ScrollableLayerGuid.h

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef GFX_SCROLLABLELAYERGUID_H

#define GFX_SCROLLABLELAYERGUID_H

#include <iosfwd>                        // for ostream

#include <stdint.h>                      // for uint8_t, uint32_t, uint64_t

#include "mozilla/layers/LayersTypes.h"  // for LayersId

#include "nsHashKeys.h"                  // for nsUint64HashKey

namespace mozilla {

namespace layers {

/**

 * This class allows us to uniquely identify a scrollable layer. The

 * mLayersId identifies the layer tree (corresponding to a child process

 * and/or tab) that the scrollable layer belongs to. The mPresShellId

 * is a temporal identifier (corresponding to the document loaded that

 * contains the scrollable layer, which may change over time). The

 * mScrollId corresponds to the actual frame that is scrollable.

*/

struct ScrollableLayerGuid {

  // We use IDs to identify frames across processes.

  typedef uint64_t ViewID;

  typedef nsUint64HashKey ViewIDHashKey;

  static const ViewID NULL_SCROLL_ID;  // This container layer does not scroll.

  static const ViewID START_SCROLL_ID = 2;  // This is the ID that scrolling

                                            // subframes will begin at.

  LayersId mLayersId;

  uint32_t mPresShellId;

  ViewID mScrollId;

  ScrollableLayerGuid();

  ScrollableLayerGuid(LayersId aLayersId, uint32_t aPresShellId,

                      ViewID aScrollId);

  ScrollableLayerGuid(const ScrollableLayerGuid& other) = default;

  ~ScrollableLayerGuid() = default;

  bool operator==(const ScrollableLayerGuid& other) const;

  bool operator!=(const ScrollableLayerGuid& other) const;

  bool operator<(const ScrollableLayerGuid& other) const;

  friend std::ostream& operator<<(std::ostream& aOut,

                                  const ScrollableLayerGuid& aGuid);

  using Comparator = bool (*)(const ScrollableLayerGuid&,

                              const ScrollableLayerGuid&);

  static bool EqualsIgnoringPresShell(const ScrollableLayerGuid& aA,

                                      const ScrollableLayerGuid& aB);

  // Helper structs to use as hash/equality functions in std::unordered_map.

  // e.g. std::unordered_map<ScrollableLayerGuid,

  //                    ValueType,

  //                    ScrollableLayerGuid::HashFn> myMap;

  // std::unordered_map<ScrollableLayerGuid,

  //                    ValueType,

  //                    ScrollableLayerGuid::HashIgnoringPresShellFn,

  //                    ScrollableLayerGuid::EqualIgnoringPresShellFn> myMap;

  struct HashFn {

    std::size_t operator()(const ScrollableLayerGuid& aGuid) const;

};

  struct HashIgnoringPresShellFn {

    std::size_t operator()(const ScrollableLayerGuid& aGuid) const;

};

  struct EqualIgnoringPresShellFn {

    bool operator()(const ScrollableLayerGuid& lhs,

                    const ScrollableLayerGuid& rhs) const;

};

};

}  // namespace layers

}  // namespace mozilla

#endif /* GFX_SCROLLABLELAYERGUID_H */