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// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef RootScrollerController_h
#define RootScrollerController_h
#include "core/CoreExport.h"
#include "platform/heap/Handle.h"
namespace blink {
class Document;
class Element;
class PaintLayer;
// Manages the root scroller associated with a given document. The root
// scroller causes browser controls movement, overscroll effects and prevents
// chaining scrolls up further in the DOM. It can be set from script using
// document.setRootScroller.
//
// There are two notions of a root scroller in this class: m_rootScroller and
// m_effectiveRootScroller. The former is the Element that was set as the root
// scroller using document.setRootScroller. If the page didn't set a root
// scroller this will be nullptr. The "effective" root scroller is the current
// Node we're using internally to apply viewport scrolling actions. Both these
// elements come from this controller's associated Document. The final "global"
// root scroller, the one whose scrolling hides browser controls, may be in a
// different frame.
//
// If the currently set m_rootScroller is a valid element to become the root
// scroller, it will be promoted to the effective root scroller. If it is not
// valid, the effective root scroller will fall back to the document Node. The
// rules for what makes an element a valid root scroller are set in
// isValidRootScroller(). The validity of the current root scroller is
// re-checked after each layout.
class CORE_EXPORT RootScrollerController
: public GarbageCollected<RootScrollerController> {
public:
// Creates a RootScrollerController for the given document. Note: instances
// of this class need to be made aware of layout updates.
static RootScrollerController* create(Document&);
DECLARE_TRACE();
// Sets the element that will be used as the root scroller. This can be
// nullptr, in which case we'll use the default element (documentElement) as
// the effective root scroller.
void set(Element*);
// Returns the element currently set as the root scroller from script. This
// differs from the effective root scroller since the set Element may not
// currently be a valid root scroller. e.g. If the page sets an Element
// with `display: none`, get() will return that element, even though the
// effective root scroller will remain the document Node.
Element* get() const;
// This returns the Element that's actually being used to control viewport
// actions right now. This is different from get() if a root scroller hasn't
// been set, or if the set root scroller isn't currently a valid scroller.
Node& effectiveRootScroller() const;
// This class needs to be informed of changes in layout so that it can
// determine if the current root scroller is still valid or if it must be
// replaced by the default root scroller.
void didUpdateLayout();
// Returns the PaintLayer associated with the currently effective root
// scroller.
PaintLayer* rootScrollerPaintLayer() const;
// Used to determine which Element should scroll the viewport. This is
// needed since Blink's scrolling machinery works on Elements whereas the
// document *Node* also scrolls so we need to designate an element one
// Element as the viewport scroller. Sadly, this is *not* the
// document.scrollingElement in general.
bool scrollsViewport(const Element&) const;
private:
RootScrollerController(Document&);
// Ensures the effective root scroller is currently valid and replaces it
// with the default if not.
void recomputeEffectiveRootScroller();
// Determines whether the given element meets the criteria to become the
// effective root scroller.
bool isValidRootScroller(const Element&) const;
// The owning Document whose root scroller this object manages.
WeakMember<Document> m_document;
// The Element that was set from script as rootScroller for this Document.
// Depending on its validity to be the root scroller (e.g. a display: none
// element isn't a valid root scroller), this may not actually be the
// Element being used as the root scroller.
WeakMember<Element> m_rootScroller;
// The Node currently being used as the root scroller in this Document.
// If the m_rootScroller is valid this will point to it. Otherwise, it'll
// use the document Node. It'll never be nullptr since the Document owns the
// RootScrollerController.
Member<Node> m_effectiveRootScroller;
bool m_documentHasDocumentElement;
};
} // namespace blink
#endif // RootScrollerController_h
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