tor-browser

gfxFT2FontBase.cpp (32456B)

---

/* -*- 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 "gfxFT2FontBase.h"
#include "gfxFT2Utils.h"
#include "harfbuzz/hb.h"
#include "mozilla/Likely.h"
#include "mozilla/StaticPrefs_gfx.h"
#include "gfxFontConstants.h"
#include "gfxFontUtils.h"
#include "gfxHarfBuzzShaper.h"
#include <algorithm>
#include <dlfcn.h>

#include FT_TRUETYPE_TAGS_H
#include FT_TRUETYPE_TABLES_H
#include FT_ADVANCES_H
#include FT_MULTIPLE_MASTERS_H

#ifndef FT_LOAD_COLOR
#  define FT_LOAD_COLOR (1L << 20)
#endif
#ifndef FT_FACE_FLAG_COLOR
#  define FT_FACE_FLAG_COLOR (1L << 14)
#endif

using namespace mozilla;
using namespace mozilla::gfx;

gfxFT2FontBase::gfxFT2FontBase(
   const RefPtr<UnscaledFontFreeType>& aUnscaledFont,
   RefPtr<mozilla::gfx::SharedFTFace>&& aFTFace, gfxFontEntry* aFontEntry,
   const gfxFontStyle* aFontStyle, int aLoadFlags, bool aEmbolden)
   : gfxFont(aUnscaledFont, aFontEntry, aFontStyle, kAntialiasDefault),
     mFTFace(std::move(aFTFace)),
     mFTLoadFlags(aLoadFlags | FT_LOAD_IGNORE_GLOBAL_ADVANCE_WIDTH |
                  FT_LOAD_COLOR),
     mEmbolden(aEmbolden),
     mFTSize(0.0) {}

gfxFT2FontBase::~gfxFT2FontBase() { mFTFace->ForgetLockOwner(this); }

FT_Face gfxFT2FontBase::LockFTFace() const
   MOZ_CAPABILITY_ACQUIRE(mFTFace) MOZ_NO_THREAD_SAFETY_ANALYSIS {
 if (!mFTFace->Lock(this)) {
   FT_Set_Transform(mFTFace->GetFace(), nullptr, nullptr);

   FT_F26Dot6 charSize = NS_lround(mFTSize * 64.0);
   FT_Set_Char_Size(mFTFace->GetFace(), charSize, charSize, 0, 0);
 }
 return mFTFace->GetFace();
}

void gfxFT2FontBase::UnlockFTFace() const
   MOZ_CAPABILITY_RELEASE(mFTFace) MOZ_NO_THREAD_SAFETY_ANALYSIS {
 mFTFace->Unlock();
}

static FT_ULong GetTableSizeFromFTFace(SharedFTFace* aFace,
                                      uint32_t aTableTag) {
 if (!aFace) {
   return 0;
 }
 FT_ULong len = 0;
 if (FT_Load_Sfnt_Table(aFace->GetFace(), aTableTag, 0, nullptr, &len) != 0) {
   return 0;
 }
 return len;
}

bool gfxFT2FontEntryBase::FaceHasTable(SharedFTFace* aFace,
                                      uint32_t aTableTag) {
 return GetTableSizeFromFTFace(aFace, aTableTag) > 0;
}

nsresult gfxFT2FontEntryBase::CopyFaceTable(SharedFTFace* aFace,
                                           uint32_t aTableTag,
                                           nsTArray<uint8_t>& aBuffer) {
 FT_ULong length = GetTableSizeFromFTFace(aFace, aTableTag);
 if (!length) {
   return NS_ERROR_NOT_AVAILABLE;
 }
 if (!aBuffer.SetLength(length, fallible)) {
   return NS_ERROR_OUT_OF_MEMORY;
 }
 if (FT_Load_Sfnt_Table(aFace->GetFace(), aTableTag, 0, aBuffer.Elements(),
                        &length) != 0) {
   aBuffer.Clear();
   return NS_ERROR_FAILURE;
 }
 return NS_OK;
}

uint32_t gfxFT2FontEntryBase::GetGlyph(uint32_t aCharCode,
                                      gfxFT2FontBase* aFont) {
 const uint32_t slotIndex = aCharCode % kNumCmapCacheSlots;
 {
   // Try to read a cached entry without taking an exclusive lock.
   AutoReadLock lock(mLock);
   if (mCmapCache) {
     const auto& slot = mCmapCache[slotIndex];
     if (slot.mCharCode == aCharCode) {
       return slot.mGlyphIndex;
     }
   }
 }

 // Create/update the charcode-to-glyphid cache.
 AutoWriteLock lock(mLock);

 // This cache algorithm and size is based on what is done in
 // cairo_scaled_font_text_to_glyphs and pango_fc_font_real_get_glyph.  I
 // think the concept is that adjacent characters probably come mostly from
 // one Unicode block.  This assumption is probably not so valid with
 // scripts with large character sets as used for East Asian languages.
 if (!mCmapCache) {
   mCmapCache = mozilla::MakeUnique<CmapCacheSlot[]>(kNumCmapCacheSlots);

   // Invalidate slot 0 by setting its char code to something that would
   // never end up in slot 0.  All other slots are already invalid
   // because they have mCharCode = 0 and a glyph for char code 0 will
   // always be in the slot 0.
   mCmapCache[0].mCharCode = 1;
 }

 auto& slot = mCmapCache[slotIndex];
 if (slot.mCharCode != aCharCode) {
   slot.mCharCode = aCharCode;
   slot.mGlyphIndex = gfxFT2LockedFace(aFont).GetGlyph(aCharCode);
 }
 return slot.mGlyphIndex;
}

size_t gfxFT2FontEntryBase::ComputedSizeOfExcludingThis(
   MallocSizeOf aMallocSizeOf) {
 size_t result = gfxFontEntry::ComputedSizeOfExcludingThis(aMallocSizeOf);

 if (const auto* data = GetUserFontData()) {
   if (data->FontData()) {
     result += aMallocSizeOf(data->FontData());
   }
 }

 return result;
}

// aScale is intended for a 16.16 x/y_scale of an FT_Size_Metrics
static inline FT_Long ScaleRoundDesignUnits(FT_Short aDesignMetric,
                                           FT_Fixed aScale) {
 FT_Long fixed26dot6 = FT_MulFix(aDesignMetric, aScale);
 return ROUND_26_6_TO_INT(fixed26dot6);
}

// Snap a line to pixels while keeping the center and size of the line as
// close to the original position as possible.
//
// Pango does similar snapping for underline and strikethrough when fonts are
// hinted, but nsCSSRendering::GetTextDecorationRectInternal always snaps the
// top and size of lines.  Optimizing the distance between the line and
// baseline is probably good for the gap between text and underline, but
// optimizing the center of the line is better for positioning strikethough.
static void SnapLineToPixels(gfxFloat& aOffset, gfxFloat& aSize) {
 gfxFloat snappedSize = std::max(floor(aSize + 0.5), 1.0);
 // Correct offset for change in size
 gfxFloat offset = aOffset - 0.5 * (aSize - snappedSize);
 // Snap offset
 aOffset = floor(offset + 0.5);
 aSize = snappedSize;
}

static inline gfxRect ScaleGlyphBounds(const IntRect& aBounds,
                                      gfxFloat aScale) {
 return gfxRect(FLOAT_FROM_26_6(aBounds.x) * aScale,
                FLOAT_FROM_26_6(aBounds.y) * aScale,
                FLOAT_FROM_26_6(aBounds.width) * aScale,
                FLOAT_FROM_26_6(aBounds.height) * aScale);
}

/**
* Get extents for a simple character representable by a single glyph.
* The return value is the glyph id of that glyph or zero if no such glyph
* exists.  aWidth/aBounds is only set when this returns a non-zero glyph id.
* This is just for use during initialization, and doesn't use the width cache.
*/
uint32_t gfxFT2FontBase::GetCharExtents(uint32_t aChar, gfxFloat* aWidth,
                                       gfxRect* aBounds) {
 FT_UInt gid = GetGlyph(aChar);
 int32_t width;
 IntRect bounds;
 if (gid && GetFTGlyphExtents(gid, aWidth ? &width : nullptr,
                              aBounds ? &bounds : nullptr)) {
   if (aWidth) {
     *aWidth = FLOAT_FROM_16_16(width);
   }
   if (aBounds) {
     *aBounds = ScaleGlyphBounds(bounds, GetAdjustedSize() / mFTSize);
   }
   return gid;
 } else {
   return 0;
 }
}

/**
* Find the closest available fixed strike size, if applicable, to the
* desired font size.
*/
static double FindClosestSize(FT_Face aFace, double aSize) {
 // FT size selection does not actually support sizes smaller than 1 and will
 // clamp this internally, regardless of what is requested. Do the clamp here
 // instead so that glyph extents/font matrix scaling will compensate it, as
 // Cairo normally would.
 if (aSize < 1.0) {
   aSize = 1.0;
 }
 if (FT_IS_SCALABLE(aFace)) {
   return aSize;
 }
 double bestDist = DBL_MAX;
 FT_Int bestSize = -1;
 for (FT_Int i = 0; i < aFace->num_fixed_sizes; i++) {
   double dist = aFace->available_sizes[i].y_ppem / 64.0 - aSize;
   // If the previous best is smaller than the desired size, prefer
   // a bigger size. Otherwise, just choose whatever size is closest.
   if (bestDist < 0 ? dist >= bestDist : fabs(dist) <= bestDist) {
     bestDist = dist;
     bestSize = i;
   }
 }
 if (bestSize < 0) {
   return aSize;
 }
 return aFace->available_sizes[bestSize].y_ppem / 64.0;
}

void gfxFT2FontBase::InitMetrics() {
 mFUnitsConvFactor = 0.0;

 if (MOZ_UNLIKELY(mStyle.AdjustedSizeMustBeZero())) {
   memset(&mMetrics, 0, sizeof(mMetrics));  // zero initialize
   mSpaceGlyph = GetGlyph(' ');
   return;
 }

 if (FontSizeAdjust::Tag(mStyle.sizeAdjustBasis) !=
         FontSizeAdjust::Tag::None &&
     mStyle.sizeAdjust >= 0.0 && GetAdjustedSize() > 0.0 && mFTSize == 0.0) {
   // If font-size-adjust is in effect, we need to get metrics in order to
   // determine the aspect ratio, then compute the final adjusted size and
   // re-initialize metrics.
   // Setting mFTSize nonzero here ensures we will not recurse again; the
   // actual value will be overridden by FindClosestSize below.
   mFTSize = 1.0;
   InitMetrics();
   // Now do the font-size-adjust calculation and set the final size.
   gfxFloat aspect;
   switch (FontSizeAdjust::Tag(mStyle.sizeAdjustBasis)) {
     default:
       MOZ_ASSERT_UNREACHABLE("unhandled sizeAdjustBasis?");
       aspect = 0.0;
       break;
     case FontSizeAdjust::Tag::ExHeight:
       aspect = mMetrics.xHeight / mAdjustedSize;
       break;
     case FontSizeAdjust::Tag::CapHeight:
       aspect = mMetrics.capHeight / mAdjustedSize;
       break;
     case FontSizeAdjust::Tag::ChWidth:
       aspect =
           mMetrics.zeroWidth > 0.0 ? mMetrics.zeroWidth / mAdjustedSize : 0.5;
       break;
     case FontSizeAdjust::Tag::IcWidth:
     case FontSizeAdjust::Tag::IcHeight: {
       bool vertical = FontSizeAdjust::Tag(mStyle.sizeAdjustBasis) ==
                       FontSizeAdjust::Tag::IcHeight;
       gfxFloat advance = GetCharAdvance(kWaterIdeograph, vertical);
       aspect = advance > 0.0 ? advance / mAdjustedSize : 1.0;
       break;
     }
   }
   if (aspect > 0.0) {
     // If we created a shaper above (to measure glyphs), discard it so we
     // get a new one for the adjusted scaling.
     delete mHarfBuzzShaper.exchange(nullptr);
     mAdjustedSize = mStyle.GetAdjustedSize(aspect);
     // Ensure the FT_Face will be reconfigured for the new size next time we
     // need to use it.
     mFTFace->ForgetLockOwner(this);
   }
 }

 // Set mAdjustedSize if it hasn't already been set by a font-size-adjust
 // computation.
 mAdjustedSize = GetAdjustedSize();

 // Cairo metrics are normalized to em-space, so that whatever fixed size
 // might actually be chosen is factored out. They are then later scaled by
 // the font matrix to the target adjusted size. Stash the chosen closest
 // size here for later scaling of the metrics.
 mFTSize = FindClosestSize(mFTFace->GetFace(), GetAdjustedSize());

 // Explicitly lock the face so we can release it early before calling
 // back into Cairo below.
 FT_Face face = LockFTFace();

 if (MOZ_UNLIKELY(!face)) {
   // No face.  This unfortunate situation might happen if the font
   // file is (re)moved at the wrong time.
   const gfxFloat emHeight = GetAdjustedSize();
   mMetrics.emHeight = emHeight;
   mMetrics.maxAscent = mMetrics.emAscent = 0.8 * emHeight;
   mMetrics.maxDescent = mMetrics.emDescent = 0.2 * emHeight;
   mMetrics.maxHeight = emHeight;
   mMetrics.internalLeading = 0.0;
   mMetrics.externalLeading = 0.2 * emHeight;
   const gfxFloat spaceWidth = 0.5 * emHeight;
   mMetrics.spaceWidth = spaceWidth;
   mMetrics.maxAdvance = spaceWidth;
   mMetrics.aveCharWidth = spaceWidth;
   mMetrics.zeroWidth = spaceWidth;
   mMetrics.ideographicWidth = emHeight;
   const gfxFloat xHeight = 0.5 * emHeight;
   mMetrics.xHeight = xHeight;
   mMetrics.capHeight = mMetrics.maxAscent;
   const gfxFloat underlineSize = emHeight / 14.0;
   mMetrics.underlineSize = underlineSize;
   mMetrics.underlineOffset = -underlineSize;
   mMetrics.strikeoutOffset = 0.25 * emHeight;
   mMetrics.strikeoutSize = underlineSize;

   SanitizeMetrics(&mMetrics, false);
   UnlockFTFace();
   return;
 }

 const FT_Size_Metrics& ftMetrics = face->size->metrics;

 mMetrics.maxAscent = FLOAT_FROM_26_6(ftMetrics.ascender);
 mMetrics.maxDescent = -FLOAT_FROM_26_6(ftMetrics.descender);
 mMetrics.maxAdvance = FLOAT_FROM_26_6(ftMetrics.max_advance);
 gfxFloat lineHeight = FLOAT_FROM_26_6(ftMetrics.height);

 gfxFloat emHeight;
 // Scale for vertical design metric conversion: pixels per design unit.
 // If this remains at 0.0, we can't use metrics from OS/2 etc.
 gfxFloat yScale = 0.0;
 if (FT_IS_SCALABLE(face)) {
   // Prefer FT_Size_Metrics::x_scale to x_ppem as x_ppem does not
   // have subpixel accuracy.
   //
   // FT_Size_Metrics::y_scale is in 16.16 fixed point format.  Its
   // (fractional) value is a factor that converts vertical metrics from
   // design units to units of 1/64 pixels, so that the result may be
   // interpreted as pixels in 26.6 fixed point format.
   mFUnitsConvFactor = FLOAT_FROM_26_6(FLOAT_FROM_16_16(ftMetrics.x_scale));
   yScale = FLOAT_FROM_26_6(FLOAT_FROM_16_16(ftMetrics.y_scale));
   emHeight = face->units_per_EM * yScale;
 } else {  // Not scalable.
   emHeight = ftMetrics.y_ppem;
   // FT_Face doc says units_per_EM and a bunch of following fields
   // are "only relevant to scalable outlines". If it's an sfnt,
   // we can get units_per_EM from the 'head' table instead; otherwise,
   // we don't have a unitsPerEm value so we can't compute/use yScale or
   // mFUnitsConvFactor (x scale).
   if (const TT_Header* head =
           static_cast<TT_Header*>(FT_Get_Sfnt_Table(face, ft_sfnt_head))) {
     gfxFloat emUnit = head->Units_Per_EM;
     mFUnitsConvFactor = ftMetrics.x_ppem / emUnit;
     // Bug 1267909 - Even if the font is not explicitly scalable,
     // if the face has color bitmaps, it should be treated as scalable
     // and scaled to the desired size. Metrics based on y_ppem need
     // to be rescaled for the adjusted size. This makes metrics agree
     // with the scales we pass to Cairo for Fontconfig fonts.
     if (face->face_flags & FT_FACE_FLAG_COLOR) {
       emHeight = GetAdjustedSize();
       gfxFloat adjustScale = emHeight / ftMetrics.y_ppem;
       mMetrics.maxAscent *= adjustScale;
       mMetrics.maxDescent *= adjustScale;
       mMetrics.maxAdvance *= adjustScale;
       lineHeight *= adjustScale;
       mFUnitsConvFactor *= adjustScale;
     }
     yScale = emHeight / emUnit;
   }
 }

 TT_OS2* os2 = static_cast<TT_OS2*>(FT_Get_Sfnt_Table(face, ft_sfnt_os2));

 if (os2 && os2->sTypoAscender && yScale > 0.0) {
   mMetrics.emAscent = os2->sTypoAscender * yScale;
   mMetrics.emDescent = -os2->sTypoDescender * yScale;
   FT_Short typoHeight =
       os2->sTypoAscender - os2->sTypoDescender + os2->sTypoLineGap;
   lineHeight = typoHeight * yScale;

   // If the OS/2 fsSelection USE_TYPO_METRICS bit is set,
   // set maxAscent/Descent from the sTypo* fields instead of hhea.
   const uint16_t kUseTypoMetricsMask = 1 << 7;
   if ((os2->fsSelection & kUseTypoMetricsMask) ||
       // maxAscent/maxDescent get used for frame heights, and some fonts
       // don't have the HHEA table ascent/descent set (bug 279032).
       (mMetrics.maxAscent == 0.0 && mMetrics.maxDescent == 0.0)) {
     // We use NS_round here to parallel the pixel-rounded values that
     // freetype gives us for ftMetrics.ascender/descender.
     mMetrics.maxAscent = NS_round(mMetrics.emAscent);
     mMetrics.maxDescent = NS_round(mMetrics.emDescent);
   }
 } else {
   mMetrics.emAscent = mMetrics.maxAscent;
   mMetrics.emDescent = mMetrics.maxDescent;
 }

 // gfxFont::Metrics::underlineOffset is the position of the top of the
 // underline.
 //
 // FT_FaceRec documentation describes underline_position as "the
 // center of the underlining stem".  This was the original definition
 // of the PostScript metric, but in the PostScript table of OpenType
 // fonts the metric is "the top of the underline"
 // (http://www.microsoft.com/typography/otspec/post.htm), and FreeType
 // (up to version 2.3.7) doesn't make any adjustment.
 //
 // Therefore get the underline position directly from the table
 // ourselves when this table exists.  Use FreeType's metrics for
 // other (including older PostScript) fonts.
 if (face->underline_position && face->underline_thickness && yScale > 0.0) {
   mMetrics.underlineSize = face->underline_thickness * yScale;
   TT_Postscript* post =
       static_cast<TT_Postscript*>(FT_Get_Sfnt_Table(face, ft_sfnt_post));
   if (post && post->underlinePosition) {
     mMetrics.underlineOffset = post->underlinePosition * yScale;
   } else {
     mMetrics.underlineOffset =
         face->underline_position * yScale + 0.5 * mMetrics.underlineSize;
   }
 } else {  // No underline info.
   // Imitate Pango.
   mMetrics.underlineSize = emHeight / 14.0;
   mMetrics.underlineOffset = -mMetrics.underlineSize;
 }

 if (os2 && os2->yStrikeoutSize && os2->yStrikeoutPosition && yScale > 0.0) {
   mMetrics.strikeoutSize = os2->yStrikeoutSize * yScale;
   mMetrics.strikeoutOffset = os2->yStrikeoutPosition * yScale;
 } else {  // No strikeout info.
   mMetrics.strikeoutSize = mMetrics.underlineSize;
   // Use OpenType spec's suggested position for Roman font.
   mMetrics.strikeoutOffset =
       emHeight * 409.0 / 2048.0 + 0.5 * mMetrics.strikeoutSize;
 }
 SnapLineToPixels(mMetrics.strikeoutOffset, mMetrics.strikeoutSize);

 if (os2 && os2->sxHeight && yScale > 0.0) {
   mMetrics.xHeight = os2->sxHeight * yScale;
 } else {
   // CSS 2.1, section 4.3.2 Lengths: "In the cases where it is
   // impossible or impractical to determine the x-height, a value of
   // 0.5em should be used."
   mMetrics.xHeight = 0.5 * emHeight;
 }

 // aveCharWidth is used for the width of text input elements so be
 // liberal rather than conservative in the estimate.
 if (os2 && os2->xAvgCharWidth) {
   // Round to pixels as this is compared with maxAdvance to guess
   // whether this is a fixed width font.
   mMetrics.aveCharWidth =
       ScaleRoundDesignUnits(os2->xAvgCharWidth, ftMetrics.x_scale);
 } else {
   mMetrics.aveCharWidth = 0.0;  // updated below
 }

 if (os2 && os2->sCapHeight && yScale > 0.0) {
   mMetrics.capHeight = os2->sCapHeight * yScale;
 } else {
   mMetrics.capHeight = mMetrics.maxAscent;
 }

 // Release the face lock to safely load glyphs with GetCharExtents if
 // necessary without recursively locking.
 UnlockFTFace();

 gfxFloat width;
 mSpaceGlyph = GetCharExtents(' ', &width);
 if (mSpaceGlyph) {
   mMetrics.spaceWidth = width;
 } else {
   mMetrics.spaceWidth = mMetrics.maxAdvance;  // guess
 }

 if (GetCharExtents('0', &width)) {
   mMetrics.zeroWidth = width;
 } else {
   mMetrics.zeroWidth = -1.0;  // indicates not found
 }

 if (GetCharExtents(kWaterIdeograph, &width)) {
   mMetrics.ideographicWidth = width;
 } else {
   mMetrics.ideographicWidth = -1.0;
 }

 // If we didn't get a usable x-height or cap-height above, try measuring
 // specific glyphs. This can be affected by hinting, leading to erratic
 // behavior across font sizes and system configuration, so we prefer to
 // use the metrics directly from the font if possible.
 // Using glyph bounds for x-height or cap-height may not really be right,
 // if fonts have fancy swashes etc. For x-height, CSS 2.1 suggests possibly
 // using the height of an "o", which may be more consistent across fonts,
 // but then curve-overshoot should also be accounted for.
 gfxFloat xWidth;
 gfxRect xBounds;
 if (mMetrics.xHeight == 0.0) {
   if (GetCharExtents('x', &xWidth, &xBounds) && xBounds.y < 0.0) {
     mMetrics.xHeight = -xBounds.y;
     mMetrics.aveCharWidth = std::max(mMetrics.aveCharWidth, xWidth);
   }
 }

 if (mMetrics.capHeight == 0.0) {
   if (GetCharExtents('H', nullptr, &xBounds) && xBounds.y < 0.0) {
     mMetrics.capHeight = -xBounds.y;
   }
 }

 mMetrics.aveCharWidth = std::max(mMetrics.aveCharWidth, mMetrics.zeroWidth);
 if (mMetrics.aveCharWidth == 0.0) {
   mMetrics.aveCharWidth = mMetrics.spaceWidth;
 }
 // Apparently hinting can mean that max_advance is not always accurate.
 mMetrics.maxAdvance = std::max(mMetrics.maxAdvance, mMetrics.aveCharWidth);

 mMetrics.maxHeight = mMetrics.maxAscent + mMetrics.maxDescent;

 // Make the line height an integer number of pixels so that lines will be
 // equally spaced (rather than just being snapped to pixels, some up and
 // some down).  Layout calculates line height from the emHeight +
 // internalLeading + externalLeading, but first each of these is rounded
 // to layout units.  To ensure that the result is an integer number of
 // pixels, round each of the components to pixels.
 mMetrics.emHeight = floor(emHeight + 0.5);

 // maxHeight will normally be an integer, but round anyway in case
 // FreeType is configured differently.
 mMetrics.internalLeading =
     floor(mMetrics.maxHeight - mMetrics.emHeight + 0.5);

 // Text input boxes currently don't work well with lineHeight
 // significantly less than maxHeight (with Verdana, for example).
 lineHeight = floor(std::max(lineHeight, mMetrics.maxHeight) + 0.5);
 mMetrics.externalLeading =
     lineHeight - mMetrics.internalLeading - mMetrics.emHeight;

 // Ensure emAscent + emDescent == emHeight
 gfxFloat sum = mMetrics.emAscent + mMetrics.emDescent;
 mMetrics.emAscent =
     sum > 0.0 ? mMetrics.emAscent * mMetrics.emHeight / sum : 0.0;
 mMetrics.emDescent = mMetrics.emHeight - mMetrics.emAscent;

 SanitizeMetrics(&mMetrics, false);

#if 0
   //    printf("font name: %s %f\n", NS_ConvertUTF16toUTF8(GetName()).get(), GetStyle()->size);
   //    printf ("pango font %s\n", pango_font_description_to_string (pango_font_describe (font)));

   fprintf (stderr, "Font: %s\n", GetName().get());
   fprintf (stderr, "    emHeight: %f emAscent: %f emDescent: %f\n", mMetrics.emHeight, mMetrics.emAscent, mMetrics.emDescent);
   fprintf (stderr, "    maxAscent: %f maxDescent: %f\n", mMetrics.maxAscent, mMetrics.maxDescent);
   fprintf (stderr, "    internalLeading: %f externalLeading: %f\n", mMetrics.externalLeading, mMetrics.internalLeading);
   fprintf (stderr, "    spaceWidth: %f aveCharWidth: %f xHeight: %f\n", mMetrics.spaceWidth, mMetrics.aveCharWidth, mMetrics.xHeight);
   fprintf (stderr, "    ideographicWidth: %f\n", mMetrics.ideographicWidth);
   fprintf (stderr, "    uOff: %f uSize: %f stOff: %f stSize: %f\n", mMetrics.underlineOffset, mMetrics.underlineSize, mMetrics.strikeoutOffset, mMetrics.strikeoutSize);
#endif
}

uint32_t gfxFT2FontBase::GetGlyph(uint32_t unicode,
                                 uint32_t variation_selector) {
 if (variation_selector) {
   uint32_t id =
       gfxFT2LockedFace(this).GetUVSGlyph(unicode, variation_selector);
   if (id) {
     return id;
   }
   unicode = gfxFontUtils::GetUVSFallback(unicode, variation_selector);
   if (unicode) {
     return GetGlyph(unicode);
   }
   return 0;
 }

 return GetGlyph(unicode);
}

bool gfxFT2FontBase::ShouldRoundXOffset(cairo_t* aCairo) const {
 // Force rounding if outputting to a Cairo context or if requested by pref to
 // disable subpixel positioning. Otherwise, allow subpixel positioning (no
 // rounding) if rendering a scalable outline font with anti-aliasing.
 // Monochrome rendering or some bitmap fonts can become too distorted with
 // subpixel positioning, so force rounding in those cases. Also be careful not
 // to use subpixel positioning if the user requests full hinting via
 // Fontconfig, which we detect by checking that neither hinting was disabled
 // nor light hinting was requested. Allow pref to force subpixel positioning
 // on even if full hinting was requested.
 return MOZ_UNLIKELY(
            StaticPrefs::
                gfx_text_subpixel_position_force_disabled_AtStartup()) ||
        aCairo != nullptr || !mFTFace || !FT_IS_SCALABLE(mFTFace->GetFace()) ||
        (mFTLoadFlags & FT_LOAD_MONOCHROME) ||
        !((mFTLoadFlags & FT_LOAD_NO_HINTING) ||
          FT_LOAD_TARGET_MODE(mFTLoadFlags) == FT_RENDER_MODE_LIGHT ||
          MOZ_UNLIKELY(
              StaticPrefs::
                  gfx_text_subpixel_position_force_enabled_AtStartup()));
}

FT_Vector gfxFT2FontBase::GetEmboldenStrength(FT_Face aFace) const {
 FT_Vector strength = {0, 0};
 if (!mEmbolden) {
   return strength;
 }

 // If it's an outline glyph, we'll be using mozilla_glyphslot_embolden_less
 // (see gfx/wr/webrender/src/platform/unix/font.rs), so we need to match its
 // emboldening strength here.
 if (aFace->glyph->format == FT_GLYPH_FORMAT_OUTLINE) {
   strength.x =
       FT_MulFix(aFace->units_per_EM, aFace->size->metrics.y_scale) / 48;
   strength.y = strength.x;
   return strength;
 }

 // This is the embolden "strength" used by FT_GlyphSlot_Embolden.
 strength.x =
     FT_MulFix(aFace->units_per_EM, aFace->size->metrics.y_scale) / 24;
 strength.y = strength.x;
 if (aFace->glyph->format == FT_GLYPH_FORMAT_BITMAP) {
   strength.x &= -64;
   if (!strength.x) {
     strength.x = 64;
   }
   strength.y &= -64;
 }
 return strength;
}

bool gfxFT2FontBase::GetFTGlyphExtents(uint16_t aGID, int32_t* aAdvance,
                                      IntRect* aBounds) {
 gfxFT2LockedFace face(this);
 MOZ_ASSERT(face.get());
 if (!face.get()) {
   // Failed to get the FT_Face? Give up already.
   NS_WARNING("failed to get FT_Face!");
   return false;
 }

 FT_Int32 flags = mFTLoadFlags;
 if (!aBounds) {
   flags |= FT_LOAD_ADVANCE_ONLY;
 }

 // Whether to disable subpixel positioning
 bool roundX = ShouldRoundXOffset(nullptr);

 // Workaround for FT_Load_Glyph not setting linearHoriAdvance for SVG glyphs.
 // See https://gitlab.freedesktop.org/freetype/freetype/-/issues/1156.
 if (!roundX &&
     GetFontEntry()->HasFontTable(TRUETYPE_TAG('S', 'V', 'G', ' '))) {
   flags &= ~FT_LOAD_COLOR;
 }

 if (Factory::LoadFTGlyph(face.get(), aGID, flags) != FT_Err_Ok) {
   // FT_Face was somehow broken/invalid? Don't try to access glyph slot.
   // This probably shouldn't happen, but does: see bug 1440938.
   NS_WARNING("failed to load glyph!");
   return false;
 }

 // Whether to interpret hinting settings (i.e. not printing)
 bool hintMetrics = ShouldHintMetrics();
 // No hinting disables X and Y hinting. Light disables only X hinting.
 bool unhintedY = (mFTLoadFlags & FT_LOAD_NO_HINTING) != 0;
 bool unhintedX =
     unhintedY || FT_LOAD_TARGET_MODE(mFTLoadFlags) == FT_RENDER_MODE_LIGHT;

 // Normalize out the loaded FT glyph size and then scale to the actually
 // desired size, in case these two sizes differ.
 gfxFloat extentsScale = GetAdjustedSize() / mFTSize;

 FT_Vector bold = GetEmboldenStrength(face.get());

 // Due to freetype bug 52683 we MUST use the linearHoriAdvance field when
 // dealing with a variation font; also use it for scalable fonts when not
 // applying hinting. Otherwise, prefer hinted width from glyph->advance.x.
 if (aAdvance) {
   FT_Fixed advance;
   if (!roundX || FT_HAS_MULTIPLE_MASTERS(face.get())) {
     advance = face.get()->glyph->linearHoriAdvance;
   } else {
     advance = face.get()->glyph->advance.x << 10;  // convert 26.6 to 16.16
   }
   if (advance) {
     advance += bold.x << 10;  // convert 26.6 to 16.16
   }
   // Hinting was requested, but FT did not apply any hinting to the metrics.
   // Round the advance here to approximate hinting as Cairo does. This must
   // happen BEFORE we apply the glyph extents scale, just like FT hinting
   // would.
   if (hintMetrics && roundX && unhintedX) {
     advance = (advance + 0x8000) & 0xffff0000u;
   }
   *aAdvance = NS_lround(advance * extentsScale);
 }

 if (aBounds) {
   const FT_Glyph_Metrics& metrics = face.get()->glyph->metrics;
   FT_F26Dot6 x = metrics.horiBearingX;
   FT_F26Dot6 y = -metrics.horiBearingY;
   FT_F26Dot6 x2 = x + metrics.width;
   FT_F26Dot6 y2 = y + metrics.height;
   // Synthetic bold moves the glyph top and right boundaries.
   y -= bold.y;
   x2 += bold.x;
   if (hintMetrics) {
     if (roundX && unhintedX) {
       x &= -64;
       x2 = (x2 + 63) & -64;
     }
     if (unhintedY) {
       y &= -64;
       y2 = (y2 + 63) & -64;
     }
   }
   *aBounds = IntRect(x, y, x2 - x, y2 - y);

   // Color fonts may not have reported the right bounds here, if there wasn't
   // an outline for the nominal glyph ID.
   // In principle we could use COLRFonts::GetColorGlyphBounds to retrieve the
   // true bounds of the rendering, but that's more expensive; probably better
   // to just use the font-wide ascent/descent as a heuristic that will
   // generally ensure everything gets rendered.
   if (aBounds->IsEmpty() &&
       GetFontEntry()->HasFontTable(TRUETYPE_TAG('C', 'O', 'L', 'R'))) {
     const auto& fm = GetMetrics(nsFontMetrics::eHorizontal);
     // aBounds is stored as FT_F26Dot6, so scale values from `fm` by 64.
     aBounds->y = int32_t(-NS_round(fm.maxAscent * 64.0));
     aBounds->height =
         int32_t(NS_round((fm.maxAscent + fm.maxDescent) * 64.0));
     aBounds->x = 0;
     aBounds->width =
         int32_t(aAdvance ? *aAdvance : NS_round(fm.maxAdvance * 64.0));
   }
 }

 return true;
}

/**
* Get the cached glyph metrics for the glyph id if available. Otherwise, query
* FreeType for the glyph extents and initialize the glyph metrics.
*/
const gfxFT2FontBase::GlyphMetrics& gfxFT2FontBase::GetCachedGlyphMetrics(
   uint16_t aGID, IntRect* aBounds) {
 {
   // Try to read cached metrics without exclusive locking.
   AutoReadLock lock(mLock);
   if (mGlyphMetrics) {
     if (auto metrics = mGlyphMetrics->Lookup(aGID)) {
       return metrics.Data();
     }
   }
 }

 // We need to create/update the cache.
 AutoWriteLock lock(mLock);
 if (!mGlyphMetrics) {
   mGlyphMetrics =
       mozilla::MakeUnique<nsTHashMap<nsUint32HashKey, GlyphMetrics>>(128);
 }

 return mGlyphMetrics->LookupOrInsertWith(aGID, [&] {
   GlyphMetrics metrics;
   IntRect bounds;
   if (GetFTGlyphExtents(aGID, &metrics.mAdvance, &bounds)) {
     metrics.SetBounds(bounds);
     if (aBounds) {
       *aBounds = bounds;
     }
   }
   return metrics;
 });
}

bool gfxFT2FontBase::GetGlyphBounds(uint16_t aGID, gfxRect* aBounds,
                                   bool aTight) {
 IntRect bounds;
 const GlyphMetrics& metrics = GetCachedGlyphMetrics(aGID, &bounds);
 if (!metrics.HasValidBounds()) {
   return false;
 }
 // Check if there are cached bounds and use those if available. Otherwise,
 // fall back to directly querying the glyph extents.
 if (metrics.HasCachedBounds()) {
   bounds = metrics.GetBounds();
 } else if (bounds.IsEmpty() && !GetFTGlyphExtents(aGID, nullptr, &bounds)) {
   return false;
 }
 // The bounds are stored unscaled, so must be scaled to the adjusted size.
 *aBounds = ScaleGlyphBounds(bounds, GetAdjustedSize() / mFTSize);
 return true;
}

// For variation fonts, figure out the variation coordinates to be applied
// for each axis, in freetype's order (which may not match the order of
// axes in mStyle.variationSettings, so we need to search by axis tag).
/*static*/
void gfxFT2FontBase::SetupVarCoords(
   FT_MM_Var* aMMVar, const nsTArray<gfxFontVariation>& aVariations,
   FT_Face aFTFace) {
 if (!aMMVar) {
   return;
 }

 nsTArray<FT_Fixed> coords;
 for (unsigned i = 0; i < aMMVar->num_axis; ++i) {
   coords.AppendElement(aMMVar->axis[i].def);
   for (const auto& v : aVariations) {
     if (aMMVar->axis[i].tag == v.mTag) {
       FT_Fixed val = v.mValue * 0x10000;
       val = std::min(val, aMMVar->axis[i].maximum);
       val = std::max(val, aMMVar->axis[i].minimum);
       coords[i] = val;
       break;
     }
   }
 }

 if (!coords.IsEmpty()) {
#if MOZ_TREE_FREETYPE
   FT_Set_Var_Design_Coordinates(aFTFace, coords.Length(), coords.Elements());
#else
   typedef FT_Error (*SetCoordsFunc)(FT_Face, FT_UInt, FT_Fixed*);
   static SetCoordsFunc setCoords;
   static bool firstTime = true;
   if (firstTime) {
     firstTime = false;
     setCoords =
         (SetCoordsFunc)dlsym(RTLD_DEFAULT, "FT_Set_Var_Design_Coordinates");
   }
   if (setCoords) {
     (*setCoords)(aFTFace, coords.Length(), coords.Elements());
   }
#endif
 }
}