third_party/WebKit/Source/core/frame/TopControls.h

// Copyright 2015 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 TopControls_h
#define TopControls_h

#include "core/CoreExport.h"
#include "platform/heap/Handle.h"
#include "public/platform/WebTopControlsState.h"
#include "wtf/OwnPtr.h"
#include "wtf/PassOwnPtr.h"

namespace blink {
class FrameHost;
class FloatSize;

// This class encapsulate data and logic required to show/hide top controls
// duplicating cc::TopControlsManager behaviour.  Top controls' self-animation
// to completion is still handled by compositor and kicks in when scrolling is
// complete (i.e, upon ScrollEnd or FlingEnd).
class CORE_EXPORT TopControls final : public GarbageCollected<TopControls> {
public:
    static TopControls* create(const FrameHost& host)
    {
        return new TopControls(host);
    }

    DECLARE_TRACE();

    // The amount that the viewport was shrunk by to accommodate the top
    // controls.
    float layoutHeight();
    // The amount that top controls are currently shown.
    float contentOffset();

    float height() const { return m_height; }
    bool shrinkViewport() const { return m_shrinkViewport; }
    void setHeight(float height, bool shrinkViewport);

    float shownRatio() const { return m_shownRatio; }
    void setShownRatio(float);

    void updateConstraints(WebTopControlsState constraints);

    void scrollBegin();

    // Scrolls top controls vertically if possible and returns the remaining scroll
    // amount.
    FloatSize scrollBy(FloatSize scrollDelta);

private:
    explicit TopControls(const FrameHost&);
    void resetBaseline();

    Member<const FrameHost> m_frameHost;

    // The top controls height regardless of whether it is visible or not.
    float m_height;

    // The top controls shown amount (normalized from 0 to 1) since the last
    // compositor commit. This value is updated from two sources:
    // (1) compositor (impl) thread at the beginning of frame if it has
    //     scrolled top controls since last commit.
    // (2) blink (main) thread updates this value if it scrolls top controls
    //     when responding to gesture scroll events.
    // This value is reflected in web layer tree and is synced with compositor
    // during the commit.
    float m_shownRatio;

    // Content offset when last re-baseline occurred.
    float m_baselineContentOffset;

    // Accumulated scroll delta since last re-baseline.
    float m_accumulatedScrollDelta;

    // If this is true, then the embedder shrunk the WebView size by the top
    // controls height.
    bool m_shrinkViewport;

    // Constraints on the top controls state
    WebTopControlsState m_permittedState;

};
} // namespace blink

#endif // TopControls_h