layout/painting/DisplayItemClipChain.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 DISPLAYITEMCLIPCHAIN_H_
   8 #define DISPLAYITEMCLIPCHAIN_H_
   9
  10 #include "mozilla/Assertions.h"
  11 #include "DisplayItemClip.h"
  12 #include "nsString.h"
  13
  14 class nsIScrollableFrame;
  15
  16 namespace mozilla {
  17
  18 struct ActiveScrolledRoot;
  19
  20 /**
  21  * A DisplayItemClipChain is a linked list of DisplayItemClips where each clip
  22  * is associated with an active scrolled root that describes what the clip
  23  * moves with.
  24  * We use a chain instead of just one intersected clip due to async scrolling:
  25  * A clip that moves along with a display item can be fused to the item's
  26  * contents when drawing the layer contents, but all other clips in the chain
  27  * need to be kept separate so that they can be applied at composition time,
  28  * after any async scroll offsets have been applied.
  29  * The clip chain is created during display list construction by the builder's
  30  * DisplayListClipState.
  31  * The clip chain order is determined by the active scrolled root order.
  32  * For every DisplayItemClipChain object |clipChain|, the following holds:
  33  * !clipChain->mParent ||
  34  * ActiveScrolledRoot::IsAncestor(clipChain->mParent->mASR, clipChain->mASR).
  35  * The clip chain can skip over active scrolled roots. That just means that
  36  * there is no clip that moves with the skipped ASR in this chain.
  37  */
  38 struct DisplayItemClipChain {
  39   /**
  40    * Get the display item clip in this chain that moves with aASR, or nullptr
  41    * if no such clip exists. aClipChain can be null.
  42    */
  43   static const DisplayItemClip* ClipForASR(
  44       const DisplayItemClipChain* aClipChain, const ActiveScrolledRoot* aASR);
  45
  46   static bool Equal(const DisplayItemClipChain* aClip1,
  47                     const DisplayItemClipChain* aClip2);
  48   /**
  49    * Hash function that returns the same value for any two clips A and B
  50    * where Equal(A, B) is true.
  51    */
  52   static uint32_t Hash(const DisplayItemClipChain* aClip);
  53
  54   static nsCString ToString(const DisplayItemClipChain* aClipChain);
  55
  56   bool HasRoundedCorners() const;
  57
  58   void AddRef() { mRefCount++; }
  59   void Release() {
  60     MOZ_ASSERT(mRefCount > 0);
  61     mRefCount--;
  62   }
  63
  64   DisplayItemClipChain(const DisplayItemClip& aClip,
  65                        const ActiveScrolledRoot* aASR,
  66                        const DisplayItemClipChain* aParent,
  67                        DisplayItemClipChain* aNextClipChainToDestroy)
  68       : mClip(aClip),
  69         mASR(aASR),
  70         mParent(aParent),
  71         mNextClipChainToDestroy(aNextClipChainToDestroy)
  72 #if defined(DEBUG) || defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
  73         ,
  74         mOnStack(true)
  75 #endif
  76   {
  77   }
  78
  79   DisplayItemClipChain()
  80       : mASR(nullptr),
  81         mNextClipChainToDestroy(nullptr)
  82 #if defined(DEBUG) || defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
  83         ,
  84         mOnStack(true)
  85 #endif
  86   {
  87   }
  88
  89   DisplayItemClip mClip;
  90   const ActiveScrolledRoot* mASR;
  91   RefPtr<const DisplayItemClipChain> mParent;
  92   uint32_t mRefCount = 0;
  93   DisplayItemClipChain* mNextClipChainToDestroy;
  94 #if defined(DEBUG) || defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
  95   bool mOnStack;
  96 #endif
  97 };
  98
  99 struct DisplayItemClipChainHasher {
 100   typedef const DisplayItemClipChain* Key;
 101
 102   std::size_t operator()(const Key& aKey) const {
 103     return DisplayItemClipChain::Hash(aKey);
 104   }
 105 };
 106
 107 struct DisplayItemClipChainEqualer {
 108   typedef const DisplayItemClipChain* Key;
 109
 110   bool operator()(const Key& lhs, const Key& rhs) const {
 111     return DisplayItemClipChain::Equal(lhs, rhs);
 112   }
 113 };
 114
 115 }  // namespace mozilla
 116
 117 #endif /* DISPLAYITEMCLIPCHAIN_H_ */