flutter_flutter/engine/platform/scroll/ScrollAnimator.cpp

/*
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#include "config.h"
#include "platform/scroll/ScrollAnimator.h"

#include "platform/geometry/FloatPoint.h"
#include "platform/scroll/ScrollableArea.h"
#include "wtf/PassOwnPtr.h"
#include <algorithm>

namespace blink {

ScrollAnimator::ScrollAnimator(ScrollableArea* scrollableArea)
    : m_scrollableArea(scrollableArea)
    , m_currentPosX(0)
    , m_currentPosY(0)
{
}

ScrollAnimator::~ScrollAnimator()
{
}

bool ScrollAnimator::scroll(ScrollbarOrientation orientation, ScrollGranularity, float step, float delta)
{
    float& currentPos = (orientation == HorizontalScrollbar) ? m_currentPosX : m_currentPosY;
    float newPos = clampScrollPosition(orientation, currentPos + step * delta);
    if (currentPos == newPos)
        return false;
    currentPos = newPos;

    notifyPositionChanged();

    return true;
}

void ScrollAnimator::scrollToOffsetWithoutAnimation(const FloatPoint& offset)
{
    m_currentPosX = offset.x();
    m_currentPosY = offset.y();
    notifyPositionChanged();
}

bool ScrollAnimator::handleWheelEvent(const PlatformWheelEvent& e)
{
    bool canScrollX = m_scrollableArea->userInputScrollable(HorizontalScrollbar);
    bool canScrollY = m_scrollableArea->userInputScrollable(VerticalScrollbar);

    // Accept the event if we are scrollable in that direction and can still
    // scroll any further.
    float deltaX = canScrollX ? e.deltaX() : 0;
    float deltaY = canScrollY ? e.deltaY() : 0;

    bool handled = false;

#if !OS(MACOSX)
    ScrollGranularity granularity = e.hasPreciseScrollingDeltas() ? ScrollByPrecisePixel : ScrollByPixel;
#else
    ScrollGranularity granularity = ScrollByPixel;
#endif

    IntSize maxForwardScrollDelta = m_scrollableArea->maximumScrollPosition() - m_scrollableArea->scrollPosition();
    IntSize maxBackwardScrollDelta = m_scrollableArea->scrollPosition() - m_scrollableArea->minimumScrollPosition();
    if ((deltaX < 0 && maxForwardScrollDelta.width() > 0)
        || (deltaX > 0 && maxBackwardScrollDelta.width() > 0)
        || (deltaY < 0 && maxForwardScrollDelta.height() > 0)
        || (deltaY > 0 && maxBackwardScrollDelta.height() > 0)) {
        handled = true;

        if (deltaY) {
            if (e.granularity() == ScrollByPageWheelEvent) {
                bool negative = deltaY < 0;
                deltaY = m_scrollableArea->pageStep(VerticalScrollbar);
                if (negative)
                    deltaY = -deltaY;
            }

            scroll(VerticalScrollbar, granularity, m_scrollableArea->pixelStep(VerticalScrollbar), -deltaY);
        }

        if (deltaX) {
            if (e.granularity() == ScrollByPageWheelEvent) {
                bool negative = deltaX < 0;
                deltaX = m_scrollableArea->pageStep(HorizontalScrollbar);
                if (negative)
                    deltaX = -deltaX;
            }

            scroll(HorizontalScrollbar, granularity, m_scrollableArea->pixelStep(HorizontalScrollbar), -deltaX);
        }
    }
    return handled;
}

void ScrollAnimator::setCurrentPosition(const FloatPoint& position)
{
    m_currentPosX = position.x();
    m_currentPosY = position.y();
}

FloatPoint ScrollAnimator::currentPosition() const
{
    return FloatPoint(m_currentPosX, m_currentPosY);
}

void ScrollAnimator::notifyPositionChanged()
{
    m_scrollableArea->setScrollOffsetFromAnimation(IntPoint(m_currentPosX, m_currentPosY));
}

float ScrollAnimator::clampScrollPosition(ScrollbarOrientation orientation, float pos)
{
    float maxScrollPos = m_scrollableArea->maximumScrollPosition(orientation);
    float minScrollPos = m_scrollableArea->minimumScrollPosition(orientation);
    return std::max(std::min(pos, maxScrollPos), minScrollPos);
}

} // namespace blink