Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 625 insertions, 0 deletions

diff --git a/layout/generic/nsLineBox.cpp b/layout/generic/nsLineBox.cpp
new file mode 100644
index 0000000000..18051aa69a
--- /dev/null
+++ b/layout/generic/nsLineBox.cpp
@@ -0,0 +1,625 @@
+/* -*- 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::StyleClearToString(StyleClear aClearType) {
+  switch (aClearType) {
+    case StyleClear::None:
+      return "none";
+    case StyleClear::Left:
+      return "left";
+    case StyleClear::Right:
+      return "right";
+    case StyleClear::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",
+      HasForcedLineBreak() ? "forced-break" : "no-break",
+      StyleClearToString(FloatClearTypeBefore()),
+      StyleClearToString(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());
+    }
+  }
+  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(nsIFrame* aFrame) const {
+  int32_t i, n = GetChildCount();
+  nsIFrame* frame = mFirstChild;
+  for (i = 0; i < n; i++) {
+    if (frame == aFrame) {
+      return i;
+    }
+    frame = frame->GetNextSibling();
+  }
+  return -1;
+}
+
+int32_t nsLineBox::RIndexOf(nsIFrame* aFrame,
+                            nsIFrame* aLastFrameInLine) const {
+  nsIFrame* frame = aLastFrameInLine;
+  for (int32_t i = GetChildCount() - 1; i >= 0; --i) {
+    MOZ_ASSERT(i != 0 || frame == mFirstChild,
+               "caller provided incorrect last frame");
+    if (frame == aFrame) {
+      return i;
+    }
+    frame = frame->GetPrevSibling();
+  }
+  return -1;
+}
+
+bool nsLineBox::IsEmpty() const {
+  if (IsBlock()) return mFirstChild->IsEmpty();
+
+  int32_t n;
+  nsIFrame* kid;
+  for (n = GetChildCount(), kid = mFirstChild; 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 {
+    int32_t n;
+    nsIFrame* kid;
+    result = true;
+    for (n = GetChildCount(), kid = mFirstChild; 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.
+  while (!aLines.empty()) {
+    nsLineBox* line = aLines.front();
+    if (MOZ_UNLIKELY(line->mFlags.mHasHashedFrames)) {
+      line->SwitchToCounter();  // Avoid expensive has table removals.
+    }
+    while (line->GetChildCount() > 0) {
+      nsIFrame* child = aFrames->RemoveFirstChild();
+      MOZ_DIAGNOSTIC_ASSERT(child->PresContext() == aPresContext);
+      MOZ_DIAGNOSTIC_ASSERT(child == line->mFirstChild, "Lines out of sync");
+      line->mFirstChild = aFrames->FirstChild();
+      line->NoteFrameRemoved(child);
+      child->Destroy(aContext);
+    }
+    MOZ_DIAGNOSTIC_ASSERT(line == aLines.front(),
+                          "destroying child frames messed up our lines!");
+    aLines.pop_front();
+    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;
+}
+
+nsCollapsingMargin nsLineBox::GetCarriedOutBEndMargin() const {
+  NS_ASSERTION(IsBlock(), "GetCarriedOutBEndMargin called on non-block line.");
+  return (IsBlock() && mBlockData) ? mBlockData->mCarriedOutBEndMargin
+                                   : nsCollapsingMargin();
+}
+
+bool nsLineBox::SetCarriedOutBEndMargin(nsCollapsingMargin 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 (mData && mData->mOverflowAreas == OverflowAreas(bounds, bounds)) {
+    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();
+  }
+}
+
+//----------------------------------------------------------------------
+
+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;
+}