flutter_flutter/engine/platform/scroll/ScrollableArea.h

/*
 * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef SKY_ENGINE_PLATFORM_SCROLL_SCROLLABLEAREA_H_
#define SKY_ENGINE_PLATFORM_SCROLL_SCROLLABLEAREA_H_

#include "sky/engine/platform/PlatformExport.h"
#include "sky/engine/platform/scroll/ScrollAnimator.h"
#include "sky/engine/platform/scroll/Scrollbar.h"
#include "sky/engine/wtf/Noncopyable.h"
#include "sky/engine/wtf/Vector.h"

namespace blink {

class FloatPoint;
class HostWindow;
class ScrollAnimator;

enum ScrollBehavior {
    ScrollBehaviorAuto,
    ScrollBehaviorInstant,
    ScrollBehaviorSmooth,
};

enum IncludeScrollbarsInRect {
    ExcludeScrollbars,
    IncludeScrollbars,
};

class PLATFORM_EXPORT ScrollableArea {
    WTF_MAKE_NONCOPYABLE(ScrollableArea);
public:
    static int pixelsPerLineStep();
    static float minFractionToStepWhenPaging();
    static int maxOverlapBetweenPages();

    // The window that hosts the ScrollView. The ScrollView will communicate scrolls and repaints to the
    // host window in the window's coordinate space.
    virtual HostWindow* hostWindow() const = 0;

    bool scroll(ScrollDirection, ScrollGranularity, float delta = 1);
    void scrollToOffsetWithoutAnimation(const FloatPoint&);
    void scrollToOffsetWithoutAnimation(ScrollbarOrientation, float offset);

    static bool scrollBehaviorFromString(const String&, ScrollBehavior&);

    // Functions for controlling if you can scroll past the end of the document.
    bool constrainsScrollingToContentEdge() const { return m_constrainsScrollingToContentEdge; }
    void setConstrainsScrollingToContentEdge(bool constrainsScrollingToContentEdge) { m_constrainsScrollingToContentEdge = constrainsScrollingToContentEdge; }

    void setVerticalScrollElasticity(ScrollElasticity scrollElasticity) { m_verticalScrollElasticity = scrollElasticity; }
    ScrollElasticity verticalScrollElasticity() const { return static_cast<ScrollElasticity>(m_verticalScrollElasticity); }

    void setHorizontalScrollElasticity(ScrollElasticity scrollElasticity) { m_horizontalScrollElasticity = scrollElasticity; }
    ScrollElasticity horizontalScrollElasticity() const { return static_cast<ScrollElasticity>(m_horizontalScrollElasticity); }

    void contentAreaDidShow() const;
    void contentAreaDidHide() const;

    void finishCurrentScrollAnimations() const;

    void didAddScrollbar(Scrollbar*, ScrollbarOrientation);
    void willRemoveScrollbar(Scrollbar*, ScrollbarOrientation);

    void contentsResized();

    bool hasOverlayScrollbars() const;

    // This getter will create a ScrollAnimator if it doesn't already exist.
    ScrollAnimator* scrollAnimator() const;

    // This getter will return null if the ScrollAnimator hasn't been created yet.
    ScrollAnimator* existingScrollAnimator() const { return m_animators ? m_animators->scrollAnimator.get() : 0; }

    const IntPoint& scrollOrigin() const { return m_scrollOrigin; }
    bool scrollOriginChanged() const { return m_scrollOriginChanged; }

    // FIXME(bokan): Meaningless name, rename to isActiveFocus
    virtual bool isActive() const = 0;
    virtual int scrollSize(ScrollbarOrientation) const = 0;

    // Convert points and rects between the scrollbar and its containing view.
    // The client needs to implement these in order to be aware of layout effects
    // like CSS transforms.
    virtual IntRect convertFromScrollbarToContainingView(const Scrollbar*, const IntRect&) const = 0;
    virtual IntRect convertFromContainingViewToScrollbar(const Scrollbar*, const IntRect&) const = 0;
    virtual IntPoint convertFromScrollbarToContainingView(const Scrollbar*, const IntPoint&) const = 0;
    virtual IntPoint convertFromContainingViewToScrollbar(const Scrollbar*, const IntPoint&) const = 0;

    virtual Scrollbar* horizontalScrollbar() const = 0;
    virtual Scrollbar* verticalScrollbar() const = 0;

    // scrollPosition is relative to the scrollOrigin. i.e. If the page is RTL
    // then scrollPosition will be negative.
    virtual IntPoint scrollPosition() const = 0;
    virtual IntPoint minimumScrollPosition() const = 0;
    virtual IntPoint maximumScrollPosition() const = 0;

    virtual IntSize contentsSize() const = 0;

    bool shouldSuspendScrollAnimations() const { return true; }

    IntPoint clampScrollPosition(const IntPoint&) const;

    // Returns true if the GraphicsLayer tree needs to be rebuilt.
    virtual bool updateAfterCompositingChange() = 0;

    virtual bool userInputScrollable(ScrollbarOrientation) const = 0;
    virtual bool shouldPlaceVerticalScrollbarOnLeft() const = 0;

    int scrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? scrollPosition().x() : scrollPosition().y(); }
    int minimumScrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? minimumScrollPosition().x() : minimumScrollPosition().y(); }
    int maximumScrollPosition(ScrollbarOrientation orientation) { return orientation == HorizontalScrollbar ? maximumScrollPosition().x() : maximumScrollPosition().y(); }
    int clampScrollPosition(ScrollbarOrientation orientation, int pos)  { return std::max(std::min(pos, maximumScrollPosition(orientation)), minimumScrollPosition(orientation)); }

protected:
    ScrollableArea();
    virtual ~ScrollableArea();

    void setScrollOrigin(const IntPoint&);
    void resetScrollOriginChanged() { m_scrollOriginChanged = false; }

private:
    void scrollPositionChanged(const IntPoint&);

    // NOTE: Only called from the ScrollAnimator.
    friend class ScrollAnimator;
    void setScrollOffsetFromAnimation(const IntPoint&);

    // This function should be overriden by subclasses to perform the actual
    // scroll of the content.
    virtual void setScrollOffset(const IntPoint&) = 0;

    int lineStep(ScrollbarOrientation) const;
    int documentStep(ScrollbarOrientation) const;
    virtual int pageStep(ScrollbarOrientation) const = 0;
    float pixelStep(ScrollbarOrientation) const;

    struct ScrollableAreaAnimators {
        OwnPtr<ScrollAnimator> scrollAnimator;
    };

    mutable OwnPtr<ScrollableAreaAnimators> m_animators;
    unsigned m_constrainsScrollingToContentEdge : 1;

    unsigned m_verticalScrollElasticity : 2; // ScrollElasticity
    unsigned m_horizontalScrollElasticity : 2; // ScrollElasticity

    unsigned m_scrollOriginChanged : 1;

    // There are 8 possible combinations of writing mode and direction. Scroll origin will be non-zero in the x or y axis
    // if there is any reversed direction or writing-mode. The combinations are:
    // writing-mode / direction     scrollOrigin.x() set    scrollOrigin.y() set
    // horizontal-tb / ltr          NO                      NO
    // horizontal-tb / rtl          YES                     NO
    // horizontal-bt / ltr          NO                      YES
    // horizontal-bt / rtl          YES                     YES
    // vertical-lr / ltr            NO                      NO
    // vertical-lr / rtl            NO                      YES
    // vertical-rl / ltr            YES                     NO
    // vertical-rl / rtl            YES                     YES
    IntPoint m_scrollOrigin;
};

} // namespace blink

#endif  // SKY_ENGINE_PLATFORM_SCROLL_SCROLLABLEAREA_H_