third_party/WebKit/Source/core/frame/BrowserControls.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 BrowserControls_h
#define BrowserControls_h

#include "core/CoreExport.h"
#include "platform/heap/Handle.h"
#include "public/platform/WebBrowserControlsState.h"

namespace blink {
class Page;
class FloatSize;

// This class encapsulate data and logic required to show/hide browser controls
// duplicating cc::BrowserControlsManager behaviour.  Browser 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 BrowserControls final
    : public GarbageCollected<BrowserControls> {
 public:
  static BrowserControls* Create(const Page& page) {
    return new BrowserControls(page);
  }

  DECLARE_TRACE();

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

  float Height() const { return height_; }
  bool ShrinkViewport() const { return shrink_viewport_; }
  void SetHeight(float height, bool shrink_viewport);

  float ShownRatio() const { return shown_ratio_; }
  void SetShownRatio(float);

  void UpdateConstraintsAndState(WebBrowserControlsState constraints,
                                 WebBrowserControlsState current,
                                 bool animate);

  void ScrollBegin();

  // Scrolls browser controls vertically if possible and returns the remaining
  // scroll amount.
  FloatSize ScrollBy(FloatSize scroll_delta);

  WebBrowserControlsState PermittedState() const { return permitted_state_; }

 private:
  explicit BrowserControls(const Page&);
  void ResetBaseline();

  Member<const Page> page_;

  // The browser controls height regardless of whether it is visible or not.
  float height_;

  // The browser 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 browser controls since last commit.
  // (2) blink (main) thread updates this value if it scrolls browser controls
  //     when responding to gesture scroll events.
  // This value is reflected in web layer tree and is synced with compositor
  // during the commit.
  float shown_ratio_;

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

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

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

  // Constraints on the browser controls state
  WebBrowserControlsState permitted_state_;
};
}  // namespace blink

#endif  // BrowserControls_h