gecko-dev/layout/painting/RetainedDisplayListHelpers.h

/* -*- 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 RETAINEDDISPLAYLISTHELPERS_H_
#define RETAINEDDISPLAYLISTHELPERS_H_

#include "PLDHashTable.h"

struct DisplayItemKey
{
  bool operator ==(const DisplayItemKey& aOther) const {
    return mFrame == aOther.mFrame &&
           mPerFrameKey == aOther.mPerFrameKey;
  }

  nsIFrame* mFrame;
  uint32_t mPerFrameKey;
};

class DisplayItemHashEntry : public PLDHashEntryHdr
{
public:
  typedef DisplayItemKey KeyType;
  typedef const DisplayItemKey* KeyTypePointer;

  explicit DisplayItemHashEntry(KeyTypePointer aKey)
    : mKey(*aKey) {}
  explicit DisplayItemHashEntry(const DisplayItemHashEntry& aCopy)=default;

  ~DisplayItemHashEntry() = default;

  KeyType GetKey() const { return mKey; }
  bool KeyEquals(KeyTypePointer aKey) const
  {
    return mKey == *aKey;
  }

  static KeyTypePointer KeyToPointer(KeyType& aKey) { return &aKey; }
  static PLDHashNumber HashKey(KeyTypePointer aKey)
  {
    if (!aKey)
      return 0;

    return mozilla::HashGeneric(aKey->mFrame, aKey->mPerFrameKey);
  }
  enum { ALLOW_MEMMOVE = true };

  DisplayItemKey mKey;
};

template <typename T>
bool SpanContains(mozilla::Span<const T>& aSpan, T aItem)
{
  for (const T& i : aSpan) {
    if (i == aItem) {
      return true;
    }
  }
  return false;
}

class OldListUnits {};
class MergedListUnits {};

template <typename Units>
struct Index {
  Index()
    : val(0)
  {}
  explicit Index(size_t aVal)
    : val(aVal)
  {}

  bool operator==(const Index<Units>& aOther) const
  {
    return val == aOther.val;
  }

  size_t val;
};
typedef Index<OldListUnits> OldListIndex;
typedef Index<MergedListUnits> MergedListIndex;


template <typename T>
class DirectedAcyclicGraph {
public:
  DirectedAcyclicGraph() {}
  DirectedAcyclicGraph(DirectedAcyclicGraph&& aOther)
    : mNodesInfo(std::move(aOther.mNodesInfo))
    , mDirectPredecessorList(std::move(aOther.mDirectPredecessorList))
  {}

  DirectedAcyclicGraph& operator=(DirectedAcyclicGraph&& aOther)
  {
    mNodesInfo = std::move(aOther.mNodesInfo);
    mDirectPredecessorList = std::move(aOther.mDirectPredecessorList);
    return *this;
  }

  Index<T> AddNode(mozilla::Span<const Index<T>> aDirectPredecessors,
                   const mozilla::Maybe<Index<T>>& aExtraPredecessor = mozilla::Nothing())
  {
    size_t index = mNodesInfo.Length();
    mNodesInfo.AppendElement(NodeInfo(mDirectPredecessorList.Length(), aDirectPredecessors.Length()));
    if (aExtraPredecessor && !SpanContains(aDirectPredecessors, aExtraPredecessor.value())) {
      mNodesInfo.LastElement().mDirectPredecessorCount++;
      mDirectPredecessorList.SetCapacity(mDirectPredecessorList.Length() + aDirectPredecessors.Length() + 1);
      mDirectPredecessorList.AppendElements(aDirectPredecessors);
      mDirectPredecessorList.AppendElement(aExtraPredecessor.value());
    } else {
      mDirectPredecessorList.AppendElements(aDirectPredecessors);
    }
    return Index<T>(index);
  }

  size_t Length()
  {
    return mNodesInfo.Length();
  }

  mozilla::Span<Index<T>> GetDirectPredecessors(Index<T> aNodeIndex)
  {
    NodeInfo& node = mNodesInfo[aNodeIndex.val];
    return mozilla::MakeSpan(mDirectPredecessorList).Subspan(node.mIndexInDirectPredecessorList,
                                                             node.mDirectPredecessorCount);
  }

  template<typename OtherUnits>
  void EnsureCapacityFor(const DirectedAcyclicGraph<OtherUnits>& aOther)
  {
    mNodesInfo.SetCapacity(aOther.mNodesInfo.Length());
    mDirectPredecessorList.SetCapacity(aOther.mDirectPredecessorList.Length());
  }

  void Clear()
  {
    mNodesInfo.Clear();
    mDirectPredecessorList.Clear();
  }

  struct NodeInfo {
    NodeInfo(size_t aIndexInDirectPredecessorList,
             size_t aDirectPredecessorCount)
      : mIndexInDirectPredecessorList(aIndexInDirectPredecessorList)
      , mDirectPredecessorCount(aDirectPredecessorCount)
    {}
    size_t mIndexInDirectPredecessorList;
    size_t mDirectPredecessorCount;
  };

  nsTArray<NodeInfo> mNodesInfo;
  nsTArray<Index<T>> mDirectPredecessorList;
};

struct RetainedDisplayListBuilder;
class nsDisplayItem;

struct OldItemInfo {
  explicit OldItemInfo(nsDisplayItem* aItem)
    : mItem(aItem)
    , mUsed(false)
    , mDiscarded(false)
  {}

  void AddedToMergedList(MergedListIndex aIndex)
  {
    MOZ_ASSERT(!IsUsed());
    mUsed = true;
    mIndex = aIndex;
    mItem = nullptr;
  }

  void AddedMatchToMergedList(RetainedDisplayListBuilder* aBuilder,
                              MergedListIndex aIndex);
  void Discard(RetainedDisplayListBuilder* aBuilder,
               nsTArray<MergedListIndex>&& aDirectPredecessors);
  bool IsUsed()
  {
    return mUsed;
  }

  bool IsDiscarded()
  {
    MOZ_ASSERT(IsUsed());
    return mDiscarded;
  }

  bool IsChanged();

  nsDisplayItem* mItem;
  bool mUsed;
  bool mDiscarded;
  MergedListIndex mIndex;
  nsTArray<MergedListIndex> mDirectPredecessors;
};

#endif // RETAINEDDISPLAYLISTHELPERS_H_