Attachment 423189 Details for Bug 223175 – Patch

[patch] Patch

bug-223175-20210315174148.patch (text/plain), 77.64 KB, created by Martin Robinson on 2021-03-15 09:41:56 PDT

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Creator: Martin Robinson

Created: 2021-03-15 09:41:56 PDT

Size: 77.64 KB

patch

obsolete

>Subversion Revision: 274413
>diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
>index 58a2371cca152bfd8449674265735afaf77c9d5e..22b355de97188548d0a5f63b1d43098ac5e5cb3d 100644
>--- a/Source/WebCore/ChangeLog
>+++ b/Source/WebCore/ChangeLog
>@@ -1,3 +1,66 @@
>+2021-03-15  Martin Robinson  <mrobinson@webkit.org>
>+
>+        [css-scroll-snap] Properly handle overflowing snap areas
>+        https://bugs.webkit.org/show_bug.cgi?id=223175
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        Properly handle overflowing snap areas. This requires rewriting the snapping
>+        algorithm. ScrollSnapOffsetsInfo now store snap area rectangles, which are
>+        used to handle overflowing snap areas. In addition, snap offset ranges are no
>+        longer kept to handle proximity. Instead this is done when choosing candidate
>+        snap offsets.
>+
>+        Because ScrollSnapOffsetsInfo now contains a rectangle type, its template needs
>+        this type as well. In order to make it simpler to use ScrollSnapOffsetsInfo this
>+        change exposes two type aliases, FloatScrollSnapOffsetsInfo and LayoutScrollSnapOffsetsInfo
>+        which are used everywhere.
>+
>+        No new tests. This change fixes the WPT test:
>+        imported/w3c/web-platform-tests/css/css-scroll-snap/overflowing-snap-areas.html
>+
>+        * page/scrolling/AsyncScrollingCoordinator.cpp: Use the new type aliases.
>+        * page/scrolling/ScrollSnapOffsetsInfo.cpp:
>+        (WebCore::findFirstSnapStopOffsetBetweenOriginAndDestination): Updated to return an offset/index
>+        pair so the return type of this function is compatible with that of calculateClosestSnapOffset.
>+        (WebCore::updateSnapOffsetsForScrollableArea): No longer store offset ranges for proximity snapping
>+        and also store snap areas converted to "offset" coordinates.
>+        (WebCore::convertOffsetInfo): No longer need to convert offset ranges, but this does now
>+        require converting offset areas.
>+        (WebCore::FloatScrollSnapOffsetsInfo::convertUnits const): Use the new type aliases.
>+        (WebCore::LayoutScrollSnapOffsetsInfo::convertUnits const): Ditto.
>+        (WebCore::maxForAxis): Added this helper which gets the maximum in a particular axis given the axis.
>+        (WebCore::minForAxis): Ditto.
>+        (WebCore::isNearEnoughToOffsetForProximity): Added this helper which replaces computeAxisProximitySnapOffsetRanges.
>+        (WebCore::calculateClosestSnapOffset): This replaces closestSnapOffsetWithOffsetsAndRanges, but also
>+        and indicesOfNearestSnapOffsets. Now written using snap areas from the data structure as well as
>+        with proper handling for overflowing snap areas.
>+        (WebCore::LayoutScrollSnapOffsetsInfo::closestSnapOffset const): Update for new method names and type aliases.
>+        (WebCore::FloatScrollSnapOffsetsInfo::closestSnapOffset const): Ditto.
>+        * page/scrolling/ScrollSnapOffsetsInfo.h:
>+        (WebCore::ScrollSnapOffsetsInfo::isEqual const): No longer look at snap offset ranges, but do take into
>+        consideration the snap areas.
>+        (WebCore::ScrollSnapOffsetsInfo::offsetsForAxis const): Renamed the template argument.
>+        (WebCore::operator<<): Removed.
>+        * page/scrolling/ScrollingStateScrollingNode.cpp: Use the new type alias.
>+        * page/scrolling/ScrollingStateScrollingNode.h: Ditto.
>+        * page/scrolling/ScrollingTreeScrollingNode.cpp: Ditto.
>+        * page/scrolling/ScrollingTreeScrollingNode.h: Ditto.
>+        * page/scrolling/mac/ScrollingTreeScrollingNodeDelegateMac.mm:
>+        (WebCore::ScrollingTreeScrollingNodeDelegateMac::updateFromStateNode): convertUnits now takes two template arguments.
>+        * platform/ScrollController.cpp:
>+        (WebCore::ScrollController::updateScrollSnapPoints): Pass in the viewport size when selecting snap points.
>+        (WebCore::ScrollController::adjustScrollDestination): Ditto.
>+        * platform/ScrollController.h: Use the new type alias.
>+        * platform/ScrollSnapAnimatorState.cpp:
>+        (WebCore::ScrollSnapAnimatorState::setupAnimationForState): Pass viewport size to targetOffsetForStartOffset.
>+        (WebCore::ScrollSnapAnimatorState::targetOffsetForStartOffset const): Ditto.
>+        (WebCore::operator<<): No longer print snap offset ranges.
>+        * platform/ScrollSnapAnimatorState.h: Removed method dealing with ranges. Now pass viewport size to targetOffsetForStartOffset.
>+        * platform/ScrollableArea.cpp: Use the new type aliases.
>+        * platform/ScrollableArea.h: Ditto.
>+        * platform/mac/ScrollAnimatorMac.mm: Ditto.
>+
> 2021-03-10  Sergio Villar Senin  <svillar@igalia.com>
> 
>         Do not shrink radio buttons bellow its size
>diff --git a/Source/WebKit/ChangeLog b/Source/WebKit/ChangeLog
>index ce543af6409610968d39a6fd903f0404b241b9a7..3b02a599f1f3149fd618806a84eba87b79d64063 100644
>--- a/Source/WebKit/ChangeLog
>+++ b/Source/WebKit/ChangeLog
>@@ -1,3 +1,26 @@
>+2021-03-15  Martin Robinson  <mrobinson@webkit.org>
>+
>+        [css-scroll-snap] Properly handle overflowing snap areas
>+        https://bugs.webkit.org/show_bug.cgi?id=223175
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        ScrollSnapOffsetsInfo no longer holds snap offset ranges, but is also templated off
>+        of a rect type. In WebKit we switch to using the FloatScrollSnapOffsetsInfo alias.
>+        Additionally, we need to pass in the viewport size when requesting a snap offset
>+        position.
>+
>+        * Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp:
>+        (ArgumentCoder<ScrollingStateScrollingNode>::decode): Switch to using the FloatScrollSnapOffsetsInfo alias.
>+        (ArgumentCoder<FloatScrollSnapOffsetsInfo>::encode): Ditto. Also we no longer need to encode the ranges.
>+        (ArgumentCoder<FloatScrollSnapOffsetsInfo>::decode): Ditto.
>+        * Shared/WebCoreArgumentCoders.cpp: Ditto.
>+        * Shared/WebCoreArgumentCoders.h: Ditto.
>+        * UIProcess/RemoteLayerTree/ios/RemoteScrollingCoordinatorProxyIOS.mm:
>+        (WebKit::RemoteScrollingCoordinatorProxy::closestSnapOffsetForMainFrameScrolling const): Pass in the viewport size now.
>+        * UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm:
>+        (-[WKScrollingNodeScrollViewDelegate scrollViewWillEndDragging:withVelocity:targetContentOffset:]): Ditto.
>+
> 2021-03-15  Kimmo Kinnunen  <kkinnunen@apple.com>
> 
>         RemoteRenderingBackend commands are not processed in order if GPU process is waiting for replies
>diff --git a/Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp b/Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp
>index 58480a2d7a8f8acbc0dc6e3d15847400479b7c97..480fe95d82b2914979fa059b66b93e71a8f7811f 100644
>--- a/Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp
>+++ b/Source/WebCore/page/scrolling/AsyncScrollingCoordinator.cpp
>@@ -92,15 +92,15 @@ void AsyncScrollingCoordinator::handleWheelEventPhase(ScrollingNodeID nodeID, Pl
> #endif
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-static inline void setStateScrollingNodeSnapOffsetsAsFloat(ScrollingStateScrollingNode& node, const ScrollSnapOffsetsInfo<LayoutUnit>* offsetInfo, float deviceScaleFactor)
>+static inline void setStateScrollingNodeSnapOffsetsAsFloat(ScrollingStateScrollingNode& node, const LayoutScrollSnapOffsetsInfo* offsetInfo, float deviceScaleFactor)
> {
>     if (!offsetInfo) {
>-        node.setSnapOffsetsInfo(ScrollSnapOffsetsInfo<float>());
>+        node.setSnapOffsetsInfo(FloatScrollSnapOffsetsInfo());
>         return;
>     }
> 
>     // FIXME: Incorporate current page scale factor in snapping to device pixel. Perhaps we should just convert to float here and let UI process do the pixel snapping?
>-    node.setSnapOffsetsInfo(offsetInfo->convertUnits<float>(deviceScaleFactor));
>+    node.setSnapOffsetsInfo(offsetInfo->convertUnits<float, FloatRect>(deviceScaleFactor));
> }
> #endif
> 
>diff --git a/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.cpp b/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.cpp
>index acfed0f38378eb4e2ec2a51b41028f5203d57cb4..01021a4cc3fd034b6d61104a3236375271673185 100644
>--- a/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.cpp
>+++ b/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.cpp
>@@ -41,68 +41,10 @@
> 
> namespace WebCore {
> 
>-template <typename LayoutType>
>-static void indicesOfNearestSnapOffsetRanges(LayoutType offset, const Vector<ScrollOffsetRange<LayoutType>>& snapOffsetRanges, unsigned& lowerIndex, unsigned& upperIndex)
>+template <typename UnitType>
>+static Optional<std::pair<UnitType, unsigned>> findFirstSnapStopOffsetBetweenOriginAndDestination(const Vector<SnapOffset<UnitType>>& snapOffsets, UnitType scrollOriginOffset, UnitType scrollDestinationOffset)
> {
>-    if (snapOffsetRanges.isEmpty()) {
>-        lowerIndex = invalidSnapOffsetIndex;
>-        upperIndex = invalidSnapOffsetIndex;
>-        return;
>-    }
>-
>-    int lowerIndexAsInt = -1;
>-    int upperIndexAsInt = snapOffsetRanges.size();
>-    do {
>-        int middleIndex = (lowerIndexAsInt + upperIndexAsInt) / 2;
>-        auto& range = snapOffsetRanges[middleIndex];
>-        if (range.start < offset && offset < range.end) {
>-            lowerIndexAsInt = middleIndex;
>-            upperIndexAsInt = middleIndex;
>-            break;
>-        }
>-
>-        if (offset > range.end)
>-            lowerIndexAsInt = middleIndex;
>-        else
>-            upperIndexAsInt = middleIndex;
>-    } while (lowerIndexAsInt < upperIndexAsInt - 1);
>-
>-    if (offset <= snapOffsetRanges.first().start)
>-        lowerIndex = invalidSnapOffsetIndex;
>-    else
>-        lowerIndex = lowerIndexAsInt;
>-
>-    if (offset >= snapOffsetRanges.last().end)
>-        upperIndex = invalidSnapOffsetIndex;
>-    else
>-        upperIndex = upperIndexAsInt;
>-}
>-
>-template <typename LayoutType>
>-static void indicesOfNearestSnapOffsets(LayoutType offset, const Vector<SnapOffset<LayoutType>>& snapOffsets, unsigned& lowerIndex, unsigned& upperIndex)
>-{
>-    lowerIndex = 0;
>-    upperIndex = snapOffsets.size() - 1;
>-    while (lowerIndex < upperIndex - 1) {
>-        int middleIndex = (lowerIndex + upperIndex) / 2;
>-        auto middleOffset = snapOffsets[middleIndex].offset;
>-        if (offset == middleOffset) {
>-            upperIndex = middleIndex;
>-            lowerIndex = middleIndex;
>-            break;
>-        }
>-
>-        if (offset > middleOffset)
>-            lowerIndex = middleIndex;
>-        else
>-            upperIndex = middleIndex;
>-    }
>-}
>-
>-template <typename LayoutType>
>-static Optional<unsigned> findFirstSnapStopOffsetBetweenOriginAndDestination(const Vector<SnapOffset<LayoutType>>& snapOffsets, LayoutType scrollOriginOffset, LayoutType scrollDestinationOffset)
>-{
>-    LayoutType difference = scrollDestinationOffset - scrollOriginOffset;
>+    UnitType difference = scrollDestinationOffset - scrollOriginOffset;
>     if (!difference)
>         return WTF::nullopt;
> 
>@@ -113,7 +55,7 @@ static Optional<unsigned> findFirstSnapStopOffsetBetweenOriginAndDestination(con
>         iteration = -1;
>     }
> 
>-    auto isPast = [difference](LayoutType mark, LayoutType candidate) {
>+    auto isPast = [difference](UnitType mark, UnitType candidate) {
>         return (difference > 0 && candidate > mark) || (difference < 0 && candidate < mark);
>     };
> 
>@@ -124,65 +66,12 @@ static Optional<unsigned> findFirstSnapStopOffsetBetweenOriginAndDestination(con
>         if (snapOffsets[i].stop != ScrollSnapStop::Always)
>             continue;
>         if (isPast(scrollOriginOffset, offset))
>-            return i;
>+            return std::make_pair(offset, static_cast<unsigned>(i));
>     }
> 
>     return WTF::nullopt;
> }
> 
>-template <typename LayoutType>
>-static std::pair<LayoutType, unsigned> closestSnapOffsetWithOffsetsAndRanges(const Vector<SnapOffset<LayoutType>>& snapOffsets, const Vector<ScrollOffsetRange<LayoutType>>& snapOffsetRanges, LayoutType scrollDestinationOffset, float velocity, Optional<LayoutType> originalOffsetForDirectionalSnapping)
>-{
>-    if (snapOffsets.isEmpty())
>-        return std::make_pair(scrollDestinationOffset, invalidSnapOffsetIndex);
>-
>-    if (originalOffsetForDirectionalSnapping.hasValue()) {
>-        auto firstSnapStopOffsetIndex = findFirstSnapStopOffsetBetweenOriginAndDestination(snapOffsets, *originalOffsetForDirectionalSnapping, scrollDestinationOffset);
>-        if (firstSnapStopOffsetIndex.hasValue())
>-            return std::make_pair(snapOffsets[*firstSnapStopOffsetIndex].offset, *firstSnapStopOffsetIndex);
>-    }
>-
>-    unsigned lowerSnapOffsetRangeIndex;
>-    unsigned upperSnapOffsetRangeIndex;
>-    indicesOfNearestSnapOffsetRanges<LayoutType>(scrollDestinationOffset, snapOffsetRanges, lowerSnapOffsetRangeIndex, upperSnapOffsetRangeIndex);
>-    if (lowerSnapOffsetRangeIndex == upperSnapOffsetRangeIndex && upperSnapOffsetRangeIndex != invalidSnapOffsetIndex)
>-        return std::make_pair(scrollDestinationOffset, invalidSnapOffsetIndex);
>-
>-    if (scrollDestinationOffset <= snapOffsets.first().offset)
>-        return std::make_pair(snapOffsets.first().offset, 0u);
>-
>-    if (scrollDestinationOffset >= snapOffsets.last().offset)
>-        return std::make_pair(snapOffsets.last().offset, snapOffsets.size() - 1);
>-
>-    unsigned lowerIndex;
>-    unsigned upperIndex;
>-    indicesOfNearestSnapOffsets<LayoutType>(scrollDestinationOffset, snapOffsets, lowerIndex, upperIndex);
>-    LayoutType lowerSnapPosition = snapOffsets[lowerIndex].offset;
>-    LayoutType upperSnapPosition = snapOffsets[upperIndex].offset;
>-    if (!std::abs(velocity)) {
>-        bool isCloserToLowerSnapPosition = scrollDestinationOffset - lowerSnapPosition <= upperSnapPosition - scrollDestinationOffset;
>-        return isCloserToLowerSnapPosition ? std::make_pair(lowerSnapPosition, lowerIndex) : std::make_pair(upperSnapPosition, upperIndex);
>-    }
>-
>-    // Non-zero velocity indicates a flick gesture. Even if another snap point is closer, we should choose the one in the direction of the flick gesture
>-    // as long as a scroll snap offset range does not lie between the scroll destination and the targeted snap offset. If we are doing directional
>-    // snapping, we should never snap to a point that was on the other side of the original position in the opposite direction of this scroll.
>-    // This allows directional scrolling to escape snap points.
>-    if (velocity < 0) {
>-        if (lowerSnapOffsetRangeIndex == invalidSnapOffsetIndex || lowerSnapPosition >= snapOffsetRanges[lowerSnapOffsetRangeIndex].end)
>-            return std::make_pair(lowerSnapPosition, lowerIndex);
>-        if (!originalOffsetForDirectionalSnapping.hasValue() || *originalOffsetForDirectionalSnapping > upperSnapPosition)
>-            return std::make_pair(upperSnapPosition, upperIndex);
>-    } else {
>-        if (upperSnapOffsetRangeIndex == invalidSnapOffsetIndex || snapOffsetRanges[upperSnapOffsetRangeIndex].start >= upperSnapPosition)
>-            return std::make_pair(upperSnapPosition, upperIndex);
>-        if (!originalOffsetForDirectionalSnapping.hasValue() || *originalOffsetForDirectionalSnapping < lowerSnapPosition)
>-            return std::make_pair(lowerSnapPosition, lowerIndex);
>-    }
>-
>-    return std::make_pair(scrollDestinationOffset, invalidSnapOffsetIndex);
>-}
>-
> enum class InsetOrOutset {
>     Inset,
>     Outset
>@@ -219,30 +108,6 @@ static LayoutUnit computeScrollSnapAlignOffset(LayoutUnit minLocation, LayoutUni
>     }
> }
> 
>-static void computeAxisProximitySnapOffsetRanges(const Vector<SnapOffset<LayoutUnit>>& snapOffsets, Vector<ScrollOffsetRange<LayoutUnit>>& offsetRanges, LayoutUnit scrollPortAxisLength)
>-{
>-    // This is an arbitrary choice for what it means to be "in proximity" of a snap offset. We should play around with
>-    // this and see what feels best.
>-    static const float ratioOfScrollPortAxisLengthToBeConsideredForProximity = 0.3;
>-    if (snapOffsets.size() < 2)
>-        return;
>-
>-    // The extra rule accounting for scroll offset ranges in between the scroll destination and a potential snap offset
>-    // handles the corner case where the user scrolls with momentum very lightly away from a snap offset, such that the
>-    // predicted scroll destination is still within proximity of the snap offset. In this case, the regular (mandatory
>-    // scroll snapping) behavior would be to snap to the next offset in the direction of momentum scrolling, but
>-    // instead, it is more intuitive to either return to the original snap position (which we arbitrarily choose here)
>-    // or scroll just outside of the snap offset range. This is another minor behavior tweak that we should play around
>-    // with to see what feels best.
>-    LayoutUnit proximityDistance { ratioOfScrollPortAxisLengthToBeConsideredForProximity * scrollPortAxisLength };
>-    for (size_t index = 1; index < snapOffsets.size(); ++index) {
>-        auto startOffset = snapOffsets[index - 1].offset + proximityDistance;
>-        auto endOffset = snapOffsets[index].offset - proximityDistance;
>-        if (startOffset < endOffset)
>-            offsetRanges.append({ startOffset, endOffset });
>-    }
>-}
>-
> void updateSnapOffsetsForScrollableArea(ScrollableArea& scrollableArea, const RenderBox& scrollingElementBox, const RenderStyle& scrollingElementStyle, LayoutRect viewportRectInBorderBoxCoordinates)
> {
>     auto scrollSnapType = scrollingElementStyle.scrollSnapType();
>@@ -262,6 +127,7 @@ void updateSnapOffsetsForScrollableArea(ScrollableArea& scrollableArea, const Re
> 
>     HashMap<float, SnapOffset<LayoutUnit>> verticalSnapOffsetsMap;
>     HashMap<float, SnapOffset<LayoutUnit>> horizontalSnapOffsetsMap;
>+    Vector<LayoutRect> snapAreas;
>     bool hasHorizontalSnapOffsets = scrollSnapType.axis == ScrollSnapAxis::Both || scrollSnapType.axis == ScrollSnapAxis::XAxis || scrollSnapType.axis == ScrollSnapAxis::Inline;
>     bool hasVerticalSnapOffsets = scrollSnapType.axis == ScrollSnapAxis::Both || scrollSnapType.axis == ScrollSnapAxis::YAxis || scrollSnapType.axis == ScrollSnapAxis::Block;
> 
>@@ -288,17 +154,29 @@ void updateSnapOffsetsForScrollableArea(ScrollableArea& scrollableArea, const Re
> 
>         scrollSnapArea = computeScrollSnapPortOrAreaRect(scrollSnapArea, child->style().scrollMargin(), InsetOrOutset::Outset);
>         LOG_WITH_STREAM(ScrollSnap, stream << "    Considering scroll snap target area " << scrollSnapArea);
>+
>         auto alignment = child->style().scrollSnapAlign();
>+        bool snapsHorizontally = hasHorizontalSnapOffsets && alignment.x != ScrollSnapAxisAlignType::None;
>+        bool snapsVertically = hasVerticalSnapOffsets && alignment.y != ScrollSnapAxisAlignType::None;
>+        if (!snapsHorizontally && !snapsVertically)
>+            continue;
>+
>+        // The scroll snap area is defined via its scroll position, so convert everything to scroll offetss here.
>+        auto snapAreaOriginRelativeToBorderEdge = scrollSnapArea.location() - scrollSnapPort.location();
>+        LayoutRect scrollSnapAreaAsOffsets(scrollableArea.scrollOffsetFromPosition(roundedIntPoint(snapAreaOriginRelativeToBorderEdge)), scrollSnapArea.size());
>+        snapAreas.append(scrollSnapAreaAsOffsets);
>+        unsigned snapAreaIndex = snapAreas.size() - 1;
>+
>         auto stop = child->style().scrollSnapStop();
>-        if (hasHorizontalSnapOffsets && alignment.x != ScrollSnapAxisAlignType::None) {
>+        if (snapsHorizontally) {
>             auto absoluteScrollXPosition = computeScrollSnapAlignOffset(scrollSnapArea.x(), scrollSnapArea.maxX(), alignment.x, scrollerIsRTL) - computeScrollSnapAlignOffset(scrollSnapPort.x(), scrollSnapPort.maxX(), alignment.x, scrollerIsRTL);
>             auto absoluteScrollOffset = clampTo<int>(scrollableArea.scrollOffsetFromPosition({ roundToInt(absoluteScrollXPosition), 0 }).x(), 0, maxScrollOffset.x());
>-            addOrUpdateStopForSnapOffset(horizontalSnapOffsetsMap, { absoluteScrollOffset, stop });
>+            addOrUpdateStopForSnapOffset(horizontalSnapOffsetsMap, { absoluteScrollOffset, stop, snapAreaIndex });
>         }
>-        if (hasVerticalSnapOffsets && alignment.y != ScrollSnapAxisAlignType::None) {
>+        if (snapsVertically) {
>             auto absoluteScrollYPosition = computeScrollSnapAlignOffset(scrollSnapArea.y(), scrollSnapArea.maxY(), alignment.y, false) - computeScrollSnapAlignOffset(scrollSnapPort.y(), scrollSnapPort.maxY(), alignment.y, false);
>             auto absoluteScrollOffset = clampTo<int>(scrollableArea.scrollOffsetFromPosition({ 0, roundToInt(absoluteScrollYPosition) }).y(), 0, maxScrollOffset.y());
>-            addOrUpdateStopForSnapOffset(verticalSnapOffsetsMap, { absoluteScrollOffset, stop });
>+            addOrUpdateStopForSnapOffset(verticalSnapOffsetsMap, { absoluteScrollOffset, stop, snapAreaIndex });
>         }
>     }
> 
>@@ -308,32 +186,25 @@ void updateSnapOffsetsForScrollableArea(ScrollableArea& scrollableArea, const Re
>     };
> 
>     Vector<SnapOffset<LayoutUnit>> horizontalSnapOffsets = copyToVector(horizontalSnapOffsetsMap.values());
>-    Vector<ScrollOffsetRange<LayoutUnit>> horizontalSnapOffsetRanges;
>     if (!horizontalSnapOffsets.isEmpty()) {
>         std::sort(horizontalSnapOffsets.begin(), horizontalSnapOffsets.end(), compareSnapOffsets);
>-        if (scrollSnapType.strictness == ScrollSnapStrictness::Proximity)
>-            computeAxisProximitySnapOffsetRanges(horizontalSnapOffsets, horizontalSnapOffsetRanges, scrollSnapPort.width());
>-
>         LOG_WITH_STREAM(ScrollSnap, stream << " => Computed horizontal scroll snap offsets: " << horizontalSnapOffsets);
>-        LOG_WITH_STREAM(ScrollSnap, stream << " => Computed horizontal scroll snap offset ranges: " << horizontalSnapOffsetRanges);
>     }
> 
>     Vector<SnapOffset<LayoutUnit>> verticalSnapOffsets = copyToVector(verticalSnapOffsetsMap.values());
>-    Vector<ScrollOffsetRange<LayoutUnit>> verticalSnapOffsetRanges;
>     if (!verticalSnapOffsets.isEmpty()) {
>         std::sort(verticalSnapOffsets.begin(), verticalSnapOffsets.end(), compareSnapOffsets);
>-        if (scrollSnapType.strictness == ScrollSnapStrictness::Proximity)
>-            computeAxisProximitySnapOffsetRanges(verticalSnapOffsets, verticalSnapOffsetRanges, scrollSnapPort.height());
>-
>         LOG_WITH_STREAM(ScrollSnap, stream << " => Computed vertical scroll snap offsets: " << verticalSnapOffsets);
>-        LOG_WITH_STREAM(ScrollSnap, stream << " => Computed vertical scroll snap offset ranges: " << verticalSnapOffsetRanges);
>     }
> 
>+    if (!snapAreas.isEmpty())
>+        LOG_WITH_STREAM(ScrollSnap, stream << " => Computed snap areas: " << snapAreas);
>+
>     scrollableArea.setScrollSnapOffsetInfo({
>+        scrollSnapType.strictness,
>         horizontalSnapOffsets,
>         verticalSnapOffsets,
>-        horizontalSnapOffsetRanges,
>-        verticalSnapOffsetRanges
>+        snapAreas,
>     });
> }
> 
>@@ -347,57 +218,179 @@ static LayoutUnit convertOffsetUnit(float input, float /* scaleFactor */)
>     return LayoutUnit(input);
> }
> 
>-template <typename InputType, typename OutputType>
>-static ScrollSnapOffsetsInfo<OutputType> convertOffsetInfo(const ScrollSnapOffsetsInfo<InputType>& input, float scaleFactor = 0.0)
>+template <typename InputType, typename InputRectType, typename OutputType, typename OutputRectType>
>+static ScrollSnapOffsetsInfo<OutputType, OutputRectType> convertOffsetInfo(const ScrollSnapOffsetsInfo<InputType, InputRectType>& input, float scaleFactor = 0.0)
> {
>     auto convertOffsets = [scaleFactor](const Vector<SnapOffset<InputType>>& input)
>     {
>         Vector<SnapOffset<OutputType>> output;
>         output.reserveInitialCapacity(input.size());
>         for (auto& offset : input)
>-            output.uncheckedAppend({ convertOffsetUnit(offset.offset, scaleFactor), offset.stop });
>+            output.uncheckedAppend({ convertOffsetUnit(offset.offset, scaleFactor), offset.stop, offset.snapAreaIndex });
>         return output;
>     };
> 
>-    auto convertOffsetRanges = [scaleFactor](const Vector<ScrollOffsetRange<InputType>>& input)
>+    auto convertRects = [scaleFactor](const Vector<InputRectType>& input)
>     {
>-        Vector<ScrollOffsetRange<OutputType>> output;
>+        Vector<OutputRectType> output;
>         output.reserveInitialCapacity(input.size());
>-        for (auto& range : input)
>-            output.uncheckedAppend({ convertOffsetUnit(range.start, scaleFactor), convertOffsetUnit(range.end, scaleFactor) });
>+        for (auto& rect : input) {
>+            OutputRectType outputRect(
>+                convertOffsetUnit(rect.x(), scaleFactor), convertOffsetUnit(rect.y(), scaleFactor),
>+                convertOffsetUnit(rect.width(), scaleFactor), convertOffsetUnit(rect.height(), scaleFactor));
>+            output.uncheckedAppend(outputRect);
>+        }
>         return output;
>     };
> 
>     return {
>+        input.strictness,
>         convertOffsets(input.horizontalSnapOffsets),
>         convertOffsets(input.verticalSnapOffsets),
>-        convertOffsetRanges(input.horizontalSnapOffsetRanges),
>-        convertOffsetRanges(input.verticalSnapOffsetRanges)
>+        convertRects(input.snapAreas),
>     };
> }
> 
> template <> template <>
>-ScrollSnapOffsetsInfo<LayoutUnit> ScrollSnapOffsetsInfo<float>::convertUnits(float /* unusedScaleFactor */) const
>+LayoutScrollSnapOffsetsInfo FloatScrollSnapOffsetsInfo::convertUnits(float /* unusedScaleFactor */) const
> {
>-    return convertOffsetInfo<float, LayoutUnit>(*this);
>+    return convertOffsetInfo<float, FloatRect, LayoutUnit, LayoutRect>(*this);
> }
> 
> template <> template <>
>-ScrollSnapOffsetsInfo<float> ScrollSnapOffsetsInfo<LayoutUnit>::convertUnits(float deviceScaleFactor) const
>+FloatScrollSnapOffsetsInfo LayoutScrollSnapOffsetsInfo::convertUnits(float deviceScaleFactor) const
> {
>-    return convertOffsetInfo<LayoutUnit, float>(*this, deviceScaleFactor);
>+    return convertOffsetInfo<LayoutUnit, LayoutRect, float, FloatRect>(*this, deviceScaleFactor);
> }
> 
>-template <>
>-std::pair<LayoutUnit, unsigned> ScrollSnapOffsetsInfo<LayoutUnit>::closestSnapOffset(ScrollEventAxis axis, LayoutUnit scrollDestinationOffset, float velocity, Optional<LayoutUnit> originalPositionForDirectionalSnapping) const
>+template <typename UnitType, typename RectType>
>+static UnitType maxForAxis(RectType rect, ScrollEventAxis axis)
> {
>-    return closestSnapOffsetWithOffsetsAndRanges(offsetsForAxis(axis), offsetRangesForAxis(axis), scrollDestinationOffset, velocity, originalPositionForDirectionalSnapping);
>+    return axis == ScrollEventAxis::Horizontal ? rect.maxX() : rect.maxY();
> }
> 
>-template <>
>-std::pair<float, unsigned> ScrollSnapOffsetsInfo<float>::closestSnapOffset(ScrollEventAxis axis, float scrollDestinationOffset, float velocity, Optional<float> originalPositionForDirectionalSnapping) const
>+template <typename UnitType, typename RectType>
>+static UnitType minForAxis(RectType rect, ScrollEventAxis axis)
>+{
>+    return axis == ScrollEventAxis::Horizontal ? rect.x() : rect.y();
>+}
>+
>+template <typename UnitType>
>+static bool isNearEnoughToOffsetForProximity(ScrollSnapStrictness strictness, UnitType scrollDestination, UnitType candidateSnapOffset, UnitType viewportLength)
>+{
>+    if (strictness != ScrollSnapStrictness::Proximity)
>+        return true;
>+
>+    // This is an arbitrary choice for what it means to be "in proximity" of a snap offset. We should play around with
>+    // this and see what feels best.
>+    static const float ratioOfScrollPortAxisLengthToBeConsideredForProximity = 0.3;
>+    return std::abs(float {candidateSnapOffset - scrollDestination}) <= (viewportLength * ratioOfScrollPortAxisLengthToBeConsideredForProximity);
>+}
>+
>+template <typename UnitType, typename RectType, typename SizeType>
>+static std::pair<UnitType, unsigned> calculateClosestSnapOffset(const ScrollSnapOffsetsInfo<UnitType, RectType>& info, ScrollEventAxis axis, const SizeType& viewportSize, UnitType scrollDestinationOffset, float velocity, Optional<UnitType> originalOffset)
>+{
>+    const auto& snapOffsets = info.offsetsForAxis(axis);
>+    auto pairForNoSnapping = std::make_pair(scrollDestinationOffset, invalidSnapOffsetIndex);
>+    if (snapOffsets.isEmpty())
>+        return pairForNoSnapping;
>+
>+    // The first snap point with `scroll-snap-stop: always` between the original position and destination takes precedence.
>+    if (originalOffset) {
>+        if (auto firstSnapStopOffset = findFirstSnapStopOffsetBetweenOriginAndDestination(snapOffsets, *originalOffset, scrollDestinationOffset))
>+            return *firstSnapStopOffset;
>+    }
>+
>+    auto viewportLength = axis == ScrollEventAxis::Horizontal ? viewportSize.width() : viewportSize.height();
>+    bool landedInsideSnapAreaThatConsumesViewport = false;
>+    Optional<std::pair<UnitType, unsigned>> previous, next;
>+    Optional<RectType> previousSnapArea, nextSnapArea;
>+    for (unsigned i = 0; i < snapOffsets.size(); i++) {
>+        const auto& snapArea = info.snapAreas[snapOffsets[i].snapAreaIndex];
>+        landedInsideSnapAreaThatConsumesViewport |= (minForAxis<UnitType>(snapArea, axis) <= scrollDestinationOffset && maxForAxis<UnitType>(snapArea, axis) >= (scrollDestinationOffset + viewportLength));
>+        // If the scroll landed exactly on a snap offset, choose that one.
>+        UnitType potentialSnapOffset = snapOffsets[i].offset;
>+        if (potentialSnapOffset == scrollDestinationOffset)
>+            return std::make_pair(potentialSnapOffset, i);
>+
>+        if (potentialSnapOffset < scrollDestinationOffset) {
>+            previous = std::make_pair(potentialSnapOffset, i);
>+            previousSnapArea = snapArea;
>+        } else if (!next && potentialSnapOffset > scrollDestinationOffset) {
>+            next = std::make_pair(potentialSnapOffset, i);
>+            nextSnapArea = snapArea;
>+        }
>+    }
>+
>+    // From https://www.w3.org/TR/css-scroll-snap-1/#snap-overflow
>+    // "If the snap area is larger than the snapport in a particular axis, then any scroll position
>+    // in which the snap area covers the snapport, and the distance between the geometrically
>+    // previous and subsequent snap positions in that axis is larger than size of the snapport in
>+    // that axis, is a valid snap position in that axis. The UA may use the specified alignment as a
>+    // more precise target for certain scroll operations (e.g. explicit paging)."
>+    if (landedInsideSnapAreaThatConsumesViewport && (!previous || !next || ((*next).first - (*previous).first) >= viewportLength))
>+        return pairForNoSnapping;
>+
>+    if (originalOffset) {
>+        // If this is a directional scroll and there are no scroll stops in a particular direction,
>+        // don't scroll past the edge of the scroll area.
>+        if (!next && previous)
>+            return std::make_pair(std::max((*previous).first, maxForAxis<UnitType>(*previousSnapArea, axis) - viewportLength), invalidSnapOffsetIndex);
>+        if (!previous && next)
>+            return std::make_pair(minForAxis<UnitType>(*nextSnapArea, axis), invalidSnapOffsetIndex);
>+
>+        // From https://www.w3.org/TR/css-scroll-snap-1/#choosing
>+        // "User agents must ensure that a user can âescapeâ a snap position, regardless of the scroll
>+        // method. For example, if the snap type is mandatory and the next snap position is more than
>+        // two screen-widths away, a naÃ¯ve âalways snap to nearestâ selection algorithm might âtrapâ the
>+        // user if their end position was only one screen-width away. Instead, a smarter algorithm that
>+        // only returned to the starting snap position if the end-point was a fairly small distance from
>+        // it, and otherwise ignored the starting snap position, would give better behavior."
>+        // We only do this if we are in a situation where we are choosing between two compatible
>+        // snap offsets.
>+        if (*originalOffset < scrollDestinationOffset && (*previous).first <= *originalOffset)
>+            previous.reset();
>+        if (*originalOffset > scrollDestinationOffset && (*next).first >= *originalOffset)
>+            next.reset();
>+    }
>+
>+    if (next && !isNearEnoughToOffsetForProximity(info.strictness, scrollDestinationOffset, (*next).first, viewportLength))
>+        next.reset();
>+    if (previous && !isNearEnoughToOffsetForProximity(info.strictness, scrollDestinationOffset, (*previous).first, viewportLength))
>+        previous.reset();
>+
>+    // If we don't have compatible offsets to choose between, just do the obvious thing
>+    // and do no snapping or only select the single compatible offset.
>+    if (!previous && !next)
>+        return pairForNoSnapping;
>+    if (!previous)
>+        return *next;
>+    if (!next)
>+        return *previous;
>+
>+    // If this scroll isn't directional, then choose whatever snap point is closer.
>+    UnitType previousSnapOffset = (*previous).first;
>+    UnitType nextSnapOffset = (*next).first;
>+    if (!std::abs(velocity)) {
>+        bool isCloserToPreviousSnapIndex = scrollDestinationOffset - previousSnapOffset <= nextSnapOffset - scrollDestinationOffset;
>+        return isCloserToPreviousSnapIndex ? *previous : *next;
>+    }
>+
>+    // Finally, if we have a directional scroll prefer the snap point that is in the scroll direction.
>+    return velocity < 0 ? *previous : *next;
>+}
>+
>+
>+template <> template <>
>+std::pair<LayoutUnit, unsigned> LayoutScrollSnapOffsetsInfo::closestSnapOffset(ScrollEventAxis axis, const LayoutSize& viewportSize, LayoutUnit scrollDestinationOffset, float velocity, Optional<LayoutUnit> originalOffsetForDirectionalSnapping) const
>+{
>+    return calculateClosestSnapOffset<LayoutUnit, LayoutRect, LayoutSize>(*this, axis, viewportSize, scrollDestinationOffset, velocity, originalOffsetForDirectionalSnapping);
>+}
>+
>+template <> template <>
>+std::pair<float, unsigned> FloatScrollSnapOffsetsInfo::closestSnapOffset(ScrollEventAxis axis, const FloatSize& viewportSize, float scrollDestinationOffset, float velocity, Optional<float> originalOffsetForDirectionalSnapping) const
> {
>-    return closestSnapOffsetWithOffsetsAndRanges(offsetsForAxis(axis), offsetRangesForAxis(axis), scrollDestinationOffset, velocity, originalPositionForDirectionalSnapping);
>+    return calculateClosestSnapOffset<float, FloatRect, FloatSize>(*this, axis, viewportSize, scrollDestinationOffset, velocity, originalOffsetForDirectionalSnapping);
> }
> 
> }
>diff --git a/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.h b/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.h
>index 20a647fea12c6cc8b55579c51bd0a3605fdce5e6..b992bafe077c762f52ee8d4b7b4d01d304744fd4 100644
>--- a/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.h
>+++ b/Source/WebCore/page/scrolling/ScrollSnapOffsetsInfo.h
>@@ -27,6 +27,10 @@
> 
> #if ENABLE(CSS_SCROLL_SNAP)
> 
>+#include "FloatRect.h"
>+#include "FloatSize.h"
>+#include "LayoutRect.h"
>+#include "LayoutSize.h"
> #include "LayoutUnit.h"
> #include "ScrollTypes.h"
> #include "StyleScrollSnapPoints.h"
>@@ -35,39 +39,29 @@
> 
> namespace WebCore {
> 
>-class LayoutRect;
> class ScrollableArea;
> class RenderBox;
> class RenderStyle;
> 
>-template <typename T>
>+template <typename OffsetType>
> struct SnapOffset {
>-    T offset;
>+    OffsetType offset;
>     ScrollSnapStop stop;
>+    unsigned snapAreaIndex;
> };
> 
>-template <typename T>
>-struct ScrollOffsetRange {
>-    T start;
>-    T end;
>-};
>-
>-template <typename T>
>+template <typename OffsetType, typename RectType>
> struct ScrollSnapOffsetsInfo {
>     WTF_MAKE_STRUCT_FAST_ALLOCATED;
>-    Vector<SnapOffset<T>> horizontalSnapOffsets;
>-    Vector<SnapOffset<T>> verticalSnapOffsets;
>+    ScrollSnapStrictness strictness;
> 
>-    // Snap offset ranges represent non-empty ranges of scroll offsets in which scrolling may rest after scroll snapping.
>-    // These are used in two cases: (1) for proximity scroll snapping, where portions of areas between adjacent snap offsets
>-    // may emit snap offset ranges, and (2) in the case where the snap area is larger than the snap port, in which case areas
>-    // where the snap port fits within the snap area are considered to be valid snap positions.
>-    Vector<ScrollOffsetRange<T>> horizontalSnapOffsetRanges;
>-    Vector<ScrollOffsetRange<T>> verticalSnapOffsetRanges;
>+    Vector<SnapOffset<OffsetType>> horizontalSnapOffsets;
>+    Vector<SnapOffset<OffsetType>> verticalSnapOffsets;
>+    Vector<RectType> snapAreas;
> 
>-    bool isEqual(const ScrollSnapOffsetsInfo<T>& other) const
>+    bool isEqual(const ScrollSnapOffsetsInfo<OffsetType, RectType>& other) const
>     {
>-        return horizontalSnapOffsets == other.horizontalSnapOffsets && verticalSnapOffsets == other.verticalSnapOffsets && horizontalSnapOffsetRanges == other.horizontalSnapOffsetRanges && verticalSnapOffsetRanges == other.verticalSnapOffsetRanges;
>+        return strictness == other.strictness && horizontalSnapOffsets == other.horizontalSnapOffsets && verticalSnapOffsets == other.verticalSnapOffsets && snapAreas == other.snapAreas;
>     }
> 
>     bool isEmpty() const
>@@ -75,29 +69,27 @@ struct ScrollSnapOffsetsInfo {
>         return horizontalSnapOffsets.isEmpty() && verticalSnapOffsets.isEmpty();
>     }
> 
>-    Vector<SnapOffset<T>> offsetsForAxis(ScrollEventAxis axis) const
>+    Vector<SnapOffset<OffsetType>> offsetsForAxis(ScrollEventAxis axis) const
>     {
>         return axis == ScrollEventAxis::Vertical ? verticalSnapOffsets : horizontalSnapOffsets;
>     }
> 
>-    Vector<ScrollOffsetRange<T>> offsetRangesForAxis(ScrollEventAxis axis) const
>-    {
>-        return axis == ScrollEventAxis::Vertical ? verticalSnapOffsetRanges : horizontalSnapOffsetRanges;
>-    }
>-
>-    template<typename OutputType> ScrollSnapOffsetsInfo<OutputType> convertUnits(float deviceScaleFactor = 0.0) const;
>-    WEBCORE_EXPORT std::pair<T, unsigned> closestSnapOffset(ScrollEventAxis, T scrollDestinationOffset, float velocity, Optional<T> originalPositionForDirectionalSnapping = WTF::nullopt) const;
>+    template<typename OutputType, typename OutputRectType> ScrollSnapOffsetsInfo<OutputType, OutputRectType> convertUnits(float deviceScaleFactor = 0.0) const;
>+    template<typename SizeType> WEBCORE_EXPORT std::pair<OffsetType, unsigned> closestSnapOffset(ScrollEventAxis, const SizeType& viewportSize, OffsetType scrollDestinationOffset, float velocity, Optional<OffsetType> originalPositionForDirectionalSnapping = WTF::nullopt) const;
> };
> 
>+using LayoutScrollSnapOffsetsInfo = ScrollSnapOffsetsInfo<LayoutUnit, LayoutRect>;
>+using FloatScrollSnapOffsetsInfo = ScrollSnapOffsetsInfo<float, FloatRect>;
>+
> template <> template <>
>-ScrollSnapOffsetsInfo<LayoutUnit> ScrollSnapOffsetsInfo<float>::convertUnits(float /* unusedScaleFactor */) const;
>-template <>
>-WEBCORE_EXPORT std::pair<float, unsigned> ScrollSnapOffsetsInfo<float>::closestSnapOffset(ScrollEventAxis, float scrollDestinationOffset, float velocity, Optional<float> originalPositionForDirectionalSnapping) const;
>+LayoutScrollSnapOffsetsInfo FloatScrollSnapOffsetsInfo::convertUnits(float /* unusedScaleFactor */) const;
>+template <> template <>
>+WEBCORE_EXPORT std::pair<float, unsigned> FloatScrollSnapOffsetsInfo::closestSnapOffset(ScrollEventAxis, const FloatSize& viewportSize, float scrollDestinationOffset, float velocity, Optional<float> originalPositionForDirectionalSnapping) const;
> 
> template <> template <>
>-ScrollSnapOffsetsInfo<float> ScrollSnapOffsetsInfo<LayoutUnit>::convertUnits(float deviceScaleFactor) const;
>-template <>
>-WEBCORE_EXPORT std::pair<LayoutUnit, unsigned> ScrollSnapOffsetsInfo<LayoutUnit>::closestSnapOffset(ScrollEventAxis, LayoutUnit scrollDestinationOffset, float velocity, Optional<LayoutUnit> originalPositionForDirectionalSnapping) const;
>+FloatScrollSnapOffsetsInfo LayoutScrollSnapOffsetsInfo::convertUnits(float deviceScaleFactor) const;
>+template <> template <>
>+WEBCORE_EXPORT std::pair<LayoutUnit, unsigned> LayoutScrollSnapOffsetsInfo::closestSnapOffset(ScrollEventAxis, const LayoutSize& viewportSize, LayoutUnit scrollDestinationOffset, float velocity, Optional<LayoutUnit> originalPositionForDirectionalSnapping) const;
> 
> const unsigned invalidSnapOffsetIndex = UINT_MAX;
> 
>@@ -106,7 +98,7 @@ const unsigned invalidSnapOffsetIndex = UINT_MAX;
> // the scrolling container's border box.
> void updateSnapOffsetsForScrollableArea(ScrollableArea&, const RenderBox& scrollingElementBox, const RenderStyle& scrollingElementStyle, LayoutRect viewportRectInBorderBoxCoordinates);
> 
>-template <typename T> WTF::TextStream& operator<<(WTF::TextStream& ts, SnapOffset<T> offset)
>+template <typename OffsetType> WTF::TextStream& operator<<(WTF::TextStream& ts, SnapOffset<OffsetType> offset)
> {
>     ts << offset.offset;
>     if (offset.stop == ScrollSnapStop::Always)
>@@ -114,13 +106,6 @@ template <typename T> WTF::TextStream& operator<<(WTF::TextStream& ts, SnapOffse
>     return ts;
> }
> 
>-template<typename T>
>-TextStream& operator<<(TextStream& ts, const ScrollOffsetRange<T>& range)
>-{
>-    ts << "start: " << range.start << " end: " << range.end;
>-    return ts;
>-}
>-
> }; // namespace WebCore
> 
> #endif // ENABLE(CSS_SCROLL_SNAP)
>diff --git a/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp b/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp
>index f40819afe3cefd3481806f41799e9059875f80e1..8432881c89f16c57b4674c24bb4a98386d7ac923 100644
>--- a/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp
>+++ b/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.cpp
>@@ -157,7 +157,7 @@ void ScrollingStateScrollingNode::setScrollOrigin(const IntPoint& scrollOrigin)
> }
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-void ScrollingStateScrollingNode::setSnapOffsetsInfo(const ScrollSnapOffsetsInfo<float>& info)
>+void ScrollingStateScrollingNode::setSnapOffsetsInfo(const FloatScrollSnapOffsetsInfo& info)
> {
>     if (m_snapOffsetsInfo.isEqual(info))
>         return;
>diff --git a/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h b/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h
>index bd4e97b9c5efdf9129def8b6bb230d37b4164044..c5d7639cf1cae0c7e037fc3599f22581baadabe8 100644
>--- a/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h
>+++ b/Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h
>@@ -71,8 +71,8 @@ public:
>     WEBCORE_EXPORT void setScrollOrigin(const IntPoint&);
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-    const ScrollSnapOffsetsInfo<float>& snapOffsetsInfo() const { return m_snapOffsetsInfo; }
>-    WEBCORE_EXPORT void setSnapOffsetsInfo(const ScrollSnapOffsetsInfo<float>& newOffsetsInfo);
>+    const FloatScrollSnapOffsetsInfo& snapOffsetsInfo() const { return m_snapOffsetsInfo; }
>+    WEBCORE_EXPORT void setSnapOffsetsInfo(const FloatScrollSnapOffsetsInfo& newOffsetsInfo);
> 
>     unsigned currentHorizontalSnapPointIndex() const { return m_currentHorizontalSnapPointIndex; }
>     WEBCORE_EXPORT void setCurrentHorizontalSnapPointIndex(unsigned);
>@@ -130,7 +130,7 @@ private:
>     IntPoint m_scrollOrigin;
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-    ScrollSnapOffsetsInfo<float> m_snapOffsetsInfo;
>+    FloatScrollSnapOffsetsInfo m_snapOffsetsInfo;
>     unsigned m_currentHorizontalSnapPointIndex { 0 };
>     unsigned m_currentVerticalSnapPointIndex { 0 };
> #endif
>diff --git a/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.cpp b/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.cpp
>index 130e73edbc28c0828831a58c22f3c51ce67d10e7..8b634e1ad64f2419bf2ba908431c837c97d6f45c 100644
>--- a/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.cpp
>+++ b/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.cpp
>@@ -327,7 +327,7 @@ void ScrollingTreeScrollingNode::dumpProperties(TextStream& ts, ScrollingStateTr
> }
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-const ScrollSnapOffsetsInfo<float>& ScrollingTreeScrollingNode::snapOffsetsInfo() const
>+const FloatScrollSnapOffsetsInfo& ScrollingTreeScrollingNode::snapOffsetsInfo() const
> {
>     return m_snapOffsetsInfo;
> }
>diff --git a/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.h b/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.h
>index be49d0b125f01b71ed6d8bcae4f6e27750c384b6..55bced3e0e612106d93f852eef7d464210525438 100644
>--- a/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.h
>+++ b/Source/WebCore/page/scrolling/ScrollingTreeScrollingNode.h
>@@ -95,7 +95,7 @@ public:
>     bool canHaveScrollbars() const { return m_scrollableAreaParameters.horizontalScrollbarMode != ScrollbarAlwaysOff || m_scrollableAreaParameters.verticalScrollbarMode != ScrollbarAlwaysOff; }
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-    const ScrollSnapOffsetsInfo<float>& snapOffsetsInfo() const;
>+    const FloatScrollSnapOffsetsInfo& snapOffsetsInfo() const;
>     unsigned currentHorizontalSnapPointIndex() const { return m_currentHorizontalSnapPointIndex; }
>     unsigned currentVerticalSnapPointIndex() const { return m_currentVerticalSnapPointIndex; }
>     void setCurrentHorizontalSnapPointIndex(unsigned index) { m_currentHorizontalSnapPointIndex = index; }
>@@ -159,7 +159,7 @@ private:
>     FloatPoint m_currentScrollPosition;
>     IntPoint m_scrollOrigin;
> #if ENABLE(CSS_SCROLL_SNAP)
>-    ScrollSnapOffsetsInfo<float> m_snapOffsetsInfo;
>+    FloatScrollSnapOffsetsInfo m_snapOffsetsInfo;
>     unsigned m_currentHorizontalSnapPointIndex { 0 };
>     unsigned m_currentVerticalSnapPointIndex { 0 };
> #endif
>diff --git a/Source/WebCore/page/scrolling/mac/ScrollingTreeScrollingNodeDelegateMac.mm b/Source/WebCore/page/scrolling/mac/ScrollingTreeScrollingNodeDelegateMac.mm
>index a5b48c203415ab7b09ce9c3fa99c15ea63740e45..3e24574ab00eff45e0f8ca10f130851a81aea767 100644
>--- a/Source/WebCore/page/scrolling/mac/ScrollingTreeScrollingNodeDelegateMac.mm
>+++ b/Source/WebCore/page/scrolling/mac/ScrollingTreeScrollingNodeDelegateMac.mm
>@@ -65,7 +65,7 @@ void ScrollingTreeScrollingNodeDelegateMac::updateFromStateNode(const ScrollingS
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>     if (scrollingStateNode.hasChangedProperty(ScrollingStateNode::Property::SnapOffsetsInfo))
>-        m_scrollController.updateScrollSnapPoints(scrollingStateNode.snapOffsetsInfo().convertUnits<LayoutUnit>());
>+        m_scrollController.updateScrollSnapPoints(scrollingStateNode.snapOffsetsInfo().convertUnits<LayoutUnit, LayoutRect>());
> 
>     if (scrollingStateNode.hasChangedProperty(ScrollingStateNode::Property::CurrentHorizontalSnapOffsetIndex))
>         m_scrollController.setActiveScrollSnapIndexForAxis(ScrollEventAxis::Horizontal, scrollingStateNode.currentHorizontalSnapPointIndex());
>diff --git a/Source/WebCore/platform/ScrollController.cpp b/Source/WebCore/platform/ScrollController.cpp
>index c3ec6c441d312f5852bbd6f2b490e27cb5e313ae..65500d10fef38107422e29fb99c056e06125db29 100644
>--- a/Source/WebCore/platform/ScrollController.cpp
>+++ b/Source/WebCore/platform/ScrollController.cpp
>@@ -67,7 +67,7 @@ void ScrollController::updateScrollSnapState(const ScrollableArea& scrollableAre
>     updateScrollSnapPoints(*snapOffsetInfo);
> }
> 
>-void ScrollController::updateScrollSnapPoints(const ScrollSnapOffsetsInfo<LayoutUnit>& snapOffsetInfo)
>+void ScrollController::updateScrollSnapPoints(const LayoutScrollSnapOffsetsInfo& snapOffsetInfo)
> {
>     if (snapOffsetInfo.isEmpty()) {
>         m_scrollSnapState = nullptr;
>@@ -115,8 +115,8 @@ void ScrollController::setNearestScrollSnapIndexForAxisAndOffset(ScrollEventAxis
>         return;
> 
>     LayoutUnit clampedOffset = std::min(std::max(LayoutUnit(offset / scaleFactor), snapOffsets.first().offset), snapOffsets.last().offset);
>-
>-    unsigned activeIndex = snapState.snapOffsetInfo().closestSnapOffset(axis, clampedOffset, 0).second;
>+    LayoutSize viewportSize(m_client.viewportSize().width(), m_client.viewportSize().height());
>+    unsigned activeIndex = snapState.snapOffsetInfo().closestSnapOffset(axis, viewportSize, clampedOffset, 0).second;
>     if (activeIndex == activeScrollSnapIndexForAxis(axis))
>         return;
> 
>@@ -137,7 +137,9 @@ float ScrollController::adjustScrollDestination(ScrollEventAxis axis, float dest
>     Optional<LayoutUnit> originalOffsetInLayoutUnits;
>     if (originalOffset.hasValue())
>         originalOffsetInLayoutUnits = LayoutUnit(*originalOffset / m_client.pageScaleFactor());
>-    LayoutUnit offset = snapState.snapOffsetInfo().closestSnapOffset(axis, LayoutUnit(destinationOffset / m_client.pageScaleFactor()), velocity, originalOffsetInLayoutUnits).first;
>+
>+    LayoutSize viewportSize(m_client.viewportSize().width(), m_client.viewportSize().height());
>+    LayoutUnit offset = snapState.snapOffsetInfo().closestSnapOffset(axis, viewportSize, LayoutUnit(destinationOffset / m_client.pageScaleFactor()), velocity, originalOffsetInLayoutUnits).first;
>     return offset * m_client.pageScaleFactor();
> }
> 
>diff --git a/Source/WebCore/platform/ScrollController.h b/Source/WebCore/platform/ScrollController.h
>index d925fd45584c0111c9ef0c2891f7c7516610eb7b..dd53ada90a2f5f2908801023c3e5a3c431ef6162 100644
>--- a/Source/WebCore/platform/ScrollController.h
>+++ b/Source/WebCore/platform/ScrollController.h
>@@ -132,7 +132,7 @@ public:
>     void scrollPositionChanged();
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-    void updateScrollSnapPoints(const ScrollSnapOffsetsInfo<LayoutUnit>&);
>+    void updateScrollSnapPoints(const LayoutScrollSnapOffsetsInfo&);
>     void setActiveScrollSnapIndexForAxis(ScrollEventAxis, unsigned);
>     void setActiveScrollSnapIndicesForOffset(ScrollOffset);
>     bool activeScrollSnapIndexDidChange() const { return m_activeScrollSnapIndexDidChange; }
>diff --git a/Source/WebCore/platform/ScrollSnapAnimatorState.cpp b/Source/WebCore/platform/ScrollSnapAnimatorState.cpp
>index 7d68d50dde76e89096cd3e58f3fc391ffc67177c..1ee74167b81983f4702d836a6f97707724720915 100644
>--- a/Source/WebCore/platform/ScrollSnapAnimatorState.cpp
>+++ b/Source/WebCore/platform/ScrollSnapAnimatorState.cpp
>@@ -51,8 +51,8 @@ void ScrollSnapAnimatorState::setupAnimationForState(ScrollSnapState state, cons
> 
>     m_momentumCalculator = ScrollingMomentumCalculator::create(viewportSize, contentSize, initialOffset, initialDelta, initialVelocity);
>     auto predictedScrollTarget = m_momentumCalculator->predictedDestinationOffset();
>-    float targetOffsetX = targetOffsetForStartOffset(ScrollEventAxis::Horizontal, contentSize.width() - viewportSize.width(), initialOffset.x(), predictedScrollTarget.width(), pageScale, initialDelta.width(), m_activeSnapIndexX);
>-    float targetOffsetY = targetOffsetForStartOffset(ScrollEventAxis::Vertical, contentSize.height() - viewportSize.height(), initialOffset.y(), predictedScrollTarget.height(), pageScale, initialDelta.height(), m_activeSnapIndexY);
>+    float targetOffsetX = targetOffsetForStartOffset(ScrollEventAxis::Horizontal, viewportSize, contentSize.width() - viewportSize.width(), initialOffset.x(), predictedScrollTarget.width(), pageScale, initialDelta.width(), m_activeSnapIndexX);
>+    float targetOffsetY = targetOffsetForStartOffset(ScrollEventAxis::Vertical, viewportSize, contentSize.height() - viewportSize.height(), initialOffset.y(), predictedScrollTarget.height(), pageScale, initialDelta.height(), m_activeSnapIndexY);
>     m_momentumCalculator->setRetargetedScrollOffset({ targetOffsetX, targetOffsetY });
>     m_startTime = MonotonicTime::now();
>     m_currentState = state;
>@@ -91,10 +91,11 @@ FloatPoint ScrollSnapAnimatorState::currentAnimatedScrollOffset(bool& isAnimatio
>     return m_momentumCalculator->scrollOffsetAfterElapsedTime(elapsedTime);
> }
> 
>-float ScrollSnapAnimatorState::targetOffsetForStartOffset(ScrollEventAxis axis, float maxScrollOffset, float startOffset, float predictedOffset, float pageScale, float initialDelta, unsigned& outActiveSnapIndex) const
>+float ScrollSnapAnimatorState::targetOffsetForStartOffset(ScrollEventAxis axis, const FloatSize& viewportSize, float maxScrollOffset, float startOffset, float predictedOffset, float pageScale, float initialDelta, unsigned& outActiveSnapIndex) const
> {
>     LayoutUnit proposedOffset;
>-    std::tie(proposedOffset, outActiveSnapIndex) = m_snapOffsetsInfo.closestSnapOffset(axis, LayoutUnit(predictedOffset / pageScale), initialDelta);
>+    LayoutSize viewportLayoutSize(viewportSize.width(), viewportSize.height());
>+    std::tie(proposedOffset, outActiveSnapIndex) = m_snapOffsetsInfo.closestSnapOffset(axis, viewportLayoutSize, LayoutUnit(predictedOffset / pageScale), initialDelta);
>     if (outActiveSnapIndex != invalidSnapOffsetIndex)
>         return pageScale * proposedOffset;
>     return clampTo<float>(startOffset, 0, maxScrollOffset);
>@@ -105,11 +106,6 @@ TextStream& operator<<(TextStream& ts, const ScrollSnapAnimatorState& state)
>     ts << "ScrollSnapAnimatorState";
>     ts.dumpProperty("snap offsets x", state.snapOffsetsForAxis(ScrollEventAxis::Horizontal));
>     ts.dumpProperty("snap offsets y", state.snapOffsetsForAxis(ScrollEventAxis::Vertical));
>-    if (!state.snapOffsetRangesForAxis(ScrollEventAxis::Horizontal).isEmpty())
>-        ts.dumpProperty("snap offsets ranges x", state.snapOffsetRangesForAxis(ScrollEventAxis::Horizontal));
>-    if (!state.snapOffsetRangesForAxis(ScrollEventAxis::Vertical).isEmpty())
>-        ts.dumpProperty("snap offsets ranges y", state.snapOffsetRangesForAxis(ScrollEventAxis::Vertical));
>-
>     ts.dumpProperty("active snap index x", state.activeSnapIndexForAxis(ScrollEventAxis::Horizontal));
>     ts.dumpProperty("active snap index y", state.activeSnapIndexForAxis(ScrollEventAxis::Vertical));
> 
>diff --git a/Source/WebCore/platform/ScrollSnapAnimatorState.h b/Source/WebCore/platform/ScrollSnapAnimatorState.h
>index 3feb1ac3b59aaee44c639b4aff0c242695821499..6b6d2275cfa345b9a2b6a69ea8189d665d614cdc 100644
>--- a/Source/WebCore/platform/ScrollSnapAnimatorState.h
>+++ b/Source/WebCore/platform/ScrollSnapAnimatorState.h
>@@ -57,24 +57,8 @@ public:
>         return axis == ScrollEventAxis::Horizontal ? m_snapOffsetsInfo.horizontalSnapOffsets : m_snapOffsetsInfo.verticalSnapOffsets;
>     }
> 
>-    const Vector<ScrollOffsetRange<LayoutUnit>>& snapOffsetRangesForAxis(ScrollEventAxis axis) const
>-    {
>-        return axis == ScrollEventAxis::Horizontal ? m_snapOffsetsInfo.horizontalSnapOffsetRanges : m_snapOffsetsInfo.verticalSnapOffsetRanges;
>-    }
>-
>-    const ScrollSnapOffsetsInfo<LayoutUnit>& snapOffsetInfo() const { return m_snapOffsetsInfo; }
>-    void setSnapOffsetInfo(const ScrollSnapOffsetsInfo<LayoutUnit>& newInfo) { m_snapOffsetsInfo = newInfo; }
>-
>-    void setSnapOffsetsAndPositionRangesForAxis(ScrollEventAxis axis, const Vector<SnapOffset<LayoutUnit>>& snapOffsets, const Vector<ScrollOffsetRange<LayoutUnit>>& snapOffsetRanges)
>-    {
>-        if (axis == ScrollEventAxis::Horizontal) {
>-            m_snapOffsetsInfo.horizontalSnapOffsets = snapOffsets;
>-            m_snapOffsetsInfo.horizontalSnapOffsetRanges = snapOffsetRanges;
>-        } else {
>-            m_snapOffsetsInfo.verticalSnapOffsets = snapOffsets;
>-            m_snapOffsetsInfo.verticalSnapOffsetRanges = snapOffsetRanges;
>-        }
>-    }
>+    const LayoutScrollSnapOffsetsInfo& snapOffsetInfo() const { return m_snapOffsetsInfo; }
>+    void setSnapOffsetInfo(const LayoutScrollSnapOffsetsInfo& newInfo) { m_snapOffsetsInfo = newInfo; }
> 
>     ScrollSnapState currentState() const { return m_currentState; }
> 
>@@ -100,13 +84,13 @@ public:
>     void transitionToDestinationReachedState();
> 
> private:
>-    float targetOffsetForStartOffset(ScrollEventAxis, float maxScrollOffset, float startOffset, float predictedOffset, float pageScale, float initialDelta, unsigned& outActiveSnapIndex) const;
>+    float targetOffsetForStartOffset(ScrollEventAxis, const FloatSize& viewportSize, float maxScrollOffset, float startOffset, float predictedOffset, float pageScale, float initialDelta, unsigned& outActiveSnapIndex) const;
>     void teardownAnimationForState(ScrollSnapState);
>     void setupAnimationForState(ScrollSnapState, const FloatSize& contentSize, const FloatSize& viewportSize, float pageScale, const FloatPoint& initialOffset, const FloatSize& initialVelocity, const FloatSize& initialDelta);
> 
>     ScrollSnapState m_currentState { ScrollSnapState::UserInteraction };
> 
>-    ScrollSnapOffsetsInfo<LayoutUnit> m_snapOffsetsInfo;
>+    LayoutScrollSnapOffsetsInfo m_snapOffsetsInfo;
> 
>     unsigned m_activeSnapIndexX { 0 };
>     unsigned m_activeSnapIndexY { 0 };
>diff --git a/Source/WebCore/platform/ScrollableArea.cpp b/Source/WebCore/platform/ScrollableArea.cpp
>index 79f9e98098a8ddca2b49ce977d2143e1cb6caf85..132aea289e097722693d12ce07006a5916961f6b 100644
>--- a/Source/WebCore/platform/ScrollableArea.cpp
>+++ b/Source/WebCore/platform/ScrollableArea.cpp
>@@ -479,19 +479,19 @@ String ScrollableArea::verticalScrollbarStateForTesting() const
> }
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-ScrollSnapOffsetsInfo<LayoutUnit>& ScrollableArea::ensureSnapOffsetsInfo()
>+LayoutScrollSnapOffsetsInfo& ScrollableArea::ensureSnapOffsetsInfo()
> {
>     if (!m_snapOffsetsInfo)
>-        m_snapOffsetsInfo = makeUnique<ScrollSnapOffsetsInfo<LayoutUnit>>();
>+        m_snapOffsetsInfo = makeUnique<LayoutScrollSnapOffsetsInfo>();
>     return *m_snapOffsetsInfo;
> }
> 
>-const ScrollSnapOffsetsInfo<LayoutUnit>* ScrollableArea::snapOffsetInfo() const
>+const LayoutScrollSnapOffsetsInfo* ScrollableArea::snapOffsetInfo() const
> {
>     return m_snapOffsetsInfo.get();
> }
> 
>-void ScrollableArea::setScrollSnapOffsetInfo(const ScrollSnapOffsetsInfo<LayoutUnit>& info)
>+void ScrollableArea::setScrollSnapOffsetInfo(const LayoutScrollSnapOffsetsInfo& info)
> {
>     if (info.isEmpty()) {
>         clearSnapOffsets();
>diff --git a/Source/WebCore/platform/ScrollableArea.h b/Source/WebCore/platform/ScrollableArea.h
>index 7eb7b540282840ab7b5f31fdfa6b2bfd58eb19dc..3587179cdb7f679398a7c877312ed497c16fe8d9 100644
>--- a/Source/WebCore/platform/ScrollableArea.h
>+++ b/Source/WebCore/platform/ScrollableArea.h
>@@ -91,9 +91,9 @@ public:
>     bool usesScrollSnap() const;
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-    WEBCORE_EXPORT const ScrollSnapOffsetsInfo<LayoutUnit>* snapOffsetInfo() const;
>+    WEBCORE_EXPORT const LayoutScrollSnapOffsetsInfo* snapOffsetInfo() const;
>     virtual void updateSnapOffsets() { };
>-    void setScrollSnapOffsetInfo(const ScrollSnapOffsetsInfo<LayoutUnit>&);
>+    void setScrollSnapOffsetInfo(const LayoutScrollSnapOffsetsInfo&);
>     void clearSnapOffsets();
>     unsigned currentHorizontalSnapPointIndex() const { return m_currentHorizontalSnapPointIndex; }
>     void setCurrentHorizontalSnapPointIndex(unsigned index) { m_currentHorizontalSnapPointIndex = index; }
>@@ -385,8 +385,8 @@ private:
>     mutable std::unique_ptr<ScrollAnimator> m_scrollAnimator;
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-    ScrollSnapOffsetsInfo<LayoutUnit>& ensureSnapOffsetsInfo();
>-    std::unique_ptr<ScrollSnapOffsetsInfo<LayoutUnit>> m_snapOffsetsInfo;
>+    LayoutScrollSnapOffsetsInfo& ensureSnapOffsetsInfo();
>+    std::unique_ptr<LayoutScrollSnapOffsetsInfo> m_snapOffsetsInfo;
>     unsigned m_currentHorizontalSnapPointIndex { 0 };
>     unsigned m_currentVerticalSnapPointIndex { 0 };
> #endif
>diff --git a/Source/WebCore/platform/mac/ScrollAnimatorMac.mm b/Source/WebCore/platform/mac/ScrollAnimatorMac.mm
>index c095cd66f5956f8b89aacb33d5b7f80230a9a7b5..d4521d658c33fad6e396f61a807e98533198bfb3 100644
>--- a/Source/WebCore/platform/mac/ScrollAnimatorMac.mm
>+++ b/Source/WebCore/platform/mac/ScrollAnimatorMac.mm
>@@ -1278,7 +1278,7 @@ bool ScrollAnimatorMac::isPinnedForScrollDelta(const FloatSize& delta) const
> }
> 
> #if ENABLE(CSS_SCROLL_SNAP)
>-static bool gestureShouldBeginSnap(const PlatformWheelEvent& wheelEvent, ScrollEventAxis axis, const ScrollSnapOffsetsInfo<LayoutUnit>* offsetInfo)
>+static bool gestureShouldBeginSnap(const PlatformWheelEvent& wheelEvent, ScrollEventAxis axis, const LayoutScrollSnapOffsetsInfo* offsetInfo)
> {
>     if (!offsetInfo)
>         return false;
>diff --git a/Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp b/Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp
>index 3e380fd145d7225bac057330c19d6ca88a0e0cd2..1c821eeb7cdbb14e03aa4d4845ba412589ed681e 100644
>--- a/Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp
>+++ b/Source/WebKit/Shared/RemoteLayerTree/RemoteScrollingCoordinatorTransaction.cpp
>@@ -98,9 +98,9 @@ template<> struct ArgumentCoder<RequestedScrollData> {
>     static WARN_UNUSED_RETURN bool decode(Decoder&, RequestedScrollData&);
> };
> 
>-template<> struct ArgumentCoder<ScrollSnapOffsetsInfo<float>> {
>-    static void encode(Encoder&, const ScrollSnapOffsetsInfo<float>&);
>-    static WARN_UNUSED_RETURN bool decode(Decoder&, ScrollSnapOffsetsInfo<float>&);
>+template<> struct ArgumentCoder<FloatScrollSnapOffsetsInfo> {
>+    static void encode(Encoder&, const FloatScrollSnapOffsetsInfo&);
>+    static WARN_UNUSED_RETURN bool decode(Decoder&, FloatScrollSnapOffsetsInfo&);
> };
> 
> template<> struct ArgumentCoder<SnapOffset<float>> {
>@@ -311,7 +311,7 @@ bool ArgumentCoder<ScrollingStateScrollingNode>::decode(Decoder& decoder, Scroll
>     SCROLLING_NODE_DECODE(ScrollingStateNode::Property::ScrollPosition, FloatPoint, setScrollPosition);
>     SCROLLING_NODE_DECODE(ScrollingStateNode::Property::ScrollOrigin, IntPoint, setScrollOrigin);
> #if ENABLE(CSS_SCROLL_SNAP)
>-    SCROLLING_NODE_DECODE(ScrollingStateNode::Property::SnapOffsetsInfo, ScrollSnapOffsetsInfo<float>, setSnapOffsetsInfo);
>+    SCROLLING_NODE_DECODE(ScrollingStateNode::Property::SnapOffsetsInfo, FloatScrollSnapOffsetsInfo, setSnapOffsetsInfo);
>     SCROLLING_NODE_DECODE(ScrollingStateNode::Property::CurrentHorizontalSnapOffsetIndex, unsigned, setCurrentHorizontalSnapPointIndex);
>     SCROLLING_NODE_DECODE(ScrollingStateNode::Property::CurrentVerticalSnapOffsetIndex, unsigned, setCurrentVerticalSnapPointIndex);
> #endif
>@@ -532,6 +532,7 @@ void ArgumentCoder<SnapOffset<float>>::encode(Encoder& encoder, const SnapOffset
> {
>     encoder << offset.offset;
>     encoder << offset.stop;
>+    encoder << offset.snapAreaIndex;
> }
> 
> bool ArgumentCoder<SnapOffset<float>>::decode(Decoder& decoder, SnapOffset<float>& offset)
>@@ -540,27 +541,26 @@ bool ArgumentCoder<SnapOffset<float>>::decode(Decoder& decoder, SnapOffset<float
>         return false;
>     if (!decoder.decode(offset.stop))
>         return false;
>+    if (!decoder.decode(offset.snapAreaIndex))
>+        return false;
>     return true;
> }
> 
> 
>-void ArgumentCoder<ScrollSnapOffsetsInfo<float>>::encode(Encoder& encoder, const ScrollSnapOffsetsInfo<float>& info)
>+void ArgumentCoder<FloatScrollSnapOffsetsInfo>::encode(Encoder& encoder, const FloatScrollSnapOffsetsInfo& info)
> {
>     encoder << info.horizontalSnapOffsets;
>     encoder << info.verticalSnapOffsets;
>-    encoder << info.horizontalSnapOffsetRanges;
>-    encoder << info.verticalSnapOffsetRanges;
>+    encoder << info.snapAreas;
> }
> 
>-bool ArgumentCoder<ScrollSnapOffsetsInfo<float>>::decode(Decoder& decoder, ScrollSnapOffsetsInfo<float>& info)
>+bool ArgumentCoder<FloatScrollSnapOffsetsInfo>::decode(Decoder& decoder, FloatScrollSnapOffsetsInfo& info)
> {
>     if (!decoder.decode(info.horizontalSnapOffsets))
>         return false;
>     if (!decoder.decode(info.verticalSnapOffsets))
>         return false;
>-    if (!decoder.decode(info.horizontalSnapOffsetRanges))
>-        return false;
>-    if (!decoder.decode(info.verticalSnapOffsetRanges))
>+    if (!decoder.decode(info.snapAreas))
>         return false;
>     return true;
> }
>diff --git a/Source/WebKit/Shared/WebCoreArgumentCoders.cpp b/Source/WebKit/Shared/WebCoreArgumentCoders.cpp
>index 38dd9d31e6c7cf794956e7730b107de4947a4b87..87e4d460ee3e41cc7986964c31485ed356f0d7b5 100644
>--- a/Source/WebKit/Shared/WebCoreArgumentCoders.cpp
>+++ b/Source/WebKit/Shared/WebCoreArgumentCoders.cpp
>@@ -2805,32 +2805,6 @@ bool ArgumentCoder<ServiceWorkerOrClientIdentifier>::decode(Decoder& decoder, Se
> }
> #endif
> 
>-#if ENABLE(CSS_SCROLL_SNAP)
>-
>-void ArgumentCoder<ScrollOffsetRange<float>>::encode(Encoder& encoder, const ScrollOffsetRange<float>& range)
>-{
>-    encoder << range.start;
>-    encoder << range.end;
>-}
>-
>-auto ArgumentCoder<ScrollOffsetRange<float>>::decode(Decoder& decoder) -> Optional<WebCore::ScrollOffsetRange<float>>
>-{
>-    WebCore::ScrollOffsetRange<float> range;
>-    float start;
>-    if (!decoder.decode(start))
>-        return WTF::nullopt;
>-
>-    float end;
>-    if (!decoder.decode(end))
>-        return WTF::nullopt;
>-
>-    range.start = start;
>-    range.end = end;
>-    return range;
>-}
>-
>-#endif
>-
> void ArgumentCoder<MediaSelectionOption>::encode(Encoder& encoder, const MediaSelectionOption& option)
> {
>     encoder << option.displayName;
>diff --git a/Source/WebKit/Shared/WebCoreArgumentCoders.h b/Source/WebKit/Shared/WebCoreArgumentCoders.h
>index 928da7560c3e89bd41d518a6b62e54e8a4eef5a8..e3ebd33c0e69cc234f1c6d5814e7b4779fa66f66 100644
>--- a/Source/WebKit/Shared/WebCoreArgumentCoders.h
>+++ b/Source/WebKit/Shared/WebCoreArgumentCoders.h
>@@ -743,15 +743,6 @@ template<> struct ArgumentCoder<WebCore::ServiceWorkerOrClientIdentifier> {
> 
> #endif
> 
>-#if ENABLE(CSS_SCROLL_SNAP)
>-
>-template<> struct ArgumentCoder<WebCore::ScrollOffsetRange<float>> {
>-    static void encode(Encoder&, const WebCore::ScrollOffsetRange<float>&);
>-    static Optional<WebCore::ScrollOffsetRange<float>> decode(Decoder&);
>-};
>-
>-#endif
>-
> template<> struct ArgumentCoder<WebCore::MediaSelectionOption> {
>     static void encode(Encoder&, const WebCore::MediaSelectionOption&);
>     static Optional<WebCore::MediaSelectionOption> decode(Decoder&);
>diff --git a/Source/WebKit/UIProcess/RemoteLayerTree/ios/RemoteScrollingCoordinatorProxyIOS.mm b/Source/WebKit/UIProcess/RemoteLayerTree/ios/RemoteScrollingCoordinatorProxyIOS.mm
>index 11675f3245ba11ac398fdba2fce363babf0aa454..0464108fd8fad48b2bd4e38f80f9c6b2a5802935 100644
>--- a/Source/WebKit/UIProcess/RemoteLayerTree/ios/RemoteScrollingCoordinatorProxyIOS.mm
>+++ b/Source/WebKit/UIProcess/RemoteLayerTree/ios/RemoteScrollingCoordinatorProxyIOS.mm
>@@ -223,14 +223,12 @@ bool RemoteScrollingCoordinatorProxy::shouldSnapForMainFrameScrolling(ScrollEven
> 
> float RemoteScrollingCoordinatorProxy::closestSnapOffsetForMainFrameScrolling(ScrollEventAxis axis, float scrollDestination, float velocity, unsigned& currentIndex) const
> {
>-    ScrollingTreeNode* root = m_scrollingTree->rootNode();
>-    ASSERT(root && root->isFrameScrollingNode());
>-    ScrollingTreeFrameScrollingNode* rootScrollingNode = static_cast<ScrollingTreeFrameScrollingNode*>(root);
>+    ScrollingTreeFrameScrollingNode* rootScrollingNode = m_scrollingTree->rootNode();
>     const auto& snapOffsetsInfo = rootScrollingNode->snapOffsetsInfo();
> 
>     float scaledScrollDestination = scrollDestination / m_webPageProxy.displayedContentScale();
>     float rawClosestSnapOffset;
>-    std::tie(rawClosestSnapOffset, currentIndex) = snapOffsetsInfo.closestSnapOffset(axis, scaledScrollDestination, velocity);
>+    std::tie(rawClosestSnapOffset, currentIndex) = snapOffsetsInfo.closestSnapOffset(axis, rootScrollingNode->layoutViewport().size(), scaledScrollDestination, velocity);
>     return rawClosestSnapOffset * m_webPageProxy.displayedContentScale();
> }
> 
>diff --git a/Source/WebKit/UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm b/Source/WebKit/UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm
>index 880c03195f89c4bd13dd6a646523f1df84c9564e..8fc6615f76f3c9fad00f594b34b13dd44c923cd0 100644
>--- a/Source/WebKit/UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm
>+++ b/Source/WebKit/UIProcess/RemoteLayerTree/ios/ScrollingTreeScrollingNodeDelegateIOS.mm
>@@ -106,16 +106,17 @@ - (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoi
>     unsigned originalHorizontalSnapPosition = _scrollingTreeNodeDelegate->scrollingNode().currentHorizontalSnapPointIndex();
>     unsigned originalVerticalSnapPosition = _scrollingTreeNodeDelegate->scrollingNode().currentVerticalSnapPointIndex();
> 
>+    WebCore::FloatSize viewportSize(static_cast<float>(CGRectGetWidth([scrollView bounds])), static_cast<float>(CGRectGetHeight([scrollView bounds])));
>     const auto& snapOffsetsInfo = _scrollingTreeNodeDelegate->scrollingNode().snapOffsetsInfo();
>     if (!snapOffsetsInfo.horizontalSnapOffsets.isEmpty()) {
>-        auto [potentialSnapPosition, index] = snapOffsetsInfo.closestSnapOffset(WebCore::ScrollEventAxis::Horizontal, horizontalTarget, velocity.x);
>+        auto [potentialSnapPosition, index] = snapOffsetsInfo.closestSnapOffset(WebCore::ScrollEventAxis::Horizontal, viewportSize, horizontalTarget, velocity.x);
>         _scrollingTreeNodeDelegate->scrollingNode().setCurrentHorizontalSnapPointIndex(index);
>         if (horizontalTarget >= 0 && horizontalTarget <= scrollView.contentSize.width)
>             targetContentOffset->x = potentialSnapPosition;
>     }
> 
>     if (!snapOffsetsInfo.verticalSnapOffsets.isEmpty()) {
>-        auto [potentialSnapPosition, index] = snapOffsetsInfo.closestSnapOffset(WebCore::ScrollEventAxis::Vertical, verticalTarget, velocity.x);
>+        auto [potentialSnapPosition, index] = snapOffsetsInfo.closestSnapOffset(WebCore::ScrollEventAxis::Vertical, viewportSize, verticalTarget, velocity.x);
>         _scrollingTreeNodeDelegate->scrollingNode().setCurrentVerticalSnapPointIndex(index);
>         if (verticalTarget >= 0 && verticalTarget <= scrollView.contentSize.height)
>             targetContentOffset->y = potentialSnapPosition;
>diff --git a/LayoutTests/ChangeLog b/LayoutTests/ChangeLog
>index 7f8a9e0f6d6ac6c8e8c00551dbd63bbc05907c02..d494bece2667cba6cab2f7b970e4910cbcd10696 100644
>--- a/LayoutTests/ChangeLog
>+++ b/LayoutTests/ChangeLog
>@@ -1,3 +1,16 @@
>+2021-03-15  Martin Robinson  <mrobinson@webkit.org>
>+
>+        [css-scroll-snap] Properly handle overflowing snap areas
>+        https://bugs.webkit.org/show_bug.cgi?id=223175
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        * css3/scroll-snap/scroll-snap-click-scrollbar-gutter.html: This test used snap areas that
>+        overflow the snapport, thus meant that it relied on non-spec compliant behavior. Rework it so
>+        that the snap areas do not overflow, maintaining the existing behavior.
>+        * tiled-drawing/scrolling/scroll-snap/scroll-snap-mandatory-mainframe-vertical-then-horizontal.html: Ditto.
>+        * tiled-drawing/scrolling/scroll-snap/scroll-snap-proximity-overflow.html: Ditto.
>+
> 2021-03-14  Yusuke Suzuki  <ysuzuki@apple.com>
> 
>         Prevent dynamic import in service worker
>diff --git a/LayoutTests/imported/w3c/ChangeLog b/LayoutTests/imported/w3c/ChangeLog
>index 1ae326c3cb0b2c4ce35683b7d8a86e5d3db25e59..54738bbd1d95967c892094641593e9a3553acdea 100644
>--- a/LayoutTests/imported/w3c/ChangeLog
>+++ b/LayoutTests/imported/w3c/ChangeLog
>@@ -1,3 +1,13 @@
>+2021-03-15  Martin Robinson  <mrobinson@webkit.org>
>+
>+        [css-scroll-snap] Properly handle overflowing snap areas
>+        https://bugs.webkit.org/show_bug.cgi?id=223175
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        * web-platform-tests/css/css-scroll-snap/overflowing-snap-areas-expected.txt: Update expectations to
>+        show that this test is now passing.
>+
> 2021-03-10  Sergio Villar Senin  <svillar@igalia.com>
> 
>         Do not shrink radio buttons bellow its size
>diff --git a/LayoutTests/css3/scroll-snap/scroll-snap-click-scrollbar-gutter.html b/LayoutTests/css3/scroll-snap/scroll-snap-click-scrollbar-gutter.html
>index 7b3526cc4dd07d51c9ec93dc89d4902bf0bd4632..94da8be531bfdeb94205f7e8ec21261d1df86bf8 100644
>--- a/LayoutTests/css3/scroll-snap/scroll-snap-click-scrollbar-gutter.html
>+++ b/LayoutTests/css3/scroll-snap/scroll-snap-click-scrollbar-gutter.html
>@@ -34,21 +34,32 @@
>                 scroll-snap-type: both mandatory;
>             }
> 
>-            .block {
>-                height: 1000px;
>-                width: 250px;
>-                scroll-snap-align: start;
>-            }
>-
>             .horizontal-drawer {
>                 height: 100%;
>                 width: 2000px;
>             }
> 
>-            .horizontal-drawer .block {
>-                width: 1000px;
>-                height: 250px;
>+            .horizontal-drawer > div {
>+                float: left;
>+                width: 990px;
>+                height: 100%;
>+            }
>+
>+            .horizontal-drawer > div.snap-point {
>+                scroll-snap-align: start;
>+                width: 10px;
>+             }
>+
>+            #vertical-container > div {
>+                width: 100%;
>+                height: 990px;
>+            }
>+
>+            #vertical-container > div.snap-point {
>+                scroll-snap-align: start;
>+                height: 10px;
>             }
>+
>         </style>
>         <script src="../../resources/js-test.js"></script>
>         <script src="../../resources/ui-helper.js"></script>
>@@ -87,13 +98,17 @@
>     <body onload="onLoad();">
>         <div id="horizontal-container" class="container">
>             <div class="horizontal-drawer">
>-                <div class="block" style="float: left; background: #80475E"></div>
>-                <div class="block" style="width: 450px; float: left; background: #CC5A71"></div>
>+                <div class="snap-point" style="background: #80475E"></div>
>+                <div></div>
>+                <div class="snap-point" style="background: #CC5A71"></div>
>+                <div></div>
>             </div>
>         </div>
>         <div id="vertical-container" class="container">
>-            <div class="block" style="background: #80475E"></div>
>-            <div class="block" style="height: 450px; background: #CC5A71"></div>
>+            <div class="snap-point" style="background: #80475E"></div>
>+            <div></div>
>+            <div class="snap-point" style="background: #CC5A71"></div>
>+            <div></div>
>         </div>
>         <p id="console"></p>
>         <script>
>diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/overflowing-snap-areas-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/overflowing-snap-areas-expected.txt
>index a45d2adcddf6cf03df39863c36365933b88e281e..259cd980c549a058a08fffa7f24321f6ac583227 100644
>--- a/LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/overflowing-snap-areas-expected.txt
>+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-scroll-snap/overflowing-snap-areas-expected.txt
>@@ -1,13 +1,13 @@
> 
> PASS Snaps to the snap position if the snap area doesn't cover the snapport on x.
>-FAIL Snaps to the snap position if the snap area covers the snapport on x on the right border. assert_equals: expected 2715 but got 200
>-FAIL Snaps to the snap position if the snap area covers the snapport on x on the left border. assert_equals: expected 200 but got 2715
>+PASS Snaps to the snap position if the snap area covers the snapport on x on the right border.
>+PASS Snaps to the snap position if the snap area covers the snapport on x on the left border.
> PASS Snaps if the distance between the previous(400) and next(800) snap positions is smaller than snapport(500) on x.
> PASS Snaps if the distance between the previous(400) and next(800) snap positions is smaller than snapport(500) on y.
>-FAIL Snap to current scroll position which is a valid snap position, as the snap area covers snapport on x and the distance between the previous(800) and next(1400) is larger than snapport(500). assert_equals: expected 900 but got 800
>-FAIL Snap to current scroll position which is a valid snap position, as the snap area covers snapport on y and the distance between the previous(800) and next(1400) is larger than snapport(500). assert_equals: expected 900 but got 800
>-FAIL Snap to current scroll position which is a valid snap position, as the snap area covers snapport on x and there is no subsequent snap positions. assert_equals: expected 1500 but got 1400
>-FAIL Snap to current scroll position which is a valid snap position, as the snap area covers snapport on y and there is no subsequent snap positions. assert_equals: expected 1500 but got 1400
>-FAIL Don't snap back even if scrollTo tries to scroll to positions which are outside of the scroll range and if a snap target element covers the snaport assert_equals: expected 3715 but got 2200
>-FAIL Snap to current scroll position on x as the area is covering x axis.However, we snap to the specified snap position on y as the area is not covering y axis. assert_equals: expected 10 but got 0
>+PASS Snap to current scroll position which is a valid snap position, as the snap area covers snapport on x and the distance between the previous(800) and next(1400) is larger than snapport(500).
>+PASS Snap to current scroll position which is a valid snap position, as the snap area covers snapport on y and the distance between the previous(800) and next(1400) is larger than snapport(500).
>+PASS Snap to current scroll position which is a valid snap position, as the snap area covers snapport on x and there is no subsequent snap positions.
>+PASS Snap to current scroll position which is a valid snap position, as the snap area covers snapport on y and there is no subsequent snap positions.
>+PASS Don't snap back even if scrollTo tries to scroll to positions which are outside of the scroll range and if a snap target element covers the snaport
>+PASS Snap to current scroll position on x as the area is covering x axis.However, we snap to the specified snap position on y as the area is not covering y axis.
> 
>diff --git a/LayoutTests/tiled-drawing/scrolling/scroll-snap/scroll-snap-mandatory-mainframe-vertical-then-horizontal.html b/LayoutTests/tiled-drawing/scrolling/scroll-snap/scroll-snap-mandatory-mainframe-vertical-then-horizontal.html
>index 6427a114e48b26be65b55e7b868df8675691a9f8..94dad2168c60de915476b1d010a643d04fe920e7 100644
>--- a/LayoutTests/tiled-drawing/scrolling/scroll-snap/scroll-snap-mandatory-mainframe-vertical-then-horizontal.html
>+++ b/LayoutTests/tiled-drawing/scrolling/scroll-snap/scroll-snap-mandatory-mainframe-vertical-then-horizontal.html
>@@ -4,6 +4,7 @@
>         <style>
>             html {
>                 scroll-snap-type: y mandatory;
>+                margin: 0;
>             }
>             .verticalGallery {
>                 width: 100vw;
>@@ -12,7 +13,7 @@
>                 padding: 0;
>             }
>             .colorBox {
>-                height: 100vh;
>+                height: 90vh;
>                 width: 100vw;
>                 float: left;
>                 scroll-snap-align: start;
>diff --git a/LayoutTests/tiled-drawing/scrolling/scroll-snap/scroll-snap-proximity-overflow.html b/LayoutTests/tiled-drawing/scrolling/scroll-snap/scroll-snap-proximity-overflow.html
>index 5b052fdbf94c84a3d8e0d1a28fcb52202aef9f2f..1531e1e3ab225e502b3b720d1d061b8be30ff62c 100644
>--- a/LayoutTests/tiled-drawing/scrolling/scroll-snap/scroll-snap-proximity-overflow.html
>+++ b/LayoutTests/tiled-drawing/scrolling/scroll-snap/scroll-snap-proximity-overflow.html
>@@ -13,21 +13,16 @@
>                 position: absolute;
>                 top: 0;
>                 left: 0;
>-                overflow-x: none;
>                 overflow-y: scroll;
>                 scroll-snap-type: y proximity;
>-                -webkit-scroll-snap-type: proximity;
>-                scroll-snap-type: proximity;
>                 opacity: 0.5;
>             }
> 
>             .area {
>-                height: 600px;
>-                width: 600px;
>+                height: 100%;
>+                width: 100%;
>                 float: left;
>                 scroll-snap-align: start;
>-                -webkit-scroll-snap-coordinate: 0 0;
>-                scroll-snap-coordinate: 0 0;
>             }
>         </style>
>         <script>

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Attachments on bug 223175: 423157 | 423166 | 423189 | 423311