summaryrefslogtreecommitdiffstats
path: root/layout/mathml/nsMathMLmunderoverFrame.cpp
blob: 21ac68c77d9d2cbe28c0b6023b21c1f6963026da (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
/* -*- 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/. */

#include "nsMathMLmunderoverFrame.h"
#include "nsLayoutUtils.h"
#include "nsPresContext.h"
#include "nsMathMLmmultiscriptsFrame.h"
#include "mozilla/dom/Document.h"
#include "mozilla/dom/MathMLElement.h"
#include <algorithm>
#include "gfxContext.h"
#include "gfxMathTable.h"
#include "gfxTextRun.h"
#include "mozilla/PresShell.h"
#include "mozilla/StaticPrefs_mathml.h"

using namespace mozilla;

//
// <munderover> -- attach an underscript-overscript pair to a base
//                 implementation
// <mover> -- attach an overscript to a base - implementation
// <munder> -- attach an underscript to a base - implementation
//

nsIFrame* NS_NewMathMLmunderoverFrame(PresShell* aPresShell,
                                      ComputedStyle* aStyle) {
  return new (aPresShell)
      nsMathMLmunderoverFrame(aStyle, aPresShell->GetPresContext());
}

NS_IMPL_FRAMEARENA_HELPERS(nsMathMLmunderoverFrame)

nsMathMLmunderoverFrame::~nsMathMLmunderoverFrame() = default;

nsresult nsMathMLmunderoverFrame::AttributeChanged(int32_t aNameSpaceID,
                                                   nsAtom* aAttribute,
                                                   int32_t aModType) {
  if (nsGkAtoms::accent_ == aAttribute ||
      nsGkAtoms::accentunder_ == aAttribute) {
    // When we have automatic data to update within ourselves, we ask our
    // parent to re-layout its children
    return ReLayoutChildren(GetParent());
  }

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

NS_IMETHODIMP
nsMathMLmunderoverFrame::UpdatePresentationData(uint32_t aFlagsValues,
                                                uint32_t aFlagsToUpdate) {
  nsMathMLContainerFrame::UpdatePresentationData(aFlagsValues, aFlagsToUpdate);
  // disable the stretch-all flag if we are going to act like a
  // subscript-superscript pair
  if (NS_MATHML_EMBELLISH_IS_MOVABLELIMITS(mEmbellishData.flags) &&
      StyleFont()->mMathStyle == StyleMathStyle::Compact) {
    mPresentationData.flags &= ~NS_MATHML_STRETCH_ALL_CHILDREN_HORIZONTALLY;
  } else {
    mPresentationData.flags |= NS_MATHML_STRETCH_ALL_CHILDREN_HORIZONTALLY;
  }
  return NS_OK;
}

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

  mPresentationData.flags |= NS_MATHML_STRETCH_ALL_CHILDREN_HORIZONTALLY;

  return NS_OK;
}

void nsMathMLmunderoverFrame::Destroy(DestroyContext& aContext) {
  if (!mPostReflowIncrementScriptLevelCommands.IsEmpty()) {
    PresShell()->CancelReflowCallback(this);
  }
  nsMathMLContainerFrame::Destroy(aContext);
}

uint8_t nsMathMLmunderoverFrame::ScriptIncrement(nsIFrame* aFrame) {
  nsIFrame* child = mFrames.FirstChild();
  if (!aFrame || aFrame == child) {
    return 0;
  }
  child = child->GetNextSibling();
  if (aFrame == child) {
    if (mContent->IsMathMLElement(nsGkAtoms::mover_)) {
      return mIncrementOver ? 1 : 0;
    }
    return mIncrementUnder ? 1 : 0;
  }
  if (child && aFrame == child->GetNextSibling()) {
    // must be a over frame of munderover
    return mIncrementOver ? 1 : 0;
  }
  return 0;  // frame not found
}

void nsMathMLmunderoverFrame::SetIncrementScriptLevel(uint32_t aChildIndex,
                                                      bool aIncrement) {
  nsIFrame* child = PrincipalChildList().FrameAt(aChildIndex);
  if (!child || !child->GetContent()->IsMathMLElement() ||
      child->GetContent()->GetPrimaryFrame() != child) {
    return;
  }

  auto element = dom::MathMLElement::FromNode(child->GetContent());
  if (element->GetIncrementScriptLevel() == aIncrement) {
    return;
  }

  if (mPostReflowIncrementScriptLevelCommands.IsEmpty()) {
    PresShell()->PostReflowCallback(this);
  }

  mPostReflowIncrementScriptLevelCommands.AppendElement(
      SetIncrementScriptLevelCommand{aChildIndex, aIncrement});
}

bool nsMathMLmunderoverFrame::ReflowFinished() {
  SetPendingPostReflowIncrementScriptLevel();
  return true;
}

void nsMathMLmunderoverFrame::ReflowCallbackCanceled() {
  // Do nothing, at this point our work will just be useless.
  mPostReflowIncrementScriptLevelCommands.Clear();
}

void nsMathMLmunderoverFrame::SetPendingPostReflowIncrementScriptLevel() {
  MOZ_ASSERT(!mPostReflowIncrementScriptLevelCommands.IsEmpty());

  nsTArray<SetIncrementScriptLevelCommand> commands =
      std::move(mPostReflowIncrementScriptLevelCommands);

  for (const auto& command : commands) {
    nsIFrame* child = PrincipalChildList().FrameAt(command.mChildIndex);
    if (!child || !child->GetContent()->IsMathMLElement()) {
      continue;
    }

    auto element = dom::MathMLElement::FromNode(child->GetContent());
    element->SetIncrementScriptLevel(command.mDoIncrement, true);
  }
}

NS_IMETHODIMP
nsMathMLmunderoverFrame::TransmitAutomaticData() {
  // At this stage, all our children are in sync and we can fully
  // resolve our own mEmbellishData struct
  //---------------------------------------------------------------------

  /*
  The REC says:

  As regards munder (respectively mover) :
  The default value of accentunder is false, unless underscript
  is an <mo> element or an embellished operator.  If underscript is
  an <mo> element, the value of its accent attribute is used as the
  default value of accentunder. If underscript is an embellished
  operator, the accent attribute of the <mo> element at its
  core is used as the default value. As with all attributes, an
  explicitly given value overrides the default.

XXX The winner is the outermost setting in conflicting settings like these:
<munder accentunder='true'>
  <mi>...</mi>
  <mo accentunder='false'> ... </mo>
</munder>

  As regards munderover:
  The accent and accentunder attributes have the same effect as
  the attributes with the same names on <mover>  and <munder>,
  respectively. Their default values are also computed in the
  same manner as described for those elements, with the default
  value of accent depending on overscript and the default value
  of accentunder depending on underscript.
  */

  nsIFrame* overscriptFrame = nullptr;
  nsIFrame* underscriptFrame = nullptr;
  nsIFrame* baseFrame = mFrames.FirstChild();

  if (baseFrame) {
    if (mContent->IsAnyOfMathMLElements(nsGkAtoms::munder_,
                                        nsGkAtoms::munderover_)) {
      underscriptFrame = baseFrame->GetNextSibling();
    } else {
      NS_ASSERTION(mContent->IsMathMLElement(nsGkAtoms::mover_),
                   "mContent->NodeInfo()->NameAtom() not recognized");
      overscriptFrame = baseFrame->GetNextSibling();
    }
  }
  if (underscriptFrame && mContent->IsMathMLElement(nsGkAtoms::munderover_)) {
    overscriptFrame = underscriptFrame->GetNextSibling();
  }

  // if our base is an embellished operator, let its state bubble to us (in
  // particular, this is where we get the flag for
  // NS_MATHML_EMBELLISH_MOVABLELIMITS). Our flags are reset to the default
  // values of false if the base frame isn't embellished.
  mPresentationData.baseFrame = baseFrame;
  GetEmbellishDataFrom(baseFrame, mEmbellishData);

  // The default value of accentunder is false, unless the underscript is
  // embellished and its core <mo> is an accent
  nsEmbellishData embellishData;
  nsAutoString value;
  if (mContent->IsAnyOfMathMLElements(nsGkAtoms::munder_,
                                      nsGkAtoms::munderover_)) {
    GetEmbellishDataFrom(underscriptFrame, embellishData);
    if (NS_MATHML_EMBELLISH_IS_ACCENT(embellishData.flags)) {
      mEmbellishData.flags |= NS_MATHML_EMBELLISH_ACCENTUNDER;
    } else {
      mEmbellishData.flags &= ~NS_MATHML_EMBELLISH_ACCENTUNDER;
    }

    // if we have an accentunder attribute, it overrides what the underscript
    // said
    if (mContent->AsElement()->GetAttr(kNameSpaceID_None,
                                       nsGkAtoms::accentunder_, value)) {
      if (value.EqualsLiteral("true")) {
        mEmbellishData.flags |= NS_MATHML_EMBELLISH_ACCENTUNDER;
      } else if (value.EqualsLiteral("false")) {
        mEmbellishData.flags &= ~NS_MATHML_EMBELLISH_ACCENTUNDER;
      }
    }
  }

  // The default value of accent is false, unless the overscript is embellished
  // and its core <mo> is an accent
  if (mContent->IsAnyOfMathMLElements(nsGkAtoms::mover_,
                                      nsGkAtoms::munderover_)) {
    GetEmbellishDataFrom(overscriptFrame, embellishData);
    if (NS_MATHML_EMBELLISH_IS_ACCENT(embellishData.flags)) {
      mEmbellishData.flags |= NS_MATHML_EMBELLISH_ACCENTOVER;
    } else {
      mEmbellishData.flags &= ~NS_MATHML_EMBELLISH_ACCENTOVER;
    }

    // if we have an accent attribute, it overrides what the overscript said
    if (mContent->AsElement()->GetAttr(kNameSpaceID_None, nsGkAtoms::accent_,
                                       value)) {
      if (value.EqualsLiteral("true")) {
        mEmbellishData.flags |= NS_MATHML_EMBELLISH_ACCENTOVER;
      } else if (value.EqualsLiteral("false")) {
        mEmbellishData.flags &= ~NS_MATHML_EMBELLISH_ACCENTOVER;
      }
    }
  }

  bool subsupDisplay =
      NS_MATHML_EMBELLISH_IS_MOVABLELIMITS(mEmbellishData.flags) &&
      StyleFont()->mMathStyle == StyleMathStyle::Compact;

  // disable the stretch-all flag if we are going to act like a superscript
  if (subsupDisplay) {
    mPresentationData.flags &= ~NS_MATHML_STRETCH_ALL_CHILDREN_HORIZONTALLY;
  }

  // Now transmit any change that we want to our children so that they
  // can update their mPresentationData structs
  //---------------------------------------------------------------------

  /* The REC says:
     Within underscript, <munderover> always sets displaystyle to "false",
     but increments scriptlevel by 1 only when accentunder is "false".

     Within overscript, <munderover> always sets displaystyle to "false",
     but increments scriptlevel by 1 only when accent is "false".

     Within subscript and superscript it increments scriptlevel by 1, and
     sets displaystyle to "false", but leaves both attributes unchanged within
     base.

     The TeXBook treats 'over' like a superscript, so p.141 or Rule 13a
     say it shouldn't be compressed. However, The TeXBook says
     that math accents and \overline change uncramped styles to their
     cramped counterparts.
  */
  if (mContent->IsAnyOfMathMLElements(nsGkAtoms::mover_,
                                      nsGkAtoms::munderover_)) {
    uint32_t compress = NS_MATHML_EMBELLISH_IS_ACCENTOVER(mEmbellishData.flags)
                            ? NS_MATHML_COMPRESSED
                            : 0;
    mIncrementOver = !NS_MATHML_EMBELLISH_IS_ACCENTOVER(mEmbellishData.flags) ||
                     subsupDisplay;
    SetIncrementScriptLevel(
        mContent->IsMathMLElement(nsGkAtoms::mover_) ? 1 : 2, mIncrementOver);
    if (mIncrementOver) {
      PropagateFrameFlagFor(overscriptFrame, NS_FRAME_MATHML_SCRIPT_DESCENDANT);
    }
    PropagatePresentationDataFor(overscriptFrame, compress, compress);
  }
  /*
     The TeXBook treats 'under' like a subscript, so p.141 or Rule 13a
     say it should be compressed
  */
  if (mContent->IsAnyOfMathMLElements(nsGkAtoms::munder_,
                                      nsGkAtoms::munderover_)) {
    mIncrementUnder =
        !NS_MATHML_EMBELLISH_IS_ACCENTUNDER(mEmbellishData.flags) ||
        subsupDisplay;
    SetIncrementScriptLevel(1, mIncrementUnder);
    if (mIncrementUnder) {
      PropagateFrameFlagFor(underscriptFrame,
                            NS_FRAME_MATHML_SCRIPT_DESCENDANT);
    }
    PropagatePresentationDataFor(underscriptFrame, NS_MATHML_COMPRESSED,
                                 NS_MATHML_COMPRESSED);
  }

  /* Set flags for dtls font feature settings.

     dtls
     Dotless Forms
     This feature provides dotless forms for Math Alphanumeric
     characters, such as U+1D422 MATHEMATICAL BOLD SMALL I,
     U+1D423 MATHEMATICAL BOLD SMALL J, U+1D456
     U+MATHEMATICAL ITALIC SMALL I, U+1D457 MATHEMATICAL ITALIC
     SMALL J, and so on.
     The dotless forms are to be used as base forms for placing
     mathematical accents over them.

     To opt out of this change, add the following to the stylesheet:
     "font-feature-settings: 'dtls' 0"
   */
  if (overscriptFrame &&
      NS_MATHML_EMBELLISH_IS_ACCENTOVER(mEmbellishData.flags) &&
      !NS_MATHML_EMBELLISH_IS_MOVABLELIMITS(mEmbellishData.flags)) {
    PropagatePresentationDataFor(baseFrame, NS_MATHML_DTLS, NS_MATHML_DTLS);
  }

  return NS_OK;
}

/*
The REC says:
*  If the base is an operator with movablelimits="true" (or an embellished
   operator whose <mo> element core has movablelimits="true"), and
   displaystyle="false", then underscript and overscript are drawn in
   a subscript and superscript position, respectively. In this case,
   the accent and accentunder attributes are ignored. This is often
   used for limits on symbols such as &sum;.

i.e.,:
 if (NS_MATHML_EMBELLISH_IS_MOVABLELIMITS(mEmbellishDataflags) &&
     StyleFont()->mMathStyle == StyleMathStyle::Compact) {
  // place like subscript-superscript pair
 }
 else {
  // place like underscript-overscript pair
 }
*/

/* virtual */
nsresult nsMathMLmunderoverFrame::Place(DrawTarget* aDrawTarget,
                                        bool aPlaceOrigin,
                                        ReflowOutput& aDesiredSize) {
  float fontSizeInflation = nsLayoutUtils::FontSizeInflationFor(this);
  if (NS_MATHML_EMBELLISH_IS_MOVABLELIMITS(mEmbellishData.flags) &&
      StyleFont()->mMathStyle == StyleMathStyle::Compact) {
    // place like sub sup or subsup
    if (mContent->IsMathMLElement(nsGkAtoms::munderover_)) {
      return nsMathMLmmultiscriptsFrame::PlaceMultiScript(
          PresContext(), aDrawTarget, aPlaceOrigin, aDesiredSize, this, 0, 0,
          fontSizeInflation);
    } else if (mContent->IsMathMLElement(nsGkAtoms::munder_)) {
      return nsMathMLmmultiscriptsFrame::PlaceMultiScript(
          PresContext(), aDrawTarget, aPlaceOrigin, aDesiredSize, this, 0, 0,
          fontSizeInflation);
    } else {
      NS_ASSERTION(mContent->IsMathMLElement(nsGkAtoms::mover_),
                   "mContent->NodeInfo()->NameAtom() not recognized");
      return nsMathMLmmultiscriptsFrame::PlaceMultiScript(
          PresContext(), aDrawTarget, aPlaceOrigin, aDesiredSize, this, 0, 0,
          fontSizeInflation);
    }
  }

  ////////////////////////////////////
  // Get the children's desired sizes

  nsBoundingMetrics bmBase, bmUnder, bmOver;
  ReflowOutput baseSize(aDesiredSize.GetWritingMode());
  ReflowOutput underSize(aDesiredSize.GetWritingMode());
  ReflowOutput overSize(aDesiredSize.GetWritingMode());
  nsIFrame* overFrame = nullptr;
  nsIFrame* underFrame = nullptr;
  nsIFrame* baseFrame = mFrames.FirstChild();
  underSize.SetBlockStartAscent(0);
  overSize.SetBlockStartAscent(0);
  bool haveError = false;
  if (baseFrame) {
    if (mContent->IsAnyOfMathMLElements(nsGkAtoms::munder_,
                                        nsGkAtoms::munderover_)) {
      underFrame = baseFrame->GetNextSibling();
    } else if (mContent->IsMathMLElement(nsGkAtoms::mover_)) {
      overFrame = baseFrame->GetNextSibling();
    }
  }
  if (underFrame && mContent->IsMathMLElement(nsGkAtoms::munderover_)) {
    overFrame = underFrame->GetNextSibling();
  }

  if (mContent->IsMathMLElement(nsGkAtoms::munder_)) {
    if (!baseFrame || !underFrame || underFrame->GetNextSibling()) {
      // report an error, encourage people to get their markups in order
      haveError = true;
    }
  }
  if (mContent->IsMathMLElement(nsGkAtoms::mover_)) {
    if (!baseFrame || !overFrame || overFrame->GetNextSibling()) {
      // report an error, encourage people to get their markups in order
      haveError = true;
    }
  }
  if (mContent->IsMathMLElement(nsGkAtoms::munderover_)) {
    if (!baseFrame || !underFrame || !overFrame ||
        overFrame->GetNextSibling()) {
      // report an error, encourage people to get their markups in order
      haveError = true;
    }
  }
  if (haveError) {
    if (aPlaceOrigin) {
      ReportChildCountError();
    }
    return PlaceForError(aDrawTarget, aPlaceOrigin, aDesiredSize);
  }
  GetReflowAndBoundingMetricsFor(baseFrame, baseSize, bmBase);
  if (underFrame) {
    GetReflowAndBoundingMetricsFor(underFrame, underSize, bmUnder);
  }
  if (overFrame) {
    GetReflowAndBoundingMetricsFor(overFrame, overSize, bmOver);
  }

  nscoord onePixel = nsPresContext::CSSPixelsToAppUnits(1);

  ////////////////////
  // Place Children

  RefPtr<nsFontMetrics> fm =
      nsLayoutUtils::GetFontMetricsForFrame(this, fontSizeInflation);

  nscoord xHeight = fm->XHeight();
  nscoord oneDevPixel = fm->AppUnitsPerDevPixel();
  RefPtr<gfxFont> mathFont = fm->GetThebesFontGroup()->GetFirstMathFont();

  nscoord ruleThickness;
  GetRuleThickness(aDrawTarget, fm, ruleThickness);

  nscoord correction = 0;
  GetItalicCorrection(bmBase, correction);

  // there are 2 different types of placement depending on
  // whether we want an accented under or not

  nscoord underDelta1 = 0;  // gap between base and underscript
  nscoord underDelta2 = 0;  // extra space beneath underscript

  if (!NS_MATHML_EMBELLISH_IS_ACCENTUNDER(mEmbellishData.flags)) {
    // Rule 13a, App. G, TeXbook
    nscoord bigOpSpacing2, bigOpSpacing4, bigOpSpacing5, dummy;
    GetBigOpSpacings(fm, dummy, bigOpSpacing2, dummy, bigOpSpacing4,
                     bigOpSpacing5);
    if (mathFont) {
      // XXXfredw The Open Type MATH table has some StretchStack* parameters
      // that we may use when the base is a stretchy horizontal operator. See
      // bug 963131.
      bigOpSpacing2 = mathFont->MathTable()->Constant(
          gfxMathTable::LowerLimitGapMin, oneDevPixel);
      bigOpSpacing4 = mathFont->MathTable()->Constant(
          gfxMathTable::LowerLimitBaselineDropMin, oneDevPixel);
      bigOpSpacing5 = 0;
    }
    underDelta1 = std::max(bigOpSpacing2, (bigOpSpacing4 - bmUnder.ascent));
    underDelta2 = bigOpSpacing5;
  } else {
    // No corresponding rule in TeXbook - we are on our own here
    // XXX tune the gap delta between base and underscript
    // XXX Should we use Rule 10 like \underline does?
    // XXXfredw Perhaps use the Underbar* parameters of the MATH table. See
    // bug 963125.
    underDelta1 = ruleThickness + onePixel / 2;
    underDelta2 = ruleThickness;
  }
  // empty under?
  if (!(bmUnder.ascent + bmUnder.descent)) {
    underDelta1 = 0;
    underDelta2 = 0;
  }

  nscoord overDelta1 = 0;  // gap between base and overscript
  nscoord overDelta2 = 0;  // extra space above overscript

  if (!NS_MATHML_EMBELLISH_IS_ACCENTOVER(mEmbellishData.flags)) {
    // Rule 13a, App. G, TeXbook
    // XXXfredw The Open Type MATH table has some StretchStack* parameters
    // that we may use when the base is a stretchy horizontal operator. See
    // bug 963131.
    nscoord bigOpSpacing1, bigOpSpacing3, bigOpSpacing5, dummy;
    GetBigOpSpacings(fm, bigOpSpacing1, dummy, bigOpSpacing3, dummy,
                     bigOpSpacing5);
    if (mathFont) {
      // XXXfredw The Open Type MATH table has some StretchStack* parameters
      // that we may use when the base is a stretchy horizontal operator. See
      // bug 963131.
      bigOpSpacing1 = mathFont->MathTable()->Constant(
          gfxMathTable::UpperLimitGapMin, oneDevPixel);
      bigOpSpacing3 = mathFont->MathTable()->Constant(
          gfxMathTable::UpperLimitBaselineRiseMin, oneDevPixel);
      bigOpSpacing5 = 0;
    }
    overDelta1 = std::max(bigOpSpacing1, (bigOpSpacing3 - bmOver.descent));
    overDelta2 = bigOpSpacing5;

    // XXX This is not a TeX rule...
    // delta1 (as computed abvove) can become really big when bmOver.descent is
    // negative,  e.g., if the content is &OverBar. In such case, we use the
    // height
    if (bmOver.descent < 0)
      overDelta1 = std::max(bigOpSpacing1,
                            (bigOpSpacing3 - (bmOver.ascent + bmOver.descent)));
  } else {
    // Rule 12, App. G, TeXbook
    // We are going to modify this rule to make it more general.
    // The idea behind Rule 12 in the TeXBook is to keep the accent
    // as close to the base as possible, while ensuring that the
    // distance between the *baseline* of the accent char and
    // the *baseline* of the base is atleast x-height.
    // The idea is that for normal use, we would like all the accents
    // on a line to line up atleast x-height above the baseline
    // if possible.
    // When the ascent of the base is >= x-height,
    // the baseline of the accent char is placed just above the base
    // (specifically, the baseline of the accent char is placed
    // above the baseline of the base by the ascent of the base).
    // For ease of implementation,
    // this assumes that the font-designer designs accents
    // in such a way that the bottom of the accent is atleast x-height
    // above its baseline, otherwise there will be collisions
    // with the base. Also there should be proper padding between
    // the bottom of the accent char and its baseline.
    // The above rule may not be obvious from a first
    // reading of rule 12 in the TeXBook !!!
    // The mathml <mover> tag can use accent chars that
    // do not follow this convention. So we modify TeX's rule
    // so that TeX's rule gets subsumed for accents that follow
    // TeX's convention,
    // while also allowing accents that do not follow the convention :
    // we try to keep the *bottom* of the accent char atleast x-height
    // from the baseline of the base char. we also slap on an extra
    // padding between the accent and base chars.
    overDelta1 = ruleThickness + onePixel / 2;
    nscoord accentBaseHeight = xHeight;
    if (mathFont) {
      accentBaseHeight = mathFont->MathTable()->Constant(
          gfxMathTable::AccentBaseHeight, oneDevPixel);
    }
    if (bmBase.ascent < accentBaseHeight) {
      // also ensure at least accentBaseHeight above the baseline of the base
      overDelta1 += accentBaseHeight - bmBase.ascent;
    }
    overDelta2 = ruleThickness;
  }
  // empty over?
  if (!(bmOver.ascent + bmOver.descent)) {
    overDelta1 = 0;
    overDelta2 = 0;
  }

  nscoord dxBase = 0, dxOver = 0, dxUnder = 0;
  nsAutoString valueAlign;

  //////////
  // pass 1, do what <mover> does: attach the overscript on the base

  // Ad-hoc - This is to override fonts which have ready-made _accent_
  // glyphs with negative lbearing and rbearing. We want to position
  // the overscript ourselves
  nscoord overWidth = bmOver.width;
  if (!overWidth && (bmOver.rightBearing - bmOver.leftBearing > 0)) {
    overWidth = bmOver.rightBearing - bmOver.leftBearing;
    dxOver = -bmOver.leftBearing;
  }

  if (NS_MATHML_EMBELLISH_IS_ACCENTOVER(mEmbellishData.flags)) {
    mBoundingMetrics.width = bmBase.width;
    dxOver += correction;
  } else {
    mBoundingMetrics.width = std::max(bmBase.width, overWidth);
    dxOver += correction / 2;
  }

  dxOver += (mBoundingMetrics.width - overWidth) / 2;
  dxBase = (mBoundingMetrics.width - bmBase.width) / 2;

  mBoundingMetrics.ascent =
      bmBase.ascent + overDelta1 + bmOver.ascent + bmOver.descent;
  mBoundingMetrics.descent = bmBase.descent;
  mBoundingMetrics.leftBearing =
      std::min(dxBase + bmBase.leftBearing, dxOver + bmOver.leftBearing);
  mBoundingMetrics.rightBearing =
      std::max(dxBase + bmBase.rightBearing, dxOver + bmOver.rightBearing);

  //////////
  // pass 2, do what <munder> does: attach the underscript on the previous
  // result. We conceptually view the previous result as an "anynomous base"
  // from where to attach the underscript. Hence if the underscript is empty,
  // we should end up like <mover>. If the overscript is empty, we should
  // end up like <munder>.

  nsBoundingMetrics bmAnonymousBase = mBoundingMetrics;
  nscoord ascentAnonymousBase =
      std::max(mBoundingMetrics.ascent + overDelta2,
               overSize.BlockStartAscent() + bmOver.descent + overDelta1 +
                   bmBase.ascent);
  ascentAnonymousBase =
      std::max(ascentAnonymousBase, baseSize.BlockStartAscent());

  // Width of non-spacing marks is zero so use left and right bearing.
  nscoord underWidth = bmUnder.width;
  if (!underWidth) {
    underWidth = bmUnder.rightBearing - bmUnder.leftBearing;
    dxUnder = -bmUnder.leftBearing;
  }

  nscoord maxWidth = std::max(bmAnonymousBase.width, underWidth);
  if (!NS_MATHML_EMBELLISH_IS_ACCENTUNDER(mEmbellishData.flags)) {
    GetItalicCorrection(bmAnonymousBase, correction);
    dxUnder += -correction / 2;
  }
  nscoord dxAnonymousBase = 0;
  dxUnder += (maxWidth - underWidth) / 2;
  dxAnonymousBase = (maxWidth - bmAnonymousBase.width) / 2;

  // adjust the offsets of the real base and overscript since their
  // final offsets should be relative to us...
  dxOver += dxAnonymousBase;
  dxBase += dxAnonymousBase;

  mBoundingMetrics.width = std::max(dxAnonymousBase + bmAnonymousBase.width,
                                    dxUnder + bmUnder.width);
  // At this point, mBoundingMetrics.ascent = bmAnonymousBase.ascent
  mBoundingMetrics.descent =
      bmAnonymousBase.descent + underDelta1 + bmUnder.ascent + bmUnder.descent;
  mBoundingMetrics.leftBearing =
      std::min(dxAnonymousBase + bmAnonymousBase.leftBearing,
               dxUnder + bmUnder.leftBearing);
  mBoundingMetrics.rightBearing =
      std::max(dxAnonymousBase + bmAnonymousBase.rightBearing,
               dxUnder + bmUnder.rightBearing);

  aDesiredSize.SetBlockStartAscent(ascentAnonymousBase);
  aDesiredSize.Height() =
      aDesiredSize.BlockStartAscent() +
      std::max(mBoundingMetrics.descent + underDelta2,
               bmAnonymousBase.descent + underDelta1 + bmUnder.ascent +
                   underSize.Height() - underSize.BlockStartAscent());
  aDesiredSize.Height() =
      std::max(aDesiredSize.Height(), aDesiredSize.BlockStartAscent() +
                                          baseSize.Height() -
                                          baseSize.BlockStartAscent());
  aDesiredSize.Width() = mBoundingMetrics.width;
  aDesiredSize.mBoundingMetrics = mBoundingMetrics;

  mReference.x = 0;
  mReference.y = aDesiredSize.BlockStartAscent();

  if (aPlaceOrigin) {
    nscoord dy;
    // place overscript
    if (overFrame) {
      dy = aDesiredSize.BlockStartAscent() - mBoundingMetrics.ascent +
           bmOver.ascent - overSize.BlockStartAscent();
      FinishReflowChild(overFrame, PresContext(), overSize, nullptr, dxOver, dy,
                        ReflowChildFlags::Default);
    }
    // place base
    dy = aDesiredSize.BlockStartAscent() - baseSize.BlockStartAscent();
    FinishReflowChild(baseFrame, PresContext(), baseSize, nullptr, dxBase, dy,
                      ReflowChildFlags::Default);
    // place underscript
    if (underFrame) {
      dy = aDesiredSize.BlockStartAscent() + mBoundingMetrics.descent -
           bmUnder.descent - underSize.BlockStartAscent();
      FinishReflowChild(underFrame, PresContext(), underSize, nullptr, dxUnder,
                        dy, ReflowChildFlags::Default);
    }
  }
  return NS_OK;
}