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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 ElementVisibilityObserver_h
#define ElementVisibilityObserver_h
#include "core/CoreExport.h"
#include "core/dom/IntersectionObserver.h"
#include "platform/heap/Heap.h"
#include "platform/heap/Member.h"
namespace blink {
class Element;
// ElementVisibilityObserver is a helper class to be used to track the
// visibility of an Element in the viewport. Creating an
// ElementVisibilityObserver is a no-op with regards to CPU cycle. The observing
// has be started by calling |start()| and can be stopped with |stop()|.
// When creating an instance, the caller will have to pass a callback taking
// a boolean as an argument. The boolean will be the new visibility state.
// The ElementVisibilityObserver is implemented on top of IntersectionObserver.
// It is a layer meant to simplify the usage for C++ Blink code checking for the
// visibility of an element.
class CORE_EXPORT ElementVisibilityObserver final
: public GarbageCollectedFinalized<ElementVisibilityObserver> {
WTF_MAKE_NONCOPYABLE(ElementVisibilityObserver);
public:
using VisibilityCallback = Function<void(bool), WTF::SameThreadAffinity>;
ElementVisibilityObserver(Element*, std::unique_ptr<VisibilityCallback>);
virtual ~ElementVisibilityObserver();
void start();
void stop();
void deliverObservationsForTesting();
DECLARE_VIRTUAL_TRACE();
private:
class ElementVisibilityCallback;
void onVisibilityChanged(
const HeapVector<Member<IntersectionObserverEntry>>&);
Member<Element> m_element;
Member<IntersectionObserver> m_intersectionObserver;
std::unique_ptr<VisibilityCallback> m_callback;
};
} // namespace blink
#endif // ElementVisibilityObserver_h
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