Added capHeight() to QRawFont and QFontMetrics(F)

Cap height is an important metric of font, in particular it is
required to make decent implementation of "initial-letter"
CSS property in QtWebKit.

Note that some fonts lack cap height metadata, so we need to
fall back to measuring H letter height.

Change-Id: Icf69d92159d070889085e20d31f2e397d796d940
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

src/gui/text/qfontengine.cpp

@@ -418,6 +418,13 @@ glyph_metrics_t QFontEngine::boundingBox(glyph_t glyph, const QTransform &matrix
     return metrics;
 }
 
+QFixed QFontEngine::calculatedCapHeight() const
+{
+    const glyph_t glyph = glyphIndex('H');
+    glyph_metrics_t bb = const_cast<QFontEngine *>(this)->boundingBox(glyph);
+    return bb.height;
+}
+
 QFixed QFontEngine::xHeight() const
 {
     const glyph_t glyph = glyphIndex('x');
@@ -1703,6 +1710,11 @@ QFixed QFontEngineBox::ascent() const
     return _size;
 }
 
+QFixed QFontEngineBox::capHeight() const
+{
+    return _size;
+}
+
 QFixed QFontEngineBox::descent() const
 {
     return 0;
@@ -2163,6 +2175,9 @@ glyph_metrics_t QFontEngineMulti::boundingBox(glyph_t glyph)
 QFixed QFontEngineMulti::ascent() const
 { return engine(0)->ascent(); }
 
+QFixed QFontEngineMulti::capHeight() const
+{ return engine(0)->capHeight(); }
+
 QFixed QFontEngineMulti::descent() const
 { return engine(0)->descent(); }
 

src/gui/text/qfontengine_ft.cpp

@@ -414,6 +414,7 @@ QFontEngine::Properties QFreetypeFace::properties() const
     p.italicAngle = 0;
     p.capHeight = p.ascent;
     p.lineWidth = face->underline_thickness;
+
     return p;
 }
 
@@ -1299,6 +1300,18 @@ QFixed QFontEngineFT::ascent() const
     return v;
 }
 
+QFixed QFontEngineFT::capHeight() const
+{
+    TT_OS2 *os2 = (TT_OS2 *)FT_Get_Sfnt_Table(freetype->face, ft_sfnt_os2);
+    if (os2 && os2->version >= 2) {
+        lockFace();
+        QFixed answer = QFixed::fromFixed(FT_MulFix(os2->sCapHeight, freetype->face->size->metrics.y_scale));
+        unlockFace();
+        return answer;
+    }
+    return calculatedCapHeight();
+}
+
 QFixed QFontEngineFT::descent() const
 {
     QFixed v = QFixed::fromFixed(-metrics.descender);

src/gui/text/qfontengine_ft_p.h

@@ -209,6 +209,7 @@ private:
     int synthesized() const Q_DECL_OVERRIDE;
 
     QFixed ascent() const Q_DECL_OVERRIDE;
+    QFixed capHeight() const Q_DECL_OVERRIDE;
     QFixed descent() const Q_DECL_OVERRIDE;
     QFixed leading() const Q_DECL_OVERRIDE;
     QFixed xHeight() const Q_DECL_OVERRIDE;

src/gui/text/qfontengine_p.h

@@ -211,6 +211,7 @@ public:
     glyph_metrics_t tightBoundingBox(const QGlyphLayout &glyphs);
 
     virtual QFixed ascent() const = 0;
+    virtual QFixed capHeight() const = 0;
     virtual QFixed descent() const = 0;
     virtual QFixed leading() const = 0;
     virtual QFixed xHeight() const;
@@ -348,6 +349,7 @@ protected:
     QFixed lastRightBearing(const QGlyphLayout &glyphs, bool round = false);
 
     inline void setUserData(const QVariant &userData) { m_userData = userData; }
+    QFixed calculatedCapHeight() const;
 
 private:
     struct GlyphCacheEntry {
@@ -414,6 +416,7 @@ public:
     virtual QFontEngine *cloneWithSize(qreal pixelSize) const Q_DECL_OVERRIDE;
 
     virtual QFixed ascent() const Q_DECL_OVERRIDE;
+    virtual QFixed capHeight() const Q_DECL_OVERRIDE;
     virtual QFixed descent() const Q_DECL_OVERRIDE;
     virtual QFixed leading() const Q_DECL_OVERRIDE;
     virtual qreal maxCharWidth() const Q_DECL_OVERRIDE;
@@ -451,6 +454,7 @@ public:
     virtual void getGlyphBearings(glyph_t glyph, qreal *leftBearing = 0, qreal *rightBearing = 0) Q_DECL_OVERRIDE;
 
     virtual QFixed ascent() const Q_DECL_OVERRIDE;
+    virtual QFixed capHeight() const Q_DECL_OVERRIDE;
     virtual QFixed descent() const Q_DECL_OVERRIDE;
     virtual QFixed leading() const Q_DECL_OVERRIDE;
     virtual QFixed xHeight() const Q_DECL_OVERRIDE;

src/gui/text/qfontengine_qpf2.cpp

@@ -459,6 +459,11 @@ QFixed QFontEngineQPF2::ascent() const
     return QFixed::fromReal(extractHeaderField(fontData, Tag_Ascent).value<qreal>());
 }
 
+QFixed QFontEngineQPF2::capHeight() const
+{
+    return calculatedCapHeight();
+}
+
 QFixed QFontEngineQPF2::descent() const
 {
     return QFixed::fromReal(extractHeaderField(fontData, Tag_Descent).value<qreal>());

src/gui/text/qfontengine_qpf2_p.h

@@ -172,6 +172,7 @@ public:
     glyph_metrics_t boundingBox(glyph_t glyph) Q_DECL_OVERRIDE;
 
     QFixed ascent() const Q_DECL_OVERRIDE;
+    QFixed capHeight() const Q_DECL_OVERRIDE;
     QFixed descent() const Q_DECL_OVERRIDE;
     QFixed leading() const Q_DECL_OVERRIDE;
     qreal maxCharWidth() const Q_DECL_OVERRIDE;

src/gui/text/qfontmetrics.cpp

@@ -274,6 +274,24 @@ int QFontMetrics::ascent() const
     return qRound(engine->ascent());
 }
 
+/*!
+    Returns the cap height of the font.
+
+    \since 5.8
+
+    The cap height of a font is the height of a capital letter above
+    the baseline. It specifically is the height of capital letters
+    that are flat - such as H or I - as opposed to round letters such
+    as O, or pointed letters like A, both of which may display overshoot.
+
+    \sa ascent()
+*/
+int QFontMetrics::capHeight() const
+{
+    QFontEngine *engine = d->engineForScript(QChar::Script_Common);
+    Q_ASSERT(engine != 0);
+    return qRound(engine->capHeight());
+}
 
 /*!
     Returns the descent of the font.
@@ -1138,6 +1156,24 @@ qreal QFontMetricsF::ascent() const
     return engine->ascent().toReal();
 }
 
+/*!
+    Returns the cap height of the font.
+
+    \since 5.8
+
+    The cap height of a font is the height of a capital letter above
+    the baseline. It specifically is the height of capital letters
+    that are flat - such as H or I - as opposed to round letters such
+    as O, or pointed letters like A, both of which may display overshoot.
+
+    \sa ascent()
+*/
+qreal QFontMetricsF::capHeight() const
+{
+    QFontEngine *engine = d->engineForScript(QChar::Script_Common);
+    Q_ASSERT(engine != 0);
+    return engine->capHeight().toReal();
+}
 
 /*!
     Returns the descent of the font.

src/gui/text/qfontmetrics.h

@@ -73,6 +73,7 @@ public:
     { qSwap(d, other.d); }
 
     int ascent() const;
+    int capHeight() const;
     int descent() const;
     int height() const;
     int leading() const;
@@ -146,6 +147,7 @@ public:
     void swap(QFontMetricsF &other) { qSwap(d, other.d); }
 
     qreal ascent() const;
+    qreal capHeight() const;
     qreal descent() const;
     qreal height() const;
     qreal leading() const;

src/gui/text/qrawfont.cpp

@@ -324,6 +324,23 @@ qreal QRawFont::ascent() const
     return d->isValid() ? d->fontEngine->ascent().toReal() : 0.0;
 }
 
+/*!
+   Returns the cap height of this QRawFont in pixel units.
+
+   \since 5.8
+
+   The cap height of a font is the height of a capital letter above
+   the baseline. It specifically is the height of capital letters
+   that are flat - such as H or I - as opposed to round letters such
+   as O, or pointed letters like A, both of which may display overshoot.
+
+   \sa QFontMetricsF::capHeight()
+*/
+qreal QRawFont::capHeight() const
+{
+    return d->isValid() ? d->fontEngine->capHeight().toReal() : 0.0;
+}
+
 /*!
    Returns the descent of this QRawFont in pixel units.
 

src/gui/text/qrawfont.h

@@ -118,6 +118,7 @@ public:
     QFont::HintingPreference hintingPreference() const;
 
     qreal ascent() const;
+    qreal capHeight() const;
     qreal descent() const;
     qreal leading() const;
     qreal xHeight() const;

src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm

@@ -378,6 +378,19 @@ QFixed QCoreTextFontEngine::ascent() const
             ? QFixed::fromReal(CTFontGetAscent(ctfont)).round()
             : QFixed::fromReal(CTFontGetAscent(ctfont));
 }
+
+QFixed QCoreTextFontEngine::capHeight() const
+{
+    QFixed c = QFixed::fromReal(CTFontGetCapHeight(ctfont));
+    if (c <= 0)
+        return calculatedCapHeight();
+
+    if (fontDef.styleStrategy & QFont::ForceIntegerMetrics)
+        c = c.round();
+
+    return c;
+}
+
 QFixed QCoreTextFontEngine::descent() const
 {
     QFixed d = QFixed::fromReal(CTFontGetDescent(ctfont));

src/platformsupport/fontdatabases/mac/qfontengine_coretext_p.h

@@ -78,6 +78,7 @@ public:
     glyph_metrics_t boundingBox(glyph_t glyph) Q_DECL_OVERRIDE;
 
     QFixed ascent() const Q_DECL_OVERRIDE;
+    QFixed capHeight() const Q_DECL_OVERRIDE;
     QFixed descent() const Q_DECL_OVERRIDE;
     QFixed leading() const Q_DECL_OVERRIDE;
     QFixed xHeight() const Q_DECL_OVERRIDE;

src/plugins/platforms/windows/qwindowsfontengine.cpp

@@ -192,6 +192,7 @@ void QWindowsFontEngine::getCMap()
         lineWidth = otm->otmsUnderscoreSize;
         fsType = otm->otmfsType;
         free(otm);
+
     } else {
         unitsPerEm = tm.tmHeight;
     }
@@ -540,6 +541,62 @@ QFixed QWindowsFontEngine::leading() const
     return tm.tmExternalLeading;
 }
 
+namespace {
+#   pragma pack(1)
+
+    struct OS2Table
+    {
+        quint16 version;
+        qint16  avgCharWidth;
+        quint16 weightClass;
+        quint16 widthClass;
+        quint16 type;
+        qint16  subscriptXSize;
+        qint16  subscriptYSize;
+        qint16  subscriptXOffset;
+        qint16  subscriptYOffset;
+        qint16  superscriptXSize;
+        qint16  superscriptYSize;
+        qint16  superscriptXOffset;
+        qint16  superscriptYOffset;
+        qint16  strikeOutSize;
+        qint16  strikeOutPosition;
+        qint16  familyClass;
+        quint8  panose[10];
+        quint32 unicodeRanges[4];
+        quint8  vendorID[4];
+        quint16 selection;
+        quint16 firstCharIndex;
+        quint16 lastCharIndex;
+        qint16  typoAscender;
+        qint16  typoDescender;
+        qint16  typoLineGap;
+        quint16 winAscent;
+        quint16 winDescent;
+        quint32 codepageRanges[2];
+        qint16  height;
+        qint16  capHeight;
+        quint16 defaultChar;
+        quint16 breakChar;
+        quint16 maxContext;
+    };
+
+#   pragma pack()
+}
+
+QFixed QWindowsFontEngine::capHeight() const
+{
+    const QByteArray tableData = getSfntTable(MAKE_TAG('O', 'S', '/', '2'));
+    if (tableData.size() >= sizeof(OS2Table)) {
+        const OS2Table *table = reinterpret_cast<const OS2Table *>(tableData.constData());
+        if (qFromBigEndian<quint16>(table->version) >= 2) {
+            qint16 capHeight = qFromBigEndian<qint16>(table->capHeight);
+            if (capHeight > 0)
+                return QFixed(capHeight) / designToDevice;
+        }
+    }
+    return calculatedCapHeight();
+}
 
 QFixed QWindowsFontEngine::xHeight() const
 {

src/plugins/platforms/windows/qwindowsfontengine.h

@@ -103,6 +103,7 @@ public:
     QFixed descent() const Q_DECL_OVERRIDE;
     QFixed leading() const Q_DECL_OVERRIDE;
     QFixed xHeight() const Q_DECL_OVERRIDE;
+    QFixed capHeight() const Q_DECL_OVERRIDE;
     QFixed averageCharWidth() const Q_DECL_OVERRIDE;
     qreal maxCharWidth() const Q_DECL_OVERRIDE;
     qreal minLeftBearing() const Q_DECL_OVERRIDE;

src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp

@@ -208,6 +208,7 @@ QWindowsFontEngineDirectWrite::QWindowsFontEngineDirectWrite(IDWriteFontFace *di
     , m_lineThickness(-1)
     , m_unitsPerEm(-1)
     , m_ascent(-1)
+    , m_capHeight(-1)
     , m_descent(-1)
     , m_xHeight(-1)
     , m_lineGap(-1)
@@ -244,6 +245,7 @@ void QWindowsFontEngineDirectWrite::collectMetrics()
 
     m_lineThickness = DESIGN_TO_LOGICAL(metrics.underlineThickness);
     m_ascent = DESIGN_TO_LOGICAL(metrics.ascent);
+    m_capHeight = DESIGN_TO_LOGICAL(metrics.capHeight);
     m_descent = DESIGN_TO_LOGICAL(metrics.descent);
     m_xHeight = DESIGN_TO_LOGICAL(metrics.xHeight);
     m_lineGap = DESIGN_TO_LOGICAL(metrics.lineGap);
@@ -461,6 +463,16 @@ QFixed QWindowsFontEngineDirectWrite::ascent() const
             : m_ascent;
 }
 
+QFixed QWindowsFontEngineDirectWrite::capHeight() const
+{
+    if (m_capHeight <= 0)
+        return calculatedCapHeight();
+
+    return fontDef.styleStrategy & QFont::ForceIntegerMetrics
+            ? m_capHeight.round()
+            : m_capHeight;
+}
+
 QFixed QWindowsFontEngineDirectWrite::descent() const
 {
     return fontDef.styleStrategy & QFont::ForceIntegerMetrics

src/plugins/platforms/windows/qwindowsfontenginedirectwrite.h

@@ -87,6 +87,7 @@ public:
                                         const QTransform &matrix, GlyphFormat) Q_DECL_OVERRIDE;
 
     QFixed ascent() const Q_DECL_OVERRIDE;
+    QFixed capHeight() const Q_DECL_OVERRIDE;
     QFixed descent() const Q_DECL_OVERRIDE;
     QFixed leading() const Q_DECL_OVERRIDE;
     QFixed xHeight() const Q_DECL_OVERRIDE;
@@ -122,6 +123,7 @@ private:
     QFixed m_underlinePosition;
     int m_unitsPerEm;
     QFixed m_ascent;
+    QFixed m_capHeight;
     QFixed m_descent;
     QFixed m_xHeight;
     QFixed m_lineGap;

tests/auto/gui/text/qrawfont/testdata.qrc

@@ -1,6 +1,7 @@
 <RCC>
     <qresource prefix="/">
         <file>testfont_bold_italic.ttf</file>
+        <file>testfont_os2_v1.ttf</file>
         <file alias="testfont.ttf">../../../shared/resources/testfont.ttf</file>
     </qresource>
 </RCC>

tests/auto/gui/text/qrawfont/tst_qrawfont.cpp

@@ -93,6 +93,7 @@ private slots:
 private:
     QString testFont;
     QString testFontBoldItalic;
+    QString testFontOs2V1;
 #endif // QT_NO_RAWFONT
 };
 
@@ -110,6 +111,7 @@ void tst_QRawFont::initTestCase()
 {
     testFont = QFINDTESTDATA("testfont.ttf");
     testFontBoldItalic = QFINDTESTDATA("testfont_bold_italic.ttf");
+    testFontOs2V1 = QFINDTESTDATA("testfont_os2_v1.ttf");
     if (testFont.isEmpty() || testFontBoldItalic.isEmpty())
         QFAIL("qrawfont unittest font files not found!");
 
@@ -184,6 +186,7 @@ void tst_QRawFont::correctFontData_data()
     QTest::addColumn<QFont::HintingPreference>("hintingPreference");
     QTest::addColumn<qreal>("unitsPerEm");
     QTest::addColumn<qreal>("pixelSize");
+    QTest::addColumn<int>("capHeight");
 
     int hintingPreferences[] = {
         int(QFont::PreferDefaultHinting),
@@ -207,7 +210,8 @@ void tst_QRawFont::correctFontData_data()
                 << QFont::Normal
                 << QFont::HintingPreference(*hintingPreference)
                 << qreal(1000.0)
-                << qreal(10.0);
+                << qreal(10.0)
+                << 7;
 
         fileName = testFontBoldItalic;
         title = fileName
@@ -221,7 +225,23 @@ void tst_QRawFont::correctFontData_data()
                 << QFont::Bold
                 << QFont::HintingPreference(*hintingPreference)
                 << qreal(1000.0)
-                << qreal(10.0);
+                << qreal(10.0)
+                << 7;
+
+        fileName = testFontOs2V1;
+        title = fileName
+              + QLatin1String(": hintingPreference=")
+              + QString::number(*hintingPreference);
+
+        QTest::newRow(qPrintable(title))
+                << fileName
+                << QString::fromLatin1("QtBidiTestFont")
+                << QFont::StyleNormal
+                << QFont::Normal
+                << QFont::HintingPreference(*hintingPreference)
+                << qreal(1000.0)
+                << qreal(10.0)
+                << 7;
 
         ++hintingPreference;
     }
@@ -236,6 +256,7 @@ void tst_QRawFont::correctFontData()
     QFETCH(QFont::HintingPreference, hintingPreference);
     QFETCH(qreal, unitsPerEm);
     QFETCH(qreal, pixelSize);
+    QFETCH(int, capHeight);
 
     QRawFont font(fileName, 10, hintingPreference);
     QVERIFY(font.isValid());
@@ -246,6 +267,11 @@ void tst_QRawFont::correctFontData()
     QCOMPARE(font.hintingPreference(), hintingPreference);
     QCOMPARE(font.unitsPerEm(), unitsPerEm);
     QCOMPARE(font.pixelSize(), pixelSize);
+
+    // Some platforms return the actual fractional height of the
+    // H character when the value is missing from the OS/2 table,
+    // so we ceil it off to match (any touched pixel counts).
+    QCOMPARE(qCeil(font.capHeight()), capHeight);
 }
 
 void tst_QRawFont::glyphIndices()