third_party/WebKit/Source/core/observer/ResizeObserverController.h

// 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 ResizeObserverController_h
#define ResizeObserverController_h

#include "platform/heap/Handle.h"

namespace blink {

class ResizeObserver;

// ResizeObserverController keeps track of all ResizeObservers
// in a single Document.
//
// The observation API is used to integrate ResizeObserver
// and the event loop. It delivers notification in a loop.
// In each iteration, only notifications deeper than the
// shallowest notification from previous iteration are delivered.
class ResizeObserverController final : public GarbageCollected<ResizeObserverController> {
public:
    static const size_t kDepthBottom = 4096;

    ResizeObserverController();

    void addObserver(ResizeObserver&);

    // observation API
    // Returns depth of shallowest observed node, kDepthLimit if none.
    size_t gatherObservations(size_t deeperThan);
    // Returns true if gatherObservations has skipped observations
    // because they were too shallow.
    bool skippedObservations();
    void deliverObservations();
    void clearObservations();
    void observerChanged()  { m_observersChanged = true; }

    DECLARE_TRACE();

private:
    // Active observers
    HeapHashSet<WeakMember<ResizeObserver>> m_observers;
    // True if any observers were changed since last notification.
    bool m_observersChanged;
};

} // namespace blink

#endif