Implement horizontal Quick Switch waterfall

Ariver

2026-06-12 63128a870cbedb841cb19cdfbf2bf54e3dfbc25c

 C1.source/Sources/Aligner/QuickSwitchRootView.swift

@@ -55,9 +55,12 @@
    private var focusedSpaceID: UInt64?
    private var debugHoveredAppGroupIndex: Int?
    private var waterfallColumns: [WaterfallColumnLayers] = []
    private var waterfallViewMode: QuickSwitchWaterfallViewMode = .verticalColumns
    private var waterfallContentWidth: CGFloat = 0
    private var waterfallScrollOffset: CGFloat = 0
    private var waterfallColumnScrollOffsets: [Int: CGFloat] = [:]
    private var horizontalMasonryContentHeight: CGFloat = 0
    private var horizontalMasonryScrollOffset: CGFloat = 0
    private var currentSelection: QuickSwitchSelection?
    private var columnSelectionHistory: [Int: Int] = [:]
    private var keyboardCommandsApplied: [String] = []
@@ -82,9 +85,12 @@
    private var lastProjectionTransitionFadeInLayerCount = 0
    private var lastProjectionTransitionFadeOutLayerCount = 0
    private var lastProjectionTransitionDurationMilliseconds: Double = 0
    private var suppressEventInput = false
    private var suppressEventBackgroundClicks = false
    var onEscape: (() -> Void)?
    var onCommitSelection: ((QuickSwitchSelection, QuickSwitchCommitSource) -> Void)?
    var onSpaceLaneClick: ((UInt64) -> Void)?
    var onSpaceLaneClick: ((UInt64, Int) -> Void)?
    var onBackgroundClick: (() -> Bool)?
    var onRequestClose: ((QuickSwitchCloseRequest) -> Void)?
    var onCloseConfirmationDisabled: (() -> Void)?

@@ -313,6 +319,18 @@
        static let horizontalRevealPadding: CGFloat = 0
    }

    private enum HorizontalMasonryMetrics {
        static let horizontalPadding: CGFloat = 12
        static let verticalPadding: CGFloat = 0
        static let cardGap: CGFloat = 16
        static let cardMinWidth: CGFloat = 220
        static let cardMaxWidth: CGFloat = 320
        static let titleBarHeight: CGFloat = 26
        static let titleGap: CGFloat = 6
        static let minThumbnailHeight: CGFloat = 92
        static let maxThumbnailHeightFraction: CGFloat = 0.40
    }

    private enum WaterfallHorizontalIntent {
        case reveal
        case alignWithAppShelf(animated: Bool)
@@ -379,6 +397,13 @@
    }

    override func keyDown(with event: NSEvent) {
        if suppressEventInput {
            DevelopmentDiagnostics.log("quickSwitch.view.keyDown.ignoredForDebugSequence", [
                "keyCode": event.keyCode
            ])
            return
        }

        switch event.keyCode {
        case TriggerKeyCode.escape where Self.shouldDismissOnEscape(event):
            onEscape?()
@@ -421,6 +446,15 @@
        }

        if shouldScrollWaterfall(for: event) {
            if isHorizontalMasonryMode {
                let currentOffset = horizontalMasonryScrollOffset
                horizontalMasonryScrollOffset = clampedHorizontalMasonryOffset(
                    currentOffset - event.scrollingDeltaY
                )
                needsLayout = true
                return
            }

            if abs(event.scrollingDeltaX) >= abs(event.scrollingDeltaY), waterfallAlignmentScrollable {
                waterfallScrollOffset = clampedWaterfallAlignmentOffset(waterfallScrollOffset - event.scrollingDeltaX)
                needsLayout = true
@@ -462,6 +496,15 @@
    }

    override func mouseDown(with event: NSEvent) {
        if suppressEventInput {
            DevelopmentDiagnostics.log("quickSwitch.view.mouseDown.ignoredForDebugSequence", [
                "x": event.locationInWindow.x,
                "y": event.locationInWindow.y,
                "bounds": NSStringFromRect(bounds)
            ])
            return
        }

        if handleCloseConfirmationMouseDown(at: event.locationInWindow) {
            return
        }
@@ -477,7 +520,7 @@
        }

        if let segment = spaceLaneSegment(at: event.locationInWindow) {
            clickSpaceLaneSegment(segment)
            clickSpaceLaneSegment(segment, clickCount: max(1, event.clickCount))
            return
        }

@@ -491,6 +534,9 @@
            "y": event.locationInWindow.y,
            "bounds": NSStringFromRect(bounds)
        ])
        if !suppressEventBackgroundClicks, onBackgroundClick?() == true {
            return
        }
        super.mouseDown(with: event)
    }

@@ -534,6 +580,15 @@
        }
    }

    func setSuppressEventBackgroundClicks(_ suppressed: Bool) {
        suppressEventBackgroundClicks = suppressed
    }

    func setSuppressEventInput(_ suppressed: Bool) {
        suppressEventInput = suppressed
        suppressEventBackgroundClicks = suppressed
    }

    func beginPerformanceFirstFrameMeasurement() {
        firstFrameMeasurementStart = CACurrentMediaTime()
    }
@@ -564,6 +619,17 @@
            closeConfirmationLayers.containerLayer.isHidden = true
            closeConfirmationArrowEdge = nil
        }
        needsLayout = true
    }

    func setWaterfallViewMode(_ mode: QuickSwitchWaterfallViewMode) {
        guard waterfallViewMode != mode else { return }

        waterfallViewMode = mode
        waterfallScrollOffset = 0
        waterfallColumnScrollOffsets = [:]
        horizontalMasonryScrollOffset = 0
        horizontalMasonryContentHeight = 0
        needsLayout = true
    }

@@ -684,6 +750,10 @@
            lastSpaceFocusedAppGroupIndex = nil
            lastSpaceLaneClickSpaceID = nil
            lastAppShelfScrollSyncedAppGroupIndex = nil
            waterfallScrollOffset = 0
            waterfallColumnScrollOffsets = [:]
            horizontalMasonryScrollOffset = 0
            horizontalMasonryContentHeight = 0
            focusedSpaceID = nil
            hoveredCloseTarget = nil
            pendingCloseTarget = nil
@@ -1021,10 +1091,15 @@
            "appShelfMinIconSize": Double(AppShelfMetrics.minIconSize),
            "appShelfItems": appShelfItemReports(),
            "waterfallFrame": dictionary(from: waterfallLayer.frame),
            "waterfallViewMode": waterfallViewMode.rawValue,
            "waterfallContentWidth": Double(waterfallContentWidth),
            "waterfallVisibleWidth": Double(waterfallLayer.bounds.width),
            "waterfallScrollOffset": Double(waterfallScrollOffset),
            "waterfallMaxScrollOffset": Double(waterfallMaxScrollOffset),
            "horizontalMasonryContentHeight": Double(horizontalMasonryContentHeight),
            "horizontalMasonryScrollOffset": Double(horizontalMasonryScrollOffset),
            "horizontalMasonryMaxScrollOffset": Double(horizontalMasonryMaxScrollOffset),
            "horizontalMasonryScrollable": horizontalMasonryMaxScrollOffset > 0,
            "waterfallAlignmentMinScrollOffset": Double(waterfallAlignmentScrollRange.lowerBound),
            "waterfallAlignmentMaxScrollOffset": Double(waterfallAlignmentScrollRange.upperBound),
            "waterfallScrollable": waterfallMaxScrollOffset > 0,
@@ -1136,8 +1211,13 @@
            recordKeyboardCommand("enter")
            commitCurrentSelection()
        case "tab":
            tabIgnoredCount += 1
            recordKeyboardCommand("tabIgnored")
            if isHorizontalMasonryMode {
                recordKeyboardCommand("tab")
                moveSelection(.right)
            } else {
                tabIgnoredCount += 1
                recordKeyboardCommand("tabIgnored")
            }
        default:
            recordKeyboardCommand("unknown:\(command)")
        }
@@ -1207,8 +1287,21 @@
            }
            recordMouseCommand("click-space:\(spaceID)")
            if let segment = spaceLaneSegment(spaceID: spaceID) {
                clickSpaceLaneSegment(segment)
                clickSpaceLaneSegment(segment, clickCount: 1)
            }
        case "double-click-space" where parts.count == 2:
            guard let spaceID = UInt64(parts[1]) else {
                recordMouseCommand("invalid:\(command)")
                return
            }
            recordMouseCommand("double-click-space:\(spaceID)")
            if let segment = spaceLaneSegment(spaceID: spaceID) {
                clickSpaceLaneSegment(segment, clickCount: 1)
                clickSpaceLaneSegment(segment, clickCount: 2)
            }
        case "click-background":
            recordMouseCommand("click-background")
            _ = onBackgroundClick?()
        case "hover-card" where parts.count == 3:
            guard let appGroupIndex = Int(parts[1]), let windowIndex = Int(parts[2]) else {
                recordMouseCommand("invalid:\(command)")
@@ -1324,13 +1417,14 @@
        focusSpace(segment.space.id, persistent: false, source: source)
    }

    private func clickSpaceLaneSegment(_ segment: SpaceLaneSegmentLayers) {
    private func clickSpaceLaneSegment(_ segment: SpaceLaneSegmentLayers, clickCount: Int = 1) {
        DevelopmentDiagnostics.log("quickSwitch.view.clickSpaceLane", [
            "spaceID": segment.space.id,
            "label": segment.space.label
            "label": segment.space.label,
            "clickCount": clickCount
        ])
        lastSpaceLaneClickSpaceID = segment.space.id
        onSpaceLaneClick?(segment.space.id)
        onSpaceLaneClick?(segment.space.id, clickCount)
        lastSpaceLaneClickSpaceID = segment.space.id
    }

@@ -1529,6 +1623,11 @@
    }

    private func moveSelection(_ direction: QuickSwitchKeyboardDirection) {
        if isHorizontalMasonryMode {
            moveHorizontalMasonrySelection(direction)
            return
        }

        guard let currentViewModel,
              let snapshot = snapshotForFocus(from: currentViewModel),
              let current = currentSelection ?? currentViewModel.initialSelection,
@@ -1558,6 +1657,113 @@
            "windowID": next.windowID
        ])
        needsLayout = true
    }

    private func moveHorizontalMasonrySelection(_ direction: QuickSwitchKeyboardDirection) {
        guard let current = currentSelection ?? currentViewModel?.initialSelection,
              let next = nextHorizontalMasonrySelection(from: current, direction: direction)
        else {
            DevelopmentDiagnostics.log("quickSwitch.view.moveHorizontalMasonrySelection.blocked", [
                "direction": String(describing: direction),
                "hasSelection": (currentSelection ?? currentViewModel?.initialSelection) != nil
            ])
            return
        }

        columnSelectionHistory[current.appGroupIndex] = current.windowIndex
        currentSelection = next
        columnSelectionHistory[next.appGroupIndex] = next.windowIndex
        ensureCurrentSelectionVisible(horizontalIntent: .alignWithAppShelf(animated: true))
        DevelopmentDiagnostics.log("quickSwitch.view.moveHorizontalMasonrySelection", [
            "direction": String(describing: direction),
            "appGroupIndex": next.appGroupIndex,
            "windowIndex": next.windowIndex,
            "windowID": next.windowID
        ])
        needsLayout = true
    }

    private func nextHorizontalMasonrySelection(
        from current: QuickSwitchSelection,
        direction: QuickSwitchKeyboardDirection
    ) -> QuickSwitchSelection? {
        layoutSubtreeIfNeeded()

        let cards = horizontalMasonryCardsInPlacementOrder()
        guard let currentIndex = cards.firstIndex(where: { $0.item.window.id == current.windowID }) else {
            return cards.first.map(selectionForCard)
        }

        switch direction {
        case .right:
            return selectionForCard(cards[(currentIndex + 1) % cards.count])
        case .left:
            return selectionForCard(cards[(currentIndex - 1 + cards.count) % cards.count])
        case .up:
            return nearestHorizontalMasonrySelection(from: cards[currentIndex], direction: .up)
                ?? selectionForCard(cards.first ?? cards[currentIndex])
        case .down:
            return nearestHorizontalMasonrySelection(from: cards[currentIndex], direction: .down)
                ?? selectionForCard(cards.last ?? cards[currentIndex])
        }
    }

    private func nearestHorizontalMasonrySelection(
        from currentCard: WaterfallCardLayers,
        direction: QuickSwitchKeyboardDirection
    ) -> QuickSwitchSelection? {
        let currentFrame = currentCard.containerLayer.frame
        let candidates = horizontalMasonryCardsInPlacementOrder().filter { card in
            guard card.item.window.id != currentCard.item.window.id else { return false }
            switch direction {
            case .up:
                return card.containerLayer.frame.minY >= currentFrame.maxY - 0.5
            case .down:
                return card.containerLayer.frame.maxY <= currentFrame.minY + 0.5
            case .left, .right:
                return false
            }
        }

        let best = candidates.min { lhs, rhs in
            let lhsFrame = lhs.containerLayer.frame
            let rhsFrame = rhs.containerLayer.frame
            let lhsPrimaryDistance = direction == .up
                ? lhsFrame.minY - currentFrame.maxY
                : currentFrame.minY - lhsFrame.maxY
            let rhsPrimaryDistance = direction == .up
                ? rhsFrame.minY - currentFrame.maxY
                : currentFrame.minY - rhsFrame.maxY
            if abs(lhsPrimaryDistance - rhsPrimaryDistance) > 0.5 {
                return lhsPrimaryDistance < rhsPrimaryDistance
            }

            let lhsHorizontalDistance = abs(lhsFrame.midX - currentFrame.midX)
            let rhsHorizontalDistance = abs(rhsFrame.midX - currentFrame.midX)
            if abs(lhsHorizontalDistance - rhsHorizontalDistance) > 0.5 {
                return lhsHorizontalDistance < rhsHorizontalDistance
            }

            return lhs.item.globalIndex < rhs.item.globalIndex
        }

        return best.map(selectionForCard)
    }

    private func horizontalMasonryCardsInPlacementOrder() -> [WaterfallCardLayers] {
        waterfallColumns
            .sorted { $0.column.appGroupIndex < $1.column.appGroupIndex }
            .flatMap { column in
                column.cards.sorted { $0.item.windowIndex < $1.item.windowIndex }
            }
    }

    private func selectionForCard(_ card: WaterfallCardLayers) -> QuickSwitchSelection {
        QuickSwitchSelection(
            appGroupIndex: card.item.appGroupIndex,
            windowIndex: card.item.windowIndex,
            windowID: card.item.window.id
        )
    }

    private func commitCurrentSelection() {
@@ -1617,9 +1823,24 @@
        _ selection: QuickSwitchSelection,
        horizontalIntent: WaterfallHorizontalIntent = .reveal
    ) {
        if isHorizontalMasonryMode {
            switch horizontalIntent {
            case .reveal:
                ensureHorizontalMasonrySelectionVisible(selection, animated: false)
            case .alignWithAppShelf(let animated):
                ensureHorizontalMasonrySelectionVisible(selection, animated: animated)
            }
            return
        }

        guard
            let column = waterfallColumns.first(where: { $0.column.appGroupIndex == selection.appGroupIndex })
        else {
            return
        }

        if waterfallShouldKeepFilteredColumnsCentered {
            ensureWaterfallCardVisibleVertically(selection)
            return
        }

@@ -1633,6 +1854,11 @@
    }

    private func ensureWaterfallCardVisibleVertically(_ selection: QuickSwitchSelection) {
        guard !isHorizontalMasonryMode else {
            ensureHorizontalMasonrySelectionVisible(selection, animated: false)
            return
        }

        let visibleHeight = max(
            1,
            waterfallLayer.bounds.height
@@ -1660,6 +1886,11 @@
    }

    private func alignWaterfallColumnWithAppShelfIcon(appGroupIndex: Int, animated: Bool) {
        if isHorizontalMasonryMode {
            ensureHorizontalMasonryAppVisible(appGroupIndex, animated: animated)
            return
        }

        guard
            let item = appShelfItems.first(where: { $0.item.appGroupIndex == appGroupIndex }),
            let column = waterfallColumns.first(where: { $0.column.appGroupIndex == appGroupIndex })
@@ -1686,6 +1917,11 @@
    }

    private func ensureWaterfallColumnVisible(_ appGroupIndex: Int) {
        if isHorizontalMasonryMode {
            ensureHorizontalMasonryAppVisible(appGroupIndex, animated: false)
            return
        }

        guard let column = waterfallColumns.first(where: { $0.column.appGroupIndex == appGroupIndex }) else {
            return
        }
@@ -1694,6 +1930,11 @@
    }

    private func ensureWaterfallColumnVisible(_ column: WaterfallColumnLayers) {
        if isHorizontalMasonryMode {
            ensureHorizontalMasonryAppVisible(column.column.appGroupIndex, animated: false)
            return
        }

        waterfallScrollOffset = clampedWaterfallOffset(
            scrollOffset(
                makingVisible: column.containerLayer.frame,
@@ -1706,6 +1947,14 @@
    }

    private var waterfallAlignmentScrollRange: ClosedRange<CGFloat> {
        if isHorizontalMasonryMode {
            return 0...0
        }

        if waterfallShouldKeepFilteredColumnsCentered {
            return 0...0
        }

        var minimumOffset: CGFloat = 0
        var maximumOffset = waterfallMaxScrollOffset

@@ -1730,6 +1979,10 @@
    private func clampedWaterfallAlignmentOffset(_ offset: CGFloat) -> CGFloat {
        let range = waterfallAlignmentScrollRange
        return min(max(range.lowerBound, offset), range.upperBound)
    }

    private var waterfallShouldKeepFilteredColumnsCentered: Bool {
        currentViewModel?.lockedSpaceID != nil && waterfallMaxScrollOffset <= 0.5
    }

    private func setWaterfallScrollOffset(_ offset: CGFloat, animated: Bool) {
@@ -1764,6 +2017,80 @@
        animation.timingFunction = CAMediaTimingFunction(name: WaterfallAlignmentMetrics.animationTimingName)
        animation.isRemovedOnCompletion = true
        waterfallContentLayer.add(animation, forKey: "waterfallColumnAlignment")
    }

    private func ensureHorizontalMasonrySelectionVisible(
        _ selection: QuickSwitchSelection,
        animated: Bool
    ) {
        guard let card = waterfallCard(
            appGroupIndex: selection.appGroupIndex,
            windowIndex: selection.windowIndex
        ) else {
            return
        }

        let visibleFrame = card.containerLayer.frame.offsetBy(
            dx: 0,
            dy: waterfallContentLayer.frame.minY
        )
        let visibleHeight = waterfallLayer.bounds.height
        let padding = WaterfallMetrics.revealPadding
        var nextOffset = horizontalMasonryScrollOffset

        if visibleFrame.maxY > visibleHeight - padding {
            nextOffset -= visibleFrame.maxY - (visibleHeight - padding)
        } else if visibleFrame.minY < padding {
            nextOffset += padding - visibleFrame.minY
        }

        setHorizontalMasonryScrollOffset(nextOffset, animated: animated)
    }

    private func ensureHorizontalMasonryAppVisible(_ appGroupIndex: Int, animated: Bool) {
        guard let firstCard = waterfallColumns
            .first(where: { $0.column.appGroupIndex == appGroupIndex })?
            .cards
            .sorted(by: { $0.item.windowIndex < $1.item.windowIndex })
            .first
        else {
            return
        }

        let cardTopDistance = horizontalMasonryContentHeight - firstCard.containerLayer.frame.maxY
        setHorizontalMasonryScrollOffset(
            cardTopDistance - WaterfallMetrics.revealPadding,
            animated: animated
        )
    }

    private func setHorizontalMasonryScrollOffset(_ offset: CGFloat, animated: Bool) {
        let nextOffset = clampedHorizontalMasonryOffset(offset)
        let previousPositionY = waterfallContentLayer.presentation()?.position.y
            ?? waterfallContentLayer.position.y

        horizontalMasonryScrollOffset = nextOffset
        CATransaction.begin()
        CATransaction.setDisableActions(true)
        waterfallContentLayer.frame = horizontalMasonryContentFrame()
        CATransaction.commit()

        let nextPositionY = waterfallContentLayer.position.y
        guard animated,
              !NSWorkspace.shared.accessibilityDisplayShouldReduceMotion,
              abs(previousPositionY - nextPositionY) > 0.5
        else {
            waterfallContentLayer.removeAnimation(forKey: "horizontalMasonryAlignment")
            return
        }

        let animation = CABasicAnimation(keyPath: "position.y")
        animation.fromValue = previousPositionY
        animation.toValue = nextPositionY
        animation.duration = WaterfallAlignmentMetrics.animationDuration
        animation.timingFunction = CAMediaTimingFunction(name: WaterfallAlignmentMetrics.animationTimingName)
        animation.isRemovedOnCompletion = true
        waterfallContentLayer.add(animation, forKey: "horizontalMasonryAlignment")
    }

    private func scrollOffset(
@@ -2443,9 +2770,11 @@
        let isActive = isHovered || isFocused || isLocked
        let isAssociated = (isAppAssociated || isWindowAssociated) && !isActive

        segment.containerLayer.borderWidth = (hasWindows || isCurrent || isActive || isAssociated) ? 1.5 : 1
        segment.containerLayer.borderWidth = isLocked
            ? 6
            : (hasWindows || isCurrent || isActive || isAssociated) ? 1.5 : 1
        segment.containerLayer.borderColor = (isActive
            ? spaceLaneOccupiedColor.withAlphaComponent(0.62)
            ? spaceLaneOccupiedColor.withAlphaComponent(isLocked ? 0.92 : 0.62)
            : isAssociated
                ? spaceLaneOccupiedColor.withAlphaComponent(0.50)
                : hasWindows
@@ -2472,17 +2801,20 @@
                colors: spaceLaneIdleOccupiedGradientColors()
            )
        }
        segment.containerLayer.shadowColor = isLocked
            ? NSColor.white.withAlphaComponent(0.98).cgColor
            : NSColor.black.cgColor
        segment.containerLayer.shadowOpacity = (hasWindows || isLocked)
            ? (isActive ? 0.26 : isAssociated ? 0.18 : isCurrent ? 0.14 : 0)
            ? (isLocked ? 0.72 : isActive ? 0.26 : isAssociated ? 0.18 : isCurrent ? 0.14 : 0)
            : 0
        segment.containerLayer.shadowRadius = (hasWindows || isLocked)
            ? (isActive ? 24 : isAssociated ? 18 : isCurrent ? 12 : 0)
            ? (isLocked ? 30 : isActive ? 24 : isAssociated ? 18 : isCurrent ? 12 : 0)
            : 0
        segment.containerLayer.shadowOffset = CGSize(
            width: 0,
            height: (hasWindows || isLocked) ? (isActive ? -6 : isAssociated ? -4 : isCurrent ? -2.5 : 0) : 0
            height: (hasWindows || isLocked) ? (isLocked ? 0 : isActive ? -6 : isAssociated ? -4 : isCurrent ? -2.5 : 0) : 0
        )
        segment.containerLayer.zPosition = isActive ? 30 : isAssociated ? 18 : isCurrent ? 10 : 0
        segment.containerLayer.zPosition = isLocked ? 42 : isActive ? 30 : isAssociated ? 18 : isCurrent ? 10 : 0
        segment.containerLayer.transform = (isActive || isAssociated)
            ? CATransform3DMakeScale(isActive ? 1.03 : 1.015, isActive ? 1.03 : 1.015, 1)
            : CATransform3DIdentity
@@ -2879,6 +3211,10 @@
            return "none"
        }

        guard !isHorizontalMasonryMode else {
            return "visible"
        }

        let visibleMinX = waterfallScrollOffset
        let visibleMaxX = waterfallScrollOffset + waterfallLayer.bounds.width
        if column.containerLayer.frame.maxX < visibleMinX + WaterfallMetrics.gap {
@@ -2961,17 +3297,24 @@
    }

    private func layoutWaterfallColumns() {
        if isHorizontalMasonryMode {
            layoutHorizontalMasonryWaterfall()
            return
        }

        guard !waterfallColumns.isEmpty else {
            waterfallContentWidth = waterfallLayer.bounds.width
            waterfallScrollOffset = 0
            horizontalMasonryContentHeight = waterfallLayer.bounds.height
            horizontalMasonryScrollOffset = 0
            waterfallContentLayer.frame = waterfallLayer.bounds
            return
        }

        let columnWidth = waterfallColumnWidth()
        let totalWidth = WaterfallMetrics.contentHorizontalPadding * 2
            + CGFloat(waterfallColumns.count) * columnWidth
        let columnsWidth = CGFloat(waterfallColumns.count) * columnWidth
            + CGFloat(max(0, waterfallColumns.count - 1)) * WaterfallMetrics.gap
        let totalWidth = WaterfallMetrics.contentHorizontalPadding * 2 + columnsWidth
        waterfallContentWidth = max(waterfallLayer.bounds.width, totalWidth)
        waterfallScrollOffset = clampedWaterfallAlignmentOffset(waterfallScrollOffset)
        waterfallContentLayer.frame = CGRect(
@@ -2981,7 +3324,7 @@
            height: waterfallLayer.bounds.height
        )

        var x = WaterfallMetrics.contentHorizontalPadding
        var x = waterfallColumnStartX(columnsWidth: columnsWidth)
        for column in waterfallColumns {
            column.containerLayer.frame = CGRect(
                x: x,
@@ -2994,7 +3337,215 @@
        }
    }

    private func layoutHorizontalMasonryWaterfall() {
        guard !waterfallColumns.isEmpty else {
            waterfallContentWidth = waterfallLayer.bounds.width
            waterfallScrollOffset = 0
            horizontalMasonryContentHeight = waterfallLayer.bounds.height
            horizontalMasonryScrollOffset = 0
            waterfallContentLayer.frame = waterfallLayer.bounds
            return
        }

        let layout = horizontalMasonryLayout()
        waterfallContentWidth = waterfallLayer.bounds.width
        waterfallScrollOffset = 0
        horizontalMasonryContentHeight = layout.contentHeight
        horizontalMasonryScrollOffset = clampedHorizontalMasonryOffset(horizontalMasonryScrollOffset)
        waterfallContentLayer.frame = horizontalMasonryContentFrame()

        for column in waterfallColumns {
            column.containerLayer.frame = CGRect(
                x: 0,
                y: 0,
                width: waterfallContentWidth,
                height: horizontalMasonryContentHeight
            )
            column.containerLayer.masksToBounds = false
            column.containerLayer.backgroundColor = NSColor.clear.cgColor
            column.containerLayer.borderColor = NSColor.clear.cgColor
            column.containerLayer.borderWidth = 0
            column.containerLayer.shadowOpacity = 0
            column.containerLayer.shadowRadius = 0
            column.containerLayer.shadowOffset = .zero
            column.headerLayer.isHidden = true
            column.appNameLayer.isHidden = true
            column.countLayer.isHidden = true

            for card in column.cards {
                if let frame = layout.cardFramesByWindowID[card.item.window.id] {
                    card.containerLayer.frame = frame
                } else {
                    card.containerLayer.frame = .zero
                }
                layoutWaterfallCard(card)
            }
        }
    }

    private struct HorizontalMasonryLayout {
        let contentHeight: CGFloat
        let cardFramesByWindowID: [UInt32: CGRect]
    }

    private func horizontalMasonryLayout() -> HorizontalMasonryLayout {
        let cards = horizontalMasonryCardsInPlacementOrder()
        guard !cards.isEmpty else {
            return HorizontalMasonryLayout(
                contentHeight: waterfallLayer.bounds.height,
                cardFramesByWindowID: [:]
            )
        }

        let viewportWidth = max(1, waterfallLayer.bounds.width)
        let availableWidth = max(
            HorizontalMasonryMetrics.cardMinWidth,
            viewportWidth - HorizontalMasonryMetrics.horizontalPadding * 2
        )
        let maximumLaneCount = max(
            1,
            Int(
                floor(
                    (availableWidth + HorizontalMasonryMetrics.cardGap)
                        / (HorizontalMasonryMetrics.cardMinWidth + HorizontalMasonryMetrics.cardGap)
                )
            )
        )
        let laneCount = min(maximumLaneCount, max(1, cards.count))
        let fittingWidth = (
            availableWidth - CGFloat(max(0, laneCount - 1)) * HorizontalMasonryMetrics.cardGap
        ) / CGFloat(laneCount)
        let cardWidth = floor(
            min(
                HorizontalMasonryMetrics.cardMaxWidth,
                max(HorizontalMasonryMetrics.cardMinWidth, fittingWidth)
            )
        )
        let usedWidth = CGFloat(laneCount) * cardWidth
            + CGFloat(max(0, laneCount - 1)) * HorizontalMasonryMetrics.cardGap
        let startX = max(
            HorizontalMasonryMetrics.horizontalPadding,
            (viewportWidth - usedWidth) / 2
        )

        var laneHeights = Array(repeating: CGFloat(0), count: laneCount)
        var plannedFrames: [(windowID: UInt32, x: CGFloat, top: CGFloat, width: CGFloat, height: CGFloat)] = []

        for card in cards {
            let laneIndex = laneHeights.enumerated().min { lhs, rhs in
                if abs(lhs.element - rhs.element) > 0.5 {
                    return lhs.element < rhs.element
                }
                return lhs.offset < rhs.offset
            }?.offset ?? 0
            let cardHeight = horizontalMasonryCardHeight(
                for: card,
                width: cardWidth,
                viewportHeight: waterfallLayer.bounds.height
            )
            let x = startX + CGFloat(laneIndex) * (cardWidth + HorizontalMasonryMetrics.cardGap)
            let top = HorizontalMasonryMetrics.verticalPadding + laneHeights[laneIndex]
            plannedFrames.append((
                windowID: card.item.window.id,
                x: x,
                top: top,
                width: cardWidth,
                height: cardHeight
            ))
            laneHeights[laneIndex] += cardHeight + HorizontalMasonryMetrics.cardGap
        }

        let tallestLane = laneHeights.max().map {
            max(0, $0 - HorizontalMasonryMetrics.cardGap)
        } ?? 0
        let contentHeight = max(
            waterfallLayer.bounds.height,
            HorizontalMasonryMetrics.verticalPadding * 2 + tallestLane
        )
        let frames = Dictionary(
            uniqueKeysWithValues: plannedFrames.map { planned in
                (
                    planned.windowID,
                    CGRect(
                        x: planned.x,
                        y: contentHeight - planned.top - planned.height,
                        width: planned.width,
                        height: planned.height
                    )
                )
            }
        )

        return HorizontalMasonryLayout(contentHeight: contentHeight, cardFramesByWindowID: frames)
    }

    private func horizontalMasonryCardHeight(
        for card: WaterfallCardLayers,
        width: CGFloat,
        viewportHeight: CGFloat
    ) -> CGFloat {
        let thumbnailHeight = min(
            max(
                HorizontalMasonryMetrics.minThumbnailHeight,
                width / horizontalMasonryThumbnailAspectRatio(for: card)
            ),
            max(1, viewportHeight * HorizontalMasonryMetrics.maxThumbnailHeightFraction)
        )
        return HorizontalMasonryMetrics.titleBarHeight
            + HorizontalMasonryMetrics.titleGap
            + thumbnailHeight
    }

    private func horizontalMasonryThumbnailAspectRatio(for card: WaterfallCardLayers) -> CGFloat {
        if card.item.window.isFullscreen {
            return 16.0 / 9.0
        }
        if card.item.window.isMinimized {
            return 4.0 / 3.0
        }

        switch Int(card.item.window.id % 4) {
        case 0:
            return 16.0 / 9.0
        case 1:
            return 3.0 / 2.0
        case 2:
            return 4.0 / 3.0
        default:
            return 5.0 / 4.0
        }
    }

    private func horizontalMasonryContentFrame() -> CGRect {
        let contentHeight = max(waterfallLayer.bounds.height, horizontalMasonryContentHeight)
        return CGRect(
            x: 0,
            y: waterfallLayer.bounds.height - contentHeight + horizontalMasonryScrollOffset,
            width: waterfallLayer.bounds.width,
            height: contentHeight
        )
    }

    private func waterfallColumnStartX(columnsWidth: CGFloat) -> CGFloat {
        guard currentViewModel?.lockedSpaceID != nil else {
            return WaterfallMetrics.contentHorizontalPadding
        }

        let centeredStart = (waterfallContentWidth - columnsWidth) / 2
        return max(WaterfallMetrics.contentHorizontalPadding, centeredStart)
    }

    private func layoutWaterfallColumn(_ column: WaterfallColumnLayers) {
        column.containerLayer.cornerRadius = 14
        column.containerLayer.masksToBounds = true
        column.containerLayer.backgroundColor = NSColor.controlBackgroundColor.withAlphaComponent(0.56).cgColor
        column.containerLayer.shadowOpacity = 0
        column.containerLayer.shadowRadius = 0
        column.containerLayer.shadowOffset = .zero
        column.headerLayer.isHidden = false
        column.appNameLayer.isHidden = false
        column.countLayer.isHidden = false

        let bounds = column.containerLayer.bounds
        let isSpaceFocused = spaceFocusWindowCount(for: column.column.appGroupIndex) > 0
        let isHovered = column.column.appGroupIndex == effectiveHoveredAppGroupIndex
@@ -3715,15 +4266,30 @@
        )
    }

    private var isHorizontalMasonryMode: Bool {
        waterfallViewMode == .horizontalMasonry
    }

    private var waterfallMaxScrollOffset: CGFloat {
        max(0, waterfallContentWidth - waterfallLayer.bounds.width)
        guard !isHorizontalMasonryMode else { return 0 }
        return max(0, waterfallContentWidth - waterfallLayer.bounds.width)
    }

    private func clampedWaterfallOffset(_ offset: CGFloat) -> CGFloat {
        min(max(0, offset), waterfallMaxScrollOffset)
    }

    private var horizontalMasonryMaxScrollOffset: CGFloat {
        max(0, horizontalMasonryContentHeight - waterfallLayer.bounds.height)
    }

    private func clampedHorizontalMasonryOffset(_ offset: CGFloat) -> CGFloat {
        min(max(0, offset), horizontalMasonryMaxScrollOffset)
    }

    private func waterfallMaxVerticalScrollOffset(for appGroupIndex: Int) -> CGFloat {
        guard !isHorizontalMasonryMode else { return 0 }

        guard
            let column = waterfallColumns.first(where: { $0.column.appGroupIndex == appGroupIndex })
        else {
@@ -4426,8 +4992,13 @@
                    "gradientColors": gradientColorDictionaries(from: segment.containerLayer),
                    "borderColor": colorDictionary(from: segment.containerLayer.borderColor),
                    "borderWidth": Double(segment.containerLayer.borderWidth),
                    "shadowColor": colorDictionary(from: segment.containerLayer.shadowColor),
                    "shadowOpacity": Double(segment.containerLayer.shadowOpacity),
                    "shadowRadius": Double(segment.containerLayer.shadowRadius),
                    "shadowOffset": [
                        "width": Double(segment.containerLayer.shadowOffset.width),
                        "height": Double(segment.containerLayer.shadowOffset.height)
                    ],
                    "appFrame": dictionary(from: segment.appLayer.frame),
                    "frame": dictionary(from: segment.containerLayer.frame),
                    "visibleFrame": dictionary(from: visibleFrame),