gecko/layout/mathml/nsMathMLmfencedFrame.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla MathML Project.
 *
 * The Initial Developer of the Original Code is
 * The University Of Queensland.
 * Portions created by the Initial Developer are Copyright (C) 1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Roger B. Sidje <rbs@maths.uq.edu.au>
 *   David J. Fiddes <D.J.Fiddes@hw.ac.uk>
 *   Pierre Phaneuf <pp@ludusdesign.com>
 *   Frederic Wang <fred.wang@free.fr>
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */


#include "nsCOMPtr.h"
#include "nsFrame.h"
#include "nsPresContext.h"
#include "nsStyleContext.h"
#include "nsStyleConsts.h"
#include "nsIRenderingContext.h"
#include "nsIFontMetrics.h"

#include "nsMathMLmfencedFrame.h"

//
// <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;

  return NS_OK;
}

NS_IMETHODIMP
nsMathMLmfencedFrame::SetInitialChildList(nsIAtom*        aListName,
                                          nsFrameList&    aChildList)
{
  // First, let the base class do its work
  nsresult rv = nsMathMLContainerFrame::SetInitialChildList(aListName, aChildList);
  if (NS_FAILED(rv)) return rv;

  // 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());
  return NS_OK;
}

NS_IMETHODIMP
nsMathMLmfencedFrame::AttributeChanged(PRInt32         aNameSpaceID,
                                       nsIAtom*        aAttribute,
                                       PRInt32         aModType)
{
  RemoveFencesAndSeparators();
  CreateFencesAndSeparators(PresContext());

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

nsresult
nsMathMLmfencedFrame::ChildListChanged(PRInt32 aModType)
{
  RemoveFencesAndSeparators();
  CreateFencesAndSeparators(PresContext());

  return nsMathMLContainerFrame::ChildListChanged(aModType);
}

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

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

void
nsMathMLmfencedFrame::CreateFencesAndSeparators(nsPresContext* aPresContext)
{
  nsAutoString value;
  PRBool isMutable = PR_FALSE;

  //////////////  
  // see if the opening fence is there ...
  if (!GetAttribute(mContent, mPresentationData.mstyle, nsGkAtoms::open,
                    value)) {
    value = PRUnichar('('); // default as per the MathML REC
  } else {
    value.CompressWhitespace();
  }

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

  //////////////
  // see if the closing fence is there ...
  if(!GetAttribute(mContent, mPresentationData.mstyle,
                    nsGkAtoms::close, value)) {
    value = PRUnichar(')'); // default as per the MathML REC
  } else {
    value.CompressWhitespace();
  }

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

  //////////////
  // see if separators are there ...
  if (!GetAttribute(mContent, mPresentationData.mstyle, 
                    nsGkAtoms::separators_, value)) {
    value = PRUnichar(','); // default as per the MathML REC
  } else {
    value.StripWhitespace();
  }

  mSeparatorsCount = value.Length();
  if (0 < mSeparatorsCount) {
    PRInt32 sepCount = mFrames.GetLength() - 1;
    if (0 < sepCount) {
      mSeparatorsChar = new nsMathMLChar[sepCount];
      nsAutoString sepChar;
      for (PRInt32 i = 0; i < sepCount; i++) {
        if (i < mSeparatorsCount) {
          sepChar = value[i];
          isMutable = nsMathMLOperators::IsMutableOperator(sepChar);
        }
        else {
          sepChar = value[mSeparatorsCount-1];
          // keep the value of isMutable that was set earlier
        }
        mSeparatorsChar[i].SetData(aPresContext, sepChar);
        ResolveMathMLCharStyle(aPresContext, mContent, mStyleContext, &mSeparatorsChar[i], isMutable);
      }
      mSeparatorsCount = sepCount;
    } else {
      // No separators.  Note that sepCount can be -1 here, so don't
      // set mSeparatorsCount to it.
      mSeparatorsCount = 0;
    }
  }
}

NS_IMETHODIMP
nsMathMLmfencedFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                       const nsRect&           aDirtyRect,
                                       const nsDisplayListSet& aLists)
{
  /////////////
  // display the content
  nsresult rv = nsMathMLContainerFrame::BuildDisplayList(aBuilder, aDirtyRect, aLists);
  NS_ENSURE_SUCCESS(rv, rv);
  
  ////////////
  // display fences and separators
  if (mOpenChar) {
    rv = mOpenChar->Display(aBuilder, this, aLists);
    NS_ENSURE_SUCCESS(rv, rv);
  }
  
  if (mCloseChar) {
    rv = mCloseChar->Display(aBuilder, this, aLists);
    NS_ENSURE_SUCCESS(rv, rv);
  }
  
  for (PRInt32 i = 0; i < mSeparatorsCount; i++) {
    rv = mSeparatorsChar[i].Display(aBuilder, this, aLists);
    NS_ENSURE_SUCCESS(rv, rv);
  }
  return NS_OK;
}

NS_IMETHODIMP
nsMathMLmfencedFrame::Reflow(nsPresContext*          aPresContext,
                             nsHTMLReflowMetrics&     aDesiredSize,
                             const nsHTMLReflowState& aReflowState,
                             nsReflowStatus&          aStatus)
{
  nsresult rv;
  aDesiredSize.width = aDesiredSize.height = 0;
  aDesiredSize.ascent = 0;
  aDesiredSize.mBoundingMetrics.Clear();

  PRInt32 i;
  nsCOMPtr<nsIFontMetrics> fm;
  const nsStyleFont* font = GetStyleFont();
  aReflowState.rendContext->SetFont(font->mFont,
                                    aPresContext->GetUserFontSet());
  aReflowState.rendContext->GetFontMetrics(*getter_AddRefs(fm));
  nscoord axisHeight, em;
  GetAxisHeight(*aReflowState.rendContext, 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;
  nsSize availSize(aReflowState.ComputedWidth(), NS_UNCONSTRAINEDSIZE);
  nsIFrame* firstChild = GetFirstChild(nsnull);
  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
    fm->GetMaxAscent(ascent);
    fm->GetMaxDescent(descent);
  }
  while (childFrame) {
    nsHTMLReflowMetrics childDesiredSize(aDesiredSize.mFlags
                                         | NS_REFLOW_CALC_BOUNDING_METRICS);
    nsHTMLReflowState childReflowState(aPresContext, aReflowState,
                                       childFrame, availSize);
    rv = ReflowChild(childFrame, aPresContext, childDesiredSize,
                     childReflowState, childStatus);
    //NS_ASSERTION(NS_FRAME_IS_COMPLETE(childStatus), "bad status");
    if (NS_FAILED(rv)) {
      // Call DidReflow() for the child frames we successfully did reflow.
      DidReflowChildren(firstChild, childFrame);
      return rv;
    }

    SaveReflowAndBoundingMetricsFor(childFrame, childDesiredSize,
                                    childDesiredSize.mBoundingMetrics);

    nscoord childDescent = childDesiredSize.height - childDesiredSize.ascent;
    if (descent < childDescent)
      descent = childDescent;
    if (ascent < childDesiredSize.ascent)
      ascent = childDesiredSize.ascent;

    childFrame = childFrame->GetNextSibling();
  }

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

  nsBoundingMetrics containerSize;
  nsStretchDirection stretchDir = NS_STRETCH_DIRECTION_VERTICAL;

  nsPresentationData presentationData;
  GetPresentationData(presentationData);
  GetPreferredStretchSize(*aReflowState.rendContext,
                          0, /* i.e., without embellishments */
                          stretchDir, containerSize);
  childFrame = firstChild;
  while (childFrame) {
    nsIMathMLFrame* mathmlChild = do_QueryFrame(childFrame);
    if (mathmlChild) {
      nsHTMLReflowMetrics childDesiredSize;
      // retrieve the metrics that was stored at the previous pass
      GetReflowAndBoundingMetricsFor(childFrame, childDesiredSize,
                                     childDesiredSize.mBoundingMetrics);
      
      mathmlChild->Stretch(*aReflowState.rendContext, 
                           stretchDir, containerSize, childDesiredSize);
      // store the updated metrics
      SaveReflowAndBoundingMetricsFor(childFrame, childDesiredSize,
                                      childDesiredSize.mBoundingMetrics);
      
      nscoord childDescent = childDesiredSize.height - childDesiredSize.ascent;
      if (descent < childDescent)
        descent = childDescent;
      if (ascent < childDesiredSize.ascent)
        ascent = childDesiredSize.ascent;
    }
    childFrame = childFrame->GetNextSibling();
  }

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

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

  // we need to center around the axis
  if (firstChild) { // do nothing for an empty <mfenced></mfenced>
    nscoord delta = NS_MAX(containerSize.ascent - axisHeight, 
                           containerSize.descent + axisHeight);
    containerSize.ascent = delta + axisHeight;
    containerSize.descent = delta - axisHeight;
  }

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

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

  i = 0;
  nscoord dx = 0;
  nsBoundingMetrics bm;
  PRBool firstTime = PR_TRUE;
  if (mOpenChar) {
    PlaceChar(mOpenChar, ascent, bm, dx);
    aDesiredSize.mBoundingMetrics = bm;
    firstTime = PR_FALSE;
  }

  childFrame = firstChild;
  while (childFrame) {
    nsHTMLReflowMetrics childSize;
    GetReflowAndBoundingMetricsFor(childFrame, childSize, bm);
    if (firstTime) {
      firstTime = PR_FALSE;
      aDesiredSize.mBoundingMetrics  = bm;
    }
    else  
      aDesiredSize.mBoundingMetrics += bm;

    FinishReflowChild(childFrame, aPresContext, nsnull, childSize, 
                      dx, ascent - childSize.ascent, 0);
    dx += childSize.width;

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

    childFrame = childFrame->GetNextSibling();
  }

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

  aDesiredSize.width = aDesiredSize.mBoundingMetrics.width;
  aDesiredSize.height = ascent + descent;
  aDesiredSize.ascent = ascent;

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

  // 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);
  return NS_OK;
}

static void
GetCharSpacing(nsMathMLChar*        aMathMLChar,
               nsOperatorFlags      aForm,
               PRInt32              aScriptLevel,
               nscoord              em,
               nscoord&             aLeftSpace,
               nscoord&             aRightSpace)
{
  nsAutoString data;
  aMathMLChar->GetData(data);
  nsOperatorFlags flags = 0;
  float lspace = 0.0f;
  float rspace = 0.0f;
  PRBool 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,
                                 nsIRenderingContext& aRenderingContext,
                                 nsMathMLChar*        aMathMLChar,
                                 nsOperatorFlags      aForm,
                                 PRInt32              aScriptLevel,
                                 nscoord              axisHeight,
                                 nscoord              leading,
                                 nscoord              em,
                                 nsBoundingMetrics&   aContainerSize,
                                 nscoord&             aAscent,
                                 nscoord&             aDescent)
{
  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, aRenderingContext,
                                        NS_STRETCH_DIRECTION_VERTICAL,
                                        aContainerSize, charSize);

    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.,
      // GetBoundingMetrics failed)
      leading = 0;
      if (NS_FAILED(res)) {
        nsAutoString data;
        aMathMLChar->GetData(data);
        nsTextDimensions dimensions;
        aRenderingContext.GetTextDimensions(data.get(), data.Length(), dimensions);
        charSize.ascent = dimensions.ascent;
        charSize.descent = dimensions.descent;
        charSize.width = dimensions.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,
                nsIRenderingContext* aRenderingContext,
                nsMathMLChar*        aMathMLChar,
                nsOperatorFlags      aForm,
                PRInt32              aScriptLevel,
                nscoord              em)
{
  nscoord width = aMathMLChar->GetMaxWidth(aPresContext, *aRenderingContext);

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

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

/* virtual */ nscoord
nsMathMLmfencedFrame::GetIntrinsicWidth(nsIRenderingContext* aRenderingContext)
{
  nscoord width = 0;

  nsPresContext* presContext = PresContext();
  const nsStyleFont* font = GetStyleFont();
  nsCOMPtr<nsIFontMetrics> fm = presContext->GetMetricsFor(font->mFont);
  nscoord em;
  GetEmHeight(fm, em);

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

  PRInt32 i = 0;
  nsIFrame* childFrame = GetFirstChild(nsnull);
  while (childFrame) {
    // 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_WIDTH);

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

    childFrame = childFrame->GetNextSibling();
  }

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

  return 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 (PRInt32 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(PRInt32 aIndex) const
{
  PRInt32 openIndex = -1;
  PRInt32 closeIndex = -1;
  PRInt32 lastIndex = mSeparatorsCount-1;

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

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

void
nsMathMLmfencedFrame::SetAdditionalStyleContext(PRInt32          aIndex, 
                                                nsStyleContext*  aStyleContext)
{
  PRInt32 openIndex = -1;
  PRInt32 closeIndex = -1;
  PRInt32 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);
  }
}