nsLineBox.cpp

/* -*- 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/. */

/* representation of one line within a block frame, a CSS line box */

#include "nsLineBox.h"

#include "mozilla/ArenaObjectID.h"
#include "mozilla/Assertions.h"
#include "mozilla/Likely.h"
#include "mozilla/PresShell.h"
#include "mozilla/Sprintf.h"
#include "mozilla/WritingModes.h"
#include "mozilla/ToString.h"
#include "nsBidiPresUtils.h"
#include "nsIFrame.h"
#include "nsIFrameInlines.h"
#include "nsPresArena.h"
#include "nsPrintfCString.h"
#include "nsWindowSizes.h"

#ifdef DEBUG
static int32_t ctorCount;
int32_t nsLineBox::GetCtorCount() { return ctorCount; }
#endif

#ifndef _MSC_VER
// static nsLineBox constant; initialized in the header file.
const uint32_t nsLineBox::kMinChildCountForHashtable;
#endif

using namespace mozilla;

nsLineBox::nsLineBox(nsIFrame* aFrame, int32_t aCount, bool aIsBlock)
    : mFirstChild(aFrame),
      mContainerSize(-1, -1),
      mBounds(WritingMode()),  // mBounds will be initialized with the correct
                               // writing mode when it is set
      mFrames(),
      mAscent(),
      mAllFlags(0),
      mData(nullptr) {
  // Assert that the union elements chosen for initialisation are at
  // least as large as all other elements in their respective unions, so
  // as to ensure that no parts are missed.
  static_assert(sizeof(mFrames) >= sizeof(mChildCount), "nsLineBox init #1");
  static_assert(sizeof(mAllFlags) >= sizeof(mFlags), "nsLineBox init #2");
  static_assert(sizeof(mData) >= sizeof(mBlockData), "nsLineBox init #3");
  static_assert(sizeof(mData) >= sizeof(mInlineData), "nsLineBox init #4");

  MOZ_COUNT_CTOR(nsLineBox);
#ifdef DEBUG
  ++ctorCount;
  NS_ASSERTION(!aIsBlock || aCount == 1, "Blocks must have exactly one child");
  nsIFrame* f = aFrame;
  for (int32_t n = aCount; n > 0; f = f->GetNextSibling(), --n) {
    NS_ASSERTION(aIsBlock == f->IsBlockOutside(), "wrong kind of child frame");
  }
#endif
  mChildCount = aCount;
  MarkDirty();
  mFlags.mBlock = aIsBlock;
}

nsLineBox::~nsLineBox() {
  MOZ_COUNT_DTOR(nsLineBox);
  if (MOZ_UNLIKELY(mFlags.mHasHashedFrames)) {
    delete mFrames;
  }
  Cleanup();
}

nsLineBox* NS_NewLineBox(PresShell* aPresShell, nsIFrame* aFrame,
                         bool aIsBlock) {
  return new (aPresShell) nsLineBox(aFrame, 1, aIsBlock);
}

nsLineBox* NS_NewLineBox(PresShell* aPresShell, nsLineBox* aFromLine,
                         nsIFrame* aFrame, int32_t aCount) {
  nsLineBox* newLine = new (aPresShell) nsLineBox(aFrame, aCount, false);
  newLine->NoteFramesMovedFrom(aFromLine);
  newLine->mContainerSize = aFromLine->mContainerSize;
  return newLine;
}

void nsLineBox::AddSizeOfExcludingThis(nsWindowSizes& aSizes) const {
  if (mFlags.mHasHashedFrames) {
    aSizes.mLayoutFramePropertiesSize +=
        mFrames->ShallowSizeOfIncludingThis(aSizes.mState.mMallocSizeOf);
  }
}

void nsLineBox::StealHashTableFrom(nsLineBox* aFromLine,
                                   uint32_t aFromLineNewCount) {
  MOZ_ASSERT(!mFlags.mHasHashedFrames);
  MOZ_ASSERT(GetChildCount() >= int32_t(aFromLineNewCount));
  mFrames = aFromLine->mFrames;
  mFlags.mHasHashedFrames = 1;
  aFromLine->mFlags.mHasHashedFrames = 0;
  aFromLine->mChildCount = aFromLineNewCount;
  // remove aFromLine's frames that aren't on this line
  nsIFrame* f = aFromLine->mFirstChild;
  for (uint32_t i = 0; i < aFromLineNewCount; f = f->GetNextSibling(), ++i) {
    mFrames->Remove(f);
  }
}

void nsLineBox::NoteFramesMovedFrom(nsLineBox* aFromLine) {
  uint32_t fromCount = aFromLine->GetChildCount();
  uint32_t toCount = GetChildCount();
  MOZ_ASSERT(toCount <= fromCount, "moved more frames than aFromLine has");
  uint32_t fromNewCount = fromCount - toCount;
  if (MOZ_LIKELY(!aFromLine->mFlags.mHasHashedFrames)) {
    aFromLine->mChildCount = fromNewCount;
    MOZ_ASSERT(toCount < kMinChildCountForHashtable);
  } else if (fromNewCount < kMinChildCountForHashtable) {
    // aFromLine has a hash table but will not have it after moving the frames
    // so this line can steal the hash table if it needs it.
    if (toCount >= kMinChildCountForHashtable) {
      StealHashTableFrom(aFromLine, fromNewCount);
    } else {
      delete aFromLine->mFrames;
      aFromLine->mFlags.mHasHashedFrames = 0;
      aFromLine->mChildCount = fromNewCount;
    }
  } else {
    // aFromLine still needs a hash table.
    if (toCount < kMinChildCountForHashtable) {
      // remove the moved frames from it
      nsIFrame* f = mFirstChild;
      for (uint32_t i = 0; i < toCount; f = f->GetNextSibling(), ++i) {
        aFromLine->mFrames->Remove(f);
      }
    } else if (toCount <= fromNewCount) {
      // This line needs a hash table, allocate a hash table for it since that
      // means fewer hash ops.
      nsIFrame* f = mFirstChild;
      for (uint32_t i = 0; i < toCount; f = f->GetNextSibling(), ++i) {
        aFromLine->mFrames->Remove(f);  // toCount RemoveEntry
      }
      SwitchToHashtable();  // toCount PutEntry
    } else {
      // This line needs a hash table, but it's fewer hash ops to steal
      // aFromLine's hash table and allocate a new hash table for that line.
      StealHashTableFrom(aFromLine, fromNewCount);  // fromNewCount RemoveEntry
      aFromLine->SwitchToHashtable();               // fromNewCount PutEntry
    }
  }
}

void* nsLineBox::operator new(size_t sz, PresShell* aPresShell) {
  return aPresShell->AllocateByObjectID(eArenaObjectID_nsLineBox, sz);
}

void nsLineBox::Destroy(PresShell* aPresShell) {
  this->nsLineBox::~nsLineBox();
  aPresShell->FreeByObjectID(eArenaObjectID_nsLineBox, this);
}

void nsLineBox::Cleanup() {
  if (mData) {
    if (IsBlock()) {
      delete mBlockData;
    } else {
      delete mInlineData;
    }
    mData = nullptr;
  }
}

#ifdef DEBUG_FRAME_DUMP
static void ListFloats(FILE* out, const char* aPrefix,
                       const nsTArray<nsIFrame*>& aFloats) {
  for (nsIFrame* f : aFloats) {
    nsCString str(aPrefix);
    str += nsPrintfCString("floatframe@%p ", static_cast<void*>(f));
    nsAutoString frameName;
    f->GetFrameName(frameName);
    str += NS_ConvertUTF16toUTF8(frameName).get();
    fprintf_stderr(out, "%s\n", str.get());
  }
}

/* static */ const char* nsLineBox::UsedClearToString(UsedClear aClearType) {
  switch (aClearType) {
    case UsedClear::None:
      return "none";
    case UsedClear::Left:
      return "left";
    case UsedClear::Right:
      return "right";
    case UsedClear::Both:
      return "both";
  }
  return "unknown";
}

void nsLineBox::List(FILE* out, int32_t aIndent,
                     nsIFrame::ListFlags aFlags) const {
  nsCString str;
  while (aIndent-- > 0) {
    str += "  ";
  }
  List(out, str.get(), aFlags);
}

void nsLineBox::List(FILE* out, const char* aPrefix,
                     nsIFrame::ListFlags aFlags) const {
  nsCString str(aPrefix);
  str += nsPrintfCString(
      "line@%p count=%d state=%s,%s,%s,%s,%s,%s,clear-before:%s,clear-after:%s",
      this, GetChildCount(), IsBlock() ? "block" : "inline",
      IsDirty() ? "dirty" : "clean",
      IsPreviousMarginDirty() ? "prevmargindirty" : "prevmarginclean",
      IsImpactedByFloat() ? "impacted" : "not-impacted",
      IsLineWrapped() ? "wrapped" : "not-wrapped",
      HasForcedLineBreakAfter() ? "forced-break-after" : "no-break",
      UsedClearToString(FloatClearTypeBefore()),
      UsedClearToString(FloatClearTypeAfter()));

  if (IsBlock() && !GetCarriedOutBEndMargin().IsZero()) {
    const nscoord bm = GetCarriedOutBEndMargin().Get();
    str += nsPrintfCString("bm=%s ",
                           nsIFrame::ConvertToString(bm, aFlags).c_str());
  }
  nsRect bounds = GetPhysicalBounds();
  str +=
      nsPrintfCString("%s ", nsIFrame::ConvertToString(bounds, aFlags).c_str());
  if (mWritingMode.IsVertical() || mWritingMode.IsBidiRTL()) {
    str += nsPrintfCString(
        "wm=%s cs=(%s) logical-rect=%s ", ToString(mWritingMode).c_str(),
        nsIFrame::ConvertToString(mContainerSize, aFlags).c_str(),
        nsIFrame::ConvertToString(mBounds, mWritingMode, aFlags).c_str());
  }
  if (mData) {
    const nsRect vo = mData->mOverflowAreas.InkOverflow();
    const nsRect so = mData->mOverflowAreas.ScrollableOverflow();
    if (!vo.IsEqualEdges(bounds) || !so.IsEqualEdges(bounds)) {
      str += nsPrintfCString("ink-overflow=%s scr-overflow=%s ",
                             nsIFrame::ConvertToString(vo, aFlags).c_str(),
                             nsIFrame::ConvertToString(so, aFlags).c_str());
    }
    if (mData->mInFlowChildBounds) {
      str += nsPrintfCString(
          "in-flow-scr-overflow=%s ",
          nsIFrame::ConvertToString(*mData->mInFlowChildBounds, aFlags)
              .c_str());
    }
  }
  fprintf_stderr(out, "%s<\n", str.get());

  nsIFrame* frame = mFirstChild;
  int32_t n = GetChildCount();
  nsCString pfx(aPrefix);
  pfx += "  ";
  while (--n >= 0) {
    frame->List(out, pfx.get(), aFlags);
    frame = frame->GetNextSibling();
  }

  if (HasFloats()) {
    fprintf_stderr(out, "%s> floats <\n", aPrefix);
    ListFloats(out, pfx.get(), mInlineData->mFloats);
  }
  fprintf_stderr(out, "%s>\n", aPrefix);
}

nsIFrame* nsLineBox::LastChild() const {
  nsIFrame* frame = mFirstChild;
  int32_t n = GetChildCount() - 1;
  while (--n >= 0) {
    frame = frame->GetNextSibling();
  }
  return frame;
}
#endif

int32_t nsLineBox::IndexOf(const nsIFrame* aFrame) const {
  int32_t i, n = GetChildCount();
  const nsIFrame* frame = mFirstChild;
  for (i = 0; i < n; i++) {
    if (frame == aFrame) {
      return i;
    }
    frame = frame->GetNextSibling();
  }
  return -1;
}

int32_t nsLineBox::RLIndexOf(const nsIFrame* aFrame,
                             const nsIFrame* aLastFrameInLine) const {
  const nsIFrame* leftFrame = mFirstChild;
  const nsIFrame* rightFrame = aLastFrameInLine;
  int32_t leftIndex = 0, rightIndex = GetChildCount() - 1;
  while (true) {
    if (aFrame == rightFrame) {
      return rightIndex;
    }
    if (leftIndex == rightIndex) {
      MOZ_ASSERT(leftFrame == rightFrame,
                 "caller provided incorrect last frame");
      break;
    }
    if (aFrame == leftFrame) {
      return leftIndex;
    }
    if (++leftIndex == rightIndex) {
      MOZ_ASSERT(leftFrame->GetNextSibling() == rightFrame,
                 "caller provided incorrect last frame");
      break;
    }
    leftFrame = leftFrame->GetNextSibling();
    rightFrame = rightFrame->GetPrevSibling();
    --rightIndex;
  }
  return -1;
}

bool nsLineBox::IsEmpty() const {
  if (IsBlock()) {
    return mFirstChild->IsEmpty();
  }

  nsIFrame* kid = mFirstChild;
  for (int32_t n = GetChildCount(); n > 0; --n, kid = kid->GetNextSibling()) {
    if (!kid->IsEmpty()) {
      return false;
    }
  }
  if (HasMarker()) {
    return false;
  }
  return true;
}

bool nsLineBox::CachedIsEmpty() {
  if (mFlags.mDirty) {
    return IsEmpty();
  }

  if (mFlags.mEmptyCacheValid) {
    return mFlags.mEmptyCacheState;
  }

  bool result;
  if (IsBlock()) {
    result = mFirstChild->CachedIsEmpty();
  } else {
    nsIFrame* kid = mFirstChild;
    result = true;
    for (int32_t n = GetChildCount(); n > 0; --n, kid = kid->GetNextSibling()) {
      if (!kid->CachedIsEmpty()) {
        result = false;
        break;
      }
    }
    if (HasMarker()) {
      result = false;
    }
  }

  mFlags.mEmptyCacheValid = true;
  mFlags.mEmptyCacheState = result;
  return result;
}

void nsLineBox::DeleteLineList(nsPresContext* aPresContext, nsLineList& aLines,
                               nsFrameList* aFrames, DestroyContext& aContext) {
  PresShell* presShell = aPresContext->PresShell();

  // Keep our line list and frame list up to date as we remove frames, in case
  // something wants to traverse the frame tree while we're destroying.
  //
  // Note: We delete the line list and the frames in each line in reverse order
  // to avoid unnecessary updates to the first-continuation and first-in-flow
  // cache. If we delete them from front to back, updating the cache has a
  // O(n^2) time complexity.
  while (!aLines.empty()) {
    nsLineBox* line = aLines.back();
    if (MOZ_UNLIKELY(line->mFlags.mHasHashedFrames)) {
      line->SwitchToCounter();  // Avoid expensive has table removals.
    }
    while (line->GetChildCount() > 0) {
      nsIFrame* child = aFrames->RemoveLastChild();
      MOZ_DIAGNOSTIC_ASSERT(child->PresContext() == aPresContext);
      line->NoteFrameRemoved(child);
      child->Destroy(aContext);
    }
    MOZ_DIAGNOSTIC_ASSERT(line == aLines.back(),
                          "destroying child frames messed up our lines!");
    aLines.pop_back();
    line->Destroy(presShell);
  }
}

bool nsLineBox::RFindLineContaining(nsIFrame* aFrame,
                                    const nsLineList::iterator& aBegin,
                                    nsLineList::iterator& aEnd,
                                    nsIFrame* aLastFrameBeforeEnd,
                                    int32_t* aFrameIndexInLine) {
  MOZ_ASSERT(aFrame, "null ptr");

  nsIFrame* curFrame = aLastFrameBeforeEnd;
  while (aBegin != aEnd) {
    --aEnd;
    NS_ASSERTION(aEnd->LastChild() == curFrame, "Unexpected curFrame");
    if (MOZ_UNLIKELY(aEnd->mFlags.mHasHashedFrames) &&
        !aEnd->Contains(aFrame)) {
      if (aEnd->mFirstChild) {
        curFrame = aEnd->mFirstChild->GetPrevSibling();
      }
      continue;
    }
    // i is the index of curFrame in aEnd
    int32_t i = aEnd->GetChildCount() - 1;
    while (i >= 0) {
      if (curFrame == aFrame) {
        *aFrameIndexInLine = i;
        return true;
      }
      --i;
      curFrame = curFrame->GetPrevSibling();
    }
    MOZ_ASSERT(!aEnd->mFlags.mHasHashedFrames, "Contains lied to us!");
  }
  *aFrameIndexInLine = -1;
  return false;
}

CollapsingMargin nsLineBox::GetCarriedOutBEndMargin() const {
  NS_ASSERTION(IsBlock(), "GetCarriedOutBEndMargin called on non-block line.");
  return (IsBlock() && mBlockData) ? mBlockData->mCarriedOutBEndMargin
                                   : CollapsingMargin();
}

bool nsLineBox::SetCarriedOutBEndMargin(CollapsingMargin aValue) {
  bool changed = false;
  if (IsBlock()) {
    if (!aValue.IsZero()) {
      if (!mBlockData) {
        mBlockData = new ExtraBlockData(GetPhysicalBounds());
      }
      changed = aValue != mBlockData->mCarriedOutBEndMargin;
      mBlockData->mCarriedOutBEndMargin = aValue;
    } else if (mBlockData) {
      changed = aValue != mBlockData->mCarriedOutBEndMargin;
      mBlockData->mCarriedOutBEndMargin = aValue;
      MaybeFreeData();
    }
  }
  return changed;
}

void nsLineBox::MaybeFreeData() {
  nsRect bounds = GetPhysicalBounds();
  // If we have space allocated for additional data but no additional data to
  // represent, just delete it.
  if (mData && mData->mOverflowAreas == OverflowAreas(bounds, bounds) &&
      !mData->mInFlowChildBounds) {
    if (IsInline()) {
      if (mInlineData->mFloats.IsEmpty()) {
        delete mInlineData;
        mInlineData = nullptr;
      }
    } else if (mBlockData->mCarriedOutBEndMargin.IsZero()) {
      delete mBlockData;
      mBlockData = nullptr;
    }
  }
}

void nsLineBox::ClearFloats() {
  MOZ_ASSERT(IsInline(), "block line can't have floats");
  if (IsInline() && mInlineData) {
    mInlineData->mFloats.Clear();
    MaybeFreeData();
  }
}

void nsLineBox::AppendFloats(nsTArray<nsIFrame*>&& aFloats) {
  MOZ_ASSERT(IsInline(), "block line can't have floats");
  if (MOZ_UNLIKELY(!IsInline())) {
    return;
  }
  if (!aFloats.IsEmpty()) {
    if (mInlineData) {
      mInlineData->mFloats.AppendElements(std::move(aFloats));
    } else {
      mInlineData = new ExtraInlineData(GetPhysicalBounds());
      mInlineData->mFloats = std::move(aFloats);
    }
  }
}

bool nsLineBox::RemoveFloat(nsIFrame* aFrame) {
  MOZ_ASSERT(IsInline(), "block line can't have floats");
  MOZ_ASSERT(aFrame);
  if (IsInline() && mInlineData) {
    if (mInlineData->mFloats.RemoveElement(aFrame)) {
      // Note: the placeholder is part of the line's child list
      // and will be removed later.
      MaybeFreeData();
      return true;
    }
  }
  return false;
}

void nsLineBox::SetFloatEdges(nscoord aStart, nscoord aEnd) {
  MOZ_ASSERT(IsInline(), "block line can't have float edges");
  if (!mInlineData) {
    mInlineData = new ExtraInlineData(GetPhysicalBounds());
  }
  mInlineData->mFloatEdgeIStart = aStart;
  mInlineData->mFloatEdgeIEnd = aEnd;
}

void nsLineBox::ClearFloatEdges() {
  MOZ_ASSERT(IsInline(), "block line can't have float edges");
  if (mInlineData) {
    mInlineData->mFloatEdgeIStart = nscoord_MIN;
    mInlineData->mFloatEdgeIEnd = nscoord_MIN;
  }
}

void nsLineBox::SetOverflowAreas(const OverflowAreas& aOverflowAreas) {
#ifdef DEBUG
  for (const auto otype : mozilla::AllOverflowTypes()) {
    NS_ASSERTION(aOverflowAreas.Overflow(otype).width >= 0,
                 "Illegal width for an overflow area!");
    NS_ASSERTION(aOverflowAreas.Overflow(otype).height >= 0,
                 "Illegal height for an overflow area!");
  }
#endif

  nsRect bounds = GetPhysicalBounds();
  if (!aOverflowAreas.InkOverflow().IsEqualInterior(bounds) ||
      !aOverflowAreas.ScrollableOverflow().IsEqualEdges(bounds)) {
    if (!mData) {
      if (IsInline()) {
        mInlineData = new ExtraInlineData(bounds);
      } else {
        mBlockData = new ExtraBlockData(bounds);
      }
    }
    mData->mOverflowAreas = aOverflowAreas;
  } else if (mData) {
    // Store away new value so that MaybeFreeData compares against
    // the right value.
    mData->mOverflowAreas = aOverflowAreas;
    MaybeFreeData();
  }
}

void nsLineBox::SetInFlowChildBounds(const Maybe<nsRect>& aInFlowChildBounds) {
  if (aInFlowChildBounds) {
    if (!mData) {
      nsRect bounds = GetPhysicalBounds();
      if (IsInline()) {
        mInlineData = new ExtraInlineData(bounds);
      } else {
        mBlockData = new ExtraBlockData(bounds);
      }
    }
    mData->mInFlowChildBounds = aInFlowChildBounds;
  } else if (mData) {
    mData->mInFlowChildBounds = Nothing{};
    MaybeFreeData();
  }
}

Maybe<nsRect> nsLineBox::GetInFlowChildBounds() const {
  if (!mData) {
    return Nothing{};
  }
  return mData->mInFlowChildBounds;
}

//----------------------------------------------------------------------

Result<nsILineIterator::LineInfo, nsresult> nsLineIterator::GetLine(
    int32_t aLineNumber) {
  const nsLineBox* line = GetLineAt(aLineNumber);
  if (!line) {
    return Err(NS_ERROR_FAILURE);
  }
  LineInfo structure;
  structure.mFirstFrameOnLine = line->mFirstChild;
  structure.mNumFramesOnLine = line->GetChildCount();
  structure.mLineBounds = line->GetPhysicalBounds();
  structure.mIsWrapped = line->IsLineWrapped();
  return structure;
}

int32_t nsLineIterator::FindLineContaining(nsIFrame* aFrame,
                                           int32_t aStartLine) {
  const nsLineBox* line = GetLineAt(aStartLine);
  MOZ_ASSERT(line, "aStartLine out of range");
  while (line) {
    if (line->Contains(aFrame)) {
      return mIndex;
    }
    line = GetNextLine();
  }
  return -1;
}

NS_IMETHODIMP
nsLineIterator::CheckLineOrder(int32_t aLine, bool* aIsReordered,
                               nsIFrame** aFirstVisual,
                               nsIFrame** aLastVisual) {
  const nsLineBox* line = GetLineAt(aLine);
  MOZ_ASSERT(line, "aLine out of range!");

  if (!line || !line->mFirstChild) {  // empty line
    *aIsReordered = false;
    *aFirstVisual = nullptr;
    *aLastVisual = nullptr;
    return NS_OK;
  }

  nsIFrame* leftmostFrame;
  nsIFrame* rightmostFrame;
  *aIsReordered =
      nsBidiPresUtils::CheckLineOrder(line->mFirstChild, line->GetChildCount(),
                                      &leftmostFrame, &rightmostFrame);

  // map leftmost/rightmost to first/last according to paragraph direction
  *aFirstVisual = mRightToLeft ? rightmostFrame : leftmostFrame;
  *aLastVisual = mRightToLeft ? leftmostFrame : rightmostFrame;

  return NS_OK;
}

NS_IMETHODIMP
nsLineIterator::FindFrameAt(int32_t aLineNumber, nsPoint aPos,
                            nsIFrame** aFrameFound,
                            bool* aPosIsBeforeFirstFrame,
                            bool* aPosIsAfterLastFrame) {
  MOZ_ASSERT(aFrameFound && aPosIsBeforeFirstFrame && aPosIsAfterLastFrame,
             "null OUT ptr");

  if (!aFrameFound || !aPosIsBeforeFirstFrame || !aPosIsAfterLastFrame) {
    return NS_ERROR_NULL_POINTER;
  }

  const nsLineBox* line = GetLineAt(aLineNumber);
  if (!line) {
    *aFrameFound = nullptr;
    *aPosIsBeforeFirstFrame = true;
    *aPosIsAfterLastFrame = false;
    return NS_OK;
  }

  if (line->ISize() == 0 && line->BSize() == 0) {
    return NS_ERROR_FAILURE;
  }

  LineFrameFinder finder(aPos, line->mContainerSize, line->mWritingMode,
                         mRightToLeft);
  int32_t n = line->GetChildCount();
  nsIFrame* frame = line->mFirstChild;
  while (n--) {
    finder.Scan(frame);
    if (finder.IsDone()) {
      break;
    }
    frame = frame->GetNextSibling();
  }
  finder.Finish(aFrameFound, aPosIsBeforeFirstFrame, aPosIsAfterLastFrame);
  return NS_OK;
}