LayoutDeviceIntRect
ContentCache::TextRectArray::GetUnionRect(uint32_t aOffset,
                                          uint32_t aLength) const
{
  LayoutDeviceIntRect rect;
  if (!InRange(aOffset, aLength)) {
    return rect;
  }
  for (uint32_t i = 0; i < aLength; i++) {
    rect = rect.Union(mRects[aOffset - mStart + i]);
  }
  return rect;
}
LayoutDeviceIntRect
ContentCache::TextRectArray::GetUnionRectAsFarAsPossible(
                               uint32_t aOffset,
                               uint32_t aLength) const
{
  LayoutDeviceIntRect rect;
  if (!IsOverlappingWith(aOffset, aLength)) {
    return rect;
  }
  uint32_t startOffset = std::max(aOffset, mStart);
  uint32_t endOffset = std::min(aOffset + aLength, EndOffset());
  for (uint32_t i = 0; i < endOffset - startOffset; i++) {
    rect = rect.Union(mRects[startOffset - mStart + i]);
  }
  return rect;
}
bool
ContentCacheInParent::GetUnionTextRects(
                        uint32_t aOffset,
                        uint32_t aLength,
                        LayoutDeviceIntRect& aUnionTextRect) const
{
  MOZ_LOG(sContentCacheLog, LogLevel::Info,
    ("ContentCacheInParent: 0x%p GetUnionTextRects(aOffset=%u, "
     "aLength=%u), mTextRectArray={ mStart=%u, mRects.Length()=%u }, "
     "mSelection={ mAnchor=%u, mFocus=%u }",
     this, aOffset, aLength, mTextRectArray.mStart,
     mTextRectArray.mRects.Length(), mSelection.mAnchor, mSelection.mFocus));

  CheckedInt<uint32_t> endOffset =
    CheckedInt<uint32_t>(aOffset) + aLength;
  if (!endOffset.isValid()) {
    return false;
  }

  if (!mSelection.Collapsed() &&
      aOffset == mSelection.StartOffset() && aLength == mSelection.Length()) {
    NS_WARN_IF(mSelection.mRect.IsEmpty());
    aUnionTextRect = mSelection.mRect;
    return !aUnionTextRect.IsEmpty();
  }

  if (aLength == 1) {
    if (!aOffset) {
      NS_WARN_IF(mFirstCharRect.IsEmpty());
      aUnionTextRect = mFirstCharRect;
      return !aUnionTextRect.IsEmpty();
    }
    if (aOffset == mSelection.mAnchor) {
      NS_WARN_IF(mSelection.mAnchorCharRect.IsEmpty());
      aUnionTextRect = mSelection.mAnchorCharRect;
      return !aUnionTextRect.IsEmpty();
    }
    if (aOffset == mSelection.mFocus) {
      NS_WARN_IF(mSelection.mFocusCharRect.IsEmpty());
      aUnionTextRect = mSelection.mFocusCharRect;
      return !aUnionTextRect.IsEmpty();
    }
  }

  // Even if some text rects are not cached of the queried range,
  // we should return union rect when the first character's rect is cached
  // since the first character rect is important and the others are not so
  // in most cases.

  if (!aOffset && aOffset != mSelection.mAnchor &&
      aOffset != mSelection.mFocus && !mTextRectArray.InRange(aOffset)) {
    // The first character rect isn't cached.
    return false;
  }

  if (mTextRectArray.IsOverlappingWith(aOffset, aLength)) {
    aUnionTextRect =
      mTextRectArray.GetUnionRectAsFarAsPossible(aOffset, aLength);
  } else {
    aUnionTextRect.SetEmpty();
  }

  if (!aOffset) {
    aUnionTextRect = aUnionTextRect.Union(mFirstCharRect);
  }
  if (aOffset <= mSelection.mAnchor && mSelection.mAnchor < endOffset.value()) {
    aUnionTextRect = aUnionTextRect.Union(mSelection.mAnchorCharRect);
  }
  if (aOffset <= mSelection.mFocus && mSelection.mFocus < endOffset.value()) {
    aUnionTextRect = aUnionTextRect.Union(mSelection.mFocusCharRect);
  }
  return !aUnionTextRect.IsEmpty();
}