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>

10 files changed, 95 insertions, 0 deletions

diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index adc8f634dc..dbd47151bd 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/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(); }
 
diff --git a/src/gui/text/qfontengine_ft.cpp b/src/gui/text/qfontengine_ft.cpp
index 51b1418bc3..b79fa6e9db 100644
--- a/src/gui/text/qfontengine_ft.cpp
+++ b/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);
diff --git a/src/gui/text/qfontengine_ft_p.h b/src/gui/text/qfontengine_ft_p.h
index 3cdf0cda47..5ca3721c71 100644
--- a/src/gui/text/qfontengine_ft_p.h
+++ b/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;
diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index f3eeddab41..69331cb0bb 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/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;
diff --git a/src/gui/text/qfontengine_qpf2.cpp b/src/gui/text/qfontengine_qpf2.cpp
index 2e4af09550..110d512d39 100644
--- a/src/gui/text/qfontengine_qpf2.cpp
+++ b/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>());
diff --git a/src/gui/text/qfontengine_qpf2_p.h b/src/gui/text/qfontengine_qpf2_p.h
index 50aac245c1..e5c38ffbaf 100644
--- a/src/gui/text/qfontengine_qpf2_p.h
+++ b/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;
diff --git a/src/gui/text/qfontmetrics.cpp b/src/gui/text/qfontmetrics.cpp
index 2189923b25..aca59d0288 100644
--- a/src/gui/text/qfontmetrics.cpp
+++ b/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.
diff --git a/src/gui/text/qfontmetrics.h b/src/gui/text/qfontmetrics.h
index 22e51f29f7..3eac309092 100644
--- a/src/gui/text/qfontmetrics.h
+++ b/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;
diff --git a/src/gui/text/qrawfont.cpp b/src/gui/text/qrawfont.cpp
index 19ac4f1dbc..1fbe0ce9d1 100644
--- a/src/gui/text/qrawfont.cpp
+++ b/src/gui/text/qrawfont.cpp
@@ -325,6 +325,23 @@ qreal QRawFont::ascent() const
 }
 
 /*!
+   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.
 
    \sa QFontMetricsF::descent()
diff --git a/src/gui/text/qrawfont.h b/src/gui/text/qrawfont.h
index 5791c6af16..0252e62370 100644
--- a/src/gui/text/qrawfont.h
+++ b/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;