Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 1864 insertions, 0 deletions

diff --git a/gfx/thebes/gfxHarfBuzzShaper.cpp b/gfx/thebes/gfxHarfBuzzShaper.cpp
new file mode 100644
index 0000000000..8dbba29cf5
--- /dev/null
+++ b/gfx/thebes/gfxHarfBuzzShaper.cpp
@@ -0,0 +1,1864 @@
+/* -*- Mode: C++; tab-width: 20; 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 "nsString.h"
+#include "gfxContext.h"
+#include "gfxFontConstants.h"
+#include "gfxHarfBuzzShaper.h"
+#include "gfxFontUtils.h"
+#include "gfxTextRun.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/intl/String.h"
+#include "mozilla/intl/UnicodeProperties.h"
+#include "mozilla/intl/UnicodeScriptCodes.h"
+#include "nsUnicodeProperties.h"
+
+#include "harfbuzz/hb.h"
+#include "harfbuzz/hb-ot.h"
+
+#include <algorithm>
+
+#define FloatToFixed(f) (65536 * (f))
+#define FixedToFloat(f) ((f) * (1.0 / 65536.0))
+// Right shifts of negative (signed) integers are undefined, as are overflows
+// when converting unsigned to negative signed integers.
+// (If speed were an issue we could make some 2's complement assumptions.)
+#define FixedToIntRound(f) \
+  ((f) > 0 ? ((32768 + (f)) >> 16) : -((32767 - (f)) >> 16))
+
+using namespace mozilla;           // for AutoSwap_* types
+using namespace mozilla::unicode;  // for Unicode property lookup
+
+/*
+ * Creation and destruction; on deletion, release any font tables we're holding
+ */
+
+gfxHarfBuzzShaper::gfxHarfBuzzShaper(gfxFont* aFont)
+    : gfxFontShaper(aFont),
+      mHBFont(nullptr),
+      mBuffer(nullptr),
+      mCallbackData(),
+      mKernTable(nullptr),
+      mHmtxTable(nullptr),
+      mVmtxTable(nullptr),
+      mVORGTable(nullptr),
+      mLocaTable(nullptr),
+      mGlyfTable(nullptr),
+      mCmapTable(nullptr),
+      mCmapFormat(-1),
+      mSubtableOffset(0),
+      mUVSTableOffset(0),
+      mNumLongHMetrics(0),
+      mNumLongVMetrics(0),
+      mDefaultVOrg(-1.0),
+      mUseFontGetGlyph(aFont->ProvidesGetGlyph()),
+      mIsSymbolFont(false),
+      mUseFontGlyphWidths(aFont->ProvidesGlyphWidths()),
+      mInitialized(false),
+      mVerticalInitialized(false),
+      mUseVerticalPresentationForms(false),
+      mLoadedLocaGlyf(false),
+      mLocaLongOffsets(false) {}
+
+gfxHarfBuzzShaper::~gfxHarfBuzzShaper() {
+  // hb_*_destroy functions are safe to call on nullptr
+  hb_blob_destroy(mCmapTable);
+  hb_blob_destroy(mHmtxTable);
+  hb_blob_destroy(mKernTable);
+  hb_blob_destroy(mVmtxTable);
+  hb_blob_destroy(mVORGTable);
+  hb_blob_destroy(mLocaTable);
+  hb_blob_destroy(mGlyfTable);
+  hb_font_destroy(mHBFont);
+  hb_buffer_destroy(mBuffer);
+}
+
+#define UNICODE_BMP_LIMIT 0x10000
+
+hb_codepoint_t gfxHarfBuzzShaper::GetGlyphUncached(
+    hb_codepoint_t unicode) const {
+  hb_codepoint_t gid = 0;
+
+  if (mUseFontGetGlyph) {
+    MutexAutoUnlock unlock(mCacheLock);
+    gid = mFont->GetGlyph(unicode, 0);
+  } else {
+    // we only instantiate a harfbuzz shaper if there's a cmap available
+    NS_ASSERTION(mCmapTable && (mCmapFormat > 0) && (mSubtableOffset > 0),
+                 "cmap data not correctly set up, expect disaster");
+
+    uint32_t length;
+    const uint8_t* data = (const uint8_t*)hb_blob_get_data(mCmapTable, &length);
+
+    switch (mCmapFormat) {
+      case 4:
+        gid =
+            unicode < UNICODE_BMP_LIMIT
+                ? gfxFontUtils::MapCharToGlyphFormat4(
+                      data + mSubtableOffset, length - mSubtableOffset, unicode)
+                : 0;
+        break;
+      case 10:
+        gid = gfxFontUtils::MapCharToGlyphFormat10(data + mSubtableOffset,
+                                                   unicode);
+        break;
+      case 12:
+      case 13:
+        gid = gfxFontUtils::MapCharToGlyphFormat12or13(data + mSubtableOffset,
+                                                       unicode);
+        break;
+      default:
+        NS_WARNING("unsupported cmap format, glyphs will be missing");
+        break;
+    }
+  }
+
+  if (!gid) {
+    if (mIsSymbolFont) {
+      // For legacy MS Symbol fonts, we try mapping the given character code
+      // to the PUA range used by these fonts' cmaps.
+      if (auto pua = gfxFontUtils::MapLegacySymbolFontCharToPUA(unicode)) {
+        gid = GetGlyphUncached(pua);
+      }
+      if (gid) {
+        return gid;
+      }
+    }
+    switch (unicode) {
+      case 0xA0: {
+        // if there's no glyph for &nbsp;, just use the space glyph instead.
+        gid = mFont->GetSpaceGlyph();
+        break;
+      }
+      case 0x2010:
+      case 0x2011: {
+        // For Unicode HYPHEN and NON-BREAKING HYPHEN, fall back to the ASCII
+        // HYPHEN-MINUS as a substitute.
+        gid = GetGlyphUncached('-');
+        break;
+      }
+    }
+  }
+
+  return gid;
+}
+
+hb_codepoint_t gfxHarfBuzzShaper::GetNominalGlyph(
+    hb_codepoint_t unicode) const {
+  MutexAutoLock lock(mCacheLock);
+  auto cached = mCmapCache->Lookup(unicode);
+  if (cached) {
+    return cached.Data().mGlyphId;
+  }
+
+  // This call can temporarily unlock the cache if mUseFontGetGlyph is true.
+  hb_codepoint_t gid = GetGlyphUncached(unicode);
+
+  if (mUseFontGetGlyph) {
+    // GetGlyphUncached may have invalidated our earlier cache lookup!
+    mCmapCache->Put(unicode, CmapCacheData{unicode, gid});
+  } else {
+    cached.Set(CmapCacheData{unicode, gid});
+  }
+
+  return gid;
+}
+
+unsigned int gfxHarfBuzzShaper::GetNominalGlyphs(
+    unsigned int count, const hb_codepoint_t* first_unicode,
+    unsigned int unicode_stride, hb_codepoint_t* first_glyph,
+    unsigned int glyph_stride) {
+  MutexAutoLock lock(mCacheLock);
+  unsigned int result = 0;
+  while (result < count) {
+    hb_codepoint_t usv = *first_unicode;
+    auto cached = mCmapCache->Lookup(usv);
+    if (cached) {
+      // Cache hit :)
+      *first_glyph = cached.Data().mGlyphId;
+    } else {
+      // Cache miss: call GetGlyphUncached (which handles things like symbol-
+      // encoding fallback) and fill in the cache entry with the result.
+      hb_codepoint_t gid = GetGlyphUncached(usv);
+      if (mUseFontGetGlyph) {
+        mCmapCache->Put(usv, CmapCacheData{usv, gid});
+      } else {
+        cached.Set(CmapCacheData{usv, gid});
+      }
+      *first_glyph = gid;
+    }
+    first_unicode = reinterpret_cast<const hb_codepoint_t*>(
+        reinterpret_cast<const char*>(first_unicode) + unicode_stride);
+    first_glyph = reinterpret_cast<hb_codepoint_t*>(
+        reinterpret_cast<char*>(first_glyph) + glyph_stride);
+    result++;
+  }
+  return result;
+}
+
+hb_codepoint_t gfxHarfBuzzShaper::GetVariationGlyph(
+    hb_codepoint_t unicode, hb_codepoint_t variation_selector) const {
+  if (mUseFontGetGlyph) {
+    return mFont->GetGlyph(unicode, variation_selector);
+  }
+
+  NS_ASSERTION(mFont->GetFontEntry()->HasCmapTable(),
+               "we cannot be using this font!");
+  NS_ASSERTION(mCmapTable && (mCmapFormat > 0) && (mSubtableOffset > 0),
+               "cmap data not correctly set up, expect disaster");
+
+  uint32_t length;
+  const uint8_t* data = (const uint8_t*)hb_blob_get_data(mCmapTable, &length);
+
+  if (mUVSTableOffset) {
+    hb_codepoint_t gid = gfxFontUtils::MapUVSToGlyphFormat14(
+        data + mUVSTableOffset, unicode, variation_selector);
+    if (gid) {
+      return gid;
+    }
+  }
+
+  uint32_t compat = gfxFontUtils::GetUVSFallback(unicode, variation_selector);
+  if (compat) {
+    switch (mCmapFormat) {
+      case 4:
+        if (compat < UNICODE_BMP_LIMIT) {
+          return gfxFontUtils::MapCharToGlyphFormat4(
+              data + mSubtableOffset, length - mSubtableOffset, compat);
+        }
+        break;
+      case 10:
+        return gfxFontUtils::MapCharToGlyphFormat10(data + mSubtableOffset,
+                                                    compat);
+        break;
+      case 12:
+      case 13:
+        return gfxFontUtils::MapCharToGlyphFormat12or13(data + mSubtableOffset,
+                                                        compat);
+        break;
+    }
+  }
+
+  return 0;
+}
+
+static int VertFormsGlyphCompare(const void* aKey, const void* aElem) {
+  return int(*((hb_codepoint_t*)(aKey))) - int(*((uint16_t*)(aElem)));
+}
+
+// Return a vertical presentation-form codepoint corresponding to the
+// given Unicode value, or 0 if no such form is available.
+hb_codepoint_t gfxHarfBuzzShaper::GetVerticalPresentationForm(
+    hb_codepoint_t aUnicode) {
+  static const uint16_t sVerticalForms[][2] = {
+      {0x2013, 0xfe32},  // EN DASH
+      {0x2014, 0xfe31},  // EM DASH
+      {0x2025, 0xfe30},  // TWO DOT LEADER
+      {0x2026, 0xfe19},  // HORIZONTAL ELLIPSIS
+      {0x3001, 0xfe11},  // IDEOGRAPHIC COMMA
+      {0x3002, 0xfe12},  // IDEOGRAPHIC FULL STOP
+      {0x3008, 0xfe3f},  // LEFT ANGLE BRACKET
+      {0x3009, 0xfe40},  // RIGHT ANGLE BRACKET
+      {0x300a, 0xfe3d},  // LEFT DOUBLE ANGLE BRACKET
+      {0x300b, 0xfe3e},  // RIGHT DOUBLE ANGLE BRACKET
+      {0x300c, 0xfe41},  // LEFT CORNER BRACKET
+      {0x300d, 0xfe42},  // RIGHT CORNER BRACKET
+      {0x300e, 0xfe43},  // LEFT WHITE CORNER BRACKET
+      {0x300f, 0xfe44},  // RIGHT WHITE CORNER BRACKET
+      {0x3010, 0xfe3b},  // LEFT BLACK LENTICULAR BRACKET
+      {0x3011, 0xfe3c},  // RIGHT BLACK LENTICULAR BRACKET
+      {0x3014, 0xfe39},  // LEFT TORTOISE SHELL BRACKET
+      {0x3015, 0xfe3a},  // RIGHT TORTOISE SHELL BRACKET
+      {0x3016, 0xfe17},  // LEFT WHITE LENTICULAR BRACKET
+      {0x3017, 0xfe18},  // RIGHT WHITE LENTICULAR BRACKET
+      {0xfe4f, 0xfe34},  // WAVY LOW LINE
+      {0xff01, 0xfe15},  // FULLWIDTH EXCLAMATION MARK
+      {0xff08, 0xfe35},  // FULLWIDTH LEFT PARENTHESIS
+      {0xff09, 0xfe36},  // FULLWIDTH RIGHT PARENTHESIS
+      {0xff0c, 0xfe10},  // FULLWIDTH COMMA
+      {0xff1a, 0xfe13},  // FULLWIDTH COLON
+      {0xff1b, 0xfe14},  // FULLWIDTH SEMICOLON
+      {0xff1f, 0xfe16},  // FULLWIDTH QUESTION MARK
+      {0xff3b, 0xfe47},  // FULLWIDTH LEFT SQUARE BRACKET
+      {0xff3d, 0xfe48},  // FULLWIDTH RIGHT SQUARE BRACKET
+      {0xff3f, 0xfe33},  // FULLWIDTH LOW LINE
+      {0xff5b, 0xfe37},  // FULLWIDTH LEFT CURLY BRACKET
+      {0xff5d, 0xfe38}   // FULLWIDTH RIGHT CURLY BRACKET
+  };
+  const uint16_t* charPair = static_cast<const uint16_t*>(
+      bsearch(&aUnicode, sVerticalForms, ArrayLength(sVerticalForms),
+              sizeof(sVerticalForms[0]), VertFormsGlyphCompare));
+  return charPair ? charPair[1] : 0;
+}
+
+static hb_bool_t HBGetNominalGlyph(hb_font_t* font, void* font_data,
+                                   hb_codepoint_t unicode,
+                                   hb_codepoint_t* glyph, void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+
+  if (fcd->mShaper->UseVerticalPresentationForms()) {
+    hb_codepoint_t verticalForm =
+        gfxHarfBuzzShaper::GetVerticalPresentationForm(unicode);
+    if (verticalForm) {
+      *glyph = fcd->mShaper->GetNominalGlyph(verticalForm);
+      if (*glyph != 0) {
+        return true;
+      }
+    }
+    // fall back to the non-vertical form if we didn't find an alternate
+  }
+
+  *glyph = fcd->mShaper->GetNominalGlyph(unicode);
+  return *glyph != 0;
+}
+
+static unsigned int HBGetNominalGlyphs(
+    hb_font_t* font, void* font_data, unsigned int count,
+    const hb_codepoint_t* first_unicode, unsigned int unicode_stride,
+    hb_codepoint_t* first_glyph, unsigned int glyph_stride, void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+  if (fcd->mShaper->UseVerticalPresentationForms()) {
+    return 0;
+  }
+
+  return fcd->mShaper->GetNominalGlyphs(count, first_unicode, unicode_stride,
+                                        first_glyph, glyph_stride);
+}
+
+static hb_bool_t HBGetVariationGlyph(hb_font_t* font, void* font_data,
+                                     hb_codepoint_t unicode,
+                                     hb_codepoint_t variation_selector,
+                                     hb_codepoint_t* glyph, void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+
+  if (fcd->mShaper->UseVerticalPresentationForms()) {
+    hb_codepoint_t verticalForm =
+        gfxHarfBuzzShaper::GetVerticalPresentationForm(unicode);
+    if (verticalForm) {
+      *glyph =
+          fcd->mShaper->GetVariationGlyph(verticalForm, variation_selector);
+      if (*glyph != 0) {
+        return true;
+      }
+    }
+    // fall back to the non-vertical form if we didn't find an alternate
+  }
+
+  *glyph = fcd->mShaper->GetVariationGlyph(unicode, variation_selector);
+  return *glyph != 0;
+}
+
+// Glyph metrics structures, shared (with appropriate reinterpretation of
+// field names) by horizontal and vertical metrics tables.
+struct LongMetric {
+  AutoSwap_PRUint16 advanceWidth;  // or advanceHeight, when vertical
+  AutoSwap_PRInt16 lsb;            // or tsb, when vertical
+};
+
+struct GlyphMetrics {
+  LongMetric metrics[1];  // actually numberOfLongMetrics
+  // the variable-length metrics[] array is immediately followed by:
+  //  AutoSwap_PRUint16    leftSideBearing[];
+};
+
+hb_position_t gfxHarfBuzzShaper::GetGlyphHAdvanceUncached(
+    hb_codepoint_t glyph) const {
+  if (mUseFontGlyphWidths) {
+    return GetFont()->GetGlyphWidth(glyph);
+  }
+
+  // Get an unhinted value directly from the font tables.
+  NS_ASSERTION((mNumLongHMetrics > 0) && mHmtxTable != nullptr,
+               "font is lacking metrics, we shouldn't be here");
+
+  if (glyph >= uint32_t(mNumLongHMetrics)) {
+    glyph = mNumLongHMetrics - 1;
+  }
+
+  // glyph must be valid now, because we checked during initialization
+  // that mNumLongHMetrics is > 0, and that the metrics table is large enough
+  // to contain mNumLongHMetrics records
+  const ::GlyphMetrics* metrics = reinterpret_cast<const ::GlyphMetrics*>(
+      hb_blob_get_data(mHmtxTable, nullptr));
+  return FloatToFixed(mFont->FUnitsToDevUnitsFactor() *
+                      uint16_t(metrics->metrics[glyph].advanceWidth));
+}
+
+hb_position_t gfxHarfBuzzShaper::GetGlyphHAdvance(hb_codepoint_t glyph) const {
+  if (mUseFontGlyphWidths) {
+    MutexAutoLock lock(mCacheLock);
+    if (auto cached = mWidthCache->Lookup(glyph)) {
+      return cached.Data().mAdvance;
+    }
+    mCacheLock.Unlock();
+    hb_position_t advance = GetFont()->GetGlyphWidth(glyph);
+    mCacheLock.Lock();
+    mWidthCache->Put(glyph, WidthCacheData{glyph, advance});
+    return advance;
+  }
+
+  return GetGlyphHAdvanceUncached(glyph);
+}
+
+void gfxHarfBuzzShaper::GetGlyphHAdvances(unsigned int count,
+                                          const hb_codepoint_t* first_glyph,
+                                          unsigned int glyph_stride,
+                                          hb_position_t* first_advance,
+                                          unsigned int advance_stride) const {
+  if (mUseFontGlyphWidths) {
+    // Take the cache lock here, hoping we'll be able to retrieve a bunch of
+    // widths from the cache for the cost of a single locking operation.
+    MutexAutoLock lock(mCacheLock);
+    for (unsigned int i = 0; i < count; ++i) {
+      hb_codepoint_t gid = *first_glyph;
+      if (auto cached = mWidthCache->Lookup(gid)) {
+        *first_advance = cached.Data().mAdvance;
+      } else {
+        // Unlock to avoid deadlock if the font needs internal locking.
+        mCacheLock.Unlock();
+        hb_position_t advance = GetFont()->GetGlyphWidth(gid);
+        mCacheLock.Lock();
+        mWidthCache->Put(gid, WidthCacheData{gid, advance});
+        *first_advance = advance;
+      }
+      first_glyph = reinterpret_cast<const hb_codepoint_t*>(
+          reinterpret_cast<const char*>(first_glyph) + glyph_stride);
+      first_advance = reinterpret_cast<hb_position_t*>(
+          reinterpret_cast<char*>(first_advance) + advance_stride);
+    }
+    return;
+  }
+
+  for (unsigned int i = 0; i < count; ++i) {
+    *first_advance = GetGlyphHAdvanceUncached(*first_glyph);
+    first_glyph = reinterpret_cast<const hb_codepoint_t*>(
+        reinterpret_cast<const char*>(first_glyph) + glyph_stride);
+    first_advance = reinterpret_cast<hb_position_t*>(
+        reinterpret_cast<char*>(first_advance) + advance_stride);
+  }
+}
+
+hb_position_t gfxHarfBuzzShaper::GetGlyphVAdvance(hb_codepoint_t glyph) {
+  InitializeVertical();
+
+  if (!mVmtxTable) {
+    // Must be a "vertical" font that doesn't actually have vertical metrics.
+    // Return an invalid (negative) value to tell the caller to fall back to
+    // something else.
+    return -1;
+  }
+
+  NS_ASSERTION(mNumLongVMetrics > 0,
+               "font is lacking metrics, we shouldn't be here");
+
+  if (glyph >= uint32_t(mNumLongVMetrics)) {
+    glyph = mNumLongVMetrics - 1;
+  }
+
+  // glyph must be valid now, because we checked during initialization
+  // that mNumLongVMetrics is > 0, and that the metrics table is large enough
+  // to contain mNumLongVMetrics records
+  const ::GlyphMetrics* metrics = reinterpret_cast<const ::GlyphMetrics*>(
+      hb_blob_get_data(mVmtxTable, nullptr));
+  return FloatToFixed(mFont->FUnitsToDevUnitsFactor() *
+                      uint16_t(metrics->metrics[glyph].advanceWidth));
+}
+
+static hb_position_t HBGetGlyphHAdvance(hb_font_t* font, void* font_data,
+                                        hb_codepoint_t glyph, void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+  return fcd->mShaper->GetGlyphHAdvance(glyph);
+}
+
+static void HBGetGlyphHAdvances(hb_font_t* font, void* font_data,
+                                unsigned int count,
+                                const hb_codepoint_t* first_glyph,
+                                unsigned int glyph_stride,
+                                hb_position_t* first_advance,
+                                unsigned int advance_stride, void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+  fcd->mShaper->GetGlyphHAdvances(count, first_glyph, glyph_stride,
+                                  first_advance, advance_stride);
+}
+
+static hb_position_t HBGetGlyphVAdvance(hb_font_t* font, void* font_data,
+                                        hb_codepoint_t glyph, void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+  // Currently, we don't offer gfxFont subclasses a method to override this
+  // and provide hinted platform-specific vertical advances (analogous to the
+  // GetGlyphWidth method for horizontal advances). If that proves necessary,
+  // we'll add a new gfxFont method and call it from here.
+  hb_position_t advance = fcd->mShaper->GetGlyphVAdvance(glyph);
+  if (advance < 0) {
+    // Not available (e.g. broken metrics in the font); use a fallback value.
+    advance = FloatToFixed(fcd->mShaper->GetFont()
+                               ->GetMetrics(nsFontMetrics::eVertical)
+                               .aveCharWidth);
+  }
+  // We negate the value from GetGlyphVAdvance here because harfbuzz shapes
+  // with a coordinate system where positive is upwards, whereas the inline
+  // direction in which glyphs advance is downwards.
+  return -advance;
+}
+
+struct VORG {
+  AutoSwap_PRUint16 majorVersion;
+  AutoSwap_PRUint16 minorVersion;
+  AutoSwap_PRInt16 defaultVertOriginY;
+  AutoSwap_PRUint16 numVertOriginYMetrics;
+};
+
+struct VORGrec {
+  AutoSwap_PRUint16 glyphIndex;
+  AutoSwap_PRInt16 vertOriginY;
+};
+
+static hb_bool_t HBGetGlyphVOrigin(hb_font_t* font, void* font_data,
+                                   hb_codepoint_t glyph, hb_position_t* x,
+                                   hb_position_t* y, void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+  fcd->mShaper->GetGlyphVOrigin(glyph, x, y);
+  return true;
+}
+
+void gfxHarfBuzzShaper::GetGlyphVOrigin(hb_codepoint_t aGlyph,
+                                        hb_position_t* aX,
+                                        hb_position_t* aY) const {
+  *aX = 0.5 * GetGlyphHAdvance(aGlyph);
+
+  if (mVORGTable) {
+    // We checked in Initialize() that the VORG table is safely readable,
+    // so no length/bounds-check needed here.
+    const VORG* vorg =
+        reinterpret_cast<const VORG*>(hb_blob_get_data(mVORGTable, nullptr));
+
+    const VORGrec* lo = reinterpret_cast<const VORGrec*>(vorg + 1);
+    const VORGrec* hi = lo + uint16_t(vorg->numVertOriginYMetrics);
+    const VORGrec* limit = hi;
+    while (lo < hi) {
+      const VORGrec* mid = lo + (hi - lo) / 2;
+      if (uint16_t(mid->glyphIndex) < aGlyph) {
+        lo = mid + 1;
+      } else {
+        hi = mid;
+      }
+    }
+
+    if (lo < limit && uint16_t(lo->glyphIndex) == aGlyph) {
+      *aY = FloatToFixed(GetFont()->FUnitsToDevUnitsFactor() *
+                         int16_t(lo->vertOriginY));
+    } else {
+      *aY = FloatToFixed(GetFont()->FUnitsToDevUnitsFactor() *
+                         int16_t(vorg->defaultVertOriginY));
+    }
+    return;
+  }
+
+  if (mVmtxTable) {
+    bool emptyGlyf;
+    const Glyf* glyf = FindGlyf(aGlyph, &emptyGlyf);
+    if (glyf) {
+      if (emptyGlyf) {
+        *aY = 0;
+        return;
+      }
+
+      const ::GlyphMetrics* metrics = reinterpret_cast<const ::GlyphMetrics*>(
+          hb_blob_get_data(mVmtxTable, nullptr));
+      int16_t lsb;
+      if (aGlyph < hb_codepoint_t(mNumLongVMetrics)) {
+        // Glyph is covered by the first (advance & sidebearing) array
+        lsb = int16_t(metrics->metrics[aGlyph].lsb);
+      } else {
+        // Glyph is covered by the second (sidebearing-only) array
+        const AutoSwap_PRInt16* sidebearings =
+            reinterpret_cast<const AutoSwap_PRInt16*>(
+                &metrics->metrics[mNumLongVMetrics]);
+        lsb = int16_t(sidebearings[aGlyph - mNumLongVMetrics]);
+      }
+      *aY = FloatToFixed(mFont->FUnitsToDevUnitsFactor() *
+                         (lsb + int16_t(glyf->yMax)));
+      return;
+    } else {
+      // XXX TODO: not a truetype font; need to get glyph extents
+      // via some other API?
+      // For now, fall through to default code below.
+    }
+  }
+
+  if (mDefaultVOrg < 0.0) {
+    // XXX should we consider using OS/2 sTypo* metrics if available?
+
+    gfxFontEntry::AutoTable hheaTable(GetFont()->GetFontEntry(),
+                                      TRUETYPE_TAG('h', 'h', 'e', 'a'));
+    if (hheaTable) {
+      uint32_t len;
+      const MetricsHeader* hhea = reinterpret_cast<const MetricsHeader*>(
+          hb_blob_get_data(hheaTable, &len));
+      if (len >= sizeof(MetricsHeader)) {
+        // divide up the default advance we're using (1em) in proportion
+        // to ascender:descender from the hhea table
+        int16_t a = int16_t(hhea->ascender);
+        int16_t d = int16_t(hhea->descender);
+        mDefaultVOrg = FloatToFixed(GetFont()->GetAdjustedSize() * a / (a - d));
+      }
+    }
+
+    if (mDefaultVOrg < 0.0) {
+      // Last resort, for non-sfnt fonts: get the horizontal metrics and
+      // compute a default VOrg from their ascent and descent.
+      const gfxFont::Metrics& mtx = mFont->GetHorizontalMetrics();
+      gfxFloat advance =
+          mFont->GetMetrics(nsFontMetrics::eVertical).aveCharWidth;
+      gfxFloat ascent = mtx.emAscent;
+      gfxFloat height = ascent + mtx.emDescent;
+      // vOrigin that will place the glyph so that its origin is shifted
+      // down most of the way within overall (vertical) advance, in
+      // proportion to the font ascent as a part of the overall font
+      // height.
+      mDefaultVOrg = FloatToFixed(advance * ascent / height);
+    }
+  }
+
+  *aY = mDefaultVOrg;
+}
+
+static hb_bool_t HBGetGlyphExtents(hb_font_t* font, void* font_data,
+                                   hb_codepoint_t glyph,
+                                   hb_glyph_extents_t* extents,
+                                   void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+  return fcd->mShaper->GetGlyphExtents(glyph, extents);
+}
+
+// Find the data for glyph ID |aGlyph| in the 'glyf' table, if present.
+// Returns null if not found, otherwise pointer to the beginning of the
+// glyph's data. Sets aEmptyGlyf true if there is no actual data;
+// otherwise, it's guaranteed that we can read at least the bounding box.
+const gfxHarfBuzzShaper::Glyf* gfxHarfBuzzShaper::FindGlyf(
+    hb_codepoint_t aGlyph, bool* aEmptyGlyf) const {
+  if (!mLoadedLocaGlyf) {
+    mLoadedLocaGlyf = true;  // only try this once; if it fails, this
+                             // isn't a truetype font
+    gfxFontEntry* entry = mFont->GetFontEntry();
+    uint32_t len;
+    gfxFontEntry::AutoTable headTable(entry, TRUETYPE_TAG('h', 'e', 'a', 'd'));
+    if (!headTable) {
+      return nullptr;
+    }
+    const HeadTable* head =
+        reinterpret_cast<const HeadTable*>(hb_blob_get_data(headTable, &len));
+    if (len < sizeof(HeadTable)) {
+      return nullptr;
+    }
+    mLocaLongOffsets = int16_t(head->indexToLocFormat) > 0;
+    mLocaTable = entry->GetFontTable(TRUETYPE_TAG('l', 'o', 'c', 'a'));
+    mGlyfTable = entry->GetFontTable(TRUETYPE_TAG('g', 'l', 'y', 'f'));
+  }
+
+  if (!mLocaTable || !mGlyfTable) {
+    // it's not a truetype font
+    return nullptr;
+  }
+
+  uint32_t offset;  // offset of glyph record in the 'glyf' table
+  uint32_t len;
+  const char* data = hb_blob_get_data(mLocaTable, &len);
+  if (mLocaLongOffsets) {
+    if ((aGlyph + 1) * sizeof(AutoSwap_PRUint32) > len) {
+      return nullptr;
+    }
+    const AutoSwap_PRUint32* offsets =
+        reinterpret_cast<const AutoSwap_PRUint32*>(data);
+    offset = offsets[aGlyph];
+    *aEmptyGlyf = (offset == uint16_t(offsets[aGlyph + 1]));
+  } else {
+    if ((aGlyph + 1) * sizeof(AutoSwap_PRUint16) > len) {
+      return nullptr;
+    }
+    const AutoSwap_PRUint16* offsets =
+        reinterpret_cast<const AutoSwap_PRUint16*>(data);
+    offset = uint16_t(offsets[aGlyph]);
+    *aEmptyGlyf = (offset == uint16_t(offsets[aGlyph + 1]));
+    offset *= 2;
+  }
+
+  data = hb_blob_get_data(mGlyfTable, &len);
+  if (offset + sizeof(Glyf) > len) {
+    return nullptr;
+  }
+
+  return reinterpret_cast<const Glyf*>(data + offset);
+}
+
+hb_bool_t gfxHarfBuzzShaper::GetGlyphExtents(
+    hb_codepoint_t aGlyph, hb_glyph_extents_t* aExtents) const {
+  bool emptyGlyf;
+  const Glyf* glyf = FindGlyf(aGlyph, &emptyGlyf);
+  if (!glyf) {
+    // TODO: for non-truetype fonts, get extents some other way?
+    return false;
+  }
+
+  if (emptyGlyf) {
+    aExtents->x_bearing = 0;
+    aExtents->y_bearing = 0;
+    aExtents->width = 0;
+    aExtents->height = 0;
+    return true;
+  }
+
+  double f = mFont->FUnitsToDevUnitsFactor();
+  aExtents->x_bearing = FloatToFixed(int16_t(glyf->xMin) * f);
+  aExtents->width =
+      FloatToFixed((int16_t(glyf->xMax) - int16_t(glyf->xMin)) * f);
+
+  // Our y-coordinates are positive-downwards, whereas harfbuzz assumes
+  // positive-upwards; hence the apparently-reversed subtractions here.
+  aExtents->y_bearing = FloatToFixed(int16_t(glyf->yMax) * f -
+                                     mFont->GetHorizontalMetrics().emAscent);
+  aExtents->height =
+      FloatToFixed((int16_t(glyf->yMin) - int16_t(glyf->yMax)) * f);
+
+  return true;
+}
+
+static hb_bool_t HBGetContourPoint(hb_font_t* font, void* font_data,
+                                   unsigned int point_index,
+                                   hb_codepoint_t glyph, hb_position_t* x,
+                                   hb_position_t* y, void* user_data) {
+  /* not yet implemented - no support for used of hinted contour points
+     to fine-tune anchor positions in GPOS AnchorFormat2 */
+  return false;
+}
+
+struct KernHeaderFmt0 {
+  AutoSwap_PRUint16 nPairs;
+  AutoSwap_PRUint16 searchRange;
+  AutoSwap_PRUint16 entrySelector;
+  AutoSwap_PRUint16 rangeShift;
+};
+
+struct KernPair {
+  AutoSwap_PRUint16 left;
+  AutoSwap_PRUint16 right;
+  AutoSwap_PRInt16 value;
+};
+
+// Find a kern pair in a Format 0 subtable.
+// The aSubtable parameter points to the subtable itself, NOT its header,
+// as the header structure differs between Windows and Mac (v0 and v1.0)
+// versions of the 'kern' table.
+// aSubtableLen is the length of the subtable EXCLUDING its header.
+// If the pair <aFirstGlyph,aSecondGlyph> is found, the kerning value is
+// added to aValue, so that multiple subtables can accumulate a total
+// kerning value for a given pair.
+static void GetKernValueFmt0(const void* aSubtable, uint32_t aSubtableLen,
+                             uint16_t aFirstGlyph, uint16_t aSecondGlyph,
+                             int32_t& aValue, bool aIsOverride = false,
+                             bool aIsMinimum = false) {
+  const KernHeaderFmt0* hdr =
+      reinterpret_cast<const KernHeaderFmt0*>(aSubtable);
+
+  const KernPair* lo = reinterpret_cast<const KernPair*>(hdr + 1);
+  const KernPair* hi = lo + uint16_t(hdr->nPairs);
+  const KernPair* limit = hi;
+
+  if (reinterpret_cast<const char*>(aSubtable) + aSubtableLen <
+      reinterpret_cast<const char*>(hi)) {
+    // subtable is not large enough to contain the claimed number
+    // of kern pairs, so just ignore it
+    return;
+  }
+
+#define KERN_PAIR_KEY(l, r) (uint32_t((uint16_t(l) << 16) + uint16_t(r)))
+
+  uint32_t key = KERN_PAIR_KEY(aFirstGlyph, aSecondGlyph);
+  while (lo < hi) {
+    const KernPair* mid = lo + (hi - lo) / 2;
+    if (KERN_PAIR_KEY(mid->left, mid->right) < key) {
+      lo = mid + 1;
+    } else {
+      hi = mid;
+    }
+  }
+
+  if (lo < limit && KERN_PAIR_KEY(lo->left, lo->right) == key) {
+    if (aIsOverride) {
+      aValue = int16_t(lo->value);
+    } else if (aIsMinimum) {
+      aValue = std::max(aValue, int32_t(lo->value));
+    } else {
+      aValue += int16_t(lo->value);
+    }
+  }
+}
+
+// Get kerning value from Apple (version 1.0) kern table,
+// subtable format 2 (simple N x M array of kerning values)
+
+// See http://developer.apple.com/fonts/TTRefMan/RM06/Chap6kern.html
+// for details of version 1.0 format 2 subtable.
+
+struct KernHeaderVersion1Fmt2 {
+  KernTableSubtableHeaderVersion1 header;
+  AutoSwap_PRUint16 rowWidth;
+  AutoSwap_PRUint16 leftOffsetTable;
+  AutoSwap_PRUint16 rightOffsetTable;
+  AutoSwap_PRUint16 array;
+};
+
+struct KernClassTableHdr {
+  AutoSwap_PRUint16 firstGlyph;
+  AutoSwap_PRUint16 nGlyphs;
+  AutoSwap_PRUint16 offsets[1];  // actually an array of nGlyphs entries
+};
+
+static int16_t GetKernValueVersion1Fmt2(const void* aSubtable,
+                                        uint32_t aSubtableLen,
+                                        uint16_t aFirstGlyph,
+                                        uint16_t aSecondGlyph) {
+  if (aSubtableLen < sizeof(KernHeaderVersion1Fmt2)) {
+    return 0;
+  }
+
+  const char* base = reinterpret_cast<const char*>(aSubtable);
+  const char* subtableEnd = base + aSubtableLen;
+
+  const KernHeaderVersion1Fmt2* h =
+      reinterpret_cast<const KernHeaderVersion1Fmt2*>(aSubtable);
+  uint32_t offset = h->array;
+
+  const KernClassTableHdr* leftClassTable =
+      reinterpret_cast<const KernClassTableHdr*>(base +
+                                                 uint16_t(h->leftOffsetTable));
+  if (reinterpret_cast<const char*>(leftClassTable) +
+          sizeof(KernClassTableHdr) >
+      subtableEnd) {
+    return 0;
+  }
+  if (aFirstGlyph >= uint16_t(leftClassTable->firstGlyph)) {
+    aFirstGlyph -= uint16_t(leftClassTable->firstGlyph);
+    if (aFirstGlyph < uint16_t(leftClassTable->nGlyphs)) {
+      if (reinterpret_cast<const char*>(leftClassTable) +
+              sizeof(KernClassTableHdr) + aFirstGlyph * sizeof(uint16_t) >=
+          subtableEnd) {
+        return 0;
+      }
+      offset = uint16_t(leftClassTable->offsets[aFirstGlyph]);
+    }
+  }
+
+  const KernClassTableHdr* rightClassTable =
+      reinterpret_cast<const KernClassTableHdr*>(base +
+                                                 uint16_t(h->rightOffsetTable));
+  if (reinterpret_cast<const char*>(rightClassTable) +
+          sizeof(KernClassTableHdr) >
+      subtableEnd) {
+    return 0;
+  }
+  if (aSecondGlyph >= uint16_t(rightClassTable->firstGlyph)) {
+    aSecondGlyph -= uint16_t(rightClassTable->firstGlyph);
+    if (aSecondGlyph < uint16_t(rightClassTable->nGlyphs)) {
+      if (reinterpret_cast<const char*>(rightClassTable) +
+              sizeof(KernClassTableHdr) + aSecondGlyph * sizeof(uint16_t) >=
+          subtableEnd) {
+        return 0;
+      }
+      offset += uint16_t(rightClassTable->offsets[aSecondGlyph]);
+    }
+  }
+
+  const AutoSwap_PRInt16* pval =
+      reinterpret_cast<const AutoSwap_PRInt16*>(base + offset);
+  if (reinterpret_cast<const char*>(pval + 1) >= subtableEnd) {
+    return 0;
+  }
+  return *pval;
+}
+
+// Get kerning value from Apple (version 1.0) kern table,
+// subtable format 3 (simple N x M array of kerning values)
+
+// See http://developer.apple.com/fonts/TTRefMan/RM06/Chap6kern.html
+// for details of version 1.0 format 3 subtable.
+
+struct KernHeaderVersion1Fmt3 {
+  KernTableSubtableHeaderVersion1 header;
+  AutoSwap_PRUint16 glyphCount;
+  uint8_t kernValueCount;
+  uint8_t leftClassCount;
+  uint8_t rightClassCount;
+  uint8_t flags;
+};
+
+static int16_t GetKernValueVersion1Fmt3(const void* aSubtable,
+                                        uint32_t aSubtableLen,
+                                        uint16_t aFirstGlyph,
+                                        uint16_t aSecondGlyph) {
+  // check that we can safely read the header fields
+  if (aSubtableLen < sizeof(KernHeaderVersion1Fmt3)) {
+    return 0;
+  }
+
+  const KernHeaderVersion1Fmt3* hdr =
+      reinterpret_cast<const KernHeaderVersion1Fmt3*>(aSubtable);
+  if (hdr->flags != 0) {
+    return 0;
+  }
+
+  uint16_t glyphCount = hdr->glyphCount;
+
+  // check that table is large enough for the arrays
+  if (sizeof(KernHeaderVersion1Fmt3) + hdr->kernValueCount * sizeof(int16_t) +
+          glyphCount + glyphCount + hdr->leftClassCount * hdr->rightClassCount >
+      aSubtableLen) {
+    return 0;
+  }
+
+  if (aFirstGlyph >= glyphCount || aSecondGlyph >= glyphCount) {
+    // glyphs are out of range for the class tables
+    return 0;
+  }
+
+  // get pointers to the four arrays within the subtable
+  const AutoSwap_PRInt16* kernValue =
+      reinterpret_cast<const AutoSwap_PRInt16*>(hdr + 1);
+  const uint8_t* leftClass =
+      reinterpret_cast<const uint8_t*>(kernValue + hdr->kernValueCount);
+  const uint8_t* rightClass = leftClass + glyphCount;
+  const uint8_t* kernIndex = rightClass + glyphCount;
+
+  uint8_t lc = leftClass[aFirstGlyph];
+  uint8_t rc = rightClass[aSecondGlyph];
+  if (lc >= hdr->leftClassCount || rc >= hdr->rightClassCount) {
+    return 0;
+  }
+
+  uint8_t ki = kernIndex[leftClass[aFirstGlyph] * hdr->rightClassCount +
+                         rightClass[aSecondGlyph]];
+  if (ki >= hdr->kernValueCount) {
+    return 0;
+  }
+
+  return kernValue[ki];
+}
+
+#define KERN0_COVERAGE_HORIZONTAL 0x0001
+#define KERN0_COVERAGE_MINIMUM 0x0002
+#define KERN0_COVERAGE_CROSS_STREAM 0x0004
+#define KERN0_COVERAGE_OVERRIDE 0x0008
+#define KERN0_COVERAGE_RESERVED 0x00F0
+
+#define KERN1_COVERAGE_VERTICAL 0x8000
+#define KERN1_COVERAGE_CROSS_STREAM 0x4000
+#define KERN1_COVERAGE_VARIATION 0x2000
+#define KERN1_COVERAGE_RESERVED 0x1F00
+
+hb_position_t gfxHarfBuzzShaper::GetHKerning(uint16_t aFirstGlyph,
+                                             uint16_t aSecondGlyph) const {
+  // We want to ignore any kern pairs involving <space>, because we are
+  // handling words in isolation, the only space characters seen here are
+  // the ones artificially added by the textRun code.
+  uint32_t spaceGlyph = mFont->GetSpaceGlyph();
+  if (aFirstGlyph == spaceGlyph || aSecondGlyph == spaceGlyph) {
+    return 0;
+  }
+
+  if (!mKernTable) {
+    mKernTable =
+        mFont->GetFontEntry()->GetFontTable(TRUETYPE_TAG('k', 'e', 'r', 'n'));
+    if (!mKernTable) {
+      mKernTable = hb_blob_get_empty();
+    }
+  }
+
+  uint32_t len;
+  const char* base = hb_blob_get_data(mKernTable, &len);
+  if (len < sizeof(KernTableVersion0)) {
+    return 0;
+  }
+  int32_t value = 0;
+
+  // First try to interpret as "version 0" kern table
+  // (see http://www.microsoft.com/typography/otspec/kern.htm)
+  const KernTableVersion0* kern0 =
+      reinterpret_cast<const KernTableVersion0*>(base);
+  if (uint16_t(kern0->version) == 0) {
+    uint16_t nTables = kern0->nTables;
+    uint32_t offs = sizeof(KernTableVersion0);
+    for (uint16_t i = 0; i < nTables; ++i) {
+      if (offs + sizeof(KernTableSubtableHeaderVersion0) > len) {
+        break;
+      }
+      const KernTableSubtableHeaderVersion0* st0 =
+          reinterpret_cast<const KernTableSubtableHeaderVersion0*>(base + offs);
+      uint16_t subtableLen = uint16_t(st0->length);
+      if (offs + subtableLen > len) {
+        break;
+      }
+      offs += subtableLen;
+      uint16_t coverage = st0->coverage;
+      if (!(coverage & KERN0_COVERAGE_HORIZONTAL)) {
+        // we only care about horizontal kerning (for now)
+        continue;
+      }
+      if (coverage & (KERN0_COVERAGE_CROSS_STREAM | KERN0_COVERAGE_RESERVED)) {
+        // we don't support cross-stream kerning, and
+        // reserved bits should be zero;
+        // ignore the subtable if not
+        continue;
+      }
+      uint8_t format = (coverage >> 8);
+      switch (format) {
+        case 0:
+          GetKernValueFmt0(st0 + 1, subtableLen - sizeof(*st0), aFirstGlyph,
+                           aSecondGlyph, value,
+                           (coverage & KERN0_COVERAGE_OVERRIDE) != 0,
+                           (coverage & KERN0_COVERAGE_MINIMUM) != 0);
+          break;
+        default:
+          // TODO: implement support for other formats,
+          // if they're ever used in practice
+#if DEBUG
+        {
+          char buf[1024];
+          SprintfLiteral(buf,
+                         "unknown kern subtable in %s: "
+                         "ver 0 format %d\n",
+                         mFont->GetName().get(), format);
+          NS_WARNING(buf);
+        }
+#endif
+        break;
+      }
+    }
+  } else {
+    // It wasn't a "version 0" table; check if it is Apple version 1.0
+    // (see http://developer.apple.com/fonts/TTRefMan/RM06/Chap6kern.html)
+    const KernTableVersion1* kern1 =
+        reinterpret_cast<const KernTableVersion1*>(base);
+    if (uint32_t(kern1->version) == 0x00010000) {
+      uint32_t nTables = kern1->nTables;
+      uint32_t offs = sizeof(KernTableVersion1);
+      for (uint32_t i = 0; i < nTables; ++i) {
+        if (offs + sizeof(KernTableSubtableHeaderVersion1) > len) {
+          break;
+        }
+        const KernTableSubtableHeaderVersion1* st1 =
+            reinterpret_cast<const KernTableSubtableHeaderVersion1*>(base +
+                                                                     offs);
+        uint32_t subtableLen = uint32_t(st1->length);
+        offs += subtableLen;
+        uint16_t coverage = st1->coverage;
+        if (coverage & (KERN1_COVERAGE_VERTICAL | KERN1_COVERAGE_CROSS_STREAM |
+                        KERN1_COVERAGE_VARIATION | KERN1_COVERAGE_RESERVED)) {
+          // we only care about horizontal kerning (for now),
+          // we don't support cross-stream kerning,
+          // we don't support variations,
+          // reserved bits should be zero;
+          // ignore the subtable if not
+          continue;
+        }
+        uint8_t format = (coverage & 0xff);
+        switch (format) {
+          case 0:
+            GetKernValueFmt0(st1 + 1, subtableLen - sizeof(*st1), aFirstGlyph,
+                             aSecondGlyph, value);
+            break;
+          case 2:
+            value = GetKernValueVersion1Fmt2(st1, subtableLen, aFirstGlyph,
+                                             aSecondGlyph);
+            break;
+          case 3:
+            value = GetKernValueVersion1Fmt3(st1, subtableLen, aFirstGlyph,
+                                             aSecondGlyph);
+            break;
+          default:
+            // TODO: implement support for other formats.
+            // Note that format 1 cannot be supported here,
+            // as it requires the full glyph array to run the FSM,
+            // not just the current glyph pair.
+#if DEBUG
+          {
+            char buf[1024];
+            SprintfLiteral(buf,
+                           "unknown kern subtable in %s: "
+                           "ver 0 format %d\n",
+                           mFont->GetName().get(), format);
+            NS_WARNING(buf);
+          }
+#endif
+          break;
+        }
+      }
+    }
+  }
+
+  if (value != 0) {
+    return FloatToFixed(mFont->FUnitsToDevUnitsFactor() * value);
+  }
+  return 0;
+}
+
+static hb_position_t HBGetHKerning(hb_font_t* font, void* font_data,
+                                   hb_codepoint_t first_glyph,
+                                   hb_codepoint_t second_glyph,
+                                   void* user_data) {
+  const gfxHarfBuzzShaper::FontCallbackData* fcd =
+      static_cast<const gfxHarfBuzzShaper::FontCallbackData*>(font_data);
+  return fcd->mShaper->GetHKerning(first_glyph, second_glyph);
+}
+
+/*
+ * HarfBuzz unicode property callbacks
+ */
+
+static hb_codepoint_t HBGetMirroring(hb_unicode_funcs_t* ufuncs,
+                                     hb_codepoint_t aCh, void* user_data) {
+  return intl::UnicodeProperties::CharMirror(aCh);
+}
+
+static hb_unicode_general_category_t HBGetGeneralCategory(
+    hb_unicode_funcs_t* ufuncs, hb_codepoint_t aCh, void* user_data) {
+  return hb_unicode_general_category_t(GetGeneralCategory(aCh));
+}
+
+static hb_script_t HBGetScript(hb_unicode_funcs_t* ufuncs, hb_codepoint_t aCh,
+                               void* user_data) {
+  return hb_script_t(
+      GetScriptTagForCode(intl::UnicodeProperties::GetScriptCode(aCh)));
+}
+
+static hb_unicode_combining_class_t HBGetCombiningClass(
+    hb_unicode_funcs_t* ufuncs, hb_codepoint_t aCh, void* user_data) {
+  return hb_unicode_combining_class_t(
+      intl::UnicodeProperties::GetCombiningClass(aCh));
+}
+
+static hb_bool_t HBUnicodeCompose(hb_unicode_funcs_t* ufuncs, hb_codepoint_t a,
+                                  hb_codepoint_t b, hb_codepoint_t* ab,
+                                  void* user_data) {
+  char32_t ch = intl::String::ComposePairNFC(a, b);
+  if (ch > 0) {
+    *ab = ch;
+    return true;
+  }
+
+  return false;
+}
+
+static hb_bool_t HBUnicodeDecompose(hb_unicode_funcs_t* ufuncs,
+                                    hb_codepoint_t ab, hb_codepoint_t* a,
+                                    hb_codepoint_t* b, void* user_data) {
+#ifdef MOZ_WIDGET_ANDROID
+  // Hack for the SamsungDevanagari font, bug 1012365:
+  // support U+0972 by decomposing it.
+  if (ab == 0x0972) {
+    *a = 0x0905;
+    *b = 0x0945;
+    return true;
+  }
+#endif
+
+  char32_t decomp[2] = {0};
+  if (intl::String::DecomposeRawNFD(ab, decomp)) {
+    if (decomp[1] || decomp[0] != ab) {
+      *a = decomp[0];
+      *b = decomp[1];
+      return true;
+    }
+  }
+
+  return false;
+}
+
+static void AddOpenTypeFeature(uint32_t aTag, uint32_t aValue, void* aUserArg) {
+  nsTArray<hb_feature_t>* features =
+      static_cast<nsTArray<hb_feature_t>*>(aUserArg);
+
+  hb_feature_t feat = {0, 0, 0, UINT_MAX};
+  feat.tag = aTag;
+  feat.value = aValue;
+  features->AppendElement(feat);
+}
+
+/*
+ * gfxFontShaper override to initialize the text run using HarfBuzz
+ */
+
+static hb_font_funcs_t* sHBFontFuncs = nullptr;
+static hb_font_funcs_t* sNominalGlyphFunc = nullptr;
+static hb_unicode_funcs_t* sHBUnicodeFuncs = nullptr;
+static const hb_script_t sMathScript =
+    hb_ot_tag_to_script(HB_TAG('m', 'a', 't', 'h'));
+
+bool gfxHarfBuzzShaper::Initialize() {
+  if (mInitialized) {
+    return mHBFont != nullptr;
+  }
+  mInitialized = true;
+  mCallbackData.mShaper = this;
+
+  if (!sHBFontFuncs) {
+    // static function callback pointers, initialized by the first
+    // harfbuzz shaper used
+    sHBFontFuncs = hb_font_funcs_create();
+    hb_font_funcs_set_nominal_glyph_func(sHBFontFuncs, HBGetNominalGlyph,
+                                         nullptr, nullptr);
+    hb_font_funcs_set_nominal_glyphs_func(sHBFontFuncs, HBGetNominalGlyphs,
+                                          nullptr, nullptr);
+    hb_font_funcs_set_variation_glyph_func(sHBFontFuncs, HBGetVariationGlyph,
+                                           nullptr, nullptr);
+    hb_font_funcs_set_glyph_h_advance_func(sHBFontFuncs, HBGetGlyphHAdvance,
+                                           nullptr, nullptr);
+    hb_font_funcs_set_glyph_h_advances_func(sHBFontFuncs, HBGetGlyphHAdvances,
+                                            nullptr, nullptr);
+    hb_font_funcs_set_glyph_v_advance_func(sHBFontFuncs, HBGetGlyphVAdvance,
+                                           nullptr, nullptr);
+    hb_font_funcs_set_glyph_v_origin_func(sHBFontFuncs, HBGetGlyphVOrigin,
+                                          nullptr, nullptr);
+    hb_font_funcs_set_glyph_extents_func(sHBFontFuncs, HBGetGlyphExtents,
+                                         nullptr, nullptr);
+    hb_font_funcs_set_glyph_contour_point_func(sHBFontFuncs, HBGetContourPoint,
+                                               nullptr, nullptr);
+    hb_font_funcs_set_glyph_h_kerning_func(sHBFontFuncs, HBGetHKerning, nullptr,
+                                           nullptr);
+    hb_font_funcs_make_immutable(sHBFontFuncs);
+
+    sNominalGlyphFunc = hb_font_funcs_create();
+    hb_font_funcs_set_nominal_glyph_func(sNominalGlyphFunc, HBGetNominalGlyph,
+                                         nullptr, nullptr);
+    hb_font_funcs_make_immutable(sNominalGlyphFunc);
+
+    sHBUnicodeFuncs = hb_unicode_funcs_create(hb_unicode_funcs_get_empty());
+    hb_unicode_funcs_set_mirroring_func(sHBUnicodeFuncs, HBGetMirroring,
+                                        nullptr, nullptr);
+    hb_unicode_funcs_set_script_func(sHBUnicodeFuncs, HBGetScript, nullptr,
+                                     nullptr);
+    hb_unicode_funcs_set_general_category_func(
+        sHBUnicodeFuncs, HBGetGeneralCategory, nullptr, nullptr);
+    hb_unicode_funcs_set_combining_class_func(
+        sHBUnicodeFuncs, HBGetCombiningClass, nullptr, nullptr);
+    hb_unicode_funcs_set_compose_func(sHBUnicodeFuncs, HBUnicodeCompose,
+                                      nullptr, nullptr);
+    hb_unicode_funcs_set_decompose_func(sHBUnicodeFuncs, HBUnicodeDecompose,
+                                        nullptr, nullptr);
+    hb_unicode_funcs_make_immutable(sHBUnicodeFuncs);
+  }
+
+  gfxFontEntry* entry = mFont->GetFontEntry();
+  if (!mUseFontGetGlyph) {
+    // get the cmap table and find offset to our subtable
+    mCmapTable = entry->GetFontTable(TRUETYPE_TAG('c', 'm', 'a', 'p'));
+    if (!mCmapTable) {
+      NS_WARNING("failed to load cmap, glyphs will be missing");
+      return false;
+    }
+    uint32_t len;
+    const uint8_t* data = (const uint8_t*)hb_blob_get_data(mCmapTable, &len);
+    mCmapFormat = gfxFontUtils::FindPreferredSubtable(
+        data, len, &mSubtableOffset, &mUVSTableOffset, &mIsSymbolFont);
+    if (mCmapFormat <= 0) {
+      return false;
+    }
+  }
+
+  // We don't need to take the cache lock here, as we're just initializing the
+  // shaper and no other thread can yet be using it.
+  MOZ_PUSH_IGNORE_THREAD_SAFETY
+  mCmapCache = MakeUnique<CmapCache>();
+
+  if (mUseFontGlyphWidths) {
+    mWidthCache = MakeUnique<WidthCache>();
+  } else {
+    // If font doesn't implement GetGlyphWidth, we will be reading
+    // the metrics table directly, so make sure we can load it.
+    if (!LoadHmtxTable()) {
+      return false;
+    }
+  }
+  MOZ_POP_THREAD_SAFETY
+
+  mBuffer = hb_buffer_create();
+  hb_buffer_set_unicode_funcs(mBuffer, sHBUnicodeFuncs);
+  hb_buffer_set_cluster_level(mBuffer,
+                              HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS);
+
+  auto* funcs =
+      mFont->GetFontEntry()->HasFontTable(TRUETYPE_TAG('C', 'F', 'F', ' '))
+          ? sNominalGlyphFunc
+          : sHBFontFuncs;
+  mHBFont = CreateHBFont(mFont, funcs, &mCallbackData);
+
+  return true;
+}
+
+hb_font_t* gfxHarfBuzzShaper::CreateHBFont(gfxFont* aFont,
+                                           hb_font_funcs_t* aFontFuncs,
+                                           FontCallbackData* aCallbackData) {
+  auto face(aFont->GetFontEntry()->GetHBFace());
+  hb_font_t* result = hb_font_create(face);
+
+  if (aFontFuncs && aCallbackData) {
+    if (aFontFuncs == sNominalGlyphFunc) {
+      hb_font_t* subfont = hb_font_create_sub_font(result);
+      hb_font_destroy(result);
+      result = subfont;
+    }
+    hb_font_set_funcs(result, aFontFuncs, aCallbackData, nullptr);
+  }
+  hb_font_set_ppem(result, aFont->GetAdjustedSize(), aFont->GetAdjustedSize());
+  uint32_t scale = FloatToFixed(aFont->GetAdjustedSize());  // 16.16 fixed-point
+  hb_font_set_scale(result, scale, scale);
+
+  AutoTArray<gfxFontVariation, 8> vars;
+  aFont->GetFontEntry()->GetVariationsForStyle(vars, *aFont->GetStyle());
+  if (vars.Length() > 0) {
+    // Fortunately, the hb_variation_t struct is compatible with our
+    // gfxFontVariation, so we can simply cast here.
+    static_assert(
+        sizeof(gfxFontVariation) == sizeof(hb_variation_t) &&
+            offsetof(gfxFontVariation, mTag) == offsetof(hb_variation_t, tag) &&
+            offsetof(gfxFontVariation, mValue) ==
+                offsetof(hb_variation_t, value),
+        "Gecko vs HarfBuzz struct mismatch!");
+    auto hbVars = reinterpret_cast<const hb_variation_t*>(vars.Elements());
+    hb_font_set_variations(result, hbVars, vars.Length());
+  }
+
+  return result;
+}
+
+bool gfxHarfBuzzShaper::LoadHmtxTable() {
+  // Read mNumLongHMetrics from metrics-head table without caching its
+  // blob, and preload/cache the metrics table.
+  gfxFontEntry* entry = mFont->GetFontEntry();
+  gfxFontEntry::AutoTable hheaTable(entry, TRUETYPE_TAG('h', 'h', 'e', 'a'));
+  if (hheaTable) {
+    uint32_t len;
+    const MetricsHeader* hhea = reinterpret_cast<const MetricsHeader*>(
+        hb_blob_get_data(hheaTable, &len));
+    if (len >= sizeof(MetricsHeader)) {
+      mNumLongHMetrics = hhea->numOfLongMetrics;
+      if (mNumLongHMetrics > 0 && int16_t(hhea->metricDataFormat) == 0) {
+        // no point reading metrics if number of entries is zero!
+        // in that case, we won't be able to use this font
+        // (this method will return FALSE below if mHmtxTable
+        // is null)
+        mHmtxTable = entry->GetFontTable(TRUETYPE_TAG('h', 'm', 't', 'x'));
+        if (mHmtxTable && hb_blob_get_length(mHmtxTable) <
+                              mNumLongHMetrics * sizeof(LongMetric)) {
+          // metrics table is not large enough for the claimed
+          // number of entries: invalid, do not use.
+          hb_blob_destroy(mHmtxTable);
+          mHmtxTable = nullptr;
+        }
+      }
+    }
+  }
+  if (!mHmtxTable) {
+    return false;
+  }
+  return true;
+}
+
+void gfxHarfBuzzShaper::InitializeVertical() {
+  // We only do this once. If we don't have a mHmtxTable after that,
+  // we'll be making up fallback metrics.
+  if (mVerticalInitialized) {
+    return;
+  }
+  mVerticalInitialized = true;
+
+  if (!mHmtxTable) {
+    if (!LoadHmtxTable()) {
+      return;
+    }
+  }
+
+  // Load vertical metrics if present in the font; if not, we'll synthesize
+  // vertical glyph advances based on (horizontal) ascent/descent metrics.
+  gfxFontEntry* entry = mFont->GetFontEntry();
+  gfxFontEntry::AutoTable vheaTable(entry, TRUETYPE_TAG('v', 'h', 'e', 'a'));
+  if (vheaTable) {
+    uint32_t len;
+    const MetricsHeader* vhea = reinterpret_cast<const MetricsHeader*>(
+        hb_blob_get_data(vheaTable, &len));
+    if (len >= sizeof(MetricsHeader)) {
+      mNumLongVMetrics = vhea->numOfLongMetrics;
+      gfxFontEntry::AutoTable maxpTable(entry,
+                                        TRUETYPE_TAG('m', 'a', 'x', 'p'));
+      int numGlyphs = -1;  // invalid if we fail to read 'maxp'
+      if (maxpTable &&
+          hb_blob_get_length(maxpTable) >= sizeof(MaxpTableHeader)) {
+        const MaxpTableHeader* maxp = reinterpret_cast<const MaxpTableHeader*>(
+            hb_blob_get_data(maxpTable, nullptr));
+        numGlyphs = uint16_t(maxp->numGlyphs);
+      }
+      if (mNumLongVMetrics > 0 && mNumLongVMetrics <= numGlyphs &&
+          int16_t(vhea->metricDataFormat) == 0) {
+        mVmtxTable = entry->GetFontTable(TRUETYPE_TAG('v', 'm', 't', 'x'));
+        if (mVmtxTable &&
+            hb_blob_get_length(mVmtxTable) <
+                mNumLongVMetrics * sizeof(LongMetric) +
+                    (numGlyphs - mNumLongVMetrics) * sizeof(int16_t)) {
+          // metrics table is not large enough for the claimed
+          // number of entries: invalid, do not use.
+          hb_blob_destroy(mVmtxTable);
+          mVmtxTable = nullptr;
+        }
+      }
+    }
+  }
+
+  // For CFF fonts only, load a VORG table if present.
+  if (entry->HasFontTable(TRUETYPE_TAG('C', 'F', 'F', ' '))) {
+    mVORGTable = entry->GetFontTable(TRUETYPE_TAG('V', 'O', 'R', 'G'));
+    if (mVORGTable) {
+      uint32_t len;
+      const VORG* vorg =
+          reinterpret_cast<const VORG*>(hb_blob_get_data(mVORGTable, &len));
+      if (len < sizeof(VORG) || uint16_t(vorg->majorVersion) != 1 ||
+          uint16_t(vorg->minorVersion) != 0 ||
+          len < sizeof(VORG) +
+                    uint16_t(vorg->numVertOriginYMetrics) * sizeof(VORGrec)) {
+        // VORG table is an unknown version, or not large enough
+        // to be valid -- discard it.
+        NS_WARNING("discarding invalid VORG table");
+        hb_blob_destroy(mVORGTable);
+        mVORGTable = nullptr;
+      }
+    }
+  }
+}
+
+bool gfxHarfBuzzShaper::ShapeText(DrawTarget* aDrawTarget,
+                                  const char16_t* aText, uint32_t aOffset,
+                                  uint32_t aLength, Script aScript,
+                                  nsAtom* aLanguage, bool aVertical,
+                                  RoundingFlags aRounding,
+                                  gfxShapedText* aShapedText) {
+  mUseVerticalPresentationForms = false;
+
+  if (!Initialize()) {
+    return false;
+  }
+
+  if (aVertical) {
+    InitializeVertical();
+    if (!mFont->GetFontEntry()->SupportsOpenTypeFeature(
+            aScript, HB_TAG('v', 'e', 'r', 't'))) {
+      mUseVerticalPresentationForms = true;
+    }
+  }
+
+  const gfxFontStyle* style = mFont->GetStyle();
+
+  // determine whether petite-caps falls back to small-caps
+  bool addSmallCaps = false;
+  if (style->variantCaps != NS_FONT_VARIANT_CAPS_NORMAL) {
+    switch (style->variantCaps) {
+      case NS_FONT_VARIANT_CAPS_ALLPETITE:
+      case NS_FONT_VARIANT_CAPS_PETITECAPS:
+        bool synLower, synUpper;
+        mFont->SupportsVariantCaps(aScript, style->variantCaps, addSmallCaps,
+                                   synLower, synUpper);
+        break;
+      default:
+        break;
+    }
+  }
+
+  gfxFontEntry* entry = mFont->GetFontEntry();
+
+  // insert any merged features into hb_feature array
+  AutoTArray<hb_feature_t, 20> features;
+  MergeFontFeatures(style, entry->mFeatureSettings,
+                    aShapedText->DisableLigatures(), entry->FamilyName(),
+                    addSmallCaps, AddOpenTypeFeature, &features);
+
+  // For CJK script, match kerning and proportional-alternates (palt) features
+  // (and their vertical counterparts) as per spec:
+  // https://learn.microsoft.com/en-us/typography/opentype/spec/features_pt#tag-palt
+  // and disable kerning by default (for font-kerning:auto).
+  if (gfxTextRun::IsCJKScript(aScript)) {
+    hb_tag_t kern =
+        aVertical ? HB_TAG('v', 'k', 'r', 'n') : HB_TAG('k', 'e', 'r', 'n');
+    hb_tag_t alt =
+        aVertical ? HB_TAG('v', 'p', 'a', 'l') : HB_TAG('p', 'a', 'l', 't');
+    struct Cmp {
+      bool Equals(const hb_feature_t& a, const hb_tag_t& b) const {
+        return a.tag == b;
+      }
+    };
+    constexpr auto NoIndex = nsTArray<hb_feature_t>::NoIndex;
+    nsTArray<hb_feature_t>::index_type i = features.IndexOf(kern, 0, Cmp());
+    if (i == NoIndex) {
+      // Kerning was not explicitly set; override harfbuzz's default to disable
+      // it.
+      features.AppendElement(hb_feature_t{kern, 0, HB_FEATURE_GLOBAL_START,
+                                          HB_FEATURE_GLOBAL_END});
+    } else if (features[i].value) {
+      // If kerning was explicitly enabled), we also turn on proportional
+      // alternates, as per the OpenType feature registry.
+      // Bug 1798297: for the Yu Gothic UI font, we don't do this, because its
+      // 'palt' feature produces badly-spaced (overcrowded) kana glyphs.
+      if (!entry->FamilyName().EqualsLiteral("Yu Gothic UI")) {
+        if (features.IndexOf(alt, 0, Cmp()) == NoIndex) {
+          features.AppendElement(hb_feature_t{alt, 1, HB_FEATURE_GLOBAL_START,
+                                              HB_FEATURE_GLOBAL_END});
+        }
+      }
+    }
+  }
+
+  bool isRightToLeft = aShapedText->IsRightToLeft();
+
+  hb_buffer_set_direction(
+      mBuffer, aVertical
+                   ? HB_DIRECTION_TTB
+                   : (isRightToLeft ? HB_DIRECTION_RTL : HB_DIRECTION_LTR));
+  hb_script_t scriptTag;
+  if (aShapedText->GetFlags() & gfx::ShapedTextFlags::TEXT_USE_MATH_SCRIPT) {
+    scriptTag = sMathScript;
+  } else {
+    scriptTag = GetHBScriptUsedForShaping(aScript);
+  }
+  hb_buffer_set_script(mBuffer, scriptTag);
+
+  hb_language_t language;
+  if (style->languageOverride) {
+    language = hb_ot_tag_to_language(style->languageOverride);
+  } else if (entry->mLanguageOverride) {
+    language = hb_ot_tag_to_language(entry->mLanguageOverride);
+  } else if (aLanguage) {
+    nsCString langString;
+    aLanguage->ToUTF8String(langString);
+    language = hb_language_from_string(langString.get(), langString.Length());
+  } else {
+    language = hb_ot_tag_to_language(HB_OT_TAG_DEFAULT_LANGUAGE);
+  }
+  hb_buffer_set_language(mBuffer, language);
+
+  uint32_t length = aLength;
+  hb_buffer_add_utf16(mBuffer, reinterpret_cast<const uint16_t*>(aText), length,
+                      0, length);
+
+  hb_shape(mHBFont, mBuffer, features.Elements(), features.Length());
+
+  if (isRightToLeft) {
+    hb_buffer_reverse(mBuffer);
+  }
+
+  nsresult rv = SetGlyphsFromRun(aShapedText, aOffset, aLength, aText,
+                                 aVertical, aRounding);
+
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "failed to store glyphs into gfxShapedWord");
+  hb_buffer_clear_contents(mBuffer);
+
+  return NS_SUCCEEDED(rv);
+}
+
+#define SMALL_GLYPH_RUN \
+  128  // some testing indicates that 90%+ of text runs
+       // will fit without requiring separate allocation
+       // for charToGlyphArray
+
+nsresult gfxHarfBuzzShaper::SetGlyphsFromRun(gfxShapedText* aShapedText,
+                                             uint32_t aOffset, uint32_t aLength,
+                                             const char16_t* aText,
+                                             bool aVertical,
+                                             RoundingFlags aRounding) {
+  typedef gfxShapedText::CompressedGlyph CompressedGlyph;
+
+  uint32_t numGlyphs;
+  const hb_glyph_info_t* ginfo = hb_buffer_get_glyph_infos(mBuffer, &numGlyphs);
+  if (numGlyphs == 0) {
+    return NS_OK;
+  }
+
+  AutoTArray<gfxTextRun::DetailedGlyph, 1> detailedGlyphs;
+
+  uint32_t wordLength = aLength;
+  static const int32_t NO_GLYPH = -1;
+  AutoTArray<int32_t, SMALL_GLYPH_RUN> charToGlyphArray;
+  if (!charToGlyphArray.SetLength(wordLength, fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  int32_t* charToGlyph = charToGlyphArray.Elements();
+  for (uint32_t offset = 0; offset < wordLength; ++offset) {
+    charToGlyph[offset] = NO_GLYPH;
+  }
+
+  for (uint32_t i = 0; i < numGlyphs; ++i) {
+    uint32_t loc = ginfo[i].cluster;
+    if (loc < wordLength) {
+      charToGlyph[loc] = i;
+    }
+  }
+
+  int32_t glyphStart = 0;  // looking for a clump that starts at this glyph
+  int32_t charStart = 0;   // and this char index within the range of the run
+
+  bool roundI, roundB;
+  if (aVertical) {
+    roundI = bool(aRounding & RoundingFlags::kRoundY);
+    roundB = bool(aRounding & RoundingFlags::kRoundX);
+  } else {
+    roundI = bool(aRounding & RoundingFlags::kRoundX);
+    roundB = bool(aRounding & RoundingFlags::kRoundY);
+  }
+
+  int32_t appUnitsPerDevUnit = aShapedText->GetAppUnitsPerDevUnit();
+  CompressedGlyph* charGlyphs = aShapedText->GetCharacterGlyphs() + aOffset;
+
+  // factor to convert 16.16 fixed-point pixels to app units
+  // (only used if not rounding)
+  double hb2appUnits = FixedToFloat(aShapedText->GetAppUnitsPerDevUnit());
+
+  // Residual from rounding of previous advance, for use in rounding the
+  // subsequent offset or advance appropriately.  16.16 fixed-point
+  //
+  // When rounding, the goal is to make the distance between glyphs and
+  // their base glyph equal to the integral number of pixels closest to that
+  // suggested by that shaper.
+  // i.e. posInfo[n].x_advance - posInfo[n].x_offset + posInfo[n+1].x_offset
+  //
+  // The value of the residual is the part of the desired distance that has
+  // not been included in integer offsets.
+  hb_position_t residual = 0;
+
+  // keep track of y-position to set glyph offsets if needed
+  nscoord bPos = 0;
+
+  const hb_glyph_position_t* posInfo =
+      hb_buffer_get_glyph_positions(mBuffer, nullptr);
+  if (!posInfo) {
+    // Some kind of unexpected failure inside harfbuzz?
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  while (glyphStart < int32_t(numGlyphs)) {
+    int32_t charEnd = ginfo[glyphStart].cluster;
+    int32_t glyphEnd = glyphStart;
+    int32_t charLimit = wordLength;
+    while (charEnd < charLimit) {
+      // This is normally executed once for each iteration of the outer loop,
+      // but in unusual cases where the character/glyph association is complex,
+      // the initial character range might correspond to a non-contiguous
+      // glyph range with "holes" in it. If so, we will repeat this loop to
+      // extend the character range until we have a contiguous glyph sequence.
+      charEnd += 1;
+      while (charEnd != charLimit && charToGlyph[charEnd] == NO_GLYPH) {
+        charEnd += 1;
+      }
+
+      // find the maximum glyph index covered by the clump so far
+      for (int32_t i = charStart; i < charEnd; ++i) {
+        if (charToGlyph[i] != NO_GLYPH) {
+          glyphEnd = std::max(glyphEnd, charToGlyph[i] + 1);
+          // update extent of glyph range
+        }
+      }
+
+      if (glyphEnd == glyphStart + 1) {
+        // for the common case of a single-glyph clump,
+        // we can skip the following checks
+        break;
+      }
+
+      if (glyphEnd == glyphStart) {
+        // no glyphs, try to extend the clump
+        continue;
+      }
+
+      // check whether all glyphs in the range are associated with the
+      // characters in our clump; if not, we have a discontinuous range, and
+      // should extend it unless we've reached the end of the text
+      bool allGlyphsAreWithinCluster = true;
+      for (int32_t i = glyphStart; i < glyphEnd; ++i) {
+        int32_t glyphCharIndex = ginfo[i].cluster;
+        if (glyphCharIndex < charStart || glyphCharIndex >= charEnd) {
+          allGlyphsAreWithinCluster = false;
+          break;
+        }
+      }
+      if (allGlyphsAreWithinCluster) {
+        break;
+      }
+    }
+
+    NS_ASSERTION(glyphStart < glyphEnd,
+                 "character/glyph clump contains no glyphs!");
+    NS_ASSERTION(charStart != charEnd,
+                 "character/glyph clump contains no characters!");
+
+    // Now charStart..charEnd is a ligature clump, corresponding to
+    // glyphStart..glyphEnd; Set baseCharIndex to the char we'll actually attach
+    // the glyphs to (1st of ligature), and endCharIndex to the limit (position
+    // beyond the last char), adjusting for the offset of the stringRange
+    // relative to the textRun.
+    int32_t baseCharIndex, endCharIndex;
+    while (charEnd < int32_t(wordLength) && charToGlyph[charEnd] == NO_GLYPH)
+      charEnd++;
+    baseCharIndex = charStart;
+    endCharIndex = charEnd;
+
+    // Then we check if the clump falls outside our actual string range;
+    // if so, just go to the next.
+    if (baseCharIndex >= int32_t(wordLength)) {
+      glyphStart = glyphEnd;
+      charStart = charEnd;
+      continue;
+    }
+    // Ensure we won't try to go beyond the valid length of the textRun's text
+    endCharIndex = std::min<int32_t>(endCharIndex, wordLength);
+
+    // Now we're ready to set the glyph info in the textRun
+    int32_t glyphsInClump = glyphEnd - glyphStart;
+
+    // Check for default-ignorable char that didn't get filtered, combined,
+    // etc by the shaping process, and remove from the run.
+    // (This may be done within harfbuzz eventually.)
+    if (glyphsInClump == 1 && baseCharIndex + 1 == endCharIndex &&
+        aShapedText->FilterIfIgnorable(aOffset + baseCharIndex,
+                                       aText[baseCharIndex])) {
+      glyphStart = glyphEnd;
+      charStart = charEnd;
+      continue;
+    }
+
+    // HarfBuzz gives us physical x- and y-coordinates, but we will store
+    // them as logical inline- and block-direction values in the textrun.
+
+    hb_position_t i_offset, i_advance;  // inline-direction offset/advance
+    hb_position_t b_offset, b_advance;  // block-direction offset/advance
+    if (aVertical) {
+      // our coordinate directions are the opposite of harfbuzz's
+      // when doing top-to-bottom shaping
+      i_offset = -posInfo[glyphStart].y_offset;
+      i_advance = -posInfo[glyphStart].y_advance;
+      b_offset = -posInfo[glyphStart].x_offset;
+      b_advance = -posInfo[glyphStart].x_advance;
+    } else {
+      i_offset = posInfo[glyphStart].x_offset;
+      i_advance = posInfo[glyphStart].x_advance;
+      b_offset = posInfo[glyphStart].y_offset;
+      b_advance = posInfo[glyphStart].y_advance;
+    }
+
+    nscoord iOffset, advance;
+    if (roundI) {
+      iOffset = appUnitsPerDevUnit * FixedToIntRound(i_offset + residual);
+      // Desired distance from the base glyph to the next reference point.
+      hb_position_t width = i_advance - i_offset;
+      int intWidth = FixedToIntRound(width);
+      residual = width - FloatToFixed(intWidth);
+      advance = appUnitsPerDevUnit * intWidth + iOffset;
+    } else {
+      iOffset = floor(hb2appUnits * i_offset + 0.5);
+      advance = floor(hb2appUnits * i_advance + 0.5);
+    }
+    // Check if it's a simple one-to-one mapping
+    if (glyphsInClump == 1 &&
+        CompressedGlyph::IsSimpleGlyphID(ginfo[glyphStart].codepoint) &&
+        CompressedGlyph::IsSimpleAdvance(advance) &&
+        charGlyphs[baseCharIndex].IsClusterStart() && iOffset == 0 &&
+        b_offset == 0 && b_advance == 0 && bPos == 0) {
+      charGlyphs[baseCharIndex].SetSimpleGlyph(advance,
+                                               ginfo[glyphStart].codepoint);
+    } else {
+      // Collect all glyphs in a list to be assigned to the first char;
+      // there must be at least one in the clump, and we already measured
+      // its advance, hence the placement of the loop-exit test and the
+      // measurement of the next glyph.
+      while (1) {
+        gfxTextRun::DetailedGlyph* details = detailedGlyphs.AppendElement();
+        details->mGlyphID = ginfo[glyphStart].codepoint;
+
+        details->mAdvance = advance;
+
+        if (aVertical) {
+          details->mOffset.x =
+              bPos - (roundB ? appUnitsPerDevUnit * FixedToIntRound(b_offset)
+                             : floor(hb2appUnits * b_offset + 0.5));
+          details->mOffset.y = iOffset;
+        } else {
+          details->mOffset.x = iOffset;
+          details->mOffset.y =
+              bPos - (roundB ? appUnitsPerDevUnit * FixedToIntRound(b_offset)
+                             : floor(hb2appUnits * b_offset + 0.5));
+        }
+
+        if (b_advance != 0) {
+          bPos -= roundB ? appUnitsPerDevUnit * FixedToIntRound(b_advance)
+                         : floor(hb2appUnits * b_advance + 0.5);
+        }
+        if (++glyphStart >= glyphEnd) {
+          break;
+        }
+
+        if (aVertical) {
+          i_offset = -posInfo[glyphStart].y_offset;
+          i_advance = -posInfo[glyphStart].y_advance;
+          b_offset = -posInfo[glyphStart].x_offset;
+          b_advance = -posInfo[glyphStart].x_advance;
+        } else {
+          i_offset = posInfo[glyphStart].x_offset;
+          i_advance = posInfo[glyphStart].x_advance;
+          b_offset = posInfo[glyphStart].y_offset;
+          b_advance = posInfo[glyphStart].y_advance;
+        }
+
+        if (roundI) {
+          iOffset = appUnitsPerDevUnit * FixedToIntRound(i_offset + residual);
+          // Desired distance to the next reference point.  The
+          // residual is considered here, and includes the residual
+          // from the base glyph offset and subsequent advances, so
+          // that the distance from the base glyph is optimized
+          // rather than the distance from combining marks.
+          i_advance += residual;
+          int intAdvance = FixedToIntRound(i_advance);
+          residual = i_advance - FloatToFixed(intAdvance);
+          advance = appUnitsPerDevUnit * intAdvance;
+        } else {
+          iOffset = floor(hb2appUnits * i_offset + 0.5);
+          advance = floor(hb2appUnits * i_advance + 0.5);
+        }
+      }
+
+      aShapedText->SetDetailedGlyphs(aOffset + baseCharIndex,
+                                     detailedGlyphs.Length(),
+                                     detailedGlyphs.Elements());
+
+      detailedGlyphs.Clear();
+    }
+
+    // the rest of the chars in the group are ligature continuations,
+    // no associated glyphs
+    while (++baseCharIndex != endCharIndex &&
+           baseCharIndex < int32_t(wordLength)) {
+      CompressedGlyph& g = charGlyphs[baseCharIndex];
+      NS_ASSERTION(!g.IsSimpleGlyph(), "overwriting a simple glyph");
+      g.SetComplex(g.IsClusterStart(), false);
+    }
+
+    glyphStart = glyphEnd;
+    charStart = charEnd;
+  }
+
+  return NS_OK;
+}