gfx/layers/ScrollableLayerGuid.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef GFX_SCROLLABLELAYERGUID_H
   8 #define GFX_SCROLLABLELAYERGUID_H
   9
  10 #include <iosfwd>                        // for ostream
  11 #include <stdint.h>                      // for uint8_t, uint32_t, uint64_t
  12 #include "mozilla/layers/LayersTypes.h"  // for LayersId
  13 #include "nsHashKeys.h"                  // for nsUint64HashKey
  14
  15 namespace mozilla {
  16 namespace layers {
  17
  18 /**
  19  * This class allows us to uniquely identify a scrollable layer. The
  20  * mLayersId identifies the layer tree (corresponding to a child process
  21  * and/or tab) that the scrollable layer belongs to. The mPresShellId
  22  * is a temporal identifier (corresponding to the document loaded that
  23  * contains the scrollable layer, which may change over time). The
  24  * mScrollId corresponds to the actual frame that is scrollable.
  25  */
  26 struct ScrollableLayerGuid {
  27   // We use IDs to identify frames across processes.
  28   typedef uint64_t ViewID;
  29   typedef nsUint64HashKey ViewIDHashKey;
  30   static const ViewID NULL_SCROLL_ID;  // This container layer does not scroll.
  31   static const ViewID START_SCROLL_ID = 2;  // This is the ID that scrolling
  32                                             // subframes will begin at.
  33
  34   LayersId mLayersId;
  35   uint32_t mPresShellId;
  36   ViewID mScrollId;
  37
  38   ScrollableLayerGuid();
  39
  40   ScrollableLayerGuid(LayersId aLayersId, uint32_t aPresShellId,
  41                       ViewID aScrollId);
  42
  43   ScrollableLayerGuid(const ScrollableLayerGuid& other) = default;
  44
  45   ~ScrollableLayerGuid() = default;
  46
  47   bool operator==(const ScrollableLayerGuid& other) const;
  48   bool operator!=(const ScrollableLayerGuid& other) const;
  49   bool operator<(const ScrollableLayerGuid& other) const;
  50
  51   friend std::ostream& operator<<(std::ostream& aOut,
  52                                   const ScrollableLayerGuid& aGuid);
  53
  54   using Comparator = bool (*)(const ScrollableLayerGuid&,
  55                               const ScrollableLayerGuid&);
  56
  57   static bool EqualsIgnoringPresShell(const ScrollableLayerGuid& aA,
  58                                       const ScrollableLayerGuid& aB);
  59
  60   // Helper structs to use as hash/equality functions in std::unordered_map.
  61   // e.g. std::unordered_map<ScrollableLayerGuid,
  62   //                    ValueType,
  63   //                    ScrollableLayerGuid::HashFn> myMap;
  64   // std::unordered_map<ScrollableLayerGuid,
  65   //                    ValueType,
  66   //                    ScrollableLayerGuid::HashIgnoringPresShellFn,
  67   //                    ScrollableLayerGuid::EqualIgnoringPresShellFn> myMap;
  68
  69   struct HashFn {
  70     std::size_t operator()(const ScrollableLayerGuid& aGuid) const;
  71   };
  72
  73   struct HashIgnoringPresShellFn {
  74     std::size_t operator()(const ScrollableLayerGuid& aGuid) const;
  75   };
  76
  77   struct EqualIgnoringPresShellFn {
  78     bool operator()(const ScrollableLayerGuid& lhs,
  79                     const ScrollableLayerGuid& rhs) const;
  80   };
  81 };
  82
  83 }  // namespace layers
  84 }  // namespace mozilla
  85
  86 #endif /* GFX_SCROLLABLELAYERGUID_H */