_horizontalOverscrollBehavior(stateNode.horizontalOverscrollBehavior())
>+    , m_verticalOverscrollBehavior(stateNode.verticalOverscrollBehavior())
>     , m_requestedScrollPositionRepresentsProgrammaticScroll(stateNode.requestedScrollPositionRepresentsProgrammaticScroll())
>     , m_expectsWheelEventTestTrigger(stateNode.expectsWheelEventTestTrigger())
> {
>@@ -87,6 +89,24 @@ void ScrollingStateScrollingNode::setReachableContentsSize(const FloatSize& reac
>     setPropertyChanged(ReachableContentsSize);
> }
> 
>+void ScrollingStateScrollingNode::setHorizontalOverscrollBehavior(OverscrollBehavior behavior)
>+{
>+    if (m_horizontalOverscrollBehavior == behavior)
>+        return;
>+
>+    m_horizontalOverscrollBehavior = behavior;
>+    setPropertyChanged(HorizontalOverscrollBehavior);
>+}
>+
>+void ScrollingStateScrollingNode::setVerticalOverscrollBehavior(OverscrollBehavior behavior)
>+{
>+    if (m_verticalOverscrollBehavior == behavior)
>+        return;
>+
>+    m_verticalOverscrollBehavior = behavior;
>+    setPropertyChanged(VerticalOverscrollBehavior);
>+}
>+
> void ScrollingStateScrollingNode::setParentRelativeScrollableRect(const LayoutRect& parentRelativeScrollableRect)
> {
>     if (m_parentRelativeScrollableRect == parentRelativeScrollableRect)
>@@ -241,6 +261,12 @@ void ScrollingStateScrollingNode::dumpProperties(TextStream& ts, ScrollingStateT
>     if (m_requestedScrollPositionRepresentsProgrammaticScroll)
>         ts.dumpProperty("requested scroll position represents programmatic scroll", m_requestedScrollPositionRepresentsProgrammaticScroll);
> 
>+    if (m_horizontalOverscrollBehavior != OverscrollBehavior::Auto)
>+        ts.dumpProperty("horizontal overscroll behavior", static_cast<int>(m_horizontalOverscrollBehavior));
>+
>+    if (m_verticalOverscrollBehavior != OverscrollBehavior::Auto)
>+        ts.dumpProperty("vertical overscroll behavior", static_cast<int>(m_verticalOverscrollBehavior));
>+
>     if (!m_parentRelativeScrollableRect.isEmpty())
>         ts.dumpProperty("parent relative scrollable rect", m_parentRelativeScrollableRect);
> 
>diff --git a/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h b/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h
>index 7de737b6487..8a11ab0a50f 100644
>--- a/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h
>+++ b/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h
>@@ -42,6 +42,8 @@ public:
>         ScrollableAreaSize = NumStateNodeBits,
>         TotalContentsSize,
>         ReachableContentsSize,
>+        HorizontalOverscrollBehavior,
>+        VerticalOverscrollBehavior,
>         ParentRelativeScrollableRect,
>         ScrollPosition,
>         ScrollOrigin,
>@@ -69,6 +71,12 @@ public:
>     const FloatSize& reachableContentsSize() const { return m_reachableContentsSize; }
>     WEBCORE_EXPORT void setReachableContentsSize(const FloatSize&);
> 
>+    const OverscrollBehavior& horizontalOverscrollBehavior() const { return m_horizontalOverscrollBehavior; }
>+    WEBCORE_EXPORT void setHorizontalOverscrollBehavior(OverscrollBehavior);
>+
>+    const OverscrollBehavior& verticalOverscrollBehavior() const { return m_verticalOverscrollBehavior; }
>+    WEBCORE_EXPORT void setVerticalOverscrollBehavior(OverscrollBehavior);
>+
>     const LayoutRect& parentRelativeScrollableRect() const { return m_parentRelativeScrollableRect; }
>     WEBCORE_EXPORT void setParentRelativeScrollableRect(const LayoutRect&);
> 
>@@ -133,6 +141,8 @@ private:
> #endif
>     ScrollableAreaParameters m_scrollableAreaParameters;
>     LayerRepresentation m_scrolledContentsLayer;
>+    OverscrollBehavior m_horizontalOverscrollBehavior { OverscrollBehavior::Auto };
>+    OverscrollBehavior m_verticalOverscrollBehavior { OverscrollBehavior::Auto };
>     bool m_requestedScrollPositionRepresentsProgrammaticScroll { false };
>     bool m_expectsWheelEventTestTrigger { false };
> };
>diff --git a/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.cpp b/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.cpp
>index 74a873dde40..43158f5d54d 100644
>--- a/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.cpp
>+++ b/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.cpp
>@@ -28,6 +28,7 @@
> 
> #if ENABLE(ASYNC_SCROLLING)
> 
>+#include "RenderStyleConstants.h"
> #include "ScrollingStateTree.h"
> #include "ScrollingTree.h"
> #include <wtf/text/TextStream.h>
>@@ -63,6 +64,12 @@ void ScrollingTreeScrollingNode::commitStateBeforeChildren(const ScrollingStateN
>     if (state.hasChangedProperty(ScrollingStateScrollingNode::ScrollPosition))
>         m_lastCommittedScrollPosition = state.scrollPosition();
> 
>+    if (state.hasChangedProperty(ScrollingStateScrollingNode::HorizontalOverscrollBehavior))
>+        m_horizontalOverscrollBehavior = state.horizontalOverscrollBehavior();
>+
>+    if (state.hasChangedProperty(ScrollingStateScrollingNode::VerticalOverscrollBehavior))
>+        m_verticalOverscrollBehavior = state.verticalOverscrollBehavior();
>+
>     if (state.hasChangedProperty(ScrollingStateScrollingNode::ParentRelativeScrollableRect))
>         m_parentRelativeScrollableRect = state.parentRelativeScrollableRect();
> 
>@@ -143,6 +150,12 @@ void ScrollingTreeScrollingNode::dumpProperties(TextStream& ts, ScrollingStateTr
>         ts.dumpProperty("reachable content size", m_reachableContentsSize);
>     ts.dumpProperty("last committed scroll position", m_lastCommittedScrollPosition);
> 
>+    if (m_horizontalOverscrollBehavior != OverscrollBehavior::Auto)
>+        ts.dumpProperty("horizontal overscroll behavior", static_cast<int>(m_horizontalOverscrollBehavior));
>+
>+    if (m_verticalOverscrollBehavior != OverscrollBehavior::Auto)
>+        ts.dumpProperty("vertical overscroll behavior", static_cast<int>(m_verticalOverscrollBehavior));
>+
>     if (!m_parentRelativeScrollableRect.isEmpty())
>         ts.dumpProperty("parent relative scrollable rect", m_parentRelativeScrollableRect);
> 
>diff --git a/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.h b/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.h
>index f6de7830374..85fb751f897 100644
>--- a/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.h
>+++ b/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.h
>@@ -87,6 +87,8 @@ protected:
>     const FloatSize& scrollableAreaSize() const { return m_scrollableAreaSize; }
>     const FloatSize& totalContentsSize() const { return m_totalContentsSize; }
>     const FloatSize& reachableContentsSize() const { return m_reachableContentsSize; }
>+    const OverscrollBehavior& horizontalOverscrollBehavior() const { return m_horizontalOverscrollBehavior; }
>+    const OverscrollBehavior& verticalOverscrollBehavior() const { return m_verticalOverscrollBehavior; }
>     const LayoutRect& parentRelativeScrollableRect() const { return m_parentRelativeScrollableRect; }
>     const IntPoint& scrollOrigin() const { return m_scrollOrigin; }
> 
>@@ -120,6 +122,8 @@ private:
>     unsigned m_currentVerticalSnapPointIndex { 0 };
> #endif
>     ScrollableAreaParameters m_scrollableAreaParameters;
>+    OverscrollBehavior m_horizontalOverscrollBehavior { OverscrollBehavior::Auto };
>+    OverscrollBehavior m_verticalOverscrollBehavior { OverscrollBehavior::Auto };
> };
> 
> } // namespace WebCore
>diff --git a/Source/WebCore/platform/ScrollTypes.h b/Source/WebCore/platform/ScrollTypes.h
>index 33f38c31168..cdf2dcdd741 100644
>--- a/Source/WebCore/platform/ScrollTypes.h
>+++ b/Source/WebCore/platform/ScrollTypes.h
>@@ -31,6 +31,12 @@
> 
> namespace WebCore {
> 
>+enum class OverscrollBehavior : uint8_t {
>+    Auto = 0,
>+    Contain,
>+    None
>+};
>+
> enum ScrollDirection : uint8_t {
>     ScrollUp,
>     ScrollDown,
>diff --git a/Source/WebCore/rendering/RenderLayerCompositor.cpp b/Source/WebCore/rendering/RenderLayerCompositor.cpp
>index ec2f5a0539d..373785cb980 100644
>--- a/Source/WebCore/rendering/RenderLayerCompositor.cpp
>+++ b/Source/WebCore/rendering/RenderLayerCompositor.cpp
>@@ -3875,6 +3875,8 @@ void RenderLayerCompositor::updateScrollCoordinationForThisFrame(ScrollingNodeID
>     ScrollingNodeID nodeID = attachScrollingNode(*m_renderView.layer(), m_renderView.frame().isMainFrame() ? MainFrameScrollingNode : SubframeScrollingNode, parentNodeID);
>     ScrollingCoordinator::ScrollingGeometry scrollingGeometry;
>     // FIXME(https://webkit.org/b/172917): Pass parentRelativeScrollableRect?
>+    scrollingGeometry.horizontalOverscrollBehavior = m_renderView.style().overscrollBehaviorX();
>+    scrollingGeometry.verticalOverscrollBehavior = m_renderView.style().overscrollBehaviorY();
>     scrollingGeometry.scrollOrigin = frameView.scrollOrigin();
>     scrollingGeometry.scrollableAreaSize = frameView.visibleContentRect().size();
>     scrollingGeometry.contentSize = frameView.totalContentsSize();
>@@ -3968,6 +3970,8 @@ void RenderLayerCompositor::updateScrollCoordinatedLayer(RenderLayer& layer, Opt
>             scrollingGeometry.scrollableAreaSize = layer.visibleSize();
>             scrollingGeometry.contentSize = layer.contentsSize();
>             scrollingGeometry.reachableContentSize = layer.scrollableContentsSize();
>+            scrollingGeometry.horizontalOverscrollBehavior = layer.renderer().style().overscrollBehaviorX();
>+            scrollingGeometry.verticalOverscrollBehavior = layer.renderer().style().overscrollBehaviorY();
> #if ENABLE(CSS_SCROLL_SNAP)
>             if (const Vector<LayoutUnit>* offsets = layer.horizontalSnapOffsets())
>                 scrollingGeometry.horizontalSnapOffsets = *offsets;
>diff --git a/Source/WebCore/rendering/style/RenderStyle.h b/Source/WebCore/rendering/style/RenderStyle.h
>index dbaaf0c763e..abd8ceb43ef 100644
>--- a/Source/WebCore/rendering/style/RenderStyle.h
>+++ b/Source/WebCore/rendering/style/RenderStyle.h
>@@ -47,6 +47,7 @@
> #include "RenderStyleConstants.h"
> #include "RoundedRect.h"
> #include "SVGRenderStyle.h"
>+#include "ScrollTypes.h"
> #include "ShadowData.h"
> #include "ShapeValue.h"
> #include "StyleBackgroundData.h"
>@@ -339,6 +340,9 @@ public:
>     Overflow overflowInlineDirection() const { return isHorizontalWritingMode() ? overflowX() : overflowY(); }
>     Overflow overflowBlockDirection() const { return isHorizontalWritingMode() ? overflowY() : overflowX(); }
>     bool isOverflowVisible() const { return overflowX() == Overflow::Visible || overflowY() == Overflow::Visible; }
>+
>+    OverscrollBehavior overscrollBehaviorX() const { return static_cast<OverscrollBehavior>(m_rareNonInheritedData->overscrollBehaviorX); }
>+    OverscrollBehavior overscrollBehaviorY() const { return static_cast<OverscrollBehavior>(m_rareNonInheritedData->overscrollBehaviorY); }
>     
>     Visibility visibility() const { return static_cast<Visibility>(m_inheritedFlags.visibility); }
>     VerticalAlign verticalAlign() const { return static_cast<VerticalAlign>(m_nonInheritedFlags.verticalAlign); }
>@@ -895,6 +899,8 @@ public:
> 
>     void setOverflowX(Overflow v) { m_nonInheritedFlags.overflowX =  static_cast<unsigned>(v); }
>     void setOverflowY(Overflow v) { m_nonInheritedFlags.overflowY = static_cast<unsigned>(v); }
>+    void setOverscrollBehaviorX(OverscrollBehavior v) { SET_VAR(m_rareNonInheritedData, overscrollBehaviorX, static_cast<unsigned>(v)); }
>+    void setOverscrollBehaviorY(OverscrollBehavior v) { SET_VAR(m_rareNonInheritedData, overscrollBehaviorY, static_cast<unsigned>(v)); }
>     void setVisibility(Visibility v) { m_inheritedFlags.visibility = static_cast<unsigned>(v); }
>     void setVerticalAlign(VerticalAlign v) { m_nonInheritedFlags.verticalAlign = static_cast<unsigned>(v); }
>     void setVerticalAlignLength(Length&& length) { setVerticalAlign(VerticalAlign::Length); SET_VAR(m_boxData, m_verticalAlign, WTFMove(length)); }
>@@ -1448,6 +1454,9 @@ public:
>     // Initial values for all the properties
>     static Overflow initialOverflowX() { return Overflow::Visible; }
>     static Overflow initialOverflowY() { return Overflow::Visible; }
>+    static OverscrollBehavior initialOverscrollBehaviorX() { return OverscrollBehavior::Auto; }
>+    static OverscrollBehavior initialOverscrollBehaviorY() { return OverscrollBehavior::Auto; }
>+
>     static Clear initialClear() { return Clear::None; }
>     static DisplayType initialDisplay() { return DisplayType::Inline; }
>     static EUnicodeBidi initialUnicodeBidi() { return UBNormal; }
>diff --git a/Source/WebCore/rendering/style/StyleRareNonInheritedData.cpp b/Source/WebCore/rendering/style/StyleRareNonInheritedData.cpp
>index a312bdaebd5..dbb6eda2b2f 100644
>--- a/Source/WebCore/rendering/style/StyleRareNonInheritedData.cpp
>+++ b/Source/WebCore/rendering/style/StyleRareNonInheritedData.cpp
>@@ -60,6 +60,8 @@ StyleRareNonInheritedData::StyleRareNonInheritedData()
>     , scrollSnapPort(StyleScrollSnapPort::create())
>     , scrollSnapArea(StyleScrollSnapArea::create())
> #endif
>+    , overscrollBehaviorX(static_cast<unsigned>(RenderStyle::initialOverscrollBehaviorX()))
>+    , overscrollBehaviorY(static_cast<unsigned>(RenderStyle::initialOverscrollBehaviorY()))
>     , willChange(RenderStyle::initialWillChange())
>     , mask(FillLayerType::Mask)
>     , objectPosition(RenderStyle::initialObjectPosition())
>@@ -137,6 +139,8 @@ inline StyleRareNonInheritedData::StyleRareNonInheritedData(const StyleRareNonIn
>     , scrollSnapPort(o.scrollSnapPort)
>     , scrollSnapArea(o.scrollSnapArea)
> #endif
>+    , overscrollBehaviorX(o.overscrollBehaviorX)
>+    , overscrollBehaviorY(o.overscrollBehaviorY)
>     , content(o.content ? o.content->clone() : nullptr)
>     , counterDirectives(o.counterDirectives ? std::make_unique<CounterDirectiveMap>(*o.counterDirectives) : nullptr)
>     , altText(o.altText)
>@@ -240,6 +244,8 @@ bool StyleRareNonInheritedData::operator==(const StyleRareNonInheritedData& o) c
>         && scrollSnapPort == o.scrollSnapPort
>         && scrollSnapArea == o.scrollSnapArea
> #endif
>+        && overscrollBehaviorX == o.overscrollBehaviorX
>+        && overscrollBehaviorY == o.overscrollBehaviorY
>         && contentDataEquivalent(o)
>         && arePointingToEqualData(counterDirectives, o.counterDirectives)
>         && altText == o.altText
>diff --git a/Source/WebCore/rendering/style/StyleRareNonInheritedData.h b/Source/WebCore/rendering/style/StyleRareNonInheritedData.h
>index f9baa142305..7c112cd80fc 100644
>--- a/Source/WebCore/rendering/style/StyleRareNonInheritedData.h
>+++ b/Source/WebCore/rendering/style/StyleRareNonInheritedData.h
>@@ -128,6 +128,9 @@ public:
>     DataRef<StyleScrollSnapArea> scrollSnapArea;
> #endif
> 
>+    unsigned overscrollBehaviorX : 2; // OverscrollBehavior
>+    unsigned overscrollBehaviorY : 2; // OverscrollBehavior
>+
>     std::unique_ptr<ContentData> content;
>     std::unique_ptr<CounterDirectiveMap> counterDirectives;
>     String altText;
>diff --git a/Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp b/Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp
>index 8d2d18c096e..c87ad0353fa 100644
>--- a/Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp
>+++ b/Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp
>@@ -119,6 +119,8 @@ void ArgumentCoder<ScrollingStateScrollingNode>::encode(Encoder& encoder, const
> {
>     encoder << static_cast<const ScrollingStateNode&>(node);
>     
>+    SCROLLING_NODE_ENCODE_ENUM(ScrollingStateScrollingNode::HorizontalOverscrollBehavior, horizontalOverscrollBehavior)
>+    SCROLLING_NODE_ENCODE_ENUM(ScrollingStateScrollingNode::VerticalOverscrollBehavior, verticalOverscrollBehavior)
>     SCROLLING_NODE_ENCODE(ScrollingStateScrollingNode::ScrollableAreaSize, scrollableAreaSize)
>     SCROLLING_NODE_ENCODE(ScrollingStateScrollingNode::TotalContentsSize, totalContentsSize)
>     SCROLLING_NODE_ENCODE(ScrollingStateScrollingNode::ReachableContentsSize, reachableContentsSize)
>@@ -193,6 +195,8 @@ bool ArgumentCoder<ScrollingStateScrollingNode>::decode(Decoder& decoder, Scroll
>     if (!decoder.decode(static_cast<ScrollingStateNode&>(node)))
>         return false;
> 
>+    SCROLLING_NODE_DECODE_ENUM(ScrollingStateScrollingNode::HorizontalOverscrollBehavior, WebCore::OverscrollBehavior, setHorizontalOverscrollBehavior);
>+    SCROLLING_NODE_DECODE_ENUM(ScrollingStateScrollingNode::VerticalOverscrollBehavior, WebCore::OverscrollBehavior, setVerticalOverscrollBehavior);
>     SCROLLING_NODE_DECODE(ScrollingStateScrollingNode::ScrollableAreaSize, FloatSize, setScrollableAreaSize);
>     SCROLLING_NODE_DECODE(ScrollingStateScrollingNode::TotalContentsSize, FloatSize, setTotalContentsSize);
>     SCROLLING_NODE_DECODE(ScrollingStateScrollingNode::ReachableContentsSize, FloatSize, setReachableContentsSize);
>@@ -456,6 +460,12 @@ bool RemoteScrollingCoordinatorTransaction::decode(IPC::Decoder& decoder)
> 
> static void dump(TextStream& ts, const ScrollingStateScrollingNode& node, bool changedPropertiesOnly)
> {
>+    if (!changedPropertiesOnly || node.hasChangedProperty(ScrollingStateScrollingNode::HorizontalOverscrollBehavior))
>+        ts.dumpProperty("horizontal-overscroll-behavior", static_cast<int>(node.horizontalOverscrollBehavior()));
>+
>+    if (!changedPropertiesOnly || node.hasChangedProperty(ScrollingStateScrollingNode::VerticalOverscrollBehavior))
>+        ts.dumpProperty("vertical-overscroll-behavior", static_cast<int>(node.verticalOverscrollBehavior()));
>+
>     if (!changedPropertiesOnly || node.hasChangedProperty(ScrollingStateScrollingNode::ScrollableAreaSize))
>         ts.dumpProperty("scrollable-area-size", node.scrollableAreaSize());
> 
>diff --git a/Source/WebKit/Shared/WebCoreArgumentCoders.h b/Source/WebKit/Shared/WebCoreArgumentCoders.h
>index 3a3ea994910..964ba0140c7 100644
>--- a/Source/WebKit/Shared/WebCoreArgumentCoders.h
>+++ b/Source/WebKit/Shared/WebCoreArgumentCoders.h
>@@ -37,6 +37,7 @@
> #include <WebCore/NotificationDirection.h>
> #include <WebCore/RealtimeMediaSource.h>
> #include <WebCore/ScrollSnapOffsetsInfo.h>
>+#include <WebCore/ScrollTypes.h>
> #include <WebCore/ServiceWorkerTypes.h>
> #include <WebCore/StoredCredentialsPolicy.h>
> #include <WebCore/WorkerType.h>
>@@ -747,6 +748,15 @@ template<> struct ArgumentCoder<WebCore::SerializedAttachmentData> {
> 
> namespace WTF {
> 
>+template<> struct EnumTraits<WebCore::OverscrollBehavior> {
>+    using values = EnumValues<
>+    WebCore::OverscrollBehavior,
>+    WebCore::OverscrollBehavior::Auto,
>+    WebCore::OverscrollBehavior::Contain,
>+    WebCore::OverscrollBehavior::None
>+    >;
>+};
>+
> template<> struct EnumTraits<WebCore::ColorSpace> {
>     using values = EnumValues<
>     WebCore::ColorSpace,
>diff --git a/Source/WebKit/Shared/WebPreferences.yaml b/Source/WebKit/Shared/WebPreferences.yaml
>index 6d25e71f13c..40cb5ce5ad4 100644
>--- a/Source/WebKit/Shared/WebPreferences.yaml
>+++ b/Source/WebKit/Shared/WebPreferences.yaml
>@@ -1233,6 +1233,13 @@ PointerEventsEnabled:
>   webcoreBinding: RuntimeEnabledFeatures
>   category: experimental
> 
>+OverscrollBehaviorEnabled:
>+  type: bool
>+  defaultValue: false
>+  humanReadableName: "CSS Overscroll Behavior"
>+  humanReadableDescription: "CSS Overscroll Behavior prototype"
>+  category: experimental
>+
> CSSOMViewScrollingAPIEnabled:
>   type: bool
>   defaultValue: false
>diff --git a/Source/WebKit/UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm b/Source/WebKit/UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm
>index 3d4060f8026..a80bfd8e3d8 100644
>--- a/Source/WebKit/UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm
>+++ b/Source/WebKit/UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm
>@@ -163,6 +163,8 @@ void ScrollingTreeScrollingNodeDelegateIOS::commitStateAfterChildren(const Scrol
> {
>     SetForScope<bool> updatingChange(m_updatingFromStateNode, true);
>     if (scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::ScrollLayer)
>+        || scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::HorizontalOverscrollBehavior)
>+        || scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::VerticalOverscrollBehavior)
>         || scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::TotalContentsSize)
>         || scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::ReachableContentsSize)
>         || scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::ScrollPosition)
>@@ -171,6 +173,24 @@ void ScrollingTreeScrollingNodeDelegateIOS::commitStateAfterChildren(const Scrol
>         UIScrollView *scrollView = (UIScrollView *)[scrollLayer() delegate];
>         ASSERT([scrollView isKindOfClass:[UIScrollView self]]);
> 
>+        // FIXME(rdar://problem/34315997): UIScrollView should have some kind of support for overscroll-behavior to enable/disable:
>+        // - non-local boundary default actions (e.g. scroll chaining).
>+        // - local boundary default actions (e.g. bouncing).
>+#if USE(APPLE_INTERNAL_SDK)
>+        // if (scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::HorizontalOverscrollBehavior))
>+        //     scrollView.overscrollBehaviorHorizontal = convertOverscrollBehaviorFromWebKitToUIKit(scrollingStateNode.horizontalOverscrollBehavior());
>+        // if (scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::VerticalOverscrollBehavior))
>+        //     scrollView.overscrollBehaviorVertical = convertOverscrollBehaviorFromWebKitToUIKit(scrollingStateNode.verticalOverscrollBehavior());
>+#endif
>+        // For now, we only disable bouncing when both overflow-x and overflow-y are none.
>+        // UIScrollView::alwaysBounce* functions cannot help here.
>+        if (scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::HorizontalOverscrollBehavior)
>+            || scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::VerticalOverscrollBehavior)) {
>+            scrollView.bounces = scrollingStateNode.horizontalOverscrollBehavior() == OverscrollBehavior::None
>+            && scrollingStateNode.verticalOverscrollBehavior() == OverscrollBehavior::None
>+            ? NO : YES;
>+        }
>+
>         if (scrollingStateNode.hasChangedProperty(ScrollingStateScrollingNode::ScrollLayer)) {
>             if (!m_scrollViewDelegate)
>                 m_scrollViewDelegate = adoptNS([[WKScrollingNodeScrollViewDelegate alloc] initWithScrollingTreeNodeDelegate:this]);
>diff --git a/Source/WebKitLegacy/mac/WebView/WebPreferenceKeysPrivate.h b/Source/WebKitLegacy/mac/WebView/WebPreferenceKeysPrivate.h
>index b73f6cb6830..47870c00099 100644
>--- a/Source/WebKitLegacy/mac/WebView/WebPreferenceKeysPrivate.h
>+++ b/Source/WebKitLegacy/mac/WebView/WebPreferenceKeysPrivate.h
>@@ -182,6 +182,7 @@
> #define WebKitDirectoryUploadEnabledPreferenceKey @"WebKitDirectoryUploadEnabled"
> #define WebKitVisualViewportEnabledPreferenceKey @"WebKitVisualViewportEnabled"
> #define WebKitVisualViewportAPIEnabledPreferenceKey @"WebKitVisualViewportAPIEnabled"
>+#define WebKitOverscrollBehaviorEnabledPreferenceKey @"WebKitOverscrollBehaviorEnabled"
> #define WebKitCSSOMViewScrollingAPIEnabledPreferenceKey @"WebKitCSSOMViewScrollingAPIEnabled"
> #define WebKitModernMediaControlsEnabledPreferenceKey @"WebKitModernMediaControlsEnabled"
> #define WebKitSubtleCryptoEnabledPreferenceKey @"WebKitSubtleCryptoEnabled"
>diff --git a/Source/WebKitLegacy/mac/WebView/WebPreferences.mm b/Source/WebKitLegacy/mac/WebView/WebPreferences.mm
>index 7e1cfc1b1e2..ece0c7ac505 100644
>--- a/Source/WebKitLegacy/mac/WebView/WebPreferences.mm
>+++ b/Source/WebKitLegacy/mac/WebView/WebPreferences.mm
>@@ -656,6 +656,7 @@ public:
> #endif
>         [NSNumber numberWithBool:NO], WebKitVisualViewportAPIEnabledPreferenceKey,
> 
>+        [NSNumber numberWithBool:NO], WebKitOverscrollBehaviorEnabledPreferenceKey,
>         [NSNumber numberWithBool:NO], WebKitCSSOMViewScrollingAPIEnabledPreferenceKey,
>         [NSNumber numberWithBool:YES], WebKitNeedsStorageAccessFromFileURLsQuirkKey,
>         [NSNumber numberWithBool:NO], WebKitAllowCrossOriginSubresourcesToAskForCredentialsKey,
>@@ -3097,6 +3098,16 @@ static NSString *classIBCreatorID = nil;
>     [self _setBoolValue:flag forKey:WebKitVisualViewportAPIEnabledPreferenceKey];
> }
> 
>+- (BOOL)overscrollBehaviorEnabled
>+{
>+    return [self _boolValueForKey:WebKitOverscrollBehaviorEnabledPreferenceKey];
>+}
>+
>+- (void)setOverscrollBehaviorEnabled:(BOOL)flag
>+{
>+    [self _setBoolValue:flag forKey:WebKitOverscrollBehaviorEnabledPreferenceKey];
>+}
>+
> - (BOOL)CSSOMViewScrollingAPIEnabled
> {
>     return [self _boolValueForKey:WebKitCSSOMViewScrollingAPIEnabledPreferenceKey];
>diff --git a/Source/WebKitLegacy/mac/WebView/WebPreferencesPrivate.h b/Source/WebKitLegacy/mac/WebView/WebPreferencesPrivate.h
>index 20b33429510..186153dbca8 100644
>--- a/Source/WebKitLegacy/mac/WebView/WebPreferencesPrivate.h
>+++ b/Source/WebKitLegacy/mac/WebView/WebPreferencesPrivate.h
>@@ -587,6 +587,7 @@ extern NSString *WebPreferencesCacheModelChangedInternalNotification WEBKIT_DEPR
> 
> @property (nonatomic) BOOL visualViewportEnabled;
> @property (nonatomic) BOOL visualViewportAPIEnabled;
>+@property (nonatomic) BOOL overscrollBehaviorEnabled;
> @property (nonatomic) BOOL CSSOMViewScrollingAPIEnabled;
> @property (nonatomic) BOOL largeImageAsyncDecodingEnabled;
> @property (nonatomic) BOOL animatedImageAsyncDecodingEnabled;
>diff --git a/Source/WebKitLegacy/mac/WebView/WebView.mm b/Source/WebKitLegacy/mac/WebView/WebView.mm
>index 5eb9575282c..758831d1922 100644
>--- a/Source/WebKitLegacy/mac/WebView/WebView.mm
>+++ b/Source/WebKitLegacy/mac/WebView/WebView.mm
>@@ -2953,6 +2953,7 @@ static bool needsSelfRetainWhileLoadingQuirk()
> 
>     settings.setVisualViewportEnabled([preferences visualViewportEnabled]);
>     settings.setVisualViewportAPIEnabled([preferences visualViewportAPIEnabled]);
>+    settings.setOverscrollBehaviorEnabled([preferences overscrollBehaviorEnabled]);
>     settings.setCSSOMViewScrollingAPIEnabled([preferences CSSOMViewScrollingAPIEnabled]);
>     settings.setMediaContentTypesRequiringHardwareSupport([preferences mediaContentTypesRequiringHardwareSupport]);
> 
>diff --git a/Source/WebKitLegacy/win/Interfaces/IWebPreferencesPrivate.idl b/Source/WebKitLegacy/win/Interfaces/IWebPreferencesPrivate.idl
>index 19882cdd0f0..7c864bdea5c 100644
>--- a/Source/WebKitLegacy/win/Interfaces/IWebPreferencesPrivate.idl
>+++ b/Source/WebKitLegacy/win/Interfaces/IWebPreferencesPrivate.idl
>@@ -221,6 +221,8 @@ interface IWebPreferencesPrivate6 : IWebPreferencesPrivate5
>     HRESULT setInspectorAdditionsEnabled([in] BOOL enabled);
>     HRESULT visualViewportAPIEnabled([out, retval] BOOL*);
>     HRESULT setVisualViewportAPIEnabled([in] BOOL enabled);
>+    HRESULT overscrollBehaviorEnabled([out, retval] BOOL*);
>+    HRESULT setOverscrollBehaviorEnabled([in] BOOL enabled);
>     HRESULT CSSOMViewScrollingAPIEnabled([out, retval] BOOL*);
>     HRESULT setCSSOMViewScrollingAPIEnabled([in] BOOL enabled);
>     HRESULT fetchAPIKeepAliveEnabled([out, retval] BOOL* enabled);
>diff --git a/Source/WebKitLegacy/win/WebPreferenceKeysPrivate.h b/Source/WebKitLegacy/win/WebPreferenceKeysPrivate.h
>index 940d5cf55d1..144be01d132 100644
>--- a/Source/WebKitLegacy/win/WebPreferenceKeysPrivate.h
>+++ b/Source/WebKitLegacy/win/WebPreferenceKeysPrivate.h
>@@ -204,5 +204,6 @@
> 
> #define WebKitServerTimingEnabledPreferenceKey "WebKitServerTimingEnabled"
> 
>+#define WebKitOverscrollBehaviorEnabledPreferenceKey "WebKitOverscrollBehaviorEnabled"
> #define WebKitCSSOMViewScrollingAPIEnabledPreferenceKey "WebKitCSSOMViewScrollingAPIEnabled"
> 
>diff --git a/Source/WebKitLegacy/win/WebPreferences.cpp b/Source/WebKitLegacy/win/WebPreferences.cpp
>index 59be0c443f4..e55d1f272fe 100644
>--- a/Source/WebKitLegacy/win/WebPreferences.cpp
>+++ b/Source/WebKitLegacy/win/WebPreferences.cpp
>@@ -326,6 +326,8 @@ void WebPreferences::initializeDefaultSettings()
> 
>     CFDictionaryAddValue(defaults, CFSTR(WebKitVisualViewportAPIEnabledPreferenceKey), kCFBooleanFalse);
> 
>+    CFDictionaryAddValue(defaults, CFSTR(WebKitOverscrollBehaviorEnabledPreferenceKey), kCFBooleanFalse);
>+
>     CFDictionaryAddValue(defaults, CFSTR(WebKitCSSOMViewScrollingAPIEnabledPreferenceKey), kCFBooleanFalse);
> 
>     defaultSettings = defaults;
>@@ -2184,6 +2186,20 @@ HRESULT WebPreferences::setVisualViewportAPIEnabled(BOOL enabled)
>     return S_OK;
> }
> 
>+HRESULT WebPreferences::overscrollBehaviorEnabled(_Out_ BOOL* enabled)
>+{
>+    if (!enabled)
>+        return E_POINTER;
>+    *enabled = boolValueForKey(WebKitOverscrollBehaviorEnabledPreferenceKey);
>+    return S_OK;
>+}
>+
>+HRESULT WebPreferences::setOverscrollBehaviorEnabled(BOOL enabled)
>+{
>+    setBoolValue(WebKitOverscrollBehaviorEnabledPreferenceKey, enabled);
>+    return S_OK;
>+}
>+
> HRESULT WebPreferences::CSSOMViewScrollingAPIEnabled(_Out_ BOOL* enabled)
> {
>     if (!enabled)
>diff --git a/Source/WebKitLegacy/win/WebPreferences.h b/Source/WebKitLegacy/win/WebPreferences.h
>index 3ce4485b8a0..d4be90f42fc 100644
>--- a/Source/WebKitLegacy/win/WebPreferences.h
>+++ b/Source/WebKitLegacy/win/WebPreferences.h
>@@ -269,6 +269,8 @@ public:
>     virtual HRESULT STDMETHODCALLTYPE setInspectorAdditionsEnabled(BOOL);
>     virtual HRESULT STDMETHODCALLTYPE visualViewportAPIEnabled(_Out_ BOOL*);
>     virtual HRESULT STDMETHODCALLTYPE setVisualViewportAPIEnabled(BOOL);
>+    virtual HRESULT STDMETHODCALLTYPE overscrollBehaviorEnabled(_Out_ BOOL*);
>+    virtual HRESULT STDMETHODCALLTYPE setOverscrollBehaviorEnabled(BOOL);
>     virtual HRESULT STDMETHODCALLTYPE CSSOMViewScrollingAPIEnabled(_Out_ BOOL*);
>     virtual HRESULT STDMETHODCALLTYPE setCSSOMViewScrollingAPIEnabled(BOOL);
>     virtual HRESULT STDMETHODCALLTYPE fetchAPIKeepAliveEnabled(_Out_ BOOL*);
>diff --git a/Source/WebKitLegacy/win/WebView.cpp b/Source/WebKitLegacy/win/WebView.cpp
>index e4b2e5f5c57..c5d2c9c9b2a 100644
>--- a/Source/WebKitLegacy/win/WebView.cpp
>+++ b/Source/WebKitLegacy/win/WebView.cpp
>@@ -5278,6 +5278,11 @@ HRESULT WebView::notifyPreferencesChanged(IWebNotification* notification)
>         return hr;
>     settings.setVisualViewportAPIEnabled(!!enabled);
> 
>+    hr = prefsPrivate->overscrollBehaviorEnabled(&enabled);
>+    if (FAILED(hr))
>+        return hr;
>+    settings.setOverscrollBehaviorEnabled(!!enabled);
>+
>     hr = prefsPrivate->CSSOMViewScrollingAPIEnabled(&enabled);
>     if (FAILED(hr))
>         return hr;
>diff --git a/Tools/DumpRenderTree/TestOptions.cpp b/Tools/DumpRenderTree/TestOptions.cpp
>index 81b2487b233..e111f2d02c9 100644
>--- a/Tools/DumpRenderTree/TestOptions.cpp
>+++ b/Tools/DumpRenderTree/TestOptions.cpp
>@@ -109,6 +109,8 @@ TestOptions::TestOptions(const std::string& pathOrURL, const std::string& absolu
>             jscOptions = value;
>         else if (key == "experimental:WebGPUEnabled")
>             enableWebGPU = parseBooleanTestHeaderValue(value);
>+        else if (key == "experimental:overscrollBehaviorEnabled")
>+            enableOverscrollBehavior = parseBooleanTestHeaderValue(value);
>         pairStart = pairEnd + 1;
>     }
> }
>diff --git a/Tools/DumpRenderTree/TestOptions.h b/Tools/DumpRenderTree/TestOptions.h
>index 8aedb946417..9fdd056a0a0 100644
>--- a/Tools/DumpRenderTree/TestOptions.h
>+++ b/Tools/DumpRenderTree/TestOptions.h
>@@ -45,6 +45,7 @@ struct TestOptions {
>     bool enableColorFilter { false };
>     bool enableSelectionAcrossShadowBoundaries { true };
>     bool enableWebGPU { false };
>+    bool enableOverscrollBehavior { false };
>     std::string jscOptions;
> 
>     TestOptions(const std::string& pathOrURL, const std::string& absolutePath);
>diff --git a/Tools/DumpRenderTree/mac/DumpRenderTree.mm b/Tools/DumpRenderTree/mac/DumpRenderTree.mm
>index 5de612c59f3..a701cdce058 100644
>--- a/Tools/DumpRenderTree/mac/DumpRenderTree.mm
>+++ b/Tools/DumpRenderTree/mac/DumpRenderTree.mm
>@@ -1011,6 +1011,7 @@ static void setWebPreferencesForTestOptions(const TestOptions& options)
>     preferences.colorFilterEnabled = options.enableColorFilter;
>     preferences.selectionAcrossShadowBoundariesEnabled = options.enableSelectionAcrossShadowBoundaries;
>     preferences.webGPUEnabled = options.enableWebGPU;
>+    preferences.overscrollBehaviorEnabled = options.enableOverscrollBehavior;
> }
> 
> // Called once on DumpRenderTree startup.
>-- 
>2.19.1
>

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