gecko-dev/layout/painting/RetainedDisplayListBuilder.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 RETAINEDDISPLAYLISTBUILDER_H_
#define RETAINEDDISPLAYLISTBUILDER_H_

#include "nsDisplayList.h"
#include "mozilla/Maybe.h"
#include "mozilla/EnumSet.h"

class nsWindowSizes;

namespace mozilla {

class nsDisplayItem;
class nsDisplayList;

/**
 * RetainedDisplayListData contains frame invalidation information.
 * Currently this is implemented as a map of frame pointers to flags.
 */
struct RetainedDisplayListData {
  enum class FrameFlag : uint8_t { Modified, HasProps, HadWillChange };
  using FrameFlags = mozilla::EnumSet<FrameFlag, uint8_t>;

  RetainedDisplayListData();

  /**
   * Adds the frame to modified frames list.
   */
  void AddModifiedFrame(nsIFrame* aFrame);

  /**
   * Removes all the frames from this RetainedDisplayListData.
   */
  void Clear() {
    mFrames.Clear();
    mModifiedFrameCount = 0;
  }

  /**
   * Returns a mutable reference to flags set for the given |aFrame|.
   */
  FrameFlags& Flags(nsIFrame* aFrame) { return mFrames.LookupOrInsert(aFrame); }

  /**
   * Returns flags set for the given |aFrame|, or FrameFlags::None if the frame
   * is not in this RetainedDisplayListData.
   */
  FrameFlags GetFlags(nsIFrame* aFrame) const { return mFrames.Get(aFrame); }

  bool IsModified(nsIFrame* aFrame) const {
    return GetFlags(aFrame).contains(FrameFlag::Modified);
  }

  bool HasProps(nsIFrame* aFrame) const {
    return GetFlags(aFrame).contains(FrameFlag::HasProps);
  }

  /**
   * Returns an iterator to the underlying frame storage.
   */
  auto ConstIterator() { return mFrames.ConstIter(); }

  /**
   * Returns true if the modified frame limit has been reached.
   */
  bool AtModifiedFrameLimit() {
    return mModifiedFrameCount >= mModifiedFrameLimit;
  }

  bool GetModifiedFrameCount() { return mModifiedFrameCount; }

  /**
   * Removes the given |aFrame| from this RetainedDisplayListData.
   */
  bool Remove(nsIFrame* aFrame) { return mFrames.Remove(aFrame); }

 private:
  nsTHashMap<nsPtrHashKey<nsIFrame>, FrameFlags> mFrames;
  uint32_t mModifiedFrameCount = 0;
  uint32_t mModifiedFrameLimit;  // initialized to a pref value in constructor
};

enum class PartialUpdateResult { Failed, NoChange, Updated };

enum class PartialUpdateFailReason {
  NA,
  EmptyList,
  RebuildLimit,
  FrameType,
  Disabled,
  Content,
  VisibleRect,
};

struct RetainedDisplayListMetrics {
  RetainedDisplayListMetrics() { Reset(); }

  void Reset() {
    mNewItems = 0;
    mRebuiltItems = 0;
    mRemovedItems = 0;
    mReusedItems = 0;
    mTotalItems = 0;
    mPartialBuildDuration = 0;
    mFullBuildDuration = 0;
    mPartialUpdateFailReason = PartialUpdateFailReason::NA;
    mPartialUpdateResult = PartialUpdateResult::NoChange;
  }

  void StartBuild() { mStartTime = mozilla::TimeStamp::Now(); }

  void EndFullBuild() { mFullBuildDuration = Elapsed(); }

  void EndPartialBuild(PartialUpdateResult aResult) {
    mPartialBuildDuration = Elapsed();
    mPartialUpdateResult = aResult;
  }

  double Elapsed() {
    return (mozilla::TimeStamp::Now() - mStartTime).ToMilliseconds();
  }

  const char* FailReasonString() const {
    switch (mPartialUpdateFailReason) {
      case PartialUpdateFailReason::NA:
        return "N/A";
      case PartialUpdateFailReason::EmptyList:
        return "Empty list";
      case PartialUpdateFailReason::RebuildLimit:
        return "Rebuild limit";
      case PartialUpdateFailReason::FrameType:
        return "Frame type";
      case PartialUpdateFailReason::Disabled:
        return "Disabled";
      case PartialUpdateFailReason::Content:
        return "Content";
      case PartialUpdateFailReason::VisibleRect:
        return "VisibleRect";
      default:
        MOZ_ASSERT_UNREACHABLE("Enum value not handled!");
    }
  }

  unsigned int mNewItems;
  unsigned int mRebuiltItems;
  unsigned int mRemovedItems;
  unsigned int mReusedItems;
  unsigned int mTotalItems;

  mozilla::TimeStamp mStartTime;
  double mPartialBuildDuration;
  double mFullBuildDuration;
  PartialUpdateFailReason mPartialUpdateFailReason;
  PartialUpdateResult mPartialUpdateResult;
};

class RetainedDisplayListBuilder {
 public:
  RetainedDisplayListBuilder(nsIFrame* aReferenceFrame,
                             nsDisplayListBuilderMode aMode, bool aBuildCaret)
      : mBuilder(aReferenceFrame, aMode, aBuildCaret, true), mList(&mBuilder) {}
  ~RetainedDisplayListBuilder() { mList.DeleteAll(&mBuilder); }

  nsDisplayListBuilder* Builder() { return &mBuilder; }

  nsDisplayList* List() { return &mList; }

  RetainedDisplayListMetrics* Metrics() { return &mMetrics; }

  RetainedDisplayListData* Data() { return &mData; }

  PartialUpdateResult AttemptPartialUpdate(nscolor aBackstop);

  /**
   * Clears the modified state for frames in the retained display list data.
   */
  void ClearFramesWithProps();

  void ClearRetainedData();

  void ClearReuseableDisplayItems() { mBuilder.ClearReuseableDisplayItems(); }

  void AddSizeOfIncludingThis(nsWindowSizes&) const;

  NS_DECLARE_FRAME_PROPERTY_DELETABLE(Cached, RetainedDisplayListBuilder)

 private:
  void GetModifiedAndFramesWithProps(nsTArray<nsIFrame*>* aOutModifiedFrames,
                                     nsTArray<nsIFrame*>* aOutFramesWithProps);

  void IncrementSubDocPresShellPaintCount(nsDisplayItem* aItem);

  /**
   * A simple early exit heuristic to avoid slow partial display list rebuilds.
   * Returns true if a partial display list build should be attempted.
   */
  bool ShouldBuildPartial(nsTArray<nsIFrame*>& aModifiedFrames);

  /**
   * Recursively pre-processes the old display list tree before building the
   * new partial display lists, and serializes the old list into an array,
   * recording indices on items for fast lookup during merging. Builds an
   * initial linear DAG for the list if we don't have an existing one. Finds
   * items that have a different AGR from the specified one, and marks them to
   * also be built so that we get relative ordering correct. Passes
   * aKeepLinked=true internally for sub-lists that can't be changed to keep the
   * original list structure linked for fast re-use.
   */
  bool PreProcessDisplayList(
      RetainedDisplayList* aList, nsIFrame* aAGR, PartialUpdateResult& aUpdated,
      nsIFrame* aAsyncAncestor, const ActiveScrolledRoot* aAsyncAncestorASR,
      nsIFrame* aOuterFrame = nullptr, uint32_t aCallerKey = 0,
      uint32_t aNestingDepth = 0, bool aKeepLinked = false);

  /**
   * Merges items from aNewList into non-invalidated items from aOldList and
   * stores the result in aOutList.
   *
   * aOuterItem is a pointer to an item that owns one of the lists, if
   * available. If both lists are populated, then both outer items must not be
   * invalidated, and identical, so either can be passed here.
   *
   * Returns true if changes were made, and the resulting display list (in
   * aOutList) is different from aOldList.
   */
  bool MergeDisplayLists(
      nsDisplayList* aNewList, RetainedDisplayList* aOldList,
      RetainedDisplayList* aOutList,
      mozilla::Maybe<const mozilla::ActiveScrolledRoot*>& aOutContainerASR,
      nsDisplayItem* aOuterItem = nullptr);

  bool ComputeRebuildRegion(nsTArray<nsIFrame*>& aModifiedFrames,
                            nsRect* aOutDirty, nsIFrame** aOutModifiedAGR,
                            nsTArray<nsIFrame*>& aOutFramesWithProps);

  bool ProcessFrame(nsIFrame* aFrame, nsDisplayListBuilder* aBuilder,
                    nsIFrame* aStopAtFrame,
                    nsTArray<nsIFrame*>& aOutFramesWithProps,
                    const bool aStopAtStackingContext, nsRect* aOutDirty,
                    nsIFrame** aOutModifiedAGR);

  nsIFrame* RootReferenceFrame() { return mBuilder.RootReferenceFrame(); }
  const nsIFrame* RootReferenceFrame() const {
    return mBuilder.RootReferenceFrame();
  }

  nsRect RootOverflowRect() const;

  /**
   * Tries to perform a simple partial display list build without display list
   * merging. In this mode, only the top-level stacking context items and their
   * contents are reused, when the frame subtree has not been modified.
   */
  bool TrySimpleUpdate(const nsTArray<nsIFrame*>& aModifiedFrames,
                       nsTArray<nsIFrame*>& aOutFramesWithProps);

  friend class MergeState;

  nsDisplayListBuilder mBuilder;
  RetainedDisplayList mList;
  RetainedDisplayListMetrics mMetrics;
  RetainedDisplayListData mData;
};

namespace RDLUtils {

void AssertFrameSubtreeUnmodified(const nsIFrame* aFrame);
void AssertDisplayItemUnmodified(nsDisplayItem* aItem);
void AssertDisplayListUnmodified(nsDisplayList* aList);

}  // namespace RDLUtils
}  // namespace mozilla

#endif  // RETAINEDDISPLAYLISTBUILDER_H_