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/TypedEnumBits.h"

class nsWindowSizes;

/**
 * RetainedDisplayListData contains frame invalidation information. It is stored
 * in root frames, and used by RetainedDisplayListBuilder.
 * Currently this is implemented as a map of frame pointers to flags.
 */
struct RetainedDisplayListData {
  NS_DECLARE_FRAME_PROPERTY_DELETABLE(DisplayListData, RetainedDisplayListData)

  enum class FrameFlags : uint8_t {
    None = 0,
    Modified = 1 << 0,
    HasProps = 1 << 1,
    HadWillChange = 1 << 2
  };

  RetainedDisplayListData() : mModifiedFramesCount(0) {}

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

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

  /**
   * Returns a mutable reference to flags set for the given |aFrame|. If the
   * frame does not exist in this RetainedDisplayListData, it is added with
   * default constructible flags FrameFlags::None.
   */
  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); }

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

  /**
   * Returns the count of modified frames in this RetainedDisplayListData.
   */
  uint32_t ModifiedFramesCount() const { return mModifiedFramesCount; }

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

 private:
  nsTHashMap<nsPtrHashKey<nsIFrame>, FrameFlags> mFrames;
  uint32_t mModifiedFramesCount;
};

MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(RetainedDisplayListData::FrameFlags)

/**
 * Returns RetainedDisplayListData property for the given |aRootFrame|, or
 * nullptr if the property is not set.
 */
RetainedDisplayListData* GetRetainedDisplayListData(nsIFrame* aRootFrame);

/**
 * Returns RetainedDisplayListData property for the given |aRootFrame|. Creates
 * and sets a new RetainedDisplayListData property if it is not already set.
 */
RetainedDisplayListData* GetOrSetRetainedDisplayListData(nsIFrame* aRootFrame);

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;
};

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

  nsDisplayListBuilder* Builder() { return &mBuilder; }

  nsDisplayList* List() { return &mList; }

  RetainedDisplayListMetrics* Metrics() { return &mMetrics; }

  PartialUpdateResult AttemptPartialUpdate(nscolor aBackstop);

  /**
   * Iterates through the display list builder reference frame document and
   * subdocuments, and clears the modified frame lists from the root frames.
   * Also clears the frame properties set by RetainedDisplayListBuilder for all
   * the frames in the modified frame lists.
   */
  void ClearFramesWithProps();
  void AddSizeOfIncludingThis(nsWindowSizes&) const;

  NS_DECLARE_FRAME_PROPERTY_DELETABLE(Cached, RetainedDisplayListBuilder)

 private:
  void IncrementSubDocPresShellPaintCount(nsDisplayItem* aItem);

  /**
   * Invalidates the current and previous caret frame if they have changed.
   */
  void InvalidateCaretFramesIfNeeded();

  /**
   * 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,
                             AnimatedGeometryRoot* aAGR,
                             PartialUpdateResult& aUpdated,
                             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,
                            AnimatedGeometryRoot** aOutModifiedAGR,
                            nsTArray<nsIFrame*>& aOutFramesWithProps);

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

  friend class MergeState;

  nsDisplayListBuilder mBuilder;
  RetainedDisplayList mList;
  nsRect mPreviousVisibleRect;
  WeakFrame mPreviousCaret;
  RetainedDisplayListMetrics mMetrics;
};

#endif  // RETAINEDDISPLAYLISTBUILDER_H_