Source/WebCore/platform/ScrollSnapAnimatorState.cpp

/*
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#include "config.h"
#include "ScrollSnapAnimatorState.h"

#include "ScrollExtents.h"
#include "ScrollingEffectsController.h"
#include <wtf/MathExtras.h>
#include <wtf/text/TextStream.h>

namespace WebCore {

ScrollSnapAnimatorState::~ScrollSnapAnimatorState() = default;

bool ScrollSnapAnimatorState::transitionToSnapAnimationState(const ScrollExtents& scrollExtents, float pageScale, const FloatPoint& initialOffset)
{
    return setupAnimationForState(ScrollSnapState::Snapping, scrollExtents, pageScale, initialOffset, { }, { });
}

bool ScrollSnapAnimatorState::transitionToGlideAnimationState(const ScrollExtents& scrollExtents, float pageScale, const FloatPoint& initialOffset, const FloatSize& initialVelocity, const FloatSize& initialDelta)
{
    return setupAnimationForState(ScrollSnapState::Gliding, scrollExtents, pageScale, initialOffset, initialVelocity, initialDelta);
}

bool ScrollSnapAnimatorState::setupAnimationForState(ScrollSnapState state, const ScrollExtents& scrollExtents, float pageScale, const FloatPoint& initialOffset, const FloatSize& initialVelocity, const FloatSize& initialDelta)
{
    ASSERT(state == ScrollSnapState::Snapping || state == ScrollSnapState::Gliding);
    if (m_currentState == state)
        return false;

    bool animating = m_scrollController.startMomentumScrollWithInitialVelocity(initialOffset, initialVelocity, initialDelta, [&](const FloatPoint& targetOffset) {
        float targetOffsetX, targetOffsetY;
        std::tie(targetOffsetX, m_activeSnapIndexX) = targetOffsetForStartOffset(ScrollEventAxis::Horizontal, scrollExtents, initialOffset.x(), targetOffset, pageScale, initialDelta.width());
        std::tie(targetOffsetY, m_activeSnapIndexY) = targetOffsetForStartOffset(ScrollEventAxis::Vertical, scrollExtents, initialOffset.y(), targetOffset, pageScale, initialDelta.height());

        return FloatPoint { targetOffsetX, targetOffsetY };
    });

    if (!animating)
        return false;

    m_currentState = state;
    return animating;
}

std::optional<unsigned> ScrollSnapAnimatorState::closestSnapPointForOffset(ScrollEventAxis axis, ScrollOffset scrollOffset, const ScrollExtents& scrollExtents, float pageScale) const
{
    LayoutPoint layoutScrollOffset(scrollOffset.x() / pageScale, scrollOffset.y() / pageScale);

    auto snapOffsets = snapOffsetsForAxis(axis);
    LayoutSize viewportSize(scrollExtents.viewportSize);
    std::optional<unsigned> activeIndex;
    if (snapOffsets.size())
        activeIndex = snapOffsetInfo().closestSnapOffset(axis, viewportSize, layoutScrollOffset, 0).second;

    return activeIndex;
}

float ScrollSnapAnimatorState::adjustedScrollDestination(ScrollEventAxis axis, FloatPoint destinationOffset, float velocity, std::optional<float> originalOffset, const ScrollExtents& scrollExtents, float pageScale) const
{
    auto snapOffsets = snapOffsetsForAxis(axis);
    if (!snapOffsets.size())
        return axis == ScrollEventAxis::Horizontal ? destinationOffset.x() : destinationOffset.y();

    std::optional<LayoutUnit> originalOffsetInLayoutUnits;
    if (originalOffset)
        originalOffsetInLayoutUnits = LayoutUnit(*originalOffset / pageScale);
    LayoutSize viewportSize(scrollExtents.viewportSize);
    LayoutPoint layoutDestinationOffset(destinationOffset.x() / pageScale, destinationOffset.y() / pageScale);
    LayoutUnit offset = snapOffsetInfo().closestSnapOffset(axis, viewportSize, layoutDestinationOffset, velocity, originalOffsetInLayoutUnits).first;
    return offset * pageScale;
}

bool ScrollSnapAnimatorState::resnapAfterLayout(ScrollOffset scrollOffset, const ScrollExtents& scrollExtents, float pageScale)
{
    bool snapPointChanged = false;
    // If we are already snapped in a particular axis, maintain that. Otherwise, snap to the nearest eligible snap point.
    auto activeHorizontalIndex = activeSnapIndexForAxis(ScrollEventAxis::Horizontal);
    if (!activeHorizontalIndex || *activeHorizontalIndex >= snapOffsetsForAxis(ScrollEventAxis::Horizontal).size())
        snapPointChanged |= setNearestScrollSnapIndexForAxisAndOffset(ScrollEventAxis::Horizontal, scrollOffset, scrollExtents, pageScale);

    auto activeVerticalIndex = activeSnapIndexForAxis(ScrollEventAxis::Vertical);
    if (!activeVerticalIndex || *activeVerticalIndex >= snapOffsetsForAxis(ScrollEventAxis::Vertical).size())
        snapPointChanged |= setNearestScrollSnapIndexForAxisAndOffset(ScrollEventAxis::Vertical, scrollOffset, scrollExtents, pageScale);

    return snapPointChanged;
}

bool ScrollSnapAnimatorState::setNearestScrollSnapIndexForAxisAndOffset(ScrollEventAxis axis, ScrollOffset scrollOffset, const ScrollExtents& scrollExtents, float pageScale)
{
    auto activeIndex = closestSnapPointForOffset(axis, scrollOffset, scrollExtents, pageScale);
    if (activeIndex == activeSnapIndexForAxis(axis))
        return false;

    setActiveSnapIndexForAxis(axis, activeIndex);
    return true;
}

bool ScrollSnapAnimatorState::setNearestScrollSnapIndexForOffset(ScrollOffset scrollOffset, const ScrollExtents& scrollExtents, float pageScale)
{
    bool snapIndexChanged = false;
    snapIndexChanged |= setNearestScrollSnapIndexForAxisAndOffset(ScrollEventAxis::Horizontal, scrollOffset, scrollExtents, pageScale);
    snapIndexChanged |= setNearestScrollSnapIndexForAxisAndOffset(ScrollEventAxis::Vertical, scrollOffset, scrollExtents, pageScale);
    return snapIndexChanged;
}

void ScrollSnapAnimatorState::transitionToUserInteractionState()
{
    teardownAnimationForState(ScrollSnapState::UserInteraction);
}

void ScrollSnapAnimatorState::transitionToDestinationReachedState()
{
    teardownAnimationForState(ScrollSnapState::DestinationReached);
}

void ScrollSnapAnimatorState::teardownAnimationForState(ScrollSnapState state)
{
    ASSERT(state == ScrollSnapState::UserInteraction || state == ScrollSnapState::DestinationReached);
    if (m_currentState == state)
        return;

    m_scrollController.stopAnimatedScroll();
    m_currentState = state;
}

std::pair<float, std::optional<unsigned>> ScrollSnapAnimatorState::targetOffsetForStartOffset(ScrollEventAxis axis, const ScrollExtents& scrollExtents, float startOffset, FloatPoint predictedOffset, float pageScale, float initialDelta) const
{
    auto minScrollOffset = (axis == ScrollEventAxis::Horizontal) ? scrollExtents.minimumScrollOffset().x() : scrollExtents.minimumScrollOffset().y();
    auto maxScrollOffset = (axis == ScrollEventAxis::Horizontal) ? scrollExtents.maximumScrollOffset().x() : scrollExtents.maximumScrollOffset().y();

    const auto& snapOffsets = m_snapOffsetsInfo.offsetsForAxis(axis);
    if (snapOffsets.isEmpty())
        return std::make_pair(clampTo<float>(axis == ScrollEventAxis::Horizontal ? predictedOffset.x() : predictedOffset.y(), minScrollOffset, maxScrollOffset), std::nullopt);

    LayoutPoint predictedLayoutOffset(predictedOffset.x() / pageScale, predictedOffset.y() / pageScale);
    auto [targetOffset, snapIndex] = m_snapOffsetsInfo.closestSnapOffset(axis, LayoutSize { scrollExtents.viewportSize }, predictedLayoutOffset, initialDelta, LayoutUnit(startOffset / pageScale));
    return std::make_pair(pageScale * clampTo<float>(float { targetOffset }, minScrollOffset, maxScrollOffset), snapIndex);
}

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));

    ts.dumpProperty("active snap index x", state.activeSnapIndexForAxis(ScrollEventAxis::Horizontal));
    ts.dumpProperty("active snap index y", state.activeSnapIndexForAxis(ScrollEventAxis::Vertical));

    return ts;
}

} // namespace WebCore