path: root/src/gui/text/qfontengine_qpa.cpp

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#include "qfontengine_qpa_p.h"

#include <QtCore/QFile>
#include <QtCore/QFileInfo>
#include <QtCore/QDir>
#include <QtCore/QBuffer>

#include <QtGui/private/qpaintengine_raster_p.h>
#include <QtGui/private/qguiapplication_p.h>
#include <qpa/qplatformfontdatabase.h>
#include <qpa/qplatformintegration.h>

QT_BEGIN_NAMESPACE

//#define DEBUG_HEADER
//#define DEBUG_FONTENGINE

static QFontEngineQPA::TagType tagTypes[QFontEngineQPA::NumTags] = {
    QFontEngineQPA::StringType, // FontName
    QFontEngineQPA::StringType, // FileName
    QFontEngineQPA::UInt32Type, // FileIndex
    QFontEngineQPA::UInt32Type, // FontRevision
    QFontEngineQPA::StringType, // FreeText
    QFontEngineQPA::FixedType,  // Ascent
    QFontEngineQPA::FixedType,  // Descent
    QFontEngineQPA::FixedType,  // Leading
    QFontEngineQPA::FixedType,  // XHeight
    QFontEngineQPA::FixedType,  // AverageCharWidth
    QFontEngineQPA::FixedType,  // MaxCharWidth
    QFontEngineQPA::FixedType,  // LineThickness
    QFontEngineQPA::FixedType,  // MinLeftBearing
    QFontEngineQPA::FixedType,  // MinRightBearing
    QFontEngineQPA::FixedType,  // UnderlinePosition
    QFontEngineQPA::UInt8Type,  // GlyphFormat
    QFontEngineQPA::UInt8Type,  // PixelSize
    QFontEngineQPA::UInt8Type,  // Weight
    QFontEngineQPA::UInt8Type,  // Style
    QFontEngineQPA::StringType, // EndOfHeader
    QFontEngineQPA::BitFieldType// WritingSystems
};


#if defined(DEBUG_HEADER)
# define DEBUG_VERIFY qDebug
#else
# define DEBUG_VERIFY if (0) qDebug
#endif

#define READ_VERIFY(type, variable) \
    if (tagPtr + sizeof(type) > endPtr) { \
        DEBUG_VERIFY() << "read verify failed in line" << __LINE__; \
        return 0; \
    } \
    variable = qFromBigEndian<type>(tagPtr); \
    DEBUG_VERIFY() << "read value" << variable << "of type " #type; \
    tagPtr += sizeof(type)

template <typename T>
T readValue(const uchar *&data)
{
    T value = qFromBigEndian<T>(data);
    data += sizeof(T);
    return value;
}

#define VERIFY(condition) \
    if (!(condition)) { \
        DEBUG_VERIFY() << "condition " #condition " failed in line" << __LINE__; \
        return 0; \
    }

#define VERIFY_TAG(condition) \
    if (!(condition)) { \
        DEBUG_VERIFY() << "verifying tag condition " #condition " failed in line" << __LINE__ << "with tag" << tag; \
        return 0; \
    }

static inline const uchar *verifyTag(const uchar *tagPtr, const uchar *endPtr)
{
    quint16 tag, length;
    READ_VERIFY(quint16, tag);
    READ_VERIFY(quint16, length);
    if (tag == QFontEngineQPA::Tag_EndOfHeader)
        return endPtr;
    if (tag < QFontEngineQPA::NumTags) {
        switch (tagTypes[tag]) {
            case QFontEngineQPA::BitFieldType:
            case QFontEngineQPA::StringType:
                // can't do anything...
                break;
            case QFontEngineQPA::UInt32Type:
                VERIFY_TAG(length == sizeof(quint32));
                break;
            case QFontEngineQPA::FixedType:
                VERIFY_TAG(length == sizeof(quint32));
                break;
            case QFontEngineQPA::UInt8Type:
                VERIFY_TAG(length == sizeof(quint8));
                break;
        }
#if defined(DEBUG_HEADER)
        if (length == 1)
            qDebug() << "tag data" << hex << *tagPtr;
        else if (length == 4)
            qDebug() << "tag data" << hex << tagPtr[0] << tagPtr[1] << tagPtr[2] << tagPtr[3];
#endif
    }
    return tagPtr + length;
}

const QFontEngineQPA::Glyph *QFontEngineQPA::findGlyph(glyph_t g) const
{
    if (!g || g >= glyphMapEntries)
        return 0;
    const quint32 *gmapPtr = reinterpret_cast<const quint32 *>(fontData + glyphMapOffset);
    quint32 glyphPos = qFromBigEndian<quint32>(gmapPtr[g]);
    if (glyphPos > glyphDataSize) {
        if (glyphPos == 0xffffffff)
            return 0;
#if defined(DEBUG_FONTENGINE)
        qDebug() << "glyph" << g << "outside of glyphData, remapping font file";
#endif
        if (glyphPos > glyphDataSize)
            return 0;
    }
    return reinterpret_cast<const Glyph *>(fontData + glyphDataOffset + glyphPos);
}

bool QFontEngineQPA::verifyHeader(const uchar *data, int size)
{
    VERIFY(size >= int(sizeof(Header)));
    const Header *header = reinterpret_cast<const Header *>(data);
    if (header->magic[0] != 'Q'
        || header->magic[1] != 'P'
        || header->magic[2] != 'F'
        || header->magic[3] != '2')
        return false;

    VERIFY(header->majorVersion <= CurrentMajorVersion);
    const quint16 dataSize = qFromBigEndian<quint16>(header->dataSize);
    VERIFY(size >= int(sizeof(Header)) + dataSize);

    const uchar *tagPtr = data + sizeof(Header);
    const uchar *tagEndPtr = tagPtr + dataSize;
    while (tagPtr < tagEndPtr - 3) {
        tagPtr = verifyTag(tagPtr, tagEndPtr);
        VERIFY(tagPtr);
    }

    VERIFY(tagPtr <= tagEndPtr);
    return true;
}

QVariant QFontEngineQPA::extractHeaderField(const uchar *data, HeaderTag requestedTag)
{
    const Header *header = reinterpret_cast<const Header *>(data);
    const uchar *tagPtr = data + sizeof(Header);
    const uchar *endPtr = tagPtr + qFromBigEndian<quint16>(header->dataSize);
    while (tagPtr < endPtr - 3) {
        quint16 tag = readValue<quint16>(tagPtr);
        quint16 length = readValue<quint16>(tagPtr);
        if (tag == requestedTag) {
            switch (tagTypes[requestedTag]) {
                case StringType:
                    return QVariant(QString::fromUtf8(reinterpret_cast<const char *>(tagPtr), length));
                case UInt32Type:
                    return QVariant(readValue<quint32>(tagPtr));
                case UInt8Type:
                    return QVariant(uint(*tagPtr));
                case FixedType:
                    return QVariant(QFixed::fromFixed(readValue<quint32>(tagPtr)).toReal());
                case BitFieldType:
                    return QVariant(QByteArray(reinterpret_cast<const char *>(tagPtr), length));
            }
            return QVariant();
        } else if (tag == Tag_EndOfHeader) {
            break;
        }
        tagPtr += length;
    }

    return QVariant();
}



static inline unsigned int getChar(const QChar *str, int &i, const int len)
{
    uint ucs4 = str[i].unicode();
    if (str[i].isHighSurrogate() && i < len-1 && str[i+1].isLowSurrogate()) {
        ++i;
        ucs4 = QChar::surrogateToUcs4(ucs4, str[i].unicode());
    }
    return ucs4;
}

QFontEngineQPA::QFontEngineQPA(const QFontDef &def, const QByteArray &data)
    : fontData(reinterpret_cast<const uchar *>(data.constData())), dataSize(data.size())
{
    fontDef = def;
    cache_cost = 100;
    externalCMap = 0;
    cmapOffset = 0;
    cmapSize = 0;
    glyphMapOffset = 0;
    glyphMapEntries = 0;
    glyphDataOffset = 0;
    glyphDataSize = 0;
    kerning_pairs_loaded = false;
    readOnly = true;

#if defined(DEBUG_FONTENGINE)
    qDebug() << "QFontEngineQPA::QFontEngineQPA( fd =" << fd << ", renderingFontEngine =" << renderingFontEngine << ')';
#endif

    if (!verifyHeader(fontData, dataSize)) {
#if defined(DEBUG_FONTENGINE)
        qDebug() << "verifyHeader failed!";
#endif
        return;
    }

    const Header *header = reinterpret_cast<const Header *>(fontData);

    readOnly = (header->lock == 0xffffffff);

    const uchar *imgData = fontData + sizeof(Header) + qFromBigEndian<quint16>(header->dataSize);
    const uchar *endPtr = fontData + dataSize;
    while (imgData <= endPtr - 8) {
        quint16 blockTag = readValue<quint16>(imgData);
        imgData += 2; // skip padding
        quint32 blockSize = readValue<quint32>(imgData);

        if (blockTag == CMapBlock) {
            cmapOffset = imgData - fontData;
            cmapSize = blockSize;
        } else if (blockTag == GMapBlock) {
            glyphMapOffset = imgData - fontData;
            glyphMapEntries = blockSize / 4;
        } else if (blockTag == GlyphBlock) {
            glyphDataOffset = imgData - fontData;
            glyphDataSize = blockSize;
        }

        imgData += blockSize;
    }

    face_id.filename = QFile::encodeName(extractHeaderField(fontData, Tag_FileName).toString());
    face_id.index = extractHeaderField(fontData, Tag_FileIndex).toInt();

    // get the real cmap
    if (cmapOffset) {
        int tableSize = cmapSize;
        const uchar *cmapPtr = getCMap(fontData + cmapOffset, tableSize, &symbol, &cmapSize);
        if (cmapPtr)
            cmapOffset = cmapPtr - fontData;
        else
            cmapOffset = 0;
    } else if (externalCMap) {
        int tableSize = cmapSize;
        externalCMap = getCMap(externalCMap, tableSize, &symbol, &cmapSize);
    }

    // verify all the positions in the glyphMap
    if (glyphMapOffset) {
        const quint32 *gmapPtr = reinterpret_cast<const quint32 *>(fontData + glyphMapOffset);
        for (uint i = 0; i < glyphMapEntries; ++i) {
            quint32 glyphDataPos = qFromBigEndian<quint32>(gmapPtr[i]);
            if (glyphDataPos == 0xffffffff)
                continue;
            if (glyphDataPos >= glyphDataSize) {
                // error
                glyphMapOffset = 0;
                glyphMapEntries = 0;
                break;
            }
        }
    }

#if defined(DEBUG_FONTENGINE)
    if (!isValid())
        qDebug() << "fontData" <<  fontData << "dataSize" << dataSize
                 << "externalCMap" << externalCMap << "cmapOffset" << cmapOffset
                 << "glyphMapOffset" << glyphMapOffset << "glyphDataOffset" << glyphDataOffset
                 << "fd" << fd << "glyphDataSize" << glyphDataSize;
#endif
}

QFontEngineQPA::~QFontEngineQPA()
{
}

bool QFontEngineQPA::getSfntTableData(uint tag, uchar *buffer, uint *length) const
{
    Q_UNUSED(tag);
    Q_UNUSED(buffer);
    *length = 0;
    return false;
}

bool QFontEngineQPA::stringToCMap(const QChar *str, int len, QGlyphLayout *glyphs, int *nglyphs, QFontEngine::ShaperFlags flags) const
{
    if (*nglyphs < len) {
        *nglyphs = len;
        return false;
    }

#if defined(DEBUG_FONTENGINE)
    QSet<QChar> seenGlyphs;
#endif

    const uchar *cmap = externalCMap ? externalCMap : (fontData + cmapOffset);

    bool mirrored = flags & QFontEngine::RightToLeft;
    int glyph_pos = 0;
    if (symbol) {
        for (int i = 0; i < len; ++i) {
            unsigned int uc = getChar(str, i, len);
            if (mirrored)
                uc = QChar::mirroredChar(uc);
            glyphs->glyphs[glyph_pos] = getTrueTypeGlyphIndex(cmap, uc);
            if(!glyphs->glyphs[glyph_pos] && uc < 0x100)
                glyphs->glyphs[glyph_pos] = getTrueTypeGlyphIndex(cmap, uc + 0xf000);
            ++glyph_pos;
        }
    } else {
        for (int i = 0; i < len; ++i) {
            unsigned int uc = getChar(str, i, len);
            if (mirrored)
                uc = QChar::mirroredChar(uc);
            glyphs->glyphs[glyph_pos] = getTrueTypeGlyphIndex(cmap, uc);
#if 0 && defined(DEBUG_FONTENGINE)
            QChar c(uc);
            if (!findGlyph(glyphs[glyph_pos].glyph) && !seenGlyphs.contains(c))
                qDebug() << "glyph for character" << c << '/' << hex << uc << "is" << dec << glyphs[glyph_pos].glyph;

            seenGlyphs.insert(c);
#endif
            ++glyph_pos;
        }
    }

    *nglyphs = glyph_pos;
    glyphs->numGlyphs = glyph_pos;

    if (!(flags & GlyphIndicesOnly))
        recalcAdvances(glyphs, flags);

    return true;
}

void QFontEngineQPA::recalcAdvances(QGlyphLayout *glyphs, QFontEngine::ShaperFlags) const
{
    for (int i = 0; i < glyphs->numGlyphs; ++i) {
        const Glyph *g = findGlyph(glyphs->glyphs[i]);
        if (!g) {
            glyphs->glyphs[i] = 0;
            continue;
        }
        glyphs->advances_x[i] = g->advance;
        glyphs->advances_y[i] = 0;
    }
}

QImage QFontEngineQPA::alphaMapForGlyph(glyph_t g)
{
    const Glyph *glyph = findGlyph(g);
    if (!glyph)
        return QImage();

    const uchar *bits = ((const uchar *) glyph) + sizeof(Glyph);

    QImage image(bits,glyph->width, glyph->height, glyph->bytesPerLine, QImage::Format_Indexed8);

    return image;
}

void QFontEngineQPA::addOutlineToPath(qreal x, qreal y, const QGlyphLayout &glyphs, QPainterPath *path, QTextItem::RenderFlags flags)
{
    addBitmapFontToPath(x, y, glyphs, path, flags);
}

glyph_metrics_t QFontEngineQPA::boundingBox(const QGlyphLayout &glyphs)
{
    glyph_metrics_t overall;
    // initialize with line height, we get the same behaviour on all platforms
    overall.y = -ascent();
    overall.height = ascent() + descent() + 1;

    QFixed ymax = 0;
    QFixed xmax = 0;
    for (int i = 0; i < glyphs.numGlyphs; i++) {
        const Glyph *g = findGlyph(glyphs.glyphs[i]);
        if (!g)
            continue;

        QFixed x = overall.xoff + glyphs.offsets[i].x + g->x;
        QFixed y = overall.yoff + glyphs.offsets[i].y + g->y;
        overall.x = qMin(overall.x, x);
        overall.y = qMin(overall.y, y);
        xmax = qMax(xmax, x + g->width);
        ymax = qMax(ymax, y + g->height);
        overall.xoff += g->advance;
    }
    overall.height = qMax(overall.height, ymax - overall.y);
    overall.width = xmax - overall.x;

    return overall;
}

glyph_metrics_t QFontEngineQPA::boundingBox(glyph_t glyph)
{
    glyph_metrics_t overall;
    const Glyph *g = findGlyph(glyph);
    if (!g)
        return overall;
    overall.x = g->x;
    overall.y = g->y;
    overall.width = g->width;
    overall.height = g->height;
    overall.xoff = g->advance;
    return overall;
}

QFixed QFontEngineQPA::ascent() const
{
    return QFixed::fromReal(extractHeaderField(fontData, Tag_Ascent).value<qreal>());
}

QFixed QFontEngineQPA::descent() const
{
    return QFixed::fromReal(extractHeaderField(fontData, Tag_Descent).value<qreal>());
}

QFixed QFontEngineQPA::leading() const
{
    return QFixed::fromReal(extractHeaderField(fontData, Tag_Leading).value<qreal>());
}

qreal QFontEngineQPA::maxCharWidth() const
{
    return extractHeaderField(fontData, Tag_MaxCharWidth).value<qreal>();
}

qreal QFontEngineQPA::minLeftBearing() const
{
    return extractHeaderField(fontData, Tag_MinLeftBearing).value<qreal>();
}

qreal QFontEngineQPA::minRightBearing() const
{
    return extractHeaderField(fontData, Tag_MinRightBearing).value<qreal>();
}

QFixed QFontEngineQPA::underlinePosition() const
{
    return QFixed::fromReal(extractHeaderField(fontData, Tag_UnderlinePosition).value<qreal>());
}

QFixed QFontEngineQPA::lineThickness() const
{
    return QFixed::fromReal(extractHeaderField(fontData, Tag_LineThickness).value<qreal>());
}

QFontEngine::Type QFontEngineQPA::type() const
{
    return QFontEngine::QPF2;
}

bool QFontEngineQPA::canRender(const QChar *string, int len)
{
    const uchar *cmap = externalCMap ? externalCMap : (fontData + cmapOffset);

    if (symbol) {
        for (int i = 0; i < len; ++i) {
            unsigned int uc = getChar(string, i, len);
            glyph_t g = getTrueTypeGlyphIndex(cmap, uc);
            if(!g && uc < 0x100)
                g = getTrueTypeGlyphIndex(cmap, uc + 0xf000);
            if (!g)
                return false;
        }
    } else {
        for (int i = 0; i < len; ++i) {
            unsigned int uc = getChar(string, i, len);
            if (!getTrueTypeGlyphIndex(cmap, uc))
                return false;
        }
    }
    return true;
}

bool QFontEngineQPA::isValid() const
{
    return fontData && dataSize && (cmapOffset || externalCMap)
           && glyphMapOffset && glyphDataOffset && glyphDataSize > 0;
}

void QPAGenerator::generate()
{
    writeHeader();
    writeGMap();
    writeBlock(QFontEngineQPA::GlyphBlock, QByteArray());

    dev->seek(4); // position of header.lock
    writeUInt32(0);
}

void QPAGenerator::writeHeader()
{
    QFontEngineQPA::Header header;

    header.magic[0] = 'Q';
    header.magic[1] = 'P';
    header.magic[2] = 'F';
    header.magic[3] = '2';
    header.lock = 1;
    header.majorVersion = QFontEngineQPA::CurrentMajorVersion;
    header.minorVersion = QFontEngineQPA::CurrentMinorVersion;
    header.dataSize = 0;
    dev->write((const char *)&header, sizeof(header));

    writeTaggedString(QFontEngineQPA::Tag_FontName, fe->fontDef.family.toUtf8());

    QFontEngine::FaceId face = fe->faceId();
    writeTaggedString(QFontEngineQPA::Tag_FileName, face.filename);
    writeTaggedUInt32(QFontEngineQPA::Tag_FileIndex, face.index);

    {
        uchar data[4];
        uint len = 4;
        bool ok = fe->getSfntTableData(MAKE_TAG('h', 'e', 'a', 'd'), data, &len);
        if (ok) {
            const quint32 revision = qFromBigEndian<quint32>(data);
            writeTaggedUInt32(QFontEngineQPA::Tag_FontRevision, revision);
        }
    }

    writeTaggedQFixed(QFontEngineQPA::Tag_Ascent, fe->ascent());
    writeTaggedQFixed(QFontEngineQPA::Tag_Descent, fe->descent());
    writeTaggedQFixed(QFontEngineQPA::Tag_Leading, fe->leading());
    writeTaggedQFixed(QFontEngineQPA::Tag_XHeight, fe->xHeight());
    writeTaggedQFixed(QFontEngineQPA::Tag_AverageCharWidth, fe->averageCharWidth());
    writeTaggedQFixed(QFontEngineQPA::Tag_MaxCharWidth, QFixed::fromReal(fe->maxCharWidth()));
    writeTaggedQFixed(QFontEngineQPA::Tag_LineThickness, fe->lineThickness());
    writeTaggedQFixed(QFontEngineQPA::Tag_MinLeftBearing, QFixed::fromReal(fe->minLeftBearing()));
    writeTaggedQFixed(QFontEngineQPA::Tag_MinRightBearing, QFixed::fromReal(fe->minRightBearing()));
    writeTaggedQFixed(QFontEngineQPA::Tag_UnderlinePosition, fe->underlinePosition());
    writeTaggedUInt8(QFontEngineQPA::Tag_PixelSize, fe->fontDef.pixelSize);
    writeTaggedUInt8(QFontEngineQPA::Tag_Weight, fe->fontDef.weight);
    writeTaggedUInt8(QFontEngineQPA::Tag_Style, fe->fontDef.style);

    writeTaggedUInt8(QFontEngineQPA::Tag_GlyphFormat, QFontEngineQPA::AlphamapGlyphs);

    writeTaggedString(QFontEngineQPA::Tag_EndOfHeader, QByteArray());
    align4();

    const quint64 size = dev->pos();
    header.dataSize = qToBigEndian<quint16>(size - sizeof(header));
    dev->seek(0);
    dev->write((const char *)&header, sizeof(header));
    dev->seek(size);
}

void QPAGenerator::writeGMap()
{
    const quint16 glyphCount = fe->glyphCount();

    writeUInt16(QFontEngineQPA::GMapBlock);
    writeUInt16(0); // padding
    writeUInt32(glyphCount * 4);

    QByteArray &buffer = dev->buffer();
    const int numBytes = glyphCount * sizeof(quint32);
    qint64 pos = buffer.size();
    buffer.resize(pos + numBytes);
    memset(buffer.data() + pos, 0xff, numBytes);
    dev->seek(pos + numBytes);
}

void QPAGenerator::writeBlock(QFontEngineQPA::BlockTag tag, const QByteArray &data)
{
    writeUInt16(tag);
    writeUInt16(0); // padding
    const int padSize = ((data.size() + 3) / 4) * 4 - data.size();
    writeUInt32(data.size() + padSize);
    dev->write(data);
    for (int i = 0; i < padSize; ++i)
        writeUInt8(0);
}

void QPAGenerator::writeTaggedString(QFontEngineQPA::HeaderTag tag, const QByteArray &string)
{
    writeUInt16(tag);
    writeUInt16(string.length());
    dev->write(string);
}

void QPAGenerator::writeTaggedUInt32(QFontEngineQPA::HeaderTag tag, quint32 value)
{
    writeUInt16(tag);
    writeUInt16(sizeof(value));
    writeUInt32(value);
}

void QPAGenerator::writeTaggedUInt8(QFontEngineQPA::HeaderTag tag, quint8 value)
{
    writeUInt16(tag);
    writeUInt16(sizeof(value));
    writeUInt8(value);
}

void QPAGenerator::writeTaggedQFixed(QFontEngineQPA::HeaderTag tag, QFixed value)
{
    writeUInt16(tag);
    writeUInt16(sizeof(quint32));
    writeUInt32(value.value());
}


/*
    Creates a new multi QPA engine.

    This function takes ownership of the QFontEngine, increasing it's refcount.
*/
QFontEngineMultiQPA::QFontEngineMultiQPA(QFontEngine *fe, int _script, const QStringList &fallbacks)
    : QFontEngineMulti(fallbacks.size() + 1),
      fallbackFamilies(fallbacks), script(_script)
    , fallbacksQueried(true)
{
    init(fe);
}

QFontEngineMultiQPA::QFontEngineMultiQPA(QFontEngine *fe, int _script)
    : QFontEngineMulti(2)
    , script(_script)
    , fallbacksQueried(false)
{
    fallbackFamilies << QString();
    init(fe);
}

void QFontEngineMultiQPA::init(QFontEngine *fe)
{
    Q_ASSERT(fe && fe->type() != QFontEngine::Multi);
    engines[0] = fe;
    fe->ref.ref();
    fontDef = engines[0]->fontDef;
    setObjectName(QStringLiteral("QFontEngineMultiQPA"));
}

void QFontEngineMultiQPA::loadEngine(int at)
{
    ensureFallbackFamiliesQueried();
    Q_ASSERT(at < engines.size());
    Q_ASSERT(engines.at(at) == 0);
    QFontDef request = fontDef;
    request.styleStrategy |= QFont::NoFontMerging;
    request.family = fallbackFamilies.at(at-1);
    engines[at] = QFontDatabase::findFont(script,
                                          /*fontprivate = */0,
                                          request, /*multi = */false);
    Q_ASSERT(engines[at]);
    engines[at]->ref.ref();
    engines[at]->fontDef = request;
}
void QFontEngineMultiQPA::ensureFallbackFamiliesQueried()
{
    if (fallbacksQueried)
        return;
    QStringList fallbacks = QGuiApplicationPrivate::instance()->platformIntegration()->fontDatabase()->fallbacksForFamily(engine(0)->fontDef.family, QFont::Style(engine(0)->fontDef.style)
                                                                                                                     , QFont::AnyStyle, QUnicodeTables::Script(script));
    setFallbackFamiliesList(fallbacks);
}

void QFontEngineMultiQPA::setFallbackFamiliesList(const QStringList &fallbacks)
{
    // Original FontEngine to restore after the fill.
    QFontEngine *fe = engines[0];
    fallbackFamilies = fallbacks;
    if (!fallbackFamilies.isEmpty()) {
        engines.fill(0, fallbackFamilies.size() + 1);
        engines[0] = fe;
    } else {
        // Turns out we lied about having any fallback at all.
        fallbackFamilies << fe->fontDef.family;
        engines[1] = fe;
        fe->ref.ref();
    }
    fallbacksQueried = true;
}

/*
  This is used indirectly by QtWebKit when using QTextLayout::setRawFont

  The purpose of this is to provide the necessary font fallbacks when drawing complex
  text. Since QtWebKit ends up repeatedly creating QTextLayout instances and passing them
  the same raw font over and over again, we want to cache the corresponding multi font engine
  as it may contain fallback font engines already.
*/
QFontEngine* QFontEngineMultiQPA::createMultiFontEngine(QFontEngine *fe, int script)
{
    QFontEngine *engine = 0;
    QFontCache::Key key(fe->fontDef, script, /*multi = */true);
    QFontCache *fc = QFontCache::instance();
    //  We can't rely on the fontDef (and hence the cache Key)
    //  alone to distinguish webfonts, since these should not be
    //  accidentally shared, even if the resulting fontcache key
    //  is strictly identical. See:
    //   http://www.w3.org/TR/css3-fonts/#font-face-rule
    const bool faceIsLocal = !fe->faceId().filename.isEmpty();
    QFontCache::EngineCache::Iterator it = fc->engineCache.find(key),
            end = fc->engineCache.end();
    while (it != end && it.key() == key) {
        QFontEngineMulti *cachedEngine = qobject_cast<QFontEngineMulti *>(it.value().data);
        if (faceIsLocal || (cachedEngine && fe == cachedEngine->engine(0))) {
            engine = cachedEngine;
            fc->updateHitCountAndTimeStamp(it.value());
            break;
        }
        it++;
    }
    if (!engine) {
        engine = QGuiApplicationPrivate::instance()->platformIntegration()->fontDatabase()->fontEngineMulti(fe, QUnicodeTables::Script(script));
        QFontCache::instance()->insertEngine(key, engine, /* insertMulti */ !faceIsLocal);
    }
    Q_ASSERT(engine);
    return engine;
}

QT_END_NAMESPACE