gecko-dev/layout/mathml/nsMathMLmfencedFrame.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 "nsMathMLmfencedFrame.h"
#include "nsRenderingContext.h"
#include "nsMathMLChar.h"
#include <algorithm>

using namespace mozilla;

//
// <mfenced> -- surround content with a pair of fences
//

nsIFrame*
NS_NewMathMLmfencedFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
{
  return new (aPresShell) nsMathMLmfencedFrame(aContext);
}

NS_IMPL_FRAMEARENA_HELPERS(nsMathMLmfencedFrame)

nsMathMLmfencedFrame::~nsMathMLmfencedFrame()
{
  RemoveFencesAndSeparators();
}

NS_IMETHODIMP
nsMathMLmfencedFrame::InheritAutomaticData(nsIFrame* aParent)
{
  // let the base class get the default from our parent
  nsMathMLContainerFrame::InheritAutomaticData(aParent);

  mPresentationData.flags |= NS_MATHML_STRETCH_ALL_CHILDREN_VERTICALLY;

  RemoveFencesAndSeparators();
  CreateFencesAndSeparators(PresContext());

  return NS_OK;
}

void
nsMathMLmfencedFrame::SetInitialChildList(ChildListID     aListID,
                                          nsFrameList&    aChildList)
{
  // First, let the base class do its work
  nsMathMLContainerFrame::SetInitialChildList(aListID, aChildList);

  // InheritAutomaticData will not get called if our parent is not a mathml
  // frame, so initialize NS_MATHML_STRETCH_ALL_CHILDREN_VERTICALLY for
  // GetPreferredStretchSize() from Reflow().
  mPresentationData.flags |= NS_MATHML_STRETCH_ALL_CHILDREN_VERTICALLY;
  // No need to track the style contexts given to our MathML chars. 
  // The Style System will use Get/SetAdditionalStyleContext() to keep them
  // up-to-date if dynamic changes arise.
  CreateFencesAndSeparators(PresContext());
}

nsresult
nsMathMLmfencedFrame::AttributeChanged(int32_t         aNameSpaceID,
                                       nsIAtom*        aAttribute,
                                       int32_t         aModType)
{
  RemoveFencesAndSeparators();
  CreateFencesAndSeparators(PresContext());

  return nsMathMLContainerFrame::
         AttributeChanged(aNameSpaceID, aAttribute, aModType);
}

nsresult
nsMathMLmfencedFrame::ChildListChanged(int32_t aModType)
{
  RemoveFencesAndSeparators();
  CreateFencesAndSeparators(PresContext());

  return nsMathMLContainerFrame::ChildListChanged(aModType);
}

void
nsMathMLmfencedFrame::RemoveFencesAndSeparators()
{
  delete mOpenChar;
  delete mCloseChar;
  if (mSeparatorsChar) delete[] mSeparatorsChar;

  mOpenChar = nullptr;
  mCloseChar = nullptr;
  mSeparatorsChar = nullptr;
  mSeparatorsCount = 0;
}

void
nsMathMLmfencedFrame::CreateFencesAndSeparators(nsPresContext* aPresContext)
{
  nsAutoString value;

  //////////////  
  // see if the opening fence is there ...
  if (!mContent->GetAttr(kNameSpaceID_None, nsGkAtoms::open, value)) {
    value = char16_t('('); // default as per the MathML REC
  } else {
    value.CompressWhitespace();
  }

  if (!value.IsEmpty()) {
    mOpenChar = new nsMathMLChar;
    mOpenChar->SetData(value);
    ResolveMathMLCharStyle(aPresContext, mContent, mStyleContext, mOpenChar);
  }

  //////////////
  // see if the closing fence is there ...
  if(!mContent->GetAttr(kNameSpaceID_None, nsGkAtoms::close, value)) {
    value = char16_t(')'); // default as per the MathML REC
  } else {
    value.CompressWhitespace();
  }

  if (!value.IsEmpty()) {
    mCloseChar = new nsMathMLChar;
    mCloseChar->SetData(value);
    ResolveMathMLCharStyle(aPresContext, mContent, mStyleContext, mCloseChar);
  }

  //////////////
  // see if separators are there ...
  if (!mContent->GetAttr(kNameSpaceID_None, nsGkAtoms::separators_, value)) {
    value = char16_t(','); // default as per the MathML REC
  } else {
    value.StripWhitespace();
  }

  mSeparatorsCount = value.Length();
  if (0 < mSeparatorsCount) {
    int32_t sepCount = mFrames.GetLength() - 1;
    if (0 < sepCount) {
      mSeparatorsChar = new nsMathMLChar[sepCount];
      nsAutoString sepChar;
      for (int32_t i = 0; i < sepCount; i++) {
        if (i < mSeparatorsCount) {
          sepChar = value[i];
        }
        else {
          sepChar = value[mSeparatorsCount-1];
        }
        mSeparatorsChar[i].SetData(sepChar);
        ResolveMathMLCharStyle(aPresContext, mContent, mStyleContext, &mSeparatorsChar[i]);
      }
      mSeparatorsCount = sepCount;
    } else {
      // No separators.  Note that sepCount can be -1 here, so don't
      // set mSeparatorsCount to it.
      mSeparatorsCount = 0;
    }
  }
}

void
nsMathMLmfencedFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                       const nsRect&           aDirtyRect,
                                       const nsDisplayListSet& aLists)
{
  /////////////
  // display the content
  nsMathMLContainerFrame::BuildDisplayList(aBuilder, aDirtyRect, aLists);
  
  ////////////
  // display fences and separators
  uint32_t count = 0;
  if (mOpenChar) {
    mOpenChar->Display(aBuilder, this, aLists, count++);
  }
  
  if (mCloseChar) {
    mCloseChar->Display(aBuilder, this, aLists, count++);
  }
  
  for (int32_t i = 0; i < mSeparatorsCount; i++) {
    mSeparatorsChar[i].Display(aBuilder, this, aLists, count++);
  }
}

/* @param aMetrics is an IN/OUT.  Provide the current metrics for the mFenced
          frame and it will be enlarged as necessary.
For simplicity the width of the container is always incremented by the width
of the nsMathMLChar.  As we only stretch fences and separators in the vertical
direction, this has no impact on overall appearance.
*/
static void
ApplyUnstretchedMetrics(nsPresContext*      aPresContext,
                        DrawTarget*         aDrawTarget,
                        float               aFontSizeInflation,
                        nsMathMLChar*       aMathMLChar,
                        nsBoundingMetrics&  aMetrics,
                        bool                aIsRTL)
{
  if (aMathMLChar && 0 < aMathMLChar->Length()) {
    nsBoundingMetrics charSize;
    aMathMLChar->Stretch(aPresContext, aDrawTarget, aFontSizeInflation,
                         NS_STRETCH_DIRECTION_DEFAULT,
                         aMetrics, // size is unimportant as we aren't stretching
                         charSize, NS_STRETCH_NONE, aIsRTL);
    aMetrics += charSize;
  }
}

void
nsMathMLmfencedFrame::Reflow(nsPresContext*          aPresContext,
                             nsHTMLReflowMetrics&     aDesiredSize,
                             const nsHTMLReflowState& aReflowState,
                             nsReflowStatus&          aStatus)
{
  MarkInReflow();
  mPresentationData.flags &= ~NS_MATHML_ERROR;
  aDesiredSize.ClearSize();
  aDesiredSize.SetBlockStartAscent(0);
  aDesiredSize.mBoundingMetrics = nsBoundingMetrics();

  int32_t i;
  const nsStyleFont* font = StyleFont();
  float fontSizeInflation = nsLayoutUtils::FontSizeInflationFor(this);
  RefPtr<nsFontMetrics> fm =
    nsLayoutUtils::GetFontMetricsForFrame(this, fontSizeInflation);
  nscoord axisHeight, em;
  GetAxisHeight(aReflowState.rendContext->GetDrawTarget(), fm, axisHeight);
  GetEmHeight(fm, em);
  // leading to be left at the top and the bottom of stretched chars
  nscoord leading = NSToCoordRound(0.2f * em); 

  /////////////
  // Reflow children
  // Asking each child to cache its bounding metrics

  // Note that we don't use the base method nsMathMLContainerFrame::Reflow()
  // because we want to stretch our fences, separators and stretchy frames using
  // the *same* initial aDesiredSize.mBoundingMetrics. If we were to use the base
  // method here, our stretchy frames will be stretched and placed, and we may
  // end up stretching our fences/separators with a different aDesiredSize.
  // XXX The above decision was revisited in bug 121748 and this code can be
  // refactored to use nsMathMLContainerFrame::Reflow() at some stage.

  nsReflowStatus childStatus;
  nsIFrame* firstChild = PrincipalChildList().FirstChild();
  nsIFrame* childFrame = firstChild;
  nscoord ascent = 0, descent = 0;
  if (firstChild || mOpenChar || mCloseChar || mSeparatorsCount > 0) {
    // We use the ASCII metrics to get our minimum height. This way,
    // if we have borders or a background, they will fit better with
    // other elements on the line.
    ascent = fm->MaxAscent();
    descent = fm->MaxDescent();
  }
  while (childFrame) {
    nsHTMLReflowMetrics childDesiredSize(aReflowState,
                                         aDesiredSize.mFlags
                                         | NS_REFLOW_CALC_BOUNDING_METRICS);
    WritingMode wm = childFrame->GetWritingMode();
    LogicalSize availSize = aReflowState.ComputedSize(wm);
    availSize.BSize(wm) = NS_UNCONSTRAINEDSIZE;
    nsHTMLReflowState childReflowState(aPresContext, aReflowState,
                                       childFrame, availSize);
    ReflowChild(childFrame, aPresContext, childDesiredSize,
                childReflowState, childStatus);
    //NS_ASSERTION(NS_FRAME_IS_COMPLETE(childStatus), "bad status");
    SaveReflowAndBoundingMetricsFor(childFrame, childDesiredSize,
                                    childDesiredSize.mBoundingMetrics);

    mozilla::WritingMode outerWM = aReflowState.GetWritingMode();
    nscoord childDescent = childDesiredSize.BSize(outerWM) -
                           childDesiredSize.BlockStartAscent();
    if (descent < childDescent)
      descent = childDescent;
    if (ascent < childDesiredSize.BlockStartAscent())
      ascent = childDesiredSize.BlockStartAscent();

    childFrame = childFrame->GetNextSibling();
  }

  /////////////
  // Ask stretchy children to stretch themselves

  nsBoundingMetrics containerSize;
  nsStretchDirection stretchDir = NS_STRETCH_DIRECTION_VERTICAL;

  DrawTarget* drawTarget = aReflowState.rendContext->GetDrawTarget();

  GetPreferredStretchSize(drawTarget,
                          0, /* i.e., without embellishments */
                          stretchDir, containerSize);
  childFrame = firstChild;
  while (childFrame) {
    nsIMathMLFrame* mathmlChild = do_QueryFrame(childFrame);
    if (mathmlChild) {
      nsHTMLReflowMetrics childDesiredSize(aReflowState);
      // retrieve the metrics that was stored at the previous pass
      GetReflowAndBoundingMetricsFor(childFrame, childDesiredSize,
                                     childDesiredSize.mBoundingMetrics);

      mathmlChild->Stretch(drawTarget,
                           stretchDir, containerSize, childDesiredSize);
      // store the updated metrics
      SaveReflowAndBoundingMetricsFor(childFrame, childDesiredSize,
                                      childDesiredSize.mBoundingMetrics);

      nscoord childDescent = childDesiredSize.Height() - childDesiredSize.BlockStartAscent();
      if (descent < childDescent)
        descent = childDescent;
      if (ascent < childDesiredSize.BlockStartAscent())
        ascent = childDesiredSize.BlockStartAscent();
    }
    childFrame = childFrame->GetNextSibling();
  }

  // bug 121748: for surrounding fences & separators, use a size that covers everything
  GetPreferredStretchSize(drawTarget, STRETCH_CONSIDER_EMBELLISHMENTS,
                          stretchDir, containerSize);

  bool isRTL = StyleVisibility()->mDirection;

  // To achieve a minimum size of "1", the container should be enlarged by the
  // unstretched metrics of the fences and separators.
  ApplyUnstretchedMetrics(aPresContext, drawTarget,
                          fontSizeInflation, mOpenChar,
                          containerSize, isRTL);
  for (i = 0; i < mSeparatorsCount; i++) {
    ApplyUnstretchedMetrics(aPresContext, drawTarget,
                            fontSizeInflation, &mSeparatorsChar[i],
                            containerSize, isRTL);
  }
  ApplyUnstretchedMetrics(aPresContext, drawTarget,
                          fontSizeInflation, mCloseChar,
                          containerSize, isRTL);

  //////////////////////////////////////////
  // Prepare the opening fence, separators, and closing fence, and
  // adjust the origin of children.

  // we need to center around the axis
  nscoord delta = std::max(containerSize.ascent - axisHeight, 
                         containerSize.descent + axisHeight);
  containerSize.ascent = delta + axisHeight;
  containerSize.descent = delta - axisHeight;

  /////////////////
  // opening fence ...
  ReflowChar(aPresContext, drawTarget, *fm,
             fontSizeInflation, mOpenChar,
             NS_MATHML_OPERATOR_FORM_PREFIX, font->mScriptLevel, 
             axisHeight, leading, em, containerSize, ascent, descent, isRTL);
  /////////////////
  // separators ...
  for (i = 0; i < mSeparatorsCount; i++) {
    ReflowChar(aPresContext, drawTarget, *fm,
               fontSizeInflation, &mSeparatorsChar[i],
               NS_MATHML_OPERATOR_FORM_INFIX, font->mScriptLevel,
               axisHeight, leading, em, containerSize, ascent, descent, isRTL);
  }
  /////////////////
  // closing fence ...
  ReflowChar(aPresContext, drawTarget, *fm,
             fontSizeInflation, mCloseChar,
             NS_MATHML_OPERATOR_FORM_POSTFIX, font->mScriptLevel,
             axisHeight, leading, em, containerSize, ascent, descent, isRTL);

  //////////////////
  // Adjust the origins of each child.
  // and update our bounding metrics

  i = 0;
  nscoord dx = 0;
  nsBoundingMetrics bm;
  bool firstTime = true;
  nsMathMLChar *leftChar, *rightChar;
  if (isRTL) {
    leftChar = mCloseChar;
    rightChar = mOpenChar;
  } else {
    leftChar = mOpenChar;
    rightChar = mCloseChar;
  }

  if (leftChar) {
    PlaceChar(leftChar, ascent, bm, dx);
    aDesiredSize.mBoundingMetrics = bm;
    firstTime = false;
  }

  if (isRTL) {
    childFrame = this->GetChildList(nsIFrame::kPrincipalList).LastChild();
  } else {
    childFrame = firstChild;
  }
  while (childFrame) {
    nsHTMLReflowMetrics childSize(aReflowState);
    GetReflowAndBoundingMetricsFor(childFrame, childSize, bm);
    if (firstTime) {
      firstTime = false;
      aDesiredSize.mBoundingMetrics  = bm;
    }
    else  
      aDesiredSize.mBoundingMetrics += bm;

    FinishReflowChild(childFrame, aPresContext, childSize, nullptr,
                      dx, ascent - childSize.BlockStartAscent(), 0);
    dx += childSize.Width();

    if (i < mSeparatorsCount) {
      PlaceChar(&mSeparatorsChar[isRTL ? mSeparatorsCount - 1 - i : i],
                ascent, bm, dx);
      aDesiredSize.mBoundingMetrics += bm;
    }
    i++;

    if (isRTL) {
      childFrame = childFrame->GetPrevSibling();
    } else {
      childFrame = childFrame->GetNextSibling();
    }
  }

  if (rightChar) {
    PlaceChar(rightChar, ascent, bm, dx);
    if (firstTime)
      aDesiredSize.mBoundingMetrics  = bm;
    else  
      aDesiredSize.mBoundingMetrics += bm;
  }

  aDesiredSize.Width() = aDesiredSize.mBoundingMetrics.width;
  aDesiredSize.Height() = ascent + descent;
  aDesiredSize.SetBlockStartAscent(ascent);

  SetBoundingMetrics(aDesiredSize.mBoundingMetrics);
  SetReference(nsPoint(0, aDesiredSize.BlockStartAscent()));

  // see if we should fix the spacing
  FixInterFrameSpacing(aDesiredSize);

  // Finished with these:
  ClearSavedChildMetrics();

  // Set our overflow area
  GatherAndStoreOverflow(&aDesiredSize);

  aStatus = NS_FRAME_COMPLETE;
  NS_FRAME_SET_TRUNCATION(aStatus, aReflowState, aDesiredSize);
}

static void
GetCharSpacing(nsMathMLChar*        aMathMLChar,
               nsOperatorFlags      aForm,
               int32_t              aScriptLevel,
               nscoord              em,
               nscoord&             aLeftSpace,
               nscoord&             aRightSpace)
{
  nsAutoString data;
  aMathMLChar->GetData(data);
  nsOperatorFlags flags = 0;
  float lspace = 0.0f;
  float rspace = 0.0f;
  bool found = nsMathMLOperators::LookupOperator(data, aForm,
                                                   &flags, &lspace, &rspace);

  // We don't want extra space when we are a script
  if (found && aScriptLevel > 0) {
    lspace /= 2.0f;
    rspace /= 2.0f;
  }

  aLeftSpace = NSToCoordRound(lspace * em);
  aRightSpace = NSToCoordRound(rspace * em);
}

// helper functions to perform the common task of formatting our chars
/*static*/ nsresult
nsMathMLmfencedFrame::ReflowChar(nsPresContext*       aPresContext,
                                 DrawTarget*          aDrawTarget,
                                 nsFontMetrics&       aFontMetrics,
                                 float                aFontSizeInflation,
                                 nsMathMLChar*        aMathMLChar,
                                 nsOperatorFlags      aForm,
                                 int32_t              aScriptLevel,
                                 nscoord              axisHeight,
                                 nscoord              leading,
                                 nscoord              em,
                                 nsBoundingMetrics&   aContainerSize,
                                 nscoord&             aAscent,
                                 nscoord&             aDescent,
                                 bool                 aRTL)
{
  if (aMathMLChar && 0 < aMathMLChar->Length()) {
    nscoord leftSpace;
    nscoord rightSpace;
    GetCharSpacing(aMathMLChar, aForm, aScriptLevel, em, leftSpace, rightSpace);

    // stretch the char to the appropriate height if it is not big enough.
    nsBoundingMetrics charSize;
    nsresult res = aMathMLChar->Stretch(aPresContext, aDrawTarget,
                                        aFontSizeInflation,
                                        NS_STRETCH_DIRECTION_VERTICAL,
                                        aContainerSize, charSize,
                                        NS_STRETCH_NORMAL, aRTL);

    if (NS_STRETCH_DIRECTION_UNSUPPORTED != aMathMLChar->GetStretchDirection()) {
      // has changed... so center the char around the axis
      nscoord height = charSize.ascent + charSize.descent;
      charSize.ascent = height/2 + axisHeight;
      charSize.descent = height - charSize.ascent;
    }
    else {
      // either it hasn't changed or stretching the char failed (i.e.,
      // nsLayoutUtils::AppUnitBoundsOfString failed)
      leading = 0;
      if (NS_FAILED(res)) {
        nsAutoString data;
        aMathMLChar->GetData(data);
        nsBoundingMetrics metrics =
          nsLayoutUtils::AppUnitBoundsOfString(data.get(), data.Length(),
                                               aFontMetrics, aDrawTarget);
        charSize.ascent = metrics.ascent;
        charSize.descent = metrics.descent;
        charSize.width = metrics.width;
        // Set this as the bounding metrics of the MathMLChar to leave
        // the necessary room to paint the char.
        aMathMLChar->SetBoundingMetrics(charSize);
      }
    }

    if (aAscent < charSize.ascent + leading) 
      aAscent = charSize.ascent + leading;
    if (aDescent < charSize.descent + leading) 
      aDescent = charSize.descent + leading;

    // account the spacing
    charSize.width += leftSpace + rightSpace;

    // x-origin is used to store lspace ...
    // y-origin is used to stored the ascent ... 
    aMathMLChar->SetRect(nsRect(leftSpace, 
                                charSize.ascent, charSize.width,
                                charSize.ascent + charSize.descent));
  }
  return NS_OK;
}

/*static*/ void
nsMathMLmfencedFrame::PlaceChar(nsMathMLChar*      aMathMLChar,
                                nscoord            aDesiredAscent,
                                nsBoundingMetrics& bm,
                                nscoord&           dx)
{
  aMathMLChar->GetBoundingMetrics(bm);

  // the char's x-origin was used to store lspace ...
  // the char's y-origin was used to store the ascent ... 
  // the char's width was used to store the advance with (with spacing) ... 
  nsRect rect;
  aMathMLChar->GetRect(rect);

  nscoord dy = aDesiredAscent - rect.y;
  if (aMathMLChar->GetStretchDirection() != NS_STRETCH_DIRECTION_UNSUPPORTED) {
    // the stretchy char will be centered around the axis
    // so we adjust the returned bounding metrics accordingly
    bm.descent = (bm.ascent + bm.descent) - rect.y;
    bm.ascent = rect.y;
  }

  aMathMLChar->SetRect(nsRect(dx + rect.x, dy, bm.width, rect.height));

  bm.leftBearing += rect.x;
  bm.rightBearing += rect.x;

  // return rect.width since it includes lspace and rspace
  bm.width = rect.width;
  dx += rect.width;
}

static nscoord
GetMaxCharWidth(nsPresContext*       aPresContext,
                DrawTarget*          aDrawTarget,
                float                aFontSizeInflation,
                nsMathMLChar*        aMathMLChar,
                nsOperatorFlags      aForm,
                int32_t              aScriptLevel,
                nscoord              em)
{
  nscoord width = aMathMLChar->GetMaxWidth(aPresContext, aDrawTarget,
                                           aFontSizeInflation);

  if (0 < aMathMLChar->Length()) {
    nscoord leftSpace;
    nscoord rightSpace;
    GetCharSpacing(aMathMLChar, aForm, aScriptLevel, em, leftSpace, rightSpace);

    width += leftSpace + rightSpace;
  }
  
  return width;
}

/* virtual */ void
nsMathMLmfencedFrame::GetIntrinsicISizeMetrics(nsRenderingContext* aRenderingContext, nsHTMLReflowMetrics& aDesiredSize)
{
  nscoord width = 0;

  nsPresContext* presContext = PresContext();
  const nsStyleFont* font = StyleFont();
  float fontSizeInflation = nsLayoutUtils:: FontSizeInflationFor(this);
  RefPtr<nsFontMetrics> fm =
    nsLayoutUtils::GetFontMetricsForFrame(this, fontSizeInflation);
  nscoord em;
  GetEmHeight(fm, em);

  if (mOpenChar) {
    width +=
      GetMaxCharWidth(presContext, aRenderingContext->GetDrawTarget(),
                      fontSizeInflation, mOpenChar,
                      NS_MATHML_OPERATOR_FORM_PREFIX, font->mScriptLevel, em);
  }

  int32_t i = 0;
  for (nsIFrame* childFrame : PrincipalChildList()) {
    // XXX This includes margin while Reflow currently doesn't consider
    // margin, so we may end up with too much space, but, with stretchy
    // characters, this is an approximation anyway.
    width += nsLayoutUtils::IntrinsicForContainer(aRenderingContext, childFrame,
                                                  nsLayoutUtils::PREF_ISIZE);

    if (i < mSeparatorsCount) {
      width +=
        GetMaxCharWidth(presContext, aRenderingContext->GetDrawTarget(),
                        fontSizeInflation, &mSeparatorsChar[i],
                        NS_MATHML_OPERATOR_FORM_INFIX, font->mScriptLevel, em);
    }
    i++;
  }

  if (mCloseChar) {
    width +=
      GetMaxCharWidth(presContext, aRenderingContext->GetDrawTarget(),
                      fontSizeInflation, mCloseChar,
                      NS_MATHML_OPERATOR_FORM_POSTFIX, font->mScriptLevel, em);
  }

  aDesiredSize.Width() = width;
  aDesiredSize.mBoundingMetrics.width = width;
  aDesiredSize.mBoundingMetrics.leftBearing = 0;
  aDesiredSize.mBoundingMetrics.rightBearing = width;
}

nscoord
nsMathMLmfencedFrame::FixInterFrameSpacing(nsHTMLReflowMetrics& aDesiredSize)
{
  nscoord gap = nsMathMLContainerFrame::FixInterFrameSpacing(aDesiredSize);
  if (!gap) return 0;

  nsRect rect;
  if (mOpenChar) {
    mOpenChar->GetRect(rect);
    rect.MoveBy(gap, 0);
    mOpenChar->SetRect(rect);
  }
  if (mCloseChar) {
    mCloseChar->GetRect(rect);
    rect.MoveBy(gap, 0);
    mCloseChar->SetRect(rect);
  }
  for (int32_t i = 0; i < mSeparatorsCount; i++) {
    mSeparatorsChar[i].GetRect(rect);
    rect.MoveBy(gap, 0);
    mSeparatorsChar[i].SetRect(rect);
  }
  return gap;
}

// ----------------------
// the Style System will use these to pass the proper style context to our MathMLChar
nsStyleContext*
nsMathMLmfencedFrame::GetAdditionalStyleContext(int32_t aIndex) const
{
  int32_t openIndex = -1;
  int32_t closeIndex = -1;
  int32_t lastIndex = mSeparatorsCount-1;

  if (mOpenChar) { 
    lastIndex++; 
    openIndex = lastIndex; 
  }
  if (mCloseChar) { 
    lastIndex++;
    closeIndex = lastIndex;
  }
  if (aIndex < 0 || aIndex > lastIndex) {
    return nullptr;
  }

  if (aIndex < mSeparatorsCount) {
    return mSeparatorsChar[aIndex].GetStyleContext();
  }
  else if (aIndex == openIndex) {
    return mOpenChar->GetStyleContext();
  }
  else if (aIndex == closeIndex) {
    return mCloseChar->GetStyleContext();
  }
  return nullptr;
}

void
nsMathMLmfencedFrame::SetAdditionalStyleContext(int32_t          aIndex, 
                                                nsStyleContext*  aStyleContext)
{
  int32_t openIndex = -1;
  int32_t closeIndex = -1;
  int32_t lastIndex = mSeparatorsCount-1;

  if (mOpenChar) {
    lastIndex++;
    openIndex = lastIndex;
  }
  if (mCloseChar) {
    lastIndex++;
    closeIndex = lastIndex;
  }
  if (aIndex < 0 || aIndex > lastIndex) {
    return;
  }

  if (aIndex < mSeparatorsCount) {
    mSeparatorsChar[aIndex].SetStyleContext(aStyleContext);
  }
  else if (aIndex == openIndex) {
    mOpenChar->SetStyleContext(aStyleContext);
  }
  else if (aIndex == closeIndex) {
    mCloseChar->SetStyleContext(aStyleContext);
  }
}