Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2492 insertions, 0 deletions

diff --git a/layout/base/nsBidiPresUtils.cpp b/layout/base/nsBidiPresUtils.cpp
new file mode 100644
index 0000000000..0bd480a0aa
--- /dev/null
+++ b/layout/base/nsBidiPresUtils.cpp
@@ -0,0 +1,2492 @@
+/* -*- 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/. */
+
+#include "nsBidiPresUtils.h"
+
+#include "mozilla/intl/Bidi.h"
+#include "mozilla/Casting.h"
+#include "mozilla/IntegerRange.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/dom/Text.h"
+
+#include "gfxContext.h"
+#include "nsFontMetrics.h"
+#include "nsGkAtoms.h"
+#include "nsPresContext.h"
+#include "nsBidiUtils.h"
+#include "nsCSSFrameConstructor.h"
+#include "nsContainerFrame.h"
+#include "nsInlineFrame.h"
+#include "nsPlaceholderFrame.h"
+#include "nsPointerHashKeys.h"
+#include "nsFirstLetterFrame.h"
+#include "nsUnicodeProperties.h"
+#include "nsTextFrame.h"
+#include "nsBlockFrame.h"
+#include "nsIFrameInlines.h"
+#include "nsStyleStructInlines.h"
+#include "RubyUtils.h"
+#include "nsRubyFrame.h"
+#include "nsRubyBaseFrame.h"
+#include "nsRubyTextFrame.h"
+#include "nsRubyBaseContainerFrame.h"
+#include "nsRubyTextContainerFrame.h"
+#include <algorithm>
+
+#undef NOISY_BIDI
+#undef REALLY_NOISY_BIDI
+
+using namespace mozilla;
+
+using BidiEngine = intl::Bidi;
+using BidiClass = intl::BidiClass;
+using BidiDirection = intl::BidiDirection;
+using BidiEmbeddingLevel = intl::BidiEmbeddingLevel;
+
+static const char16_t kSpace = 0x0020;
+static const char16_t kZWSP = 0x200B;
+static const char16_t kLineSeparator = 0x2028;
+static const char16_t kObjectSubstitute = 0xFFFC;
+static const char16_t kLRE = 0x202A;
+static const char16_t kRLE = 0x202B;
+static const char16_t kLRO = 0x202D;
+static const char16_t kRLO = 0x202E;
+static const char16_t kPDF = 0x202C;
+static const char16_t kLRI = 0x2066;
+static const char16_t kRLI = 0x2067;
+static const char16_t kFSI = 0x2068;
+static const char16_t kPDI = 0x2069;
+// All characters with Bidi type Segment Separator or Block Separator
+static const char16_t kSeparators[] = {
+    char16_t('\t'), char16_t('\r'),   char16_t('\n'), char16_t(0xb),
+    char16_t(0x1c), char16_t(0x1d),   char16_t(0x1e), char16_t(0x1f),
+    char16_t(0x85), char16_t(0x2029), char16_t(0)};
+
+#define NS_BIDI_CONTROL_FRAME ((nsIFrame*)0xfffb1d1)
+
+// This exists just to be a type; the value doesn't matter.
+enum class BidiControlFrameType { Value };
+
+static bool IsIsolateControl(char16_t aChar) {
+  return aChar == kLRI || aChar == kRLI || aChar == kFSI;
+}
+
+// Given a ComputedStyle, return any bidi control character necessary to
+// implement style properties that override directionality (i.e. if it has
+// unicode-bidi:bidi-override, or text-orientation:upright in vertical
+// writing mode) when applying the bidi algorithm.
+//
+// Returns 0 if no override control character is implied by this style.
+static char16_t GetBidiOverride(ComputedStyle* aComputedStyle) {
+  const nsStyleVisibility* vis = aComputedStyle->StyleVisibility();
+  if ((vis->mWritingMode == StyleWritingModeProperty::VerticalRl ||
+       vis->mWritingMode == StyleWritingModeProperty::VerticalLr) &&
+      vis->mTextOrientation == StyleTextOrientation::Upright) {
+    return kLRO;
+  }
+  const nsStyleTextReset* text = aComputedStyle->StyleTextReset();
+  if (text->mUnicodeBidi == StyleUnicodeBidi::BidiOverride ||
+      text->mUnicodeBidi == StyleUnicodeBidi::IsolateOverride) {
+    return StyleDirection::Rtl == vis->mDirection ? kRLO : kLRO;
+  }
+  return 0;
+}
+
+// Given a ComputedStyle, return any bidi control character necessary to
+// implement style properties that affect bidi resolution (i.e. if it
+// has unicode-bidiembed, isolate, or plaintext) when applying the bidi
+// algorithm.
+//
+// Returns 0 if no control character is implied by the style.
+//
+// Note that GetBidiOverride and GetBidiControl need to be separate
+// because in the case of unicode-bidi:isolate-override we need both
+// FSI and LRO/RLO.
+static char16_t GetBidiControl(ComputedStyle* aComputedStyle) {
+  const nsStyleVisibility* vis = aComputedStyle->StyleVisibility();
+  const nsStyleTextReset* text = aComputedStyle->StyleTextReset();
+  switch (text->mUnicodeBidi) {
+    case StyleUnicodeBidi::Embed:
+      return StyleDirection::Rtl == vis->mDirection ? kRLE : kLRE;
+    case StyleUnicodeBidi::Isolate:
+      // <bdi> element already has its directionality set from content so
+      // we never need to return kFSI.
+      return StyleDirection::Rtl == vis->mDirection ? kRLI : kLRI;
+    case StyleUnicodeBidi::IsolateOverride:
+    case StyleUnicodeBidi::Plaintext:
+      return kFSI;
+    case StyleUnicodeBidi::Normal:
+    case StyleUnicodeBidi::BidiOverride:
+      break;
+  }
+
+  return 0;
+}
+
+#ifdef DEBUG
+static inline bool AreContinuationsInOrder(nsIFrame* aFrame1,
+                                           nsIFrame* aFrame2) {
+  nsIFrame* f = aFrame1;
+  do {
+    f = f->GetNextContinuation();
+  } while (f && f != aFrame2);
+  return !!f;
+}
+#endif
+
+struct MOZ_STACK_CLASS BidiParagraphData {
+  struct FrameInfo {
+    FrameInfo(nsIFrame* aFrame, nsBlockInFlowLineIterator& aLineIter)
+        : mFrame(aFrame),
+          mBlockContainer(aLineIter.GetContainer()),
+          mInOverflow(aLineIter.GetInOverflow()) {}
+
+    explicit FrameInfo(BidiControlFrameType aValue)
+        : mFrame(NS_BIDI_CONTROL_FRAME),
+          mBlockContainer(nullptr),
+          mInOverflow(false) {}
+
+    FrameInfo()
+        : mFrame(nullptr), mBlockContainer(nullptr), mInOverflow(false) {}
+
+    nsIFrame* mFrame;
+
+    // The block containing mFrame (i.e., which continuation).
+    nsBlockFrame* mBlockContainer;
+
+    // true if mFrame is in mBlockContainer's overflow lines, false if
+    // in primary lines
+    bool mInOverflow;
+  };
+
+  nsAutoString mBuffer;
+  AutoTArray<char16_t, 16> mEmbeddingStack;
+  AutoTArray<FrameInfo, 16> mLogicalFrames;
+  nsTHashMap<nsPtrHashKey<const nsIContent>, int32_t> mContentToFrameIndex;
+  // Cached presentation context for the frames we're processing.
+  nsPresContext* mPresContext;
+  bool mIsVisual;
+  bool mRequiresBidi;
+  BidiEmbeddingLevel mParaLevel;
+  nsIContent* mPrevContent;
+
+  /**
+   * This class is designed to manage the process of mapping a frame to
+   * the line that it's in, when we know that (a) the frames we ask it
+   * about are always in the block's lines and (b) each successive frame
+   * we ask it about is the same as or after (in depth-first search
+   * order) the previous.
+   *
+   * Since we move through the lines at a different pace in Traverse and
+   * ResolveParagraph, we use one of these for each.
+   *
+   * The state of the mapping is also different between TraverseFrames
+   * and ResolveParagraph since since resolving can call functions
+   * (EnsureBidiContinuation or SplitInlineAncestors) that can create
+   * new frames and thus break lines.
+   *
+   * The TraverseFrames iterator is only used in some edge cases.
+   */
+  struct FastLineIterator {
+    FastLineIterator() : mPrevFrame(nullptr), mNextLineStart(nullptr) {}
+
+    // These iterators *and* mPrevFrame track the line list that we're
+    // iterating over.
+    //
+    // mPrevFrame, if non-null, should be either the frame we're currently
+    // handling (in ResolveParagraph or TraverseFrames, depending on the
+    // iterator) or a frame before it, and is also guaranteed to either be in
+    // mCurrentLine or have been in mCurrentLine until recently.
+    //
+    // In case the splitting causes block frames to break lines, however, we
+    // also track the first frame of the next line.  If that changes, it means
+    // we've broken lines and we have to invalidate mPrevFrame.
+    nsBlockInFlowLineIterator mLineIterator;
+    nsIFrame* mPrevFrame;
+    nsIFrame* mNextLineStart;
+
+    nsLineList::iterator GetLine() { return mLineIterator.GetLine(); }
+
+    static bool IsFrameInCurrentLine(nsBlockInFlowLineIterator* aLineIter,
+                                     nsIFrame* aPrevFrame, nsIFrame* aFrame) {
+      MOZ_ASSERT(!aPrevFrame || aLineIter->GetLine()->Contains(aPrevFrame),
+                 "aPrevFrame must be in aLineIter's current line");
+      nsIFrame* endFrame = aLineIter->IsLastLineInList()
+                               ? nullptr
+                               : aLineIter->GetLine().next()->mFirstChild;
+      nsIFrame* startFrame =
+          aPrevFrame ? aPrevFrame : aLineIter->GetLine()->mFirstChild;
+      for (nsIFrame* frame = startFrame; frame && frame != endFrame;
+           frame = frame->GetNextSibling()) {
+        if (frame == aFrame) return true;
+      }
+      return false;
+    }
+
+    static nsIFrame* FirstChildOfNextLine(
+        nsBlockInFlowLineIterator& aIterator) {
+      const nsLineList::iterator line = aIterator.GetLine();
+      const nsLineList::iterator lineEnd = aIterator.End();
+      MOZ_ASSERT(line != lineEnd, "iterator should start off valid");
+      const nsLineList::iterator nextLine = line.next();
+
+      return nextLine != lineEnd ? nextLine->mFirstChild : nullptr;
+    }
+
+    // Advance line iterator to the line containing aFrame, assuming
+    // that aFrame is already in the line list our iterator is iterating
+    // over.
+    void AdvanceToFrame(nsIFrame* aFrame) {
+      if (mPrevFrame && FirstChildOfNextLine(mLineIterator) != mNextLineStart) {
+        // Something has caused a line to split.  We need to invalidate
+        // mPrevFrame since it may now be in a *later* line, though it may
+        // still be in this line, so we need to start searching for it from
+        // the start of this line.
+        mPrevFrame = nullptr;
+      }
+      nsIFrame* child = aFrame;
+      nsIFrame* parent = nsLayoutUtils::GetParentOrPlaceholderFor(child);
+      while (parent && !parent->IsBlockFrameOrSubclass()) {
+        child = parent;
+        parent = nsLayoutUtils::GetParentOrPlaceholderFor(child);
+      }
+      MOZ_ASSERT(parent, "aFrame is not a descendent of a block frame");
+      while (!IsFrameInCurrentLine(&mLineIterator, mPrevFrame, child)) {
+#ifdef DEBUG
+        bool hasNext =
+#endif
+            mLineIterator.Next();
+        MOZ_ASSERT(hasNext, "Can't find frame in lines!");
+        mPrevFrame = nullptr;
+      }
+      mPrevFrame = child;
+      mNextLineStart = FirstChildOfNextLine(mLineIterator);
+    }
+
+    // Advance line iterator to the line containing aFrame, which may
+    // require moving forward into overflow lines or into a later
+    // continuation (or both).
+    void AdvanceToLinesAndFrame(const FrameInfo& aFrameInfo) {
+      if (mLineIterator.GetContainer() != aFrameInfo.mBlockContainer ||
+          mLineIterator.GetInOverflow() != aFrameInfo.mInOverflow) {
+        MOZ_ASSERT(
+            mLineIterator.GetContainer() == aFrameInfo.mBlockContainer
+                ? (!mLineIterator.GetInOverflow() && aFrameInfo.mInOverflow)
+                : (!mLineIterator.GetContainer() ||
+                   AreContinuationsInOrder(mLineIterator.GetContainer(),
+                                           aFrameInfo.mBlockContainer)),
+            "must move forwards");
+        nsBlockFrame* block = aFrameInfo.mBlockContainer;
+        nsLineList::iterator lines =
+            aFrameInfo.mInOverflow ? block->GetOverflowLines()->mLines.begin()
+                                   : block->LinesBegin();
+        mLineIterator =
+            nsBlockInFlowLineIterator(block, lines, aFrameInfo.mInOverflow);
+        mPrevFrame = nullptr;
+      }
+      AdvanceToFrame(aFrameInfo.mFrame);
+    }
+  };
+
+  FastLineIterator mCurrentTraverseLine, mCurrentResolveLine;
+
+#ifdef DEBUG
+  // Only used for NOISY debug output.
+  // Matches the current TraverseFrames state, not the ResolveParagraph
+  // state.
+  nsBlockFrame* mCurrentBlock;
+#endif
+
+  explicit BidiParagraphData(nsBlockFrame* aBlockFrame)
+      : mPresContext(aBlockFrame->PresContext()),
+        mIsVisual(mPresContext->IsVisualMode()),
+        mRequiresBidi(false),
+        mParaLevel(nsBidiPresUtils::BidiLevelFromStyle(aBlockFrame->Style())),
+        mPrevContent(nullptr)
+#ifdef DEBUG
+        ,
+        mCurrentBlock(aBlockFrame)
+#endif
+  {
+    if (mParaLevel > 0) {
+      mRequiresBidi = true;
+    }
+
+    if (mIsVisual) {
+      /**
+       * Drill up in content to detect whether this is an element that needs to
+       * be rendered with logical order even on visual pages.
+       *
+       * We always use logical order on form controls, firstly so that text
+       * entry will be in logical order, but also because visual pages were
+       * written with the assumption that even if the browser had no support
+       * for right-to-left text rendering, it would use native widgets with
+       * bidi support to display form controls.
+       *
+       * We also use logical order in XUL elements, since we expect that if a
+       * XUL element appears in a visual page, it will be generated by an XBL
+       * binding and contain localized text which will be in logical order.
+       */
+      for (nsIContent* content = aBlockFrame->GetContent(); content;
+           content = content->GetParent()) {
+        if (content->IsXULElement() || content->IsHTMLFormControlElement()) {
+          mIsVisual = false;
+          break;
+        }
+      }
+    }
+  }
+
+  nsresult SetPara() {
+    if (mPresContext->BidiEngine().SetParagraph(mBuffer, mParaLevel).isErr()) {
+      return NS_ERROR_FAILURE;
+    };
+    return NS_OK;
+  }
+
+  /**
+   * mParaLevel can be BidiDirection::LTR as well as
+   * BidiDirection::LTR or BidiDirection::RTL.
+   * GetParagraphEmbeddingLevel() returns the actual (resolved) paragraph level
+   * which is always either BidiDirection::LTR or
+   * BidiDirection::RTL
+   */
+  BidiEmbeddingLevel GetParagraphEmbeddingLevel() {
+    BidiEmbeddingLevel paraLevel = mParaLevel;
+    if (paraLevel == BidiEmbeddingLevel::DefaultLTR() ||
+        paraLevel == BidiEmbeddingLevel::DefaultRTL()) {
+      paraLevel = mPresContext->BidiEngine().GetParagraphEmbeddingLevel();
+    }
+    return paraLevel;
+  }
+
+  BidiEngine::ParagraphDirection GetParagraphDirection() {
+    return mPresContext->BidiEngine().GetParagraphDirection();
+  }
+
+  nsresult CountRuns(int32_t* runCount) {
+    auto result = mPresContext->BidiEngine().CountRuns();
+    if (result.isErr()) {
+      return NS_ERROR_FAILURE;
+    }
+    *runCount = result.unwrap();
+    return NS_OK;
+  }
+
+  void GetLogicalRun(int32_t aLogicalStart, int32_t* aLogicalLimit,
+                     BidiEmbeddingLevel* aLevel) {
+    mPresContext->BidiEngine().GetLogicalRun(aLogicalStart, aLogicalLimit,
+                                             aLevel);
+    if (mIsVisual) {
+      *aLevel = GetParagraphEmbeddingLevel();
+    }
+  }
+
+  void ResetData() {
+    mLogicalFrames.Clear();
+    mContentToFrameIndex.Clear();
+    mBuffer.SetLength(0);
+    mPrevContent = nullptr;
+    for (uint32_t i = 0; i < mEmbeddingStack.Length(); ++i) {
+      mBuffer.Append(mEmbeddingStack[i]);
+      mLogicalFrames.AppendElement(FrameInfo(BidiControlFrameType::Value));
+    }
+  }
+
+  void AppendFrame(nsIFrame* aFrame, FastLineIterator& aLineIter,
+                   nsIContent* aContent = nullptr) {
+    if (aContent) {
+      mContentToFrameIndex.InsertOrUpdate(aContent, FrameCount());
+    }
+
+    // We don't actually need to advance aLineIter to aFrame, since all we use
+    // from it is the block and is-overflow state, which are correct already.
+    mLogicalFrames.AppendElement(FrameInfo(aFrame, aLineIter.mLineIterator));
+  }
+
+  void AdvanceAndAppendFrame(nsIFrame** aFrame, FastLineIterator& aLineIter,
+                             nsIFrame** aNextSibling) {
+    nsIFrame* frame = *aFrame;
+    nsIFrame* nextSibling = *aNextSibling;
+
+    frame = frame->GetNextContinuation();
+    if (frame) {
+      AppendFrame(frame, aLineIter, nullptr);
+
+      /*
+       * If we have already overshot the saved next-sibling while
+       * scanning the frame's continuations, advance it.
+       */
+      if (frame == nextSibling) {
+        nextSibling = frame->GetNextSibling();
+      }
+    }
+
+    *aFrame = frame;
+    *aNextSibling = nextSibling;
+  }
+
+  int32_t GetLastFrameForContent(nsIContent* aContent) {
+    return mContentToFrameIndex.Get(aContent);
+  }
+
+  int32_t FrameCount() { return mLogicalFrames.Length(); }
+
+  int32_t BufferLength() { return mBuffer.Length(); }
+
+  nsIFrame* FrameAt(int32_t aIndex) { return mLogicalFrames[aIndex].mFrame; }
+
+  const FrameInfo& FrameInfoAt(int32_t aIndex) {
+    return mLogicalFrames[aIndex];
+  }
+
+  void AppendUnichar(char16_t aCh) { mBuffer.Append(aCh); }
+
+  void AppendString(const nsDependentSubstring& aString) {
+    mBuffer.Append(aString);
+  }
+
+  void AppendControlChar(char16_t aCh) {
+    mLogicalFrames.AppendElement(FrameInfo(BidiControlFrameType::Value));
+    AppendUnichar(aCh);
+  }
+
+  void PushBidiControl(char16_t aCh) {
+    AppendControlChar(aCh);
+    mEmbeddingStack.AppendElement(aCh);
+  }
+
+  void AppendPopChar(char16_t aCh) {
+    AppendControlChar(IsIsolateControl(aCh) ? kPDI : kPDF);
+  }
+
+  void PopBidiControl(char16_t aCh) {
+    MOZ_ASSERT(mEmbeddingStack.Length(), "embedding/override underflow");
+    MOZ_ASSERT(aCh == mEmbeddingStack.LastElement());
+    AppendPopChar(aCh);
+    mEmbeddingStack.RemoveLastElement();
+  }
+
+  void ClearBidiControls() {
+    for (char16_t c : Reversed(mEmbeddingStack)) {
+      AppendPopChar(c);
+    }
+  }
+};
+
+struct MOZ_STACK_CLASS BidiLineData {
+  AutoTArray<nsIFrame*, 16> mLogicalFrames;
+  AutoTArray<nsIFrame*, 16> mVisualFrames;
+  AutoTArray<int32_t, 16> mIndexMap;
+  AutoTArray<BidiEmbeddingLevel, 16> mLevels;
+  bool mIsReordered;
+
+  BidiLineData(nsIFrame* aFirstFrameOnLine, int32_t aNumFramesOnLine) {
+    /**
+     * Initialize the logically-ordered array of frames using the top-level
+     * frames of a single line
+     */
+    bool isReordered = false;
+    bool hasRTLFrames = false;
+    bool hasVirtualControls = false;
+
+    auto appendFrame = [&](nsIFrame* frame, BidiEmbeddingLevel level) {
+      mLogicalFrames.AppendElement(frame);
+      mLevels.AppendElement(level);
+      mIndexMap.AppendElement(0);
+      if (level.IsRTL()) {
+        hasRTLFrames = true;
+      }
+    };
+
+    bool firstFrame = true;
+    for (nsIFrame* frame = aFirstFrameOnLine; frame && aNumFramesOnLine--;
+         frame = frame->GetNextSibling()) {
+      FrameBidiData bidiData = nsBidiPresUtils::GetFrameBidiData(frame);
+      // Ignore virtual control before the first frame. Doing so should
+      // not affect the visual result, but could avoid running into the
+      // stripping code below for many cases.
+      if (!firstFrame && bidiData.precedingControl != kBidiLevelNone) {
+        appendFrame(NS_BIDI_CONTROL_FRAME, bidiData.precedingControl);
+        hasVirtualControls = true;
+      }
+      appendFrame(frame, bidiData.embeddingLevel);
+      firstFrame = false;
+    }
+
+    // Reorder the line
+    BidiEngine::ReorderVisual(mLevels.Elements(), FrameCount(),
+                              mIndexMap.Elements());
+
+    // Strip virtual frames
+    if (hasVirtualControls) {
+      auto originalCount = mLogicalFrames.Length();
+      AutoTArray<int32_t, 16> realFrameMap;
+      realFrameMap.SetCapacity(originalCount);
+      size_t count = 0;
+      for (auto i : IntegerRange(originalCount)) {
+        if (mLogicalFrames[i] == NS_BIDI_CONTROL_FRAME) {
+          realFrameMap.AppendElement(-1);
+        } else {
+          mLogicalFrames[count] = mLogicalFrames[i];
+          mLevels[count] = mLevels[i];
+          realFrameMap.AppendElement(count);
+          count++;
+        }
+      }
+      // Only keep index map for real frames.
+      for (size_t i = 0, j = 0; i < originalCount; ++i) {
+        auto newIndex = realFrameMap[mIndexMap[i]];
+        if (newIndex != -1) {
+          mIndexMap[j] = newIndex;
+          j++;
+        }
+      }
+      mLogicalFrames.TruncateLength(count);
+      mLevels.TruncateLength(count);
+      mIndexMap.TruncateLength(count);
+    }
+
+    for (int32_t i = 0; i < FrameCount(); i++) {
+      mVisualFrames.AppendElement(LogicalFrameAt(mIndexMap[i]));
+      if (i != mIndexMap[i]) {
+        isReordered = true;
+      }
+    }
+
+    // If there's an RTL frame, assume the line is reordered
+    mIsReordered = isReordered || hasRTLFrames;
+  }
+
+  int32_t FrameCount() const { return mLogicalFrames.Length(); }
+
+  nsIFrame* LogicalFrameAt(int32_t aIndex) const {
+    return mLogicalFrames[aIndex];
+  }
+
+  nsIFrame* VisualFrameAt(int32_t aIndex) const {
+    return mVisualFrames[aIndex];
+  }
+};
+
+#ifdef DEBUG
+extern "C" {
+void MOZ_EXPORT DumpFrameArray(const nsTArray<nsIFrame*>& aFrames) {
+  for (nsIFrame* frame : aFrames) {
+    if (frame == NS_BIDI_CONTROL_FRAME) {
+      fprintf_stderr(stderr, "(Bidi control frame)\n");
+    } else {
+      frame->List();
+    }
+  }
+}
+
+void MOZ_EXPORT DumpBidiLine(BidiLineData* aData, bool aVisualOrder) {
+  DumpFrameArray(aVisualOrder ? aData->mVisualFrames : aData->mLogicalFrames);
+}
+}
+#endif
+
+/* Some helper methods for Resolve() */
+
+// Should this frame be split between text runs?
+static bool IsBidiSplittable(nsIFrame* aFrame) {
+  MOZ_ASSERT(aFrame);
+  // Bidi inline containers should be split, unless they're line frames.
+  LayoutFrameType frameType = aFrame->Type();
+  return (aFrame->IsFrameOfType(nsIFrame::eBidiInlineContainer) &&
+          frameType != LayoutFrameType::Line) ||
+         frameType == LayoutFrameType::Text;
+}
+
+// Should this frame be treated as a leaf (e.g. when building mLogicalFrames)?
+static bool IsBidiLeaf(const nsIFrame* aFrame) {
+  nsIFrame* kid = aFrame->PrincipalChildList().FirstChild();
+  if (kid) {
+    if (aFrame->IsFrameOfType(nsIFrame::eBidiInlineContainer) ||
+        RubyUtils::IsRubyBox(aFrame->Type())) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/**
+ * Create non-fluid continuations for the ancestors of a given frame all the way
+ * up the frame tree until we hit a non-splittable frame (a line or a block).
+ *
+ * @param aParent the first parent frame to be split
+ * @param aFrame the child frames after this frame are reparented to the
+ *        newly-created continuation of aParent.
+ *        If aFrame is null, all the children of aParent are reparented.
+ */
+static void SplitInlineAncestors(nsContainerFrame* aParent,
+                                 nsLineList::iterator aLine, nsIFrame* aFrame) {
+  PresShell* presShell = aParent->PresShell();
+  nsIFrame* frame = aFrame;
+  nsContainerFrame* parent = aParent;
+  nsContainerFrame* newParent;
+
+  while (IsBidiSplittable(parent)) {
+    nsContainerFrame* grandparent = parent->GetParent();
+    NS_ASSERTION(grandparent,
+                 "Couldn't get parent's parent in "
+                 "nsBidiPresUtils::SplitInlineAncestors");
+
+    // Split the child list after |frame|, unless it is the last child.
+    if (!frame || frame->GetNextSibling()) {
+      newParent = static_cast<nsContainerFrame*>(
+          presShell->FrameConstructor()->CreateContinuingFrame(
+              parent, grandparent, false));
+
+      nsFrameList tail = parent->StealFramesAfter(frame);
+
+      // Reparent views as necessary
+      nsContainerFrame::ReparentFrameViewList(tail, parent, newParent);
+
+      // The parent's continuation adopts the siblings after the split.
+      MOZ_ASSERT(!newParent->IsBlockFrameOrSubclass(),
+                 "blocks should not be IsBidiSplittable");
+      newParent->InsertFrames(FrameChildListID::NoReflowPrincipal, nullptr,
+                              nullptr, std::move(tail));
+
+      // While passing &aLine to InsertFrames for a non-block isn't harmful
+      // because it's a no-op, it doesn't really make sense.  However, the
+      // MOZ_ASSERT() we need to guarantee that it's safe only works if the
+      // parent is actually the block.
+      const nsLineList::iterator* parentLine;
+      if (grandparent->IsBlockFrameOrSubclass()) {
+        MOZ_ASSERT(aLine->Contains(parent));
+        parentLine = &aLine;
+      } else {
+        parentLine = nullptr;
+      }
+
+      // The list name FrameChildListID::NoReflowPrincipal would indicate we
+      // don't want reflow
+      grandparent->InsertFrames(FrameChildListID::NoReflowPrincipal, parent,
+                                parentLine, nsFrameList(newParent, newParent));
+    }
+
+    frame = parent;
+    parent = grandparent;
+  }
+}
+
+static void MakeContinuationFluid(nsIFrame* aFrame, nsIFrame* aNext) {
+  NS_ASSERTION(!aFrame->GetNextInFlow() || aFrame->GetNextInFlow() == aNext,
+               "next-in-flow is not next continuation!");
+  aFrame->SetNextInFlow(aNext);
+
+  NS_ASSERTION(!aNext->GetPrevInFlow() || aNext->GetPrevInFlow() == aFrame,
+               "prev-in-flow is not prev continuation!");
+  aNext->SetPrevInFlow(aFrame);
+}
+
+static void MakeContinuationsNonFluidUpParentChain(nsIFrame* aFrame,
+                                                   nsIFrame* aNext) {
+  nsIFrame* frame;
+  nsIFrame* next;
+
+  for (frame = aFrame, next = aNext;
+       frame && next && next != frame && next == frame->GetNextInFlow() &&
+       IsBidiSplittable(frame);
+       frame = frame->GetParent(), next = next->GetParent()) {
+    frame->SetNextContinuation(next);
+    next->SetPrevContinuation(frame);
+  }
+}
+
+// If aFrame is the last child of its parent, convert bidi continuations to
+// fluid continuations for all of its inline ancestors.
+// If it isn't the last child, make sure that its continuation is fluid.
+static void JoinInlineAncestors(nsIFrame* aFrame) {
+  nsIFrame* frame = aFrame;
+  while (frame && IsBidiSplittable(frame)) {
+    nsIFrame* next = frame->GetNextContinuation();
+    if (next) {
+      MakeContinuationFluid(frame, next);
+    }
+    // Join the parent only as long as we're its last child.
+    if (frame->GetNextSibling()) break;
+    frame = frame->GetParent();
+  }
+}
+
+static void CreateContinuation(nsIFrame* aFrame,
+                               const nsLineList::iterator aLine,
+                               nsIFrame** aNewFrame, bool aIsFluid) {
+  MOZ_ASSERT(aNewFrame, "null OUT ptr");
+  MOZ_ASSERT(aFrame, "null ptr");
+
+  *aNewFrame = nullptr;
+
+  nsPresContext* presContext = aFrame->PresContext();
+  PresShell* presShell = presContext->PresShell();
+  NS_ASSERTION(presShell,
+               "PresShell must be set on PresContext before calling "
+               "nsBidiPresUtils::CreateContinuation");
+
+  nsContainerFrame* parent = aFrame->GetParent();
+  NS_ASSERTION(
+      parent,
+      "Couldn't get frame parent in nsBidiPresUtils::CreateContinuation");
+
+  // While passing &aLine to InsertFrames for a non-block isn't harmful
+  // because it's a no-op, it doesn't really make sense.  However, the
+  // MOZ_ASSERT() we need to guarantee that it's safe only works if the
+  // parent is actually the block.
+  const nsLineList::iterator* parentLine;
+  if (parent->IsBlockFrameOrSubclass()) {
+    MOZ_ASSERT(aLine->Contains(aFrame));
+    parentLine = &aLine;
+  } else {
+    parentLine = nullptr;
+  }
+
+  // Have to special case floating first letter frames because the continuation
+  // doesn't go in the first letter frame. The continuation goes with the rest
+  // of the text that the first letter frame was made out of.
+  if (parent->IsLetterFrame() && parent->IsFloating()) {
+    nsFirstLetterFrame* letterFrame = do_QueryFrame(parent);
+    letterFrame->CreateContinuationForFloatingParent(aFrame, aNewFrame,
+                                                     aIsFluid);
+    return;
+  }
+
+  *aNewFrame = presShell->FrameConstructor()->CreateContinuingFrame(
+      aFrame, parent, aIsFluid);
+
+  // The list name FrameChildListID::NoReflowPrincipal would indicate we don't
+  // want reflow
+  // XXXbz this needs higher-level framelist love
+  parent->InsertFrames(FrameChildListID::NoReflowPrincipal, aFrame, parentLine,
+                       nsFrameList(*aNewFrame, *aNewFrame));
+
+  if (!aIsFluid) {
+    // Split inline ancestor frames
+    SplitInlineAncestors(parent, aLine, aFrame);
+  }
+}
+
+/*
+ * Overview of the implementation of Resolve():
+ *
+ *  Walk through the descendants of aBlockFrame and build:
+ *   * mLogicalFrames: an nsTArray of nsIFrame* pointers in logical order
+ *   * mBuffer: an nsString containing a representation of
+ *     the content of the frames.
+ *     In the case of text frames, this is the actual text context of the
+ *     frames, but some other elements are represented in a symbolic form which
+ *     will make the Unicode Bidi Algorithm give the correct results.
+ *     Bidi isolates, embeddings, and overrides set by CSS, <bdi>, or <bdo>
+ *     elements are represented by the corresponding Unicode control characters.
+ *     <br> elements are represented by U+2028 LINE SEPARATOR
+ *     Other inline elements are represented by U+FFFC OBJECT REPLACEMENT
+ *     CHARACTER
+ *
+ *  Then pass mBuffer to the Bidi engine for resolving of embedding levels
+ *  by nsBidi::SetPara() and division into directional runs by
+ *  nsBidi::CountRuns().
+ *
+ *  Finally, walk these runs in logical order using nsBidi::GetLogicalRun() and
+ *  correlate them with the frames indexed in mLogicalFrames, setting the
+ *  baseLevel and embeddingLevel properties according to the results returned
+ *  by the Bidi engine.
+ *
+ *  The rendering layer requires each text frame to contain text in only one
+ *  direction, so we may need to call EnsureBidiContinuation() to split frames.
+ *  We may also need to call RemoveBidiContinuation() to convert frames created
+ *  by EnsureBidiContinuation() in previous reflows into fluid continuations.
+ */
+nsresult nsBidiPresUtils::Resolve(nsBlockFrame* aBlockFrame) {
+  BidiParagraphData bpd(aBlockFrame);
+
+  // Handle bidi-override being set on the block itself before calling
+  // TraverseFrames.
+  // No need to call GetBidiControl as well, because isolate and embed
+  // values of unicode-bidi property are redundant on block elements.
+  // unicode-bidi:plaintext on a block element is handled by block frame
+  // via using nsIFrame::GetWritingMode(nsIFrame*).
+  char16_t ch = GetBidiOverride(aBlockFrame->Style());
+  if (ch != 0) {
+    bpd.PushBidiControl(ch);
+    bpd.mRequiresBidi = true;
+  } else {
+    // If there are no unicode-bidi properties and no RTL characters in the
+    // block's content, then it is pure LTR and we can skip the rest of bidi
+    // resolution.
+    nsIContent* currContent = nullptr;
+    for (nsBlockFrame* block = aBlockFrame; block;
+         block = static_cast<nsBlockFrame*>(block->GetNextContinuation())) {
+      block->RemoveStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION);
+      if (!bpd.mRequiresBidi &&
+          ChildListMayRequireBidi(block->PrincipalChildList().FirstChild(),
+                                  &currContent)) {
+        bpd.mRequiresBidi = true;
+      }
+      if (!bpd.mRequiresBidi) {
+        nsBlockFrame::FrameLines* overflowLines = block->GetOverflowLines();
+        if (overflowLines) {
+          if (ChildListMayRequireBidi(overflowLines->mFrames.FirstChild(),
+                                      &currContent)) {
+            bpd.mRequiresBidi = true;
+          }
+        }
+      }
+    }
+    if (!bpd.mRequiresBidi) {
+      return NS_OK;
+    }
+  }
+
+  for (nsBlockFrame* block = aBlockFrame; block;
+       block = static_cast<nsBlockFrame*>(block->GetNextContinuation())) {
+#ifdef DEBUG
+    bpd.mCurrentBlock = block;
+#endif
+    block->RemoveStateBits(NS_BLOCK_NEEDS_BIDI_RESOLUTION);
+    bpd.mCurrentTraverseLine.mLineIterator =
+        nsBlockInFlowLineIterator(block, block->LinesBegin());
+    bpd.mCurrentTraverseLine.mPrevFrame = nullptr;
+    TraverseFrames(block->PrincipalChildList().FirstChild(), &bpd);
+    nsBlockFrame::FrameLines* overflowLines = block->GetOverflowLines();
+    if (overflowLines) {
+      bpd.mCurrentTraverseLine.mLineIterator =
+          nsBlockInFlowLineIterator(block, overflowLines->mLines.begin(), true);
+      bpd.mCurrentTraverseLine.mPrevFrame = nullptr;
+      TraverseFrames(overflowLines->mFrames.FirstChild(), &bpd);
+    }
+  }
+
+  if (ch != 0) {
+    bpd.PopBidiControl(ch);
+  }
+
+  return ResolveParagraph(&bpd);
+}
+
+nsresult nsBidiPresUtils::ResolveParagraph(BidiParagraphData* aBpd) {
+  if (aBpd->BufferLength() < 1) {
+    return NS_OK;
+  }
+  aBpd->mBuffer.ReplaceChar(kSeparators, kSpace);
+
+  int32_t runCount;
+
+  nsresult rv = aBpd->SetPara();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  BidiEmbeddingLevel embeddingLevel = aBpd->GetParagraphEmbeddingLevel();
+
+  rv = aBpd->CountRuns(&runCount);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  int32_t runLength = 0;     // the length of the current run of text
+  int32_t logicalLimit = 0;  // the end of the current run + 1
+  int32_t numRun = -1;
+  int32_t fragmentLength = 0;  // the length of the current text frame
+  int32_t frameIndex = -1;     // index to the frames in mLogicalFrames
+  int32_t frameCount = aBpd->FrameCount();
+  int32_t contentOffset = 0;  // offset of current frame in its content node
+  bool isTextFrame = false;
+  nsIFrame* frame = nullptr;
+  BidiParagraphData::FrameInfo frameInfo;
+  nsIContent* content = nullptr;
+  int32_t contentTextLength = 0;
+
+#ifdef DEBUG
+#  ifdef NOISY_BIDI
+  printf(
+      "Before Resolve(), mCurrentBlock=%p, mBuffer='%s', frameCount=%d, "
+      "runCount=%d\n",
+      (void*)aBpd->mCurrentBlock, NS_ConvertUTF16toUTF8(aBpd->mBuffer).get(),
+      frameCount, runCount);
+#    ifdef REALLY_NOISY_BIDI
+  printf(" block frame tree=:\n");
+  aBpd->mCurrentBlock->List(stdout);
+#    endif
+#  endif
+#endif
+
+  if (runCount == 1 && frameCount == 1 &&
+      aBpd->GetParagraphDirection() == BidiEngine::ParagraphDirection::LTR &&
+      aBpd->GetParagraphEmbeddingLevel() == 0) {
+    // We have a single left-to-right frame in a left-to-right paragraph,
+    // without bidi isolation from the surrounding text.
+    // Make sure that the embedding level and base level frame properties aren't
+    // set (because if they are this frame used to have some other direction,
+    // so we can't do this optimization), and we're done.
+    nsIFrame* frame = aBpd->FrameAt(0);
+    if (frame != NS_BIDI_CONTROL_FRAME) {
+      FrameBidiData bidiData = frame->GetBidiData();
+      if (!bidiData.embeddingLevel && !bidiData.baseLevel) {
+#ifdef DEBUG
+#  ifdef NOISY_BIDI
+        printf("early return for single direction frame %p\n", (void*)frame);
+#  endif
+#endif
+        frame->AddStateBits(NS_FRAME_IS_BIDI);
+        return NS_OK;
+      }
+    }
+  }
+
+  BidiParagraphData::FrameInfo lastRealFrame;
+  BidiEmbeddingLevel lastEmbeddingLevel = kBidiLevelNone;
+  BidiEmbeddingLevel precedingControl = kBidiLevelNone;
+
+  auto storeBidiDataToFrame = [&]() {
+    FrameBidiData bidiData;
+    bidiData.embeddingLevel = embeddingLevel;
+    bidiData.baseLevel = aBpd->GetParagraphEmbeddingLevel();
+    // If a control character doesn't have a lower embedding level than
+    // both the preceding and the following frame, it isn't something
+    // needed for getting the correct result. This optimization should
+    // remove almost all of embeds and overrides, and some of isolates.
+    if (precedingControl >= embeddingLevel ||
+        precedingControl >= lastEmbeddingLevel) {
+      bidiData.precedingControl = kBidiLevelNone;
+    } else {
+      bidiData.precedingControl = precedingControl;
+    }
+    precedingControl = kBidiLevelNone;
+    lastEmbeddingLevel = embeddingLevel;
+    frame->SetProperty(nsIFrame::BidiDataProperty(), bidiData);
+  };
+
+  for (;;) {
+    if (fragmentLength <= 0) {
+      // Get the next frame from mLogicalFrames
+      if (++frameIndex >= frameCount) {
+        break;
+      }
+      frameInfo = aBpd->FrameInfoAt(frameIndex);
+      frame = frameInfo.mFrame;
+      if (frame == NS_BIDI_CONTROL_FRAME || !frame->IsTextFrame()) {
+        /*
+         * Any non-text frame corresponds to a single character in the text
+         * buffer (a bidi control character, LINE SEPARATOR, or OBJECT
+         * SUBSTITUTE)
+         */
+        isTextFrame = false;
+        fragmentLength = 1;
+      } else {
+        aBpd->mCurrentResolveLine.AdvanceToLinesAndFrame(frameInfo);
+        content = frame->GetContent();
+        if (!content) {
+          rv = NS_OK;
+          break;
+        }
+        contentTextLength = content->TextLength();
+        auto [start, end] = frame->GetOffsets();
+        NS_ASSERTION(!(contentTextLength < end - start),
+                     "Frame offsets don't fit in content");
+        fragmentLength = std::min(contentTextLength, end - start);
+        contentOffset = start;
+        isTextFrame = true;
+      }
+    }  // if (fragmentLength <= 0)
+
+    if (runLength <= 0) {
+      // Get the next run of text from the Bidi engine
+      if (++numRun >= runCount) {
+        // We've run out of runs of text; but don't forget to store bidi data
+        // to the frame before breaking out of the loop (bug 1426042).
+        storeBidiDataToFrame();
+        if (isTextFrame) {
+          frame->AdjustOffsetsForBidi(contentOffset,
+                                      contentOffset + fragmentLength);
+        }
+        break;
+      }
+      int32_t lineOffset = logicalLimit;
+      aBpd->GetLogicalRun(lineOffset, &logicalLimit, &embeddingLevel);
+      runLength = logicalLimit - lineOffset;
+    }  // if (runLength <= 0)
+
+    if (frame == NS_BIDI_CONTROL_FRAME) {
+      // In theory, we only need to do this for isolates. However, it is
+      // easier to do this for all here because we do not maintain the
+      // index to get corresponding character from buffer. Since we do
+      // have proper embedding level for all those characters, including
+      // them wouldn't affect the final result.
+      precedingControl = std::min(precedingControl, embeddingLevel);
+    } else {
+      storeBidiDataToFrame();
+      if (isTextFrame) {
+        if (contentTextLength == 0) {
+          // Set the base level and embedding level of the current run even
+          // on an empty frame. Otherwise frame reordering will not be correct.
+          frame->AdjustOffsetsForBidi(0, 0);
+          // Nothing more to do for an empty frame, except update
+          // lastRealFrame like we do below.
+          lastRealFrame = frameInfo;
+          continue;
+        }
+        nsLineList::iterator currentLine = aBpd->mCurrentResolveLine.GetLine();
+        if ((runLength > 0) && (runLength < fragmentLength)) {
+          /*
+           * The text in this frame continues beyond the end of this directional
+           * run. Create a non-fluid continuation frame for the next directional
+           * run.
+           */
+          currentLine->MarkDirty();
+          nsIFrame* nextBidi;
+          int32_t runEnd = contentOffset + runLength;
+          EnsureBidiContinuation(frame, currentLine, &nextBidi, contentOffset,
+                                 runEnd);
+          nextBidi->AdjustOffsetsForBidi(runEnd,
+                                         contentOffset + fragmentLength);
+          frame = nextBidi;
+          frameInfo.mFrame = frame;
+          contentOffset = runEnd;
+
+          aBpd->mCurrentResolveLine.AdvanceToFrame(frame);
+        }  // if (runLength < fragmentLength)
+        else {
+          if (contentOffset + fragmentLength == contentTextLength) {
+            /*
+             * We have finished all the text in this content node. Convert any
+             * further non-fluid continuations to fluid continuations and
+             * advance frameIndex to the last frame in the content node
+             */
+            int32_t newIndex = aBpd->GetLastFrameForContent(content);
+            if (newIndex > frameIndex) {
+              currentLine->MarkDirty();
+              RemoveBidiContinuation(aBpd, frame, frameIndex, newIndex);
+              frameIndex = newIndex;
+              frameInfo = aBpd->FrameInfoAt(frameIndex);
+              frame = frameInfo.mFrame;
+            }
+          } else if (fragmentLength > 0 && runLength > fragmentLength) {
+            /*
+             * There is more text that belongs to this directional run in the
+             * next text frame: make sure it is a fluid continuation of the
+             * current frame. Do not advance frameIndex, because the next frame
+             * may contain multi-directional text and need to be split
+             */
+            int32_t newIndex = frameIndex;
+            do {
+            } while (++newIndex < frameCount &&
+                     aBpd->FrameAt(newIndex) == NS_BIDI_CONTROL_FRAME);
+            if (newIndex < frameCount) {
+              currentLine->MarkDirty();
+              RemoveBidiContinuation(aBpd, frame, frameIndex, newIndex);
+            }
+          } else if (runLength == fragmentLength) {
+            /*
+             * If the directional run ends at the end of the frame, make sure
+             * that any continuation is non-fluid, and do the same up the
+             * parent chain
+             */
+            nsIFrame* next = frame->GetNextInFlow();
+            if (next) {
+              currentLine->MarkDirty();
+              MakeContinuationsNonFluidUpParentChain(frame, next);
+            }
+          }
+          frame->AdjustOffsetsForBidi(contentOffset,
+                                      contentOffset + fragmentLength);
+        }
+      }  // isTextFrame
+    }    // not bidi control frame
+    int32_t temp = runLength;
+    runLength -= fragmentLength;
+    fragmentLength -= temp;
+
+    // Record last real frame so that we can do splitting properly even
+    // if a run ends after a virtual bidi control frame.
+    if (frame != NS_BIDI_CONTROL_FRAME) {
+      lastRealFrame = frameInfo;
+    }
+    if (lastRealFrame.mFrame && fragmentLength <= 0) {
+      // If the frame is at the end of a run, and this is not the end of our
+      // paragraph, split all ancestor inlines that need splitting.
+      // To determine whether we're at the end of the run, we check that we've
+      // finished processing the current run, and that the current frame
+      // doesn't have a fluid continuation (it could have a fluid continuation
+      // of zero length, so testing runLength alone is not sufficient).
+      if (runLength <= 0 && !lastRealFrame.mFrame->GetNextInFlow()) {
+        if (numRun + 1 < runCount) {
+          nsIFrame* child = lastRealFrame.mFrame;
+          nsContainerFrame* parent = child->GetParent();
+          // As long as we're on the last sibling, the parent doesn't have to
+          // be split.
+          // However, if the parent has a fluid continuation, we do have to make
+          // it non-fluid. This can happen e.g. when we have a first-letter
+          // frame and the end of the first-letter coincides with the end of a
+          // directional run.
+          while (parent && IsBidiSplittable(parent) &&
+                 !child->GetNextSibling()) {
+            nsIFrame* next = parent->GetNextInFlow();
+            if (next) {
+              parent->SetNextContinuation(next);
+              next->SetPrevContinuation(parent);
+            }
+            child = parent;
+            parent = child->GetParent();
+          }
+          if (parent && IsBidiSplittable(parent)) {
+            aBpd->mCurrentResolveLine.AdvanceToLinesAndFrame(lastRealFrame);
+            SplitInlineAncestors(parent, aBpd->mCurrentResolveLine.GetLine(),
+                                 child);
+
+            aBpd->mCurrentResolveLine.AdvanceToLinesAndFrame(lastRealFrame);
+          }
+        }
+      } else if (frame != NS_BIDI_CONTROL_FRAME) {
+        // We're not at an end of a run. If |frame| is the last child of its
+        // parent, and its ancestors happen to have bidi continuations, convert
+        // them into fluid continuations.
+        JoinInlineAncestors(frame);
+      }
+    }
+  }  // for
+
+#ifdef DEBUG
+#  ifdef REALLY_NOISY_BIDI
+  printf("---\nAfter Resolve(), frameTree =:\n");
+  aBpd->mCurrentBlock->List(stdout);
+  printf("===\n");
+#  endif
+#endif
+
+  return rv;
+}
+
+void nsBidiPresUtils::TraverseFrames(nsIFrame* aCurrentFrame,
+                                     BidiParagraphData* aBpd) {
+  if (!aCurrentFrame) return;
+
+#ifdef DEBUG
+  nsBlockFrame* initialLineContainer =
+      aBpd->mCurrentTraverseLine.mLineIterator.GetContainer();
+#endif
+
+  nsIFrame* childFrame = aCurrentFrame;
+  do {
+    /*
+     * It's important to get the next sibling and next continuation *before*
+     * handling the frame: If we encounter a forced paragraph break and call
+     * ResolveParagraph within this loop, doing GetNextSibling and
+     * GetNextContinuation after that could return a bidi continuation that had
+     * just been split from the original childFrame and we would process it
+     * twice.
+     */
+    nsIFrame* nextSibling = childFrame->GetNextSibling();
+
+    // If the real frame for a placeholder is a first letter frame, we need to
+    // drill down into it and include its contents in Bidi resolution.
+    // If not, we just use the placeholder.
+    nsIFrame* frame = childFrame;
+    if (childFrame->IsPlaceholderFrame()) {
+      nsIFrame* realFrame =
+          nsPlaceholderFrame::GetRealFrameForPlaceholder(childFrame);
+      if (realFrame->IsLetterFrame()) {
+        frame = realFrame;
+      }
+    }
+
+    auto DifferentBidiValues = [](ComputedStyle* aSC1, nsIFrame* aFrame2) {
+      ComputedStyle* sc2 = aFrame2->Style();
+      return GetBidiControl(aSC1) != GetBidiControl(sc2) ||
+             GetBidiOverride(aSC1) != GetBidiOverride(sc2);
+    };
+
+    ComputedStyle* sc = frame->Style();
+    nsIFrame* nextContinuation = frame->GetNextContinuation();
+    nsIFrame* prevContinuation = frame->GetPrevContinuation();
+    bool isLastFrame =
+        !nextContinuation || DifferentBidiValues(sc, nextContinuation);
+    bool isFirstFrame =
+        !prevContinuation || DifferentBidiValues(sc, prevContinuation);
+
+    char16_t controlChar = 0;
+    char16_t overrideChar = 0;
+    LayoutFrameType frameType = frame->Type();
+    if (frame->IsFrameOfType(nsIFrame::eBidiInlineContainer) ||
+        RubyUtils::IsRubyBox(frameType)) {
+      if (!frame->HasAnyStateBits(NS_FRAME_FIRST_REFLOW)) {
+        nsContainerFrame* c = static_cast<nsContainerFrame*>(frame);
+        MOZ_ASSERT(c == do_QueryFrame(frame),
+                   "eBidiInlineContainer and ruby frame must be"
+                   " a nsContainerFrame subclass");
+        c->DrainSelfOverflowList();
+      }
+
+      controlChar = GetBidiControl(sc);
+      overrideChar = GetBidiOverride(sc);
+
+      // Add dummy frame pointers representing bidi control codes before
+      // the first frames of elements specifying override, isolation, or
+      // plaintext.
+      if (isFirstFrame) {
+        if (controlChar != 0) {
+          aBpd->PushBidiControl(controlChar);
+        }
+        if (overrideChar != 0) {
+          aBpd->PushBidiControl(overrideChar);
+        }
+      }
+    }
+
+    if (IsBidiLeaf(frame)) {
+      /* Bidi leaf frame: add the frame to the mLogicalFrames array,
+       * and add its index to the mContentToFrameIndex hashtable. This
+       * will be used in RemoveBidiContinuation() to identify the last
+       * frame in the array with a given content.
+       */
+      nsIContent* content = frame->GetContent();
+      aBpd->AppendFrame(frame, aBpd->mCurrentTraverseLine, content);
+
+      // Append the content of the frame to the paragraph buffer
+      if (LayoutFrameType::Text == frameType) {
+        if (content != aBpd->mPrevContent) {
+          aBpd->mPrevContent = content;
+          if (!frame->StyleText()->NewlineIsSignificant(
+                  static_cast<nsTextFrame*>(frame))) {
+            content->GetAsText()->AppendTextTo(aBpd->mBuffer);
+          } else {
+            /*
+             * For preformatted text we have to do bidi resolution on each line
+             * separately.
+             */
+            nsAutoString text;
+            content->GetAsText()->AppendTextTo(text);
+            nsIFrame* next;
+            do {
+              next = nullptr;
+
+              auto [start, end] = frame->GetOffsets();
+              int32_t endLine = text.FindChar('\n', start);
+              if (endLine == -1) {
+                /*
+                 * If there is no newline in the text content, just save the
+                 * text from this frame and its continuations, and do bidi
+                 * resolution later
+                 */
+                aBpd->AppendString(Substring(text, start));
+                while (frame && nextSibling) {
+                  aBpd->AdvanceAndAppendFrame(
+                      &frame, aBpd->mCurrentTraverseLine, &nextSibling);
+                }
+                break;
+              }
+
+              /*
+               * If there is a newline in the frame, break the frame after the
+               * newline, do bidi resolution and repeat until the last sibling
+               */
+              ++endLine;
+
+              /*
+               * If the frame ends before the new line, save the text and move
+               * into the next continuation
+               */
+              aBpd->AppendString(
+                  Substring(text, start, std::min(end, endLine) - start));
+              while (end < endLine && nextSibling) {
+                aBpd->AdvanceAndAppendFrame(&frame, aBpd->mCurrentTraverseLine,
+                                            &nextSibling);
+                NS_ASSERTION(frame, "Premature end of continuation chain");
+                std::tie(start, end) = frame->GetOffsets();
+                aBpd->AppendString(
+                    Substring(text, start, std::min(end, endLine) - start));
+              }
+
+              if (end < endLine) {
+                aBpd->mPrevContent = nullptr;
+                break;
+              }
+
+              bool createdContinuation = false;
+              if (uint32_t(endLine) < text.Length()) {
+                /*
+                 * Timing is everything here: if the frame already has a bidi
+                 * continuation, we need to make the continuation fluid *before*
+                 * resetting the length of the current frame. Otherwise
+                 * nsTextFrame::SetLength won't set the continuation frame's
+                 * text offsets correctly.
+                 *
+                 * On the other hand, if the frame doesn't have a continuation,
+                 * we need to create one *after* resetting the length, or
+                 * CreateContinuingFrame will complain that there is no more
+                 * content for the continuation.
+                 */
+                next = frame->GetNextInFlow();
+                if (!next) {
+                  // If the frame already has a bidi continuation, make it fluid
+                  next = frame->GetNextContinuation();
+                  if (next) {
+                    MakeContinuationFluid(frame, next);
+                    JoinInlineAncestors(frame);
+                  }
+                }
+
+                nsTextFrame* textFrame = static_cast<nsTextFrame*>(frame);
+                textFrame->SetLength(endLine - start, nullptr);
+
+                // If it weren't for CreateContinuation needing this to
+                // be current, we could restructure the marking dirty
+                // below to use mCurrentResolveLine and eliminate
+                // mCurrentTraverseLine entirely.
+                aBpd->mCurrentTraverseLine.AdvanceToFrame(frame);
+
+                if (!next) {
+                  // If the frame has no next in flow, create one.
+                  CreateContinuation(
+                      frame, aBpd->mCurrentTraverseLine.GetLine(), &next, true);
+                  createdContinuation = true;
+                }
+                // Mark the line before the newline as dirty.
+                aBpd->mCurrentTraverseLine.GetLine()->MarkDirty();
+              }
+              ResolveParagraphWithinBlock(aBpd);
+
+              if (!nextSibling && !createdContinuation) {
+                break;
+              }
+              if (next) {
+                frame = next;
+                aBpd->AppendFrame(frame, aBpd->mCurrentTraverseLine);
+                // Mark the line after the newline as dirty.
+                aBpd->mCurrentTraverseLine.AdvanceToFrame(frame);
+                aBpd->mCurrentTraverseLine.GetLine()->MarkDirty();
+              }
+
+              /*
+               * If we have already overshot the saved next-sibling while
+               * scanning the frame's continuations, advance it.
+               */
+              if (frame && frame == nextSibling) {
+                nextSibling = frame->GetNextSibling();
+              }
+
+            } while (next);
+          }
+        }
+      } else if (LayoutFrameType::Br == frameType) {
+        // break frame -- append line separator
+        aBpd->AppendUnichar(kLineSeparator);
+        ResolveParagraphWithinBlock(aBpd);
+      } else {
+        // other frame type -- see the Unicode Bidi Algorithm:
+        // "...inline objects (such as graphics) are treated as if they are ...
+        // U+FFFC"
+        // <wbr>, however, is treated as U+200B ZERO WIDTH SPACE. See
+        // http://dev.w3.org/html5/spec/Overview.html#phrasing-content-1
+        aBpd->AppendUnichar(
+            content->IsHTMLElement(nsGkAtoms::wbr) ? kZWSP : kObjectSubstitute);
+        if (!frame->IsInlineOutside()) {
+          // if it is not inline, end the paragraph
+          ResolveParagraphWithinBlock(aBpd);
+        }
+      }
+    } else {
+      // For a non-leaf frame, recurse into TraverseFrames
+      nsIFrame* kid = frame->PrincipalChildList().FirstChild();
+      MOZ_ASSERT(!frame->GetChildList(FrameChildListID::Overflow).FirstChild(),
+                 "should have drained the overflow list above");
+      if (kid) {
+        TraverseFrames(kid, aBpd);
+      }
+    }
+
+    // If the element is attributed by dir, indicate direction pop (add PDF
+    // frame)
+    if (isLastFrame) {
+      // Add a dummy frame pointer representing a bidi control code after the
+      // last frame of an element specifying embedding or override
+      if (overrideChar != 0) {
+        aBpd->PopBidiControl(overrideChar);
+      }
+      if (controlChar != 0) {
+        aBpd->PopBidiControl(controlChar);
+      }
+    }
+    childFrame = nextSibling;
+  } while (childFrame);
+
+  MOZ_ASSERT(initialLineContainer ==
+             aBpd->mCurrentTraverseLine.mLineIterator.GetContainer());
+}
+
+bool nsBidiPresUtils::ChildListMayRequireBidi(nsIFrame* aFirstChild,
+                                              nsIContent** aCurrContent) {
+  MOZ_ASSERT(!aFirstChild || !aFirstChild->GetPrevSibling(),
+             "Expecting to traverse from the start of a child list");
+
+  for (nsIFrame* childFrame = aFirstChild; childFrame;
+       childFrame = childFrame->GetNextSibling()) {
+    nsIFrame* frame = childFrame;
+
+    // If the real frame for a placeholder is a first-letter frame, we need to
+    // consider its contents for potential Bidi resolution.
+    if (childFrame->IsPlaceholderFrame()) {
+      nsIFrame* realFrame =
+          nsPlaceholderFrame::GetRealFrameForPlaceholder(childFrame);
+      if (realFrame->IsLetterFrame()) {
+        frame = realFrame;
+      }
+    }
+
+    // If unicode-bidi properties are present, we should do bidi resolution.
+    ComputedStyle* sc = frame->Style();
+    if (GetBidiControl(sc) || GetBidiOverride(sc)) {
+      return true;
+    }
+
+    if (IsBidiLeaf(frame)) {
+      if (frame->IsTextFrame()) {
+        // If the frame already has a BidiDataProperty, we know we need to
+        // perform bidi resolution (even if no bidi content is NOW present --
+        // we might need to remove the property set by a previous reflow, if
+        // content has changed; see bug 1366623).
+        if (frame->HasProperty(nsIFrame::BidiDataProperty())) {
+          return true;
+        }
+
+        // Check whether the text frame has any RTL characters; if so, bidi
+        // resolution will be needed.
+        dom::Text* content = frame->GetContent()->AsText();
+        if (content != *aCurrContent) {
+          *aCurrContent = content;
+          const nsTextFragment* txt = &content->TextFragment();
+          if (txt->Is2b() &&
+              HasRTLChars(Span(txt->Get2b(), txt->GetLength()))) {
+            return true;
+          }
+        }
+      }
+    } else if (ChildListMayRequireBidi(frame->PrincipalChildList().FirstChild(),
+                                       aCurrContent)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void nsBidiPresUtils::ResolveParagraphWithinBlock(BidiParagraphData* aBpd) {
+  aBpd->ClearBidiControls();
+  ResolveParagraph(aBpd);
+  aBpd->ResetData();
+}
+
+/* static */
+nscoord nsBidiPresUtils::ReorderFrames(nsIFrame* aFirstFrameOnLine,
+                                       int32_t aNumFramesOnLine,
+                                       WritingMode aLineWM,
+                                       const nsSize& aContainerSize,
+                                       nscoord aStart) {
+  nsSize containerSize(aContainerSize);
+
+  // If this line consists of a line frame, reorder the line frame's children.
+  if (aFirstFrameOnLine->IsLineFrame()) {
+    // The line frame is positioned at the start-edge, so use its size
+    // as the container size.
+    containerSize = aFirstFrameOnLine->GetSize();
+
+    aFirstFrameOnLine = aFirstFrameOnLine->PrincipalChildList().FirstChild();
+    if (!aFirstFrameOnLine) {
+      return 0;
+    }
+    // All children of the line frame are on the first line. Setting
+    // aNumFramesOnLine to -1 makes InitLogicalArrayFromLine look at all of
+    // them.
+    aNumFramesOnLine = -1;
+    // As the line frame itself has been adjusted at its inline-start position
+    // by the caller, we do not want to apply this to its children.
+    aStart = 0;
+  }
+
+  BidiLineData bld(aFirstFrameOnLine, aNumFramesOnLine);
+  return RepositionInlineFrames(&bld, aLineWM, containerSize, aStart);
+}
+
+nsIFrame* nsBidiPresUtils::GetFirstLeaf(nsIFrame* aFrame) {
+  nsIFrame* firstLeaf = aFrame;
+  while (!IsBidiLeaf(firstLeaf)) {
+    nsIFrame* firstChild = firstLeaf->PrincipalChildList().FirstChild();
+    nsIFrame* realFrame = nsPlaceholderFrame::GetRealFrameFor(firstChild);
+    firstLeaf = (realFrame->IsLetterFrame()) ? realFrame : firstChild;
+  }
+  return firstLeaf;
+}
+
+FrameBidiData nsBidiPresUtils::GetFrameBidiData(nsIFrame* aFrame) {
+  return GetFirstLeaf(aFrame)->GetBidiData();
+}
+
+BidiEmbeddingLevel nsBidiPresUtils::GetFrameEmbeddingLevel(nsIFrame* aFrame) {
+  return GetFirstLeaf(aFrame)->GetEmbeddingLevel();
+}
+
+BidiEmbeddingLevel nsBidiPresUtils::GetFrameBaseLevel(const nsIFrame* aFrame) {
+  const nsIFrame* firstLeaf = aFrame;
+  while (!IsBidiLeaf(firstLeaf)) {
+    firstLeaf = firstLeaf->PrincipalChildList().FirstChild();
+  }
+  return firstLeaf->GetBaseLevel();
+}
+
+void nsBidiPresUtils::IsFirstOrLast(nsIFrame* aFrame,
+                                    nsContinuationStates* aContinuationStates,
+                                    bool aSpanDirMatchesLineDir,
+                                    bool& aIsFirst /* out */,
+                                    bool& aIsLast /* out */) {
+  /*
+   * Since we lay out frames in the line's direction, visiting a frame with
+   * 'mFirstVisualFrame == nullptr', means it's the first appearance of one
+   * of its continuation chain frames on the line.
+   * To determine if it's the last visual frame of its continuation chain on
+   * the line or not, we count the number of frames of the chain on the line,
+   * and then reduce it when we lay out a frame of the chain. If this value
+   * becomes 1 it means that it's the last visual frame of its continuation
+   * chain on this line.
+   */
+
+  bool firstInLineOrder, lastInLineOrder;
+  nsFrameContinuationState* frameState = aContinuationStates->Get(aFrame);
+  nsFrameContinuationState* firstFrameState;
+
+  if (!frameState->mFirstVisualFrame) {
+    // aFrame is the first visual frame of its continuation chain
+    nsFrameContinuationState* contState;
+    nsIFrame* frame;
+
+    frameState->mFrameCount = 1;
+    frameState->mFirstVisualFrame = aFrame;
+
+    /**
+     * Traverse continuation chain of aFrame in both backward and forward
+     * directions while the frames are on this line. Count the frames and
+     * set their mFirstVisualFrame to aFrame.
+     */
+    // Traverse continuation chain backward
+    for (frame = aFrame->GetPrevContinuation();
+         frame && (contState = aContinuationStates->Get(frame));
+         frame = frame->GetPrevContinuation()) {
+      frameState->mFrameCount++;
+      contState->mFirstVisualFrame = aFrame;
+    }
+    frameState->mHasContOnPrevLines = (frame != nullptr);
+
+    // Traverse continuation chain forward
+    for (frame = aFrame->GetNextContinuation();
+         frame && (contState = aContinuationStates->Get(frame));
+         frame = frame->GetNextContinuation()) {
+      frameState->mFrameCount++;
+      contState->mFirstVisualFrame = aFrame;
+    }
+    frameState->mHasContOnNextLines = (frame != nullptr);
+
+    firstInLineOrder = true;
+    firstFrameState = frameState;
+  } else {
+    // aFrame is not the first visual frame of its continuation chain
+    firstInLineOrder = false;
+    firstFrameState = aContinuationStates->Get(frameState->mFirstVisualFrame);
+  }
+
+  lastInLineOrder = (firstFrameState->mFrameCount == 1);
+
+  if (aSpanDirMatchesLineDir) {
+    aIsFirst = firstInLineOrder;
+    aIsLast = lastInLineOrder;
+  } else {
+    aIsFirst = lastInLineOrder;
+    aIsLast = firstInLineOrder;
+  }
+
+  if (frameState->mHasContOnPrevLines) {
+    aIsFirst = false;
+  }
+  if (firstFrameState->mHasContOnNextLines) {
+    aIsLast = false;
+  }
+
+  if ((aIsFirst || aIsLast) &&
+      aFrame->HasAnyStateBits(NS_FRAME_PART_OF_IBSPLIT)) {
+    // For ib splits, don't treat anything except the last part as
+    // endmost or anything except the first part as startmost.
+    // As an optimization, only get the first continuation once.
+    nsIFrame* firstContinuation = aFrame->FirstContinuation();
+    if (firstContinuation->FrameIsNonLastInIBSplit()) {
+      // We are not endmost
+      aIsLast = false;
+    }
+    if (firstContinuation->FrameIsNonFirstInIBSplit()) {
+      // We are not startmost
+      aIsFirst = false;
+    }
+  }
+
+  // Reduce number of remaining frames of the continuation chain on the line.
+  firstFrameState->mFrameCount--;
+
+  nsInlineFrame* testFrame = do_QueryFrame(aFrame);
+
+  if (testFrame) {
+    aFrame->AddStateBits(NS_INLINE_FRAME_BIDI_VISUAL_STATE_IS_SET);
+
+    if (aIsFirst) {
+      aFrame->AddStateBits(NS_INLINE_FRAME_BIDI_VISUAL_IS_FIRST);
+    } else {
+      aFrame->RemoveStateBits(NS_INLINE_FRAME_BIDI_VISUAL_IS_FIRST);
+    }
+
+    if (aIsLast) {
+      aFrame->AddStateBits(NS_INLINE_FRAME_BIDI_VISUAL_IS_LAST);
+    } else {
+      aFrame->RemoveStateBits(NS_INLINE_FRAME_BIDI_VISUAL_IS_LAST);
+    }
+  }
+}
+
+/* static */
+void nsBidiPresUtils::RepositionRubyContentFrame(
+    nsIFrame* aFrame, WritingMode aFrameWM,
+    const LogicalMargin& aBorderPadding) {
+  const nsFrameList& childList = aFrame->PrincipalChildList();
+  if (childList.IsEmpty()) {
+    return;
+  }
+
+  // Reorder the children.
+  nscoord isize =
+      ReorderFrames(childList.FirstChild(), childList.GetLength(), aFrameWM,
+                    aFrame->GetSize(), aBorderPadding.IStart(aFrameWM));
+  isize += aBorderPadding.IEnd(aFrameWM);
+
+  if (aFrame->StyleText()->mRubyAlign == StyleRubyAlign::Start) {
+    return;
+  }
+  nscoord residualISize = aFrame->ISize(aFrameWM) - isize;
+  if (residualISize <= 0) {
+    return;
+  }
+
+  // When ruby-align is not "start", if the content does not fill this
+  // frame, we need to center the children.
+  const nsSize dummyContainerSize;
+  for (nsIFrame* child : childList) {
+    LogicalRect rect = child->GetLogicalRect(aFrameWM, dummyContainerSize);
+    rect.IStart(aFrameWM) += residualISize / 2;
+    child->SetRect(aFrameWM, rect, dummyContainerSize);
+  }
+}
+
+/* static */
+nscoord nsBidiPresUtils::RepositionRubyFrame(
+    nsIFrame* aFrame, nsContinuationStates* aContinuationStates,
+    const WritingMode aContainerWM, const LogicalMargin& aBorderPadding) {
+  LayoutFrameType frameType = aFrame->Type();
+  MOZ_ASSERT(RubyUtils::IsRubyBox(frameType));
+
+  nscoord icoord = 0;
+  WritingMode frameWM = aFrame->GetWritingMode();
+  bool isLTR = frameWM.IsBidiLTR();
+  nsSize frameSize = aFrame->GetSize();
+  if (frameType == LayoutFrameType::Ruby) {
+    icoord += aBorderPadding.IStart(frameWM);
+    // Reposition ruby segments in a ruby container
+    for (RubySegmentEnumerator e(static_cast<nsRubyFrame*>(aFrame)); !e.AtEnd();
+         e.Next()) {
+      nsRubyBaseContainerFrame* rbc = e.GetBaseContainer();
+      AutoRubyTextContainerArray textContainers(rbc);
+
+      nscoord segmentISize = RepositionFrame(
+          rbc, isLTR, icoord, aContinuationStates, frameWM, false, frameSize);
+      for (nsRubyTextContainerFrame* rtc : textContainers) {
+        nscoord isize = RepositionFrame(rtc, isLTR, icoord, aContinuationStates,
+                                        frameWM, false, frameSize);
+        segmentISize = std::max(segmentISize, isize);
+      }
+      icoord += segmentISize;
+    }
+    icoord += aBorderPadding.IEnd(frameWM);
+  } else if (frameType == LayoutFrameType::RubyBaseContainer) {
+    // Reposition ruby columns in a ruby segment
+    auto rbc = static_cast<nsRubyBaseContainerFrame*>(aFrame);
+    AutoRubyTextContainerArray textContainers(rbc);
+
+    for (RubyColumnEnumerator e(rbc, textContainers); !e.AtEnd(); e.Next()) {
+      RubyColumn column;
+      e.GetColumn(column);
+
+      nscoord columnISize =
+          RepositionFrame(column.mBaseFrame, isLTR, icoord, aContinuationStates,
+                          frameWM, false, frameSize);
+      for (nsRubyTextFrame* rt : column.mTextFrames) {
+        nscoord isize = RepositionFrame(rt, isLTR, icoord, aContinuationStates,
+                                        frameWM, false, frameSize);
+        columnISize = std::max(columnISize, isize);
+      }
+      icoord += columnISize;
+    }
+  } else {
+    if (frameType == LayoutFrameType::RubyBase ||
+        frameType == LayoutFrameType::RubyText) {
+      RepositionRubyContentFrame(aFrame, frameWM, aBorderPadding);
+    }
+    // Note that, ruby text container is not present in all conditions
+    // above. It is intended, because the children of rtc are reordered
+    // with the children of ruby base container simultaneously. We only
+    // need to return its isize here, as it should not be changed.
+    icoord += aFrame->ISize(aContainerWM);
+  }
+  return icoord;
+}
+
+/* static */
+nscoord nsBidiPresUtils::RepositionFrame(
+    nsIFrame* aFrame, bool aIsEvenLevel, nscoord aStartOrEnd,
+    nsContinuationStates* aContinuationStates, WritingMode aContainerWM,
+    bool aContainerReverseDir, const nsSize& aContainerSize) {
+  nscoord lineSize =
+      aContainerWM.IsVertical() ? aContainerSize.height : aContainerSize.width;
+  NS_ASSERTION(lineSize != NS_UNCONSTRAINEDSIZE,
+               "Unconstrained inline line size in bidi frame reordering");
+  if (!aFrame) return 0;
+
+  bool isFirst, isLast;
+  WritingMode frameWM = aFrame->GetWritingMode();
+  IsFirstOrLast(aFrame, aContinuationStates,
+                aContainerWM.IsBidiLTR() == frameWM.IsBidiLTR(),
+                isFirst /* out */, isLast /* out */);
+
+  // We only need the margin if the frame is first or last in its own
+  // writing mode, but we're traversing the frames in the order of the
+  // container's writing mode. To get the right values, we set start and
+  // end margins on a logical margin in the frame's writing mode, and
+  // then convert the margin to the container's writing mode to set the
+  // coordinates.
+
+  // This method is called from nsBlockFrame::PlaceLine via the call to
+  // bidiUtils->ReorderFrames, so this is guaranteed to be after the inlines
+  // have been reflowed, which is required for GetUsedMargin/Border/Padding
+  nscoord frameISize = aFrame->ISize();
+  LogicalMargin frameMargin = aFrame->GetLogicalUsedMargin(frameWM);
+  LogicalMargin borderPadding = aFrame->GetLogicalUsedBorderAndPadding(frameWM);
+  // Since the visual order of frame could be different from the continuation
+  // order, we need to remove any inline border/padding [that is already applied
+  // based on continuation order] and then add it back based on the visual order
+  // (i.e. isFirst/isLast) to get the correct isize for the current frame.
+  // We don't need to do that for 'box-decoration-break:clone' because then all
+  // continuations have border/padding/margin applied.
+  if (aFrame->StyleBorder()->mBoxDecorationBreak ==
+      StyleBoxDecorationBreak::Slice) {
+    // First remove the border/padding that was applied based on logical order.
+    if (!aFrame->GetPrevContinuation()) {
+      frameISize -= borderPadding.IStart(frameWM);
+    }
+    if (!aFrame->GetNextContinuation()) {
+      frameISize -= borderPadding.IEnd(frameWM);
+    }
+    // Set margin/border/padding based on visual order.
+    if (!isFirst) {
+      frameMargin.IStart(frameWM) = 0;
+      borderPadding.IStart(frameWM) = 0;
+    }
+    if (!isLast) {
+      frameMargin.IEnd(frameWM) = 0;
+      borderPadding.IEnd(frameWM) = 0;
+    }
+    // Add the border/padding which is now based on visual order.
+    frameISize += borderPadding.IStartEnd(frameWM);
+  }
+
+  nscoord icoord = 0;
+  if (IsBidiLeaf(aFrame)) {
+    icoord +=
+        frameWM.IsOrthogonalTo(aContainerWM) ? aFrame->BSize() : frameISize;
+  } else if (RubyUtils::IsRubyBox(aFrame->Type())) {
+    icoord += RepositionRubyFrame(aFrame, aContinuationStates, aContainerWM,
+                                  borderPadding);
+  } else {
+    bool reverseDir = aIsEvenLevel != frameWM.IsBidiLTR();
+    icoord += reverseDir ? borderPadding.IEnd(frameWM)
+                         : borderPadding.IStart(frameWM);
+    LogicalSize logicalSize(frameWM, frameISize, aFrame->BSize());
+    nsSize frameSize = logicalSize.GetPhysicalSize(frameWM);
+    // Reposition the child frames
+    for (nsIFrame* f : aFrame->PrincipalChildList()) {
+      icoord += RepositionFrame(f, aIsEvenLevel, icoord, aContinuationStates,
+                                frameWM, reverseDir, frameSize);
+    }
+    icoord += reverseDir ? borderPadding.IStart(frameWM)
+                         : borderPadding.IEnd(frameWM);
+  }
+
+  // In the following variables, if aContainerReverseDir is true, i.e.
+  // the container is positioning its children in reverse of its logical
+  // direction, the "StartOrEnd" refers to the distance from the frame
+  // to the inline end edge of the container, elsewise, it refers to the
+  // distance to the inline start edge.
+  const LogicalMargin margin = frameMargin.ConvertTo(aContainerWM, frameWM);
+  nscoord marginStartOrEnd = aContainerReverseDir ? margin.IEnd(aContainerWM)
+                                                  : margin.IStart(aContainerWM);
+  nscoord frameStartOrEnd = aStartOrEnd + marginStartOrEnd;
+
+  LogicalRect rect = aFrame->GetLogicalRect(aContainerWM, aContainerSize);
+  rect.ISize(aContainerWM) = icoord;
+  rect.IStart(aContainerWM) = aContainerReverseDir
+                                  ? lineSize - frameStartOrEnd - icoord
+                                  : frameStartOrEnd;
+  aFrame->SetRect(aContainerWM, rect, aContainerSize);
+
+  return icoord + margin.IStartEnd(aContainerWM);
+}
+
+void nsBidiPresUtils::InitContinuationStates(
+    nsIFrame* aFrame, nsContinuationStates* aContinuationStates) {
+  aContinuationStates->Insert(aFrame);
+  if (!IsBidiLeaf(aFrame)) {
+    // Continue for child frames
+    for (nsIFrame* frame : aFrame->PrincipalChildList()) {
+      InitContinuationStates(frame, aContinuationStates);
+    }
+  }
+}
+
+/* static */
+nscoord nsBidiPresUtils::RepositionInlineFrames(BidiLineData* aBld,
+                                                WritingMode aLineWM,
+                                                const nsSize& aContainerSize,
+                                                nscoord aStart) {
+  nscoord start = aStart;
+  nsIFrame* frame;
+  int32_t count = aBld->mVisualFrames.Length();
+  int32_t index;
+  nsContinuationStates continuationStates;
+
+  // Initialize continuation states to (nullptr, 0) for
+  // each frame on the line.
+  for (index = 0; index < count; index++) {
+    InitContinuationStates(aBld->VisualFrameAt(index), &continuationStates);
+  }
+
+  // Reposition frames in visual order
+  int32_t step, limit;
+  if (aLineWM.IsBidiLTR()) {
+    index = 0;
+    step = 1;
+    limit = count;
+  } else {
+    index = count - 1;
+    step = -1;
+    limit = -1;
+  }
+  for (; index != limit; index += step) {
+    frame = aBld->VisualFrameAt(index);
+    start += RepositionFrame(
+        frame, !(aBld->mLevels[aBld->mIndexMap[index]].IsRTL()), start,
+        &continuationStates, aLineWM, false, aContainerSize);
+  }
+  return start;
+}
+
+bool nsBidiPresUtils::CheckLineOrder(nsIFrame* aFirstFrameOnLine,
+                                     int32_t aNumFramesOnLine,
+                                     nsIFrame** aFirstVisual,
+                                     nsIFrame** aLastVisual) {
+  BidiLineData bld(aFirstFrameOnLine, aNumFramesOnLine);
+  int32_t count = bld.FrameCount();
+
+  if (aFirstVisual) {
+    *aFirstVisual = bld.VisualFrameAt(0);
+  }
+  if (aLastVisual) {
+    *aLastVisual = bld.VisualFrameAt(count - 1);
+  }
+
+  return bld.mIsReordered;
+}
+
+nsIFrame* nsBidiPresUtils::GetFrameToRightOf(const nsIFrame* aFrame,
+                                             nsIFrame* aFirstFrameOnLine,
+                                             int32_t aNumFramesOnLine) {
+  BidiLineData bld(aFirstFrameOnLine, aNumFramesOnLine);
+
+  int32_t count = bld.mVisualFrames.Length();
+
+  if (aFrame == nullptr && count) return bld.VisualFrameAt(0);
+
+  for (int32_t i = 0; i < count - 1; i++) {
+    if (bld.VisualFrameAt(i) == aFrame) {
+      return bld.VisualFrameAt(i + 1);
+    }
+  }
+
+  return nullptr;
+}
+
+nsIFrame* nsBidiPresUtils::GetFrameToLeftOf(const nsIFrame* aFrame,
+                                            nsIFrame* aFirstFrameOnLine,
+                                            int32_t aNumFramesOnLine) {
+  BidiLineData bld(aFirstFrameOnLine, aNumFramesOnLine);
+
+  int32_t count = bld.mVisualFrames.Length();
+
+  if (aFrame == nullptr && count) return bld.VisualFrameAt(count - 1);
+
+  for (int32_t i = 1; i < count; i++) {
+    if (bld.VisualFrameAt(i) == aFrame) {
+      return bld.VisualFrameAt(i - 1);
+    }
+  }
+
+  return nullptr;
+}
+
+inline void nsBidiPresUtils::EnsureBidiContinuation(
+    nsIFrame* aFrame, const nsLineList::iterator aLine, nsIFrame** aNewFrame,
+    int32_t aStart, int32_t aEnd) {
+  MOZ_ASSERT(aNewFrame, "null OUT ptr");
+  MOZ_ASSERT(aFrame, "aFrame is null");
+
+  aFrame->AdjustOffsetsForBidi(aStart, aEnd);
+  CreateContinuation(aFrame, aLine, aNewFrame, false);
+}
+
+void nsBidiPresUtils::RemoveBidiContinuation(BidiParagraphData* aBpd,
+                                             nsIFrame* aFrame,
+                                             int32_t aFirstIndex,
+                                             int32_t aLastIndex) {
+  FrameBidiData bidiData = aFrame->GetBidiData();
+  bidiData.precedingControl = kBidiLevelNone;
+  for (int32_t index = aFirstIndex + 1; index <= aLastIndex; index++) {
+    nsIFrame* frame = aBpd->FrameAt(index);
+    if (frame != NS_BIDI_CONTROL_FRAME) {
+      // Make the frame and its continuation ancestors fluid,
+      // so they can be reused or deleted by normal reflow code
+      frame->SetProperty(nsIFrame::BidiDataProperty(), bidiData);
+      frame->AddStateBits(NS_FRAME_IS_BIDI);
+      while (frame && IsBidiSplittable(frame)) {
+        nsIFrame* prev = frame->GetPrevContinuation();
+        if (prev) {
+          MakeContinuationFluid(prev, frame);
+          frame = frame->GetParent();
+        } else {
+          break;
+        }
+      }
+    }
+  }
+
+  // Make sure that the last continuation we made fluid does not itself have a
+  // fluid continuation (this can happen when re-resolving after dynamic changes
+  // to content)
+  nsIFrame* lastFrame = aBpd->FrameAt(aLastIndex);
+  MakeContinuationsNonFluidUpParentChain(lastFrame, lastFrame->GetNextInFlow());
+}
+
+nsresult nsBidiPresUtils::FormatUnicodeText(nsPresContext* aPresContext,
+                                            char16_t* aText,
+                                            int32_t& aTextLength,
+                                            BidiClass aBidiClass) {
+  nsresult rv = NS_OK;
+  // ahmed
+  // adjusted for correct numeral shaping
+  uint32_t bidiOptions = aPresContext->GetBidi();
+  switch (GET_BIDI_OPTION_NUMERAL(bidiOptions)) {
+    case IBMBIDI_NUMERAL_HINDI:
+      HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_HINDI);
+      break;
+
+    case IBMBIDI_NUMERAL_ARABIC:
+      HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_ARABIC);
+      break;
+
+    case IBMBIDI_NUMERAL_PERSIAN:
+      HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_PERSIAN);
+      break;
+
+    case IBMBIDI_NUMERAL_REGULAR:
+
+      switch (aBidiClass) {
+        case BidiClass::EuropeanNumber:
+          HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_ARABIC);
+          break;
+
+        case BidiClass::ArabicNumber:
+          HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_HINDI);
+          break;
+
+        default:
+          break;
+      }
+      break;
+
+    case IBMBIDI_NUMERAL_HINDICONTEXT:
+      if (((GET_BIDI_OPTION_DIRECTION(bidiOptions) ==
+            IBMBIDI_TEXTDIRECTION_RTL) &&
+           (IS_ARABIC_DIGIT(aText[0]))) ||
+          (BidiClass::ArabicNumber == aBidiClass)) {
+        HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_HINDI);
+      } else if (BidiClass::EuropeanNumber == aBidiClass) {
+        HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_ARABIC);
+      }
+      break;
+
+    case IBMBIDI_NUMERAL_PERSIANCONTEXT:
+      if (((GET_BIDI_OPTION_DIRECTION(bidiOptions) ==
+            IBMBIDI_TEXTDIRECTION_RTL) &&
+           (IS_ARABIC_DIGIT(aText[0]))) ||
+          (BidiClass::ArabicNumber == aBidiClass)) {
+        HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_PERSIAN);
+      } else if (BidiClass::EuropeanNumber == aBidiClass) {
+        HandleNumbers(aText, aTextLength, IBMBIDI_NUMERAL_ARABIC);
+      }
+      break;
+
+    case IBMBIDI_NUMERAL_NOMINAL:
+    default:
+      break;
+  }
+
+  StripBidiControlCharacters(aText, aTextLength);
+  return rv;
+}
+
+void nsBidiPresUtils::StripBidiControlCharacters(char16_t* aText,
+                                                 int32_t& aTextLength) {
+  if ((nullptr == aText) || (aTextLength < 1)) {
+    return;
+  }
+
+  int32_t stripLen = 0;
+
+  for (int32_t i = 0; i < aTextLength; i++) {
+    // XXX: This silently ignores surrogate characters.
+    //      As of Unicode 4.0, all Bidi control characters are within the BMP.
+    if (IsBidiControl((uint32_t)aText[i])) {
+      ++stripLen;
+    } else {
+      aText[i - stripLen] = aText[i];
+    }
+  }
+  aTextLength -= stripLen;
+}
+
+void nsBidiPresUtils::CalculateBidiClass(
+    const char16_t* aText, int32_t& aOffset, int32_t aBidiClassLimit,
+    int32_t& aRunLimit, int32_t& aRunLength, int32_t& aRunCount,
+    BidiClass& aBidiClass, BidiClass& aPrevBidiClass) {
+  bool strongTypeFound = false;
+  int32_t offset;
+  BidiClass bidiClass;
+
+  aBidiClass = BidiClass::OtherNeutral;
+
+  int32_t charLen;
+  for (offset = aOffset; offset < aBidiClassLimit; offset += charLen) {
+    // Make sure we give RTL chartype to all characters that would be classified
+    // as Right-To-Left by a bidi platform.
+    // (May differ from the UnicodeData, eg we set RTL chartype to some NSMs.)
+    charLen = 1;
+    uint32_t ch = aText[offset];
+    if (IS_HEBREW_CHAR(ch)) {
+      bidiClass = BidiClass::RightToLeft;
+    } else if (IS_ARABIC_ALPHABETIC(ch)) {
+      bidiClass = BidiClass::RightToLeftArabic;
+    } else {
+      if (offset + 1 < aBidiClassLimit &&
+          NS_IS_SURROGATE_PAIR(ch, aText[offset + 1])) {
+        ch = SURROGATE_TO_UCS4(ch, aText[offset + 1]);
+        charLen = 2;
+      }
+      bidiClass = intl::UnicodeProperties::GetBidiClass(ch);
+    }
+
+    if (!BIDICLASS_IS_WEAK(bidiClass)) {
+      if (strongTypeFound && (bidiClass != aPrevBidiClass) &&
+          (BIDICLASS_IS_RTL(bidiClass) || BIDICLASS_IS_RTL(aPrevBidiClass))) {
+        // Stop at this point to ensure uni-directionality of the text
+        // (from platform's point of view).
+        // Also, don't mix Arabic and Hebrew content (since platform may
+        // provide BIDI support to one of them only).
+        aRunLength = offset - aOffset;
+        aRunLimit = offset;
+        ++aRunCount;
+        break;
+      }
+
+      if ((BidiClass::RightToLeftArabic == aPrevBidiClass ||
+           BidiClass::ArabicNumber == aPrevBidiClass) &&
+          BidiClass::EuropeanNumber == bidiClass) {
+        bidiClass = BidiClass::ArabicNumber;
+      }
+
+      // Set PrevBidiClass to the last strong type in this frame
+      // (for correct numeric shaping)
+      aPrevBidiClass = bidiClass;
+
+      strongTypeFound = true;
+      aBidiClass = bidiClass;
+    }
+  }
+  aOffset = offset;
+}
+
+nsresult nsBidiPresUtils::ProcessText(const char16_t* aText, size_t aLength,
+                                      BidiEmbeddingLevel aBaseLevel,
+                                      nsPresContext* aPresContext,
+                                      BidiProcessor& aprocessor, Mode aMode,
+                                      nsBidiPositionResolve* aPosResolve,
+                                      int32_t aPosResolveCount, nscoord* aWidth,
+                                      BidiEngine& aBidiEngine) {
+  MOZ_ASSERT((aPosResolve == nullptr) != (aPosResolveCount > 0),
+             "Incorrect aPosResolve / aPosResolveCount arguments");
+
+  // Caller should have already replaced any separators in the original text
+  // with <space> characters.
+  MOZ_ASSERT(nsDependentSubstring(aText, aLength).FindCharInSet(kSeparators) ==
+             kNotFound);
+
+  for (int nPosResolve = 0; nPosResolve < aPosResolveCount; ++nPosResolve) {
+    aPosResolve[nPosResolve].visualIndex = kNotFound;
+    aPosResolve[nPosResolve].visualLeftTwips = kNotFound;
+    aPosResolve[nPosResolve].visualWidth = kNotFound;
+  }
+
+  // For a single-char string, or a string that is purely LTR, use a simplified
+  // path as it cannot have multiple direction or bidi-class runs.
+  if (aLength == 1 ||
+      (aLength == 2 && NS_IS_SURROGATE_PAIR(aText[0], aText[1])) ||
+      (aBaseLevel.Direction() == BidiDirection::LTR &&
+       !encoding_mem_is_utf16_bidi(aText, aLength))) {
+    ProcessSimpleRun(aText, aLength, aBaseLevel, aPresContext, aprocessor,
+                     aMode, aPosResolve, aPosResolveCount, aWidth);
+    return NS_OK;
+  }
+
+  if (aBidiEngine.SetParagraph(Span(aText, aLength), aBaseLevel).isErr()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  auto result = aBidiEngine.CountRuns();
+  if (result.isErr()) {
+    return NS_ERROR_FAILURE;
+  }
+  int32_t runCount = result.unwrap();
+
+  nscoord xOffset = 0;
+  nscoord width, xEndRun = 0;
+  nscoord totalWidth = 0;
+  int32_t i, start, limit, length;
+  uint32_t visualStart = 0;
+  BidiClass bidiClass;
+  BidiClass prevClass = BidiClass::LeftToRight;
+
+  for (i = 0; i < runCount; i++) {
+    aBidiEngine.GetVisualRun(i, &start, &length);
+
+    BidiEmbeddingLevel level;
+    aBidiEngine.GetLogicalRun(start, &limit, &level);
+
+    BidiDirection dir = level.Direction();
+    int32_t subRunLength = limit - start;
+    int32_t lineOffset = start;
+    int32_t typeLimit = std::min(limit, AssertedCast<int32_t>(aLength));
+    int32_t subRunCount = 1;
+    int32_t subRunLimit = typeLimit;
+
+    /*
+     * If |level| is even, i.e. the direction of the run is left-to-right, we
+     * render the subruns from left to right and increment the x-coordinate
+     * |xOffset| by the width of each subrun after rendering.
+     *
+     * If |level| is odd, i.e. the direction of the run is right-to-left, we
+     * render the subruns from right to left. We begin by incrementing |xOffset|
+     * by the width of the whole run, and then decrement it by the width of each
+     * subrun before rendering. After rendering all the subruns, we restore the
+     * x-coordinate of the end of the run for the start of the next run.
+     */
+
+    if (dir == BidiDirection::RTL) {
+      aprocessor.SetText(aText + start, subRunLength, BidiDirection::RTL);
+      width = aprocessor.GetWidth();
+      xOffset += width;
+      xEndRun = xOffset;
+    }
+
+    while (subRunCount > 0) {
+      // CalculateBidiClass can increment subRunCount if the run
+      // contains mixed character types
+      CalculateBidiClass(aText, lineOffset, typeLimit, subRunLimit,
+                         subRunLength, subRunCount, bidiClass, prevClass);
+
+      nsAutoString runVisualText(aText + start, subRunLength);
+      if (aPresContext) {
+        FormatUnicodeText(aPresContext, runVisualText.BeginWriting(),
+                          subRunLength, bidiClass);
+      }
+
+      aprocessor.SetText(runVisualText.get(), subRunLength, dir);
+      width = aprocessor.GetWidth();
+      totalWidth += width;
+      if (dir == BidiDirection::RTL) {
+        xOffset -= width;
+      }
+      if (aMode == MODE_DRAW) {
+        aprocessor.DrawText(xOffset);
+      }
+
+      /*
+       * The caller may request to calculate the visual position of one
+       * or more characters.
+       */
+      for (int nPosResolve = 0; nPosResolve < aPosResolveCount; ++nPosResolve) {
+        nsBidiPositionResolve* posResolve = &aPosResolve[nPosResolve];
+        /*
+         * Did we already resolve this position's visual metric? If so, skip.
+         */
+        if (posResolve->visualLeftTwips != kNotFound) continue;
+
+        /*
+         * First find out if the logical position is within this run.
+         */
+        if (start <= posResolve->logicalIndex &&
+            start + subRunLength > posResolve->logicalIndex) {
+          /*
+           * If this run is only one character long, we have an easy case:
+           * the visual position is the x-coord of the start of the run
+           * less the x-coord of the start of the whole text.
+           */
+          if (subRunLength == 1) {
+            posResolve->visualIndex = visualStart;
+            posResolve->visualLeftTwips = xOffset;
+            posResolve->visualWidth = width;
+          }
+          /*
+           * Otherwise, we need to measure the width of the run's part
+           * which is to the visual left of the index.
+           * In other words, the run is broken in two, around the logical index,
+           * and we measure the part which is visually left.
+           * If the run is right-to-left, this part will span from after the
+           * index up to the end of the run; if it is left-to-right, this part
+           * will span from the start of the run up to (and inclduing) the
+           * character before the index.
+           */
+          else {
+            /*
+             * Here is a description of how the width of the current character
+             * (posResolve->visualWidth) is calculated:
+             *
+             * LTR (current char: "P"):
+             *    S A M P L E          (logical index: 3, visual index: 3)
+             *    ^ (visualLeftPart)
+             *    ^ (visualRightSide)
+             *    visualLeftLength == 3
+             *    ^^^^^^ (subWidth)
+             *    ^^^^^^^^ (aprocessor.GetWidth() -- with visualRightSide)
+             *          ^^ (posResolve->visualWidth)
+             *
+             * RTL (current char: "M"):
+             *    E L P M A S          (logical index: 2, visual index: 3)
+             *        ^ (visualLeftPart)
+             *          ^ (visualRightSide)
+             *    visualLeftLength == 3
+             *    ^^^^^^ (subWidth)
+             *    ^^^^^^^^ (aprocessor.GetWidth() -- with visualRightSide)
+             *          ^^ (posResolve->visualWidth)
+             */
+            nscoord subWidth;
+            // The position in the text where this run's "left part" begins.
+            const char16_t* visualLeftPart;
+            const char16_t* visualRightSide;
+            if (dir == BidiDirection::RTL) {
+              // One day, son, this could all be replaced with
+              // mPresContext->BidiEngine().GetVisualIndex() ...
+              posResolve->visualIndex =
+                  visualStart +
+                  (subRunLength - (posResolve->logicalIndex + 1 - start));
+              // Skipping to the "left part".
+              visualLeftPart = aText + posResolve->logicalIndex + 1;
+              // Skipping to the right side of the current character
+              visualRightSide = visualLeftPart - 1;
+            } else {
+              posResolve->visualIndex =
+                  visualStart + (posResolve->logicalIndex - start);
+              // Skipping to the "left part".
+              visualLeftPart = aText + start;
+              // In LTR mode this is the same as visualLeftPart
+              visualRightSide = visualLeftPart;
+            }
+            // The delta between the start of the run and the left part's end.
+            int32_t visualLeftLength = posResolve->visualIndex - visualStart;
+            aprocessor.SetText(visualLeftPart, visualLeftLength, dir);
+            subWidth = aprocessor.GetWidth();
+            aprocessor.SetText(visualRightSide, visualLeftLength + 1, dir);
+            posResolve->visualLeftTwips = xOffset + subWidth;
+            posResolve->visualWidth = aprocessor.GetWidth() - subWidth;
+          }
+        }
+      }
+
+      if (dir == BidiDirection::LTR) {
+        xOffset += width;
+      }
+
+      --subRunCount;
+      start = lineOffset;
+      subRunLimit = typeLimit;
+      subRunLength = typeLimit - lineOffset;
+    }  // while
+    if (dir == BidiDirection::RTL) {
+      xOffset = xEndRun;
+    }
+
+    visualStart += length;
+  }  // for
+
+  if (aWidth) {
+    *aWidth = totalWidth;
+  }
+  return NS_OK;
+}
+
+// This is called either for a single character (one code unit, or a surrogate
+// pair), or for a run that is known to be purely LTR.
+void nsBidiPresUtils::ProcessSimpleRun(const char16_t* aText, size_t aLength,
+                                       BidiEmbeddingLevel aBaseLevel,
+                                       nsPresContext* aPresContext,
+                                       BidiProcessor& aprocessor, Mode aMode,
+                                       nsBidiPositionResolve* aPosResolve,
+                                       int32_t aPosResolveCount,
+                                       nscoord* aWidth) {
+  // Get bidi class from the first (or only) character.
+  uint32_t ch = aText[0];
+  if (aLength > 1 && NS_IS_HIGH_SURROGATE(ch) &&
+      NS_IS_LOW_SURROGATE(aText[1])) {
+    ch = SURROGATE_TO_UCS4(aText[0], aText[1]);
+  }
+  BidiClass bidiClass = intl::UnicodeProperties::GetBidiClass(ch);
+
+  nsAutoString runVisualText(aText, aLength);
+  int32_t length = aLength;
+  if (aPresContext) {
+    FormatUnicodeText(aPresContext, runVisualText.BeginWriting(), length,
+                      bidiClass);
+  }
+
+  BidiDirection dir = bidiClass == BidiClass::RightToLeft ||
+                              bidiClass == BidiClass::RightToLeftArabic
+                          ? BidiDirection::RTL
+                          : BidiDirection::LTR;
+  aprocessor.SetText(runVisualText.get(), length, dir);
+
+  if (aMode == MODE_DRAW) {
+    aprocessor.DrawText(0);
+  }
+
+  if (!aWidth && !aPosResolve) {
+    return;
+  }
+
+  nscoord width = aprocessor.GetWidth();
+
+  for (int nPosResolve = 0; nPosResolve < aPosResolveCount; ++nPosResolve) {
+    nsBidiPositionResolve* posResolve = &aPosResolve[nPosResolve];
+    if (posResolve->visualLeftTwips != kNotFound) {
+      continue;
+    }
+    if (0 <= posResolve->logicalIndex && length > posResolve->logicalIndex) {
+      posResolve->visualIndex = 0;
+      posResolve->visualLeftTwips = 0;
+      posResolve->visualWidth = width;
+    }
+  }
+
+  if (aWidth) {
+    *aWidth = width;
+  }
+}
+
+class MOZ_STACK_CLASS nsIRenderingContextBidiProcessor final
+    : public nsBidiPresUtils::BidiProcessor {
+ public:
+  typedef gfx::DrawTarget DrawTarget;
+
+  nsIRenderingContextBidiProcessor(gfxContext* aCtx,
+                                   DrawTarget* aTextRunConstructionDrawTarget,
+                                   nsFontMetrics* aFontMetrics,
+                                   const nsPoint& aPt)
+      : mCtx(aCtx),
+        mTextRunConstructionDrawTarget(aTextRunConstructionDrawTarget),
+        mFontMetrics(aFontMetrics),
+        mPt(aPt),
+        mText(nullptr),
+        mLength(0) {}
+
+  ~nsIRenderingContextBidiProcessor() { mFontMetrics->SetTextRunRTL(false); }
+
+  virtual void SetText(const char16_t* aText, int32_t aLength,
+                       BidiDirection aDirection) override {
+    mFontMetrics->SetTextRunRTL(aDirection == BidiDirection::RTL);
+    mText = aText;
+    mLength = aLength;
+  }
+
+  virtual nscoord GetWidth() override {
+    return nsLayoutUtils::AppUnitWidthOfString(mText, mLength, *mFontMetrics,
+                                               mTextRunConstructionDrawTarget);
+  }
+
+  virtual void DrawText(nscoord aIOffset) override {
+    nsPoint pt(mPt);
+    if (mFontMetrics->GetVertical()) {
+      pt.y += aIOffset;
+    } else {
+      pt.x += aIOffset;
+    }
+    mFontMetrics->DrawString(mText, mLength, pt.x, pt.y, mCtx,
+                             mTextRunConstructionDrawTarget);
+  }
+
+ private:
+  gfxContext* mCtx;
+  DrawTarget* mTextRunConstructionDrawTarget;
+  nsFontMetrics* mFontMetrics;
+  nsPoint mPt;
+  const char16_t* mText;
+  int32_t mLength;
+};
+
+nsresult nsBidiPresUtils::ProcessTextForRenderingContext(
+    const char16_t* aText, int32_t aLength, BidiEmbeddingLevel aBaseLevel,
+    nsPresContext* aPresContext, gfxContext& aRenderingContext,
+    DrawTarget* aTextRunConstructionDrawTarget, nsFontMetrics& aFontMetrics,
+    Mode aMode, nscoord aX, nscoord aY, nsBidiPositionResolve* aPosResolve,
+    int32_t aPosResolveCount, nscoord* aWidth) {
+  nsIRenderingContextBidiProcessor processor(&aRenderingContext,
+                                             aTextRunConstructionDrawTarget,
+                                             &aFontMetrics, nsPoint(aX, aY));
+  nsAutoString text(aText, aLength);
+  text.ReplaceChar(kSeparators, ' ');
+  return ProcessText(text.BeginReading(), text.Length(), aBaseLevel,
+                     aPresContext, processor, aMode, aPosResolve,
+                     aPosResolveCount, aWidth, aPresContext->BidiEngine());
+}
+
+/* static */
+BidiEmbeddingLevel nsBidiPresUtils::BidiLevelFromStyle(
+    ComputedStyle* aComputedStyle) {
+  if (aComputedStyle->StyleTextReset()->mUnicodeBidi ==
+      StyleUnicodeBidi::Plaintext) {
+    return BidiEmbeddingLevel::DefaultLTR();
+  }
+
+  if (aComputedStyle->StyleVisibility()->mDirection == StyleDirection::Rtl) {
+    return BidiEmbeddingLevel::RTL();
+  }
+
+  return BidiEmbeddingLevel::LTR();
+}