SkPDFFont.cpp

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/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
#include "src/pdf/SkPDFFont.h"
 
#include "include/core/SkBitmap.h"
#include "include/core/SkCanvas.h"
#include "include/core/SkData.h"
#include "include/core/SkDrawable.h"
#include "include/core/SkFont.h"
#include "include/core/SkFontMetrics.h"
#include "include/core/SkFontStyle.h"
#include "include/core/SkFontTypes.h"
#include "include/core/SkImage.h"
#include "include/core/SkImageInfo.h"
#include "include/core/SkMatrix.h"
#include "include/core/SkPaint.h"
#include "include/core/SkPath.h"
#include "include/core/SkPoint.h"
#include "include/core/SkRect.h"
#include "include/core/SkRefCnt.h"
#include "include/core/SkScalar.h"
#include "include/core/SkStream.h"
#include "include/core/SkString.h"
#include "include/core/SkSurfaceProps.h"
#include "include/private/base/SkDebug.h"
#include "include/private/base/SkTPin.h"
#include "include/private/base/SkTo.h"
#include "src/base/SkBitmaskEnum.h"
#include "src/base/SkUTF.h"
#include "src/core/SkDevice.h"
#include "src/core/SkGlyph.h"
#include "src/core/SkMask.h"
#include "src/core/SkScalerContext.h"
#include "src/core/SkStrike.h"
#include "src/core/SkStrikeSpec.h"
#include "src/core/SkTHash.h"
#include "src/pdf/SkPDFBitmap.h"
#include "src/pdf/SkPDFDevice.h"
#include "src/pdf/SkPDFDocumentPriv.h"
#include "src/pdf/SkPDFFormXObject.h"
#include "src/pdf/SkPDFMakeCIDGlyphWidthsArray.h"
#include "src/pdf/SkPDFMakeToUnicodeCmap.h"
#include "src/pdf/SkPDFSubsetFont.h"
#include "src/pdf/SkPDFType1Font.h"
#include "src/pdf/SkPDFUtils.h"
 
#include <limits.h>
#include <algorithm>
#include <cstddef>
#include <initializer_list>
#include <memory>
#include <utility>
 
void SkPDFFont::GetType1GlyphNames(const SkTypeface& face, SkString* dst) {
    face.getPostScriptGlyphNames(dst);
}
 
namespace {
// PDF's notion of symbolic vs non-symbolic is related to the character set, not
// symbols vs. characters.  Rarely is a font the right character set to call it
// non-symbolic, so always call it symbolic.  (PDF 1.4 spec, section 5.7.1)
static const int32_t kPdfSymbolic = 4;
static const SkFontTableTag kCOLRTableTag = SkSetFourByteTag('C', 'O', 'L', 'R');
 
// scale from em-units to base-1000, returning as a SkScalar
inline SkScalar from_font_units(SkScalar scaled, uint16_t emSize) {
    return emSize == 1000 ? scaled : scaled * 1000 / emSize;
}
 
inline SkScalar scaleFromFontUnits(int16_t val, uint16_t emSize) {
    return from_font_units(SkIntToScalar(val), emSize);
}
 
void setGlyphWidthAndBoundingBox(SkScalar width, SkIRect box,
                                 SkDynamicMemoryWStream* content) {
    // Specify width and bounding box for the glyph.
    SkPDFUtils::AppendScalar(width, content);
    content->writeText(" 0 ");
    content->writeDecAsText(box.fLeft);
    content->writeText(" ");
    content->writeDecAsText(box.fTop);
    content->writeText(" ");
    content->writeDecAsText(box.fRight);
    content->writeText(" ");
    content->writeDecAsText(box.fBottom);
    content->writeText(" d1\n");
}
}  // namespace
 
///////////////////////////////////////////////////////////////////////////////
// class SkPDFFont
///////////////////////////////////////////////////////////////////////////////
 
/* Resources are canonicalized and uniqueified by pointer so there has to be
 * some additional state indicating which subset of the font is used.  It
 * must be maintained at the document granularity.
 */
 
SkPDFFont::~SkPDFFont() = default;
 
SkPDFFont::SkPDFFont(SkPDFFont&&) = default;
 
SkPDFFont& SkPDFFont::operator=(SkPDFFont&&) = default;
 
static bool can_embed(const SkAdvancedTypefaceMetrics& metrics) {
    return !SkToBool(metrics.fFlags & SkAdvancedTypefaceMetrics::kNotEmbeddable_FontFlag);
}
 
static bool can_subset(const SkAdvancedTypefaceMetrics& metrics) {
    return !SkToBool(metrics.fFlags & SkAdvancedTypefaceMetrics::kNotSubsettable_FontFlag);
}
 
const SkAdvancedTypefaceMetrics* SkPDFFont::GetMetrics(const SkTypeface* typeface,
                                                       SkPDFDocument* canon) {
    SkASSERT(typeface);
    SkTypefaceID id = typeface->uniqueID();
    if (std::unique_ptr<SkAdvancedTypefaceMetrics>* ptr = canon->fTypefaceMetrics.find(id)) {
        return ptr->get();  // canon retains ownership.
    }
    int count = typeface->countGlyphs();
    if (count <= 0 || count > 1 + SkTo<int>(UINT16_MAX)) {
        // Cache nullptr to skip this check.  Use SkSafeUnref().
        canon->fTypefaceMetrics.set(id, nullptr);
        return nullptr;
    }
    std::unique_ptr<SkAdvancedTypefaceMetrics> metrics = typeface->getAdvancedMetrics();
    if (!metrics) {
        metrics = std::make_unique<SkAdvancedTypefaceMetrics>();
    }
 
    if (0 == metrics->fStemV || 0 == metrics->fCapHeight) {
        SkFont font;
        font.setHinting(SkFontHinting::kNone);
        font.setTypeface(sk_ref_sp(typeface));
        font.setSize(1000);  // glyph coordinate system
        if (0 == metrics->fStemV) {
            // Figure out a good guess for StemV - Min width of i, I, !, 1.
            // This probably isn't very good with an italic font.
            int16_t stemV = SHRT_MAX;
            for (char c : {'i', 'I', '!', '1'}) {
                uint16_t g = font.unicharToGlyph(c);
                SkRect bounds;
                font.getBounds(&g, 1, &bounds, nullptr);
                stemV = std::min(stemV, SkToS16(SkScalarRoundToInt(bounds.width())));
            }
            metrics->fStemV = stemV;
        }
        if (0 == metrics->fCapHeight) {
            // Figure out a good guess for CapHeight: average the height of M and X.
            SkScalar capHeight = 0;
            for (char c : {'M', 'X'}) {
                uint16_t g = font.unicharToGlyph(c);
                SkRect bounds;
                font.getBounds(&g, 1, &bounds, nullptr);
                capHeight += bounds.height();
            }
            metrics->fCapHeight = SkToS16(SkScalarRoundToInt(capHeight / 2));
        }
    }
    // Fonts are always subset, so always prepend the subset tag.
    metrics->fPostScriptName.prepend(canon->nextFontSubsetTag());
    return canon->fTypefaceMetrics.set(id, std::move(metrics))->get();
}
 
const std::vector<SkUnichar>& SkPDFFont::GetUnicodeMap(const SkTypeface* typeface,
                                                       SkPDFDocument* canon) {
    SkASSERT(typeface);
    SkASSERT(canon);
    SkTypefaceID id = typeface->uniqueID();
    if (std::vector<SkUnichar>* ptr = canon->fToUnicodeMap.find(id)) {
        return *ptr;
    }
    std::vector<SkUnichar> buffer(typeface->countGlyphs());
    typeface->getGlyphToUnicodeMap(buffer.data());
    return *canon->fToUnicodeMap.set(id, std::move(buffer));
}
 
SkAdvancedTypefaceMetrics::FontType SkPDFFont::FontType(const SkTypeface& typeface,
                                                        const SkAdvancedTypefaceMetrics& metrics) {
    if (SkToBool(metrics.fFlags & SkAdvancedTypefaceMetrics::kVariable_FontFlag) ||
        // PDF is actually interested in the encoding of the data, not just the logical format.
        // If the TrueType is actually wOFF or wOF2 then it should not be directly embedded in PDF.
        // For now export these as Type3 until the subsetter can handle table based fonts.
        // See https://github.com/harfbuzz/harfbuzz/issues/3609 and
        // https://skia-review.googlesource.com/c/skia/+/543485
        SkToBool(metrics.fFlags & SkAdvancedTypefaceMetrics::kAltDataFormat_FontFlag) ||
        SkToBool(metrics.fFlags & SkAdvancedTypefaceMetrics::kNotEmbeddable_FontFlag)) {
        // force Type3 fallback.
        return SkAdvancedTypefaceMetrics::kOther_Font;
    }
    if (typeface.getTableSize(kCOLRTableTag)) {
        // https://bugs.chromium.org/p/skia/issues/detail?id=12650
        // Don't embed COLRv0 / COLRv1 fonts, fall back to bitmaps.
        return SkAdvancedTypefaceMetrics::kOther_Font;
    }
    return metrics.fType;
}
 
static SkGlyphID first_nonzero_glyph_for_single_byte_encoding(SkGlyphID gid) {
    return gid != 0 ? gid - (gid - 1) % 255 : 1;
}
 
SkPDFFont* SkPDFFont::GetFontResource(SkPDFDocument* doc,
                                      const SkGlyph* glyph,
                                      SkTypeface* face) {
    SkASSERT(doc);
    SkASSERT(face);  // All SkPDFDevice::internalDrawText ensures this.
    const SkAdvancedTypefaceMetrics* fontMetrics = SkPDFFont::GetMetrics(face, doc);
    SkASSERT(fontMetrics);  // SkPDFDevice::internalDrawText ensures the typeface is good.
                            // GetMetrics only returns null to signify a bad typeface.
    const SkAdvancedTypefaceMetrics& metrics = *fontMetrics;
    SkAdvancedTypefaceMetrics::FontType type = SkPDFFont::FontType(*face, metrics);
    if (!(glyph->isEmpty() || glyph->path())) {
        type = SkAdvancedTypefaceMetrics::kOther_Font;
    }
    bool multibyte = SkPDFFont::IsMultiByte(type);
    SkGlyphID subsetCode =
            multibyte ? 0 : first_nonzero_glyph_for_single_byte_encoding(glyph->getGlyphID());
    uint64_t typefaceID = (static_cast<uint64_t>(face->uniqueID()) << 16) | subsetCode;
 
    if (SkPDFFont* found = doc->fFontMap.find(typefaceID)) {
        SkASSERT(multibyte == found->multiByteGlyphs());
        return found;
    }
 
    sk_sp<SkTypeface> typeface(sk_ref_sp(face));
    SkASSERT(typeface);
 
    SkGlyphID lastGlyph = SkToU16(typeface->countGlyphs() - 1);
 
    // should be caught by SkPDFDevice::internalDrawText
    SkASSERT(glyph->getGlyphID() <= lastGlyph);
 
    SkGlyphID firstNonZeroGlyph;
    if (multibyte) {
        firstNonZeroGlyph = 1;
    } else {
        firstNonZeroGlyph = subsetCode;
        lastGlyph = SkToU16(std::min<int>((int)lastGlyph, 254 + (int)subsetCode));
    }
    auto ref = doc->reserveRef();
    return doc->fFontMap.set(
            typefaceID, SkPDFFont(std::move(typeface), firstNonZeroGlyph, lastGlyph, type, ref));
}
 
SkPDFFont::SkPDFFont(sk_sp<SkTypeface> typeface,
                     SkGlyphID firstGlyphID,
                     SkGlyphID lastGlyphID,
                     SkAdvancedTypefaceMetrics::FontType fontType,
                     SkPDFIndirectReference indirectReference)
    : fTypeface(std::move(typeface))
    , fGlyphUsage(firstGlyphID, lastGlyphID)
    , fIndirectReference(indirectReference)
    , fFontType(fontType)
{
    // Always include glyph 0
    this->noteGlyphUsage(0);
}
 
void SkPDFFont::PopulateCommonFontDescriptor(SkPDFDict* descriptor,
                                             const SkAdvancedTypefaceMetrics& metrics,
                                             uint16_t emSize,
                                             int16_t defaultWidth) {
    descriptor->insertName("FontName", metrics.fPostScriptName);
    descriptor->insertInt("Flags", (size_t)(metrics.fStyle | kPdfSymbolic));
    descriptor->insertScalar("Ascent",
            scaleFromFontUnits(metrics.fAscent, emSize));
    descriptor->insertScalar("Descent",
            scaleFromFontUnits(metrics.fDescent, emSize));
    descriptor->insertScalar("StemV",
            scaleFromFontUnits(metrics.fStemV, emSize));
    descriptor->insertScalar("CapHeight",
            scaleFromFontUnits(metrics.fCapHeight, emSize));
    descriptor->insertInt("ItalicAngle", metrics.fItalicAngle);
    descriptor->insertObject("FontBBox",
                             SkPDFMakeArray(scaleFromFontUnits(metrics.fBBox.left(), emSize),
                                            scaleFromFontUnits(metrics.fBBox.bottom(), emSize),
                                            scaleFromFontUnits(metrics.fBBox.right(), emSize),
                                            scaleFromFontUnits(metrics.fBBox.top(), emSize)));
    if (defaultWidth > 0) {
        descriptor->insertScalar("MissingWidth",
                scaleFromFontUnits(defaultWidth, emSize));
    }
}
 
///////////////////////////////////////////////////////////////////////////////
//  Type0Font
///////////////////////////////////////////////////////////////////////////////
 
static void emit_subset_type0(const SkPDFFont& font, SkPDFDocument* doc) {
    const SkAdvancedTypefaceMetrics* metricsPtr = SkPDFFont::GetMetrics(font.typeface(), doc);
    SkASSERT(metricsPtr);
    if (!metricsPtr) {
        return;
    }
    const SkAdvancedTypefaceMetrics& metrics = *metricsPtr;
    SkASSERT(can_embed(metrics));
    SkAdvancedTypefaceMetrics::FontType type = font.getType();
    SkTypeface* face = font.typeface();
    SkASSERT(face);
 
    auto descriptor = SkPDFMakeDict("FontDescriptor");
    uint16_t emSize = SkToU16(font.typeface()->getUnitsPerEm());
    SkPDFFont::PopulateCommonFontDescriptor(descriptor.get(), metrics, emSize, 0);
 
    int ttcIndex;
    std::unique_ptr<SkStreamAsset> fontAsset = face->openStream(&ttcIndex);
    size_t fontSize = fontAsset ? fontAsset->getLength() : 0;
    if (0 == fontSize) {
        SkDebugf("Error: (SkTypeface)(%p)::openStream() returned "
                 "empty stream (%p) when identified as kType1CID_Font "
                 "or kTrueType_Font.\n", face, fontAsset.get());
    } else if (type == SkAdvancedTypefaceMetrics::kTrueType_Font ||
               type == SkAdvancedTypefaceMetrics::kCFF_Font)
    {
        sk_sp<SkData> subsetFontData;
        if (can_subset(metrics)) {
            SkASSERT(font.firstGlyphID() == 1);
            subsetFontData = SkPDFSubsetFont(*face, font.glyphUsage());
        }
        std::unique_ptr<SkStreamAsset> subsetFontAsset;
        if (subsetFontData) {
            subsetFontAsset = SkMemoryStream::Make(std::move(subsetFontData));
        } else {
            // If subsetting fails, fall back to original font data.
            subsetFontAsset = std::move(fontAsset);
        }
        std::unique_ptr<SkPDFDict> streamDict = SkPDFMakeDict();
        streamDict->insertInt("Length1", subsetFontAsset->getLength());
        const char* fontFileKey;
        if (type == SkAdvancedTypefaceMetrics::kTrueType_Font) {
            fontFileKey = "FontFile2";
        } else {
            streamDict->insertName("Subtype", "OpenType");
            fontFileKey = "FontFile3";
        }
        descriptor->insertRef(fontFileKey,
                              SkPDFStreamOut(std::move(streamDict), std::move(subsetFontAsset),
                                             doc, SkPDFSteamCompressionEnabled::Yes));
    } else if (type == SkAdvancedTypefaceMetrics::kType1CID_Font) {
        std::unique_ptr<SkPDFDict> streamDict = SkPDFMakeDict();
        streamDict->insertName("Subtype", "CIDFontType0C");
        descriptor->insertRef("FontFile3",
                              SkPDFStreamOut(std::move(streamDict), std::move(fontAsset),
                                             doc, SkPDFSteamCompressionEnabled::Yes));
    } else {
        SkASSERT(false);
    }
 
    auto newCIDFont = SkPDFMakeDict("Font");
    newCIDFont->insertRef("FontDescriptor", doc->emit(*descriptor));
    newCIDFont->insertName("BaseFont", metrics.fPostScriptName);
 
    switch (type) {
        case SkAdvancedTypefaceMetrics::kType1CID_Font:
            newCIDFont->insertName("Subtype", "CIDFontType0");
            break;
        case SkAdvancedTypefaceMetrics::kCFF_Font:
            newCIDFont->insertName("Subtype", "CIDFontType0");
            newCIDFont->insertName("CIDToGIDMap", "Identity");
            break;
        case SkAdvancedTypefaceMetrics::kTrueType_Font:
            newCIDFont->insertName("Subtype", "CIDFontType2");
            newCIDFont->insertName("CIDToGIDMap", "Identity");
            break;
        default:
            SkASSERT(false);
    }
    auto sysInfo = SkPDFMakeDict();
    // These are actually ASCII strings.
    sysInfo->insertByteString("Registry", "Adobe");
    sysInfo->insertByteString("Ordering", "Identity");
    sysInfo->insertInt("Supplement", 0);
    newCIDFont->insertObject("CIDSystemInfo", std::move(sysInfo));
 
    // Unfortunately, poppler enforces DW (default width) must be an integer.
    int32_t defaultWidth = 0;
    {
        std::unique_ptr<SkPDFArray> widths = SkPDFMakeCIDGlyphWidthsArray(
                *face, font.glyphUsage(), &defaultWidth);
        if (widths && widths->size() > 0) {
            newCIDFont->insertObject("W", std::move(widths));
        }
        newCIDFont->insertInt("DW", defaultWidth);
    }
 
    ////////////////////////////////////////////////////////////////////////////
 
    SkPDFDict fontDict("Font");
    fontDict.insertName("Subtype", "Type0");
    fontDict.insertName("BaseFont", metrics.fPostScriptName);
    fontDict.insertName("Encoding", "Identity-H");
    auto descendantFonts = SkPDFMakeArray();
    descendantFonts->appendRef(doc->emit(*newCIDFont));
    fontDict.insertObject("DescendantFonts", std::move(descendantFonts));
 
    const std::vector<SkUnichar>& glyphToUnicode =
        SkPDFFont::GetUnicodeMap(font.typeface(), doc);
    SkASSERT(SkToSizeT(font.typeface()->countGlyphs()) == glyphToUnicode.size());
    std::unique_ptr<SkStreamAsset> toUnicode =
            SkPDFMakeToUnicodeCmap(glyphToUnicode.data(),
                                   &font.glyphUsage(),
                                   font.multiByteGlyphs(),
                                   font.firstGlyphID(),
                                   font.lastGlyphID());
    fontDict.insertRef("ToUnicode", SkPDFStreamOut(nullptr, std::move(toUnicode), doc));
 
    doc->emit(fontDict, font.indirectReference());
}
 
///////////////////////////////////////////////////////////////////////////////
// PDFType3Font
///////////////////////////////////////////////////////////////////////////////
 
namespace {
// returns [0, first, first+1, ... last-1,  last]
struct SingleByteGlyphIdIterator {
    SingleByteGlyphIdIterator(SkGlyphID first, SkGlyphID last)
        : fFirst(first), fLast(last) {
        SkASSERT(fFirst > 0);
        SkASSERT(fLast >= first);
    }
    struct Iter {
        void operator++() {
            fCurrent = (0 == fCurrent) ? fFirst : fCurrent + 1;
        }
        // This is an input_iterator
        SkGlyphID operator*() const { return (SkGlyphID)fCurrent; }
        bool operator!=(const Iter& rhs) const {
            return fCurrent != rhs.fCurrent;
        }
        Iter(SkGlyphID f, int c) : fFirst(f), fCurrent(c) {}
    private:
        const SkGlyphID fFirst;
        int fCurrent; // must be int to make fLast+1 to fit
    };
    Iter begin() const { return Iter(fFirst, 0); }
    Iter end() const { return Iter(fFirst, (int)fLast + 1); }
private:
    const SkGlyphID fFirst;
    const SkGlyphID fLast;
};
}  // namespace
 
struct ImageAndOffset {
    sk_sp<SkImage> fImage;
    SkIPoint fOffset;
};
static ImageAndOffset to_image(SkGlyphID gid, SkBulkGlyphMetricsAndImages* smallGlyphs) {
    const SkGlyph* glyph = smallGlyphs->glyph(SkPackedGlyphID{gid});
    SkMask mask = glyph->mask();
    if (!mask.fImage) {
        return {nullptr, {0, 0}};
    }
    SkIRect bounds = mask.fBounds;
    SkBitmap bm;
    switch (mask.fFormat) {
        case SkMask::kBW_Format:
            bm.allocPixels(SkImageInfo::MakeA8(bounds.width(), bounds.height()));
            for (int y = 0; y < bm.height(); ++y) {
                for (int x8 = 0; x8 < bm.width(); x8 += 8) {
                    uint8_t v = *mask.getAddr1(x8 + bounds.x(), y + bounds.y());
                    int e = std::min(x8 + 8, bm.width());
                    for (int x = x8; x < e; ++x) {
                        *bm.getAddr8(x, y) = (v >> (x & 0x7)) & 0x1 ? 0xFF : 0x00;
                    }
                }
            }
            bm.setImmutable();
            return {bm.asImage(), {bounds.x(), bounds.y()}};
        case SkMask::kA8_Format:
            return {SkImages::RasterFromData(
                        SkImageInfo::MakeA8(bounds.width(), bounds.height()),
                        SkData::MakeWithCopy(mask.fImage, mask.computeTotalImageSize()),
                        mask.fRowBytes),
                    {bounds.x(), bounds.y()}};
        case SkMask::kARGB32_Format:
            return {SkImages::RasterFromData(
                        SkImageInfo::MakeN32Premul(bounds.width(), bounds.height()),
                        SkData::MakeWithCopy(mask.fImage, mask.computeTotalImageSize()),
                        mask.fRowBytes),
                    {bounds.x(), bounds.y()}};
        case SkMask::k3D_Format:
        case SkMask::kLCD16_Format:
        default:
            SkASSERT(false);
            return {nullptr, {0, 0}};
    }
}
 
static SkPDFIndirectReference type3_descriptor(SkPDFDocument* doc,
                                               const SkTypeface* typeface,
                                               SkScalar xHeight) {
    if (SkPDFIndirectReference* ptr = doc->fType3FontDescriptors.find(typeface->uniqueID())) {
        return *ptr;
    }
 
    SkPDFDict descriptor("FontDescriptor");
    int32_t fontDescriptorFlags = kPdfSymbolic;
 
    /** PDF32000_2008: FontFamily should be used for Type3 fonts in Tagged PDF documents. */
    SkString familyName;
    typeface->getFamilyName(&familyName);
    if (!familyName.isEmpty()) {
        descriptor.insertByteString("FontFamily", familyName);
    }
 
    /** PDF32000_2008: FontStretch should be used for Type3 fonts in Tagged PDF documents. */
    static constexpr const char* stretchNames[9] = {
        "UltraCondensed",
        "ExtraCondensed",
        "Condensed",
        "SemiCondensed",
        "Normal",
        "SemiExpanded",
        "Expanded",
        "ExtraExpanded",
        "UltraExpanded",
    };
    const char* stretchName = stretchNames[typeface->fontStyle().width() - 1];
    descriptor.insertName("FontStretch", stretchName);
 
    /** PDF32000_2008: FontWeight should be used for Type3 fonts in Tagged PDF documents. */
    int weight = (typeface->fontStyle().weight() + 50) / 100;
    descriptor.insertInt("FontWeight", SkTPin(weight, 1, 9) * 100);
 
    if (const SkAdvancedTypefaceMetrics* metrics = SkPDFFont::GetMetrics(typeface, doc)) {
        // Type3 FontDescriptor does not require all the same fields.
        descriptor.insertName("FontName", metrics->fPostScriptName);
        descriptor.insertInt("ItalicAngle", metrics->fItalicAngle);
        fontDescriptorFlags |= (int32_t)metrics->fStyle;
        // Adobe requests CapHeight, XHeight, and StemV be added
        // to "greatly help our workflow downstream".
        if (metrics->fCapHeight != 0) { descriptor.insertInt("CapHeight", metrics->fCapHeight); }
        if (metrics->fStemV     != 0) { descriptor.insertInt("StemV",     metrics->fStemV);     }
        if (xHeight != 0) {
            descriptor.insertScalar("XHeight", xHeight);
        }
    }
    descriptor.insertInt("Flags", fontDescriptorFlags);
    SkPDFIndirectReference ref = doc->emit(descriptor);
    doc->fType3FontDescriptors.set(typeface->uniqueID(), ref);
    return ref;
}
 
#ifdef SK_PDF_BITMAP_GLYPH_RASTER_SIZE
static constexpr float kBitmapFontSize = SK_PDF_BITMAP_GLYPH_RASTER_SIZE;
#else
static constexpr float kBitmapFontSize = 64;
#endif
 
SkStrikeSpec make_small_strike(const SkTypeface& typeface) {
    SkFont font(sk_ref_sp(&typeface), kBitmapFontSize);
    font.setHinting(SkFontHinting::kNone);
    font.setEdging(SkFont::Edging::kAlias);
    return SkStrikeSpec::MakeMask(font,
                                  SkPaint(),
                                  SkSurfaceProps(),
                                  SkScalerContextFlags::kFakeGammaAndBoostContrast,
                                  SkMatrix::I());
}
 
static void emit_subset_type3(const SkPDFFont& pdfFont, SkPDFDocument* doc) {
    SkTypeface* typeface = pdfFont.typeface();
    SkGlyphID firstGlyphID = pdfFont.firstGlyphID();
    SkGlyphID lastGlyphID = pdfFont.lastGlyphID();
    const SkPDFGlyphUse& subset = pdfFont.glyphUsage();
    SkASSERT(lastGlyphID >= firstGlyphID);
    // Remove unused glyphs at the end of the range.
    // Keep the lastGlyphID >= firstGlyphID invariant true.
    while (lastGlyphID > firstGlyphID && !subset.has(lastGlyphID)) {
        --lastGlyphID;
    }
    int unitsPerEm;
    SkStrikeSpec strikeSpec = SkStrikeSpec::MakePDFVector(*typeface, &unitsPerEm);
    auto strike = strikeSpec.findOrCreateStrike();
    SkASSERT(strike);
    SkScalar emSize = (SkScalar)unitsPerEm;
    SkScalar xHeight = strike->getFontMetrics().fXHeight;
    SkBulkGlyphMetricsAndPaths metricsAndPaths((sk_sp<SkStrike>(strike)));
    SkBulkGlyphMetricsAndDrawables metricsAndDrawables(std::move(strike));
 
    SkStrikeSpec strikeSpecSmall = kBitmapFontSize > 0 ? make_small_strike(*typeface)
                                                       : strikeSpec;
 
    SkBulkGlyphMetricsAndImages smallGlyphs(strikeSpecSmall);
    float bitmapScale = kBitmapFontSize > 0 ? emSize / kBitmapFontSize : 1.0f;
 
    SkPDFDict font("Font");
    font.insertName("Subtype", "Type3");
    // Flip about the x-axis and scale by 1/emSize.
    SkMatrix fontMatrix;
    fontMatrix.setScale(SkScalarInvert(emSize), -SkScalarInvert(emSize));
    font.insertObject("FontMatrix", SkPDFUtils::MatrixToArray(fontMatrix));
 
    auto charProcs = SkPDFMakeDict();
    auto encoding = SkPDFMakeDict("Encoding");
 
    auto encDiffs = SkPDFMakeArray();
    // length(firstGlyphID .. lastGlyphID) ==  lastGlyphID - firstGlyphID + 1
    // plus 1 for glyph 0;
    SkASSERT(firstGlyphID > 0);
    SkASSERT(lastGlyphID >= firstGlyphID);
    int glyphCount = lastGlyphID - firstGlyphID + 2;
    // one other entry for the index of first glyph.
    encDiffs->reserve(glyphCount + 1);
    encDiffs->appendInt(0);  // index of first glyph
 
    auto widthArray = SkPDFMakeArray();
    widthArray->reserve(glyphCount);
 
    SkIRect bbox = SkIRect::MakeEmpty();
 
    std::vector<std::pair<SkGlyphID, SkPDFIndirectReference>> imageGlyphs;
    for (SkGlyphID gID : SingleByteGlyphIdIterator(firstGlyphID, lastGlyphID)) {
        bool skipGlyph = gID != 0 && !subset.has(gID);
        SkString characterName;
        SkScalar advance = 0.0f;
        SkIRect glyphBBox;
        if (skipGlyph) {
            characterName.set("g0");
        } else {
            characterName.printf("g%X", gID);
            const SkGlyph* pathGlyph = metricsAndPaths.glyph(gID);
            const SkGlyph* drawableGlyph = metricsAndDrawables.glyph(gID);
            advance = pathGlyph->advanceX();
            glyphBBox = pathGlyph->iRect();
            bbox.join(glyphBBox);
            const SkPath* path = pathGlyph->path();
            SkDrawable* drawable = drawableGlyph->drawable();
            SkDynamicMemoryWStream content;
            if (drawable && !drawable->getBounds().isEmpty()) {
                sk_sp<SkPDFDevice> glyphDevice = sk_make_sp<SkPDFDevice>(glyphBBox.size(), doc);
                SkCanvas canvas(glyphDevice);
                canvas.translate(-glyphBBox.fLeft, -glyphBBox.fTop);
                canvas.drawDrawable(drawable);
                SkPDFIndirectReference xobject = SkPDFMakeFormXObject(
                        doc, glyphDevice->content(),
                        SkPDFMakeArray(0, 0, glyphBBox.width(), glyphBBox.height()),
                        glyphDevice->makeResourceDict(),
                        SkMatrix::Translate(glyphBBox.fLeft, glyphBBox.fTop), nullptr);
                imageGlyphs.emplace_back(gID, xobject);
                SkPDFUtils::AppendScalar(drawableGlyph->advanceX(), &content);
                content.writeText(" 0 d0\n1 0 0 1 0 0 cm\n/X");
                content.write(characterName.c_str(), characterName.size());
                content.writeText(" Do\n");
            } else if (path && !path->isEmpty()) {
                setGlyphWidthAndBoundingBox(pathGlyph->advanceX(), glyphBBox, &content);
                SkPDFUtils::EmitPath(*path, SkPaint::kFill_Style, &content);
                SkPDFUtils::PaintPath(SkPaint::kFill_Style, path->getFillType(), &content);
            } else {
                auto pimg = to_image(gID, &smallGlyphs);
                if (!pimg.fImage) {
                    setGlyphWidthAndBoundingBox(pathGlyph->advanceX(), glyphBBox, &content);
                } else {
                    using SkPDFUtils::AppendScalar;
                    imageGlyphs.emplace_back(gID, SkPDFSerializeImage(pimg.fImage.get(), doc));
                    AppendScalar(pathGlyph->advanceX(), &content);
                    content.writeText(" 0 d0\n");
                    AppendScalar(pimg.fImage->width() * bitmapScale, &content);
                    content.writeText(" 0 0 ");
                    AppendScalar(-pimg.fImage->height() * bitmapScale, &content);
                    content.writeText(" ");
                    AppendScalar(pimg.fOffset.x() * bitmapScale, &content);
                    content.writeText(" ");
                    AppendScalar((pimg.fImage->height() + pimg.fOffset.y()) * bitmapScale,
                                 &content);
                    content.writeText(" cm\n/X");
                    content.write(characterName.c_str(), characterName.size());
                    content.writeText(" Do\n");
                }
            }
            charProcs->insertRef(characterName, SkPDFStreamOut(nullptr,
                                                               content.detachAsStream(), doc));
        }
        encDiffs->appendName(std::move(characterName));
        widthArray->appendScalar(advance);
    }
 
    if (!imageGlyphs.empty()) {
        auto d0 = SkPDFMakeDict();
        for (const auto& pair : imageGlyphs) {
            d0->insertRef(SkStringPrintf("Xg%X", pair.first), pair.second);
        }
        auto d1 = SkPDFMakeDict();
        d1->insertObject("XObject", std::move(d0));
        font.insertObject("Resources", std::move(d1));
    }
 
    encoding->insertObject("Differences", std::move(encDiffs));
    font.insertInt("FirstChar", 0);
    font.insertInt("LastChar", lastGlyphID - firstGlyphID + 1);
    /* FontBBox: "A rectangle expressed in the glyph coordinate
      system, specifying the font bounding box. This is the smallest
      rectangle enclosing the shape that would result if all of the
      glyphs of the font were placed with their origins coincident and
      then filled." */
    font.insertObject("FontBBox", SkPDFMakeArray(bbox.left(),
                                                  bbox.bottom(),
                                                  bbox.right(),
                                                  bbox.top()));
 
    font.insertName("CIDToGIDMap", "Identity");
 
    const std::vector<SkUnichar>& glyphToUnicode = SkPDFFont::GetUnicodeMap(typeface, doc);
    SkASSERT(glyphToUnicode.size() == SkToSizeT(typeface->countGlyphs()));
    auto toUnicodeCmap = SkPDFMakeToUnicodeCmap(glyphToUnicode.data(),
                                                &subset,
                                                false,
                                                firstGlyphID,
                                                lastGlyphID);
    font.insertRef("ToUnicode", SkPDFStreamOut(nullptr, std::move(toUnicodeCmap), doc));
    font.insertRef("FontDescriptor", type3_descriptor(doc, typeface, xHeight));
    font.insertObject("Widths", std::move(widthArray));
    font.insertObject("Encoding", std::move(encoding));
    font.insertObject("CharProcs", std::move(charProcs));
 
    doc->emit(font, pdfFont.indirectReference());
}
 
void SkPDFFont::emitSubset(SkPDFDocument* doc) const {
    switch (fFontType) {
        case SkAdvancedTypefaceMetrics::kType1CID_Font:
        case SkAdvancedTypefaceMetrics::kTrueType_Font:
        case SkAdvancedTypefaceMetrics::kCFF_Font:
            return emit_subset_type0(*this, doc);
#ifndef SK_PDF_DO_NOT_SUPPORT_TYPE_1_FONTS
        case SkAdvancedTypefaceMetrics::kType1_Font:
            return SkPDFEmitType1Font(*this, doc);
#endif
        default:
            return emit_subset_type3(*this, doc);
    }
}
 
////////////////////////////////////////////////////////////////////////////////
 
bool SkPDFFont::CanEmbedTypeface(SkTypeface* typeface, SkPDFDocument* doc) {
    const SkAdvancedTypefaceMetrics* metrics = SkPDFFont::GetMetrics(typeface, doc);
    return metrics && can_embed(*metrics);
}