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Use consistent vertical metrics on all platforms 

Qt assumes that ascent+descent is the bounding height of the
text, but for historical reasons, the ascent for some fonts
will not contain the diacritics. On Windows, the preference
is to use data from the OS/2 table which were explicitly
invented to work around this, but on other platforms we
are not respecting this table. This causes a text layout
that looks fine on Windows to have overlapping characters
on e.g. macOS.

To make vertical metrics (ascent, descent, leading) consistent
across all platforms, we don't blindly trust the values we get
from the underlying font system, but apply in the following order:

1. If OS/2 table exists and USE_TYPO_METRICS flag is set, we
use the typo metrics from OS/2 table
2. If OS/2 table exists and USE_TYPO_METRICS flag is not set,
we use winAscent/winDescent from OS/2 and the line gap from
HHEA table.
3. If no OS/2 table exists, we try to get ascent, descent and
line gap from the HHEA table.
4. If the HHEA table does not exist (not an SFNT), we fall back
to the system-provided metrics. (on macOS, we know the
system-provided metrics will match the data in HHEA, so we
skip parsing that table and use the data from CoreText if
there is no OS/2 table).

Task-number: QTBUG-80554
Change-Id: I41e6561a99513698c8e42451b4ec98bd5eb6892f
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
bb10
Eskil Abrahamsen Blomfeldt 2019-12-06 07:13:28 +01:00
parent 7d8093df55
commit f761ad3cd9
10 changed files with 159 additions and 119 deletions
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86
src/gui/text/qfontengine.cpp
View File

@ -148,6 +148,7 @@ QFontEngine::QFontEngine(Type type)
: m_type(type), ref(0),
font_(),
face_(),
m_heightMetricsQueried(false),
m_minLeftBearing(kBearingNotInitialized),
m_minRightBearing(kBearingNotInitialized)
{
@ -427,6 +428,91 @@ void QFontEngine::getGlyphBearings(glyph_t glyph, qreal *leftBearing, qreal *rig
*rightBearing = gi.rightBearing().toReal();
}
bool QFontEngine::processHheaTable() const
{
QByteArray hhea = getSfntTable(MAKE_TAG('h', 'h', 'e', 'a'));
if (hhea.size() >= 10) {
qint16 ascent = qFromBigEndian<qint16>(hhea.constData() + 4);
qint16 descent = qFromBigEndian<qint16>(hhea.constData() + 6);
qint16 leading = qFromBigEndian<qint16>(hhea.constData() + 8);
QFixed unitsPerEm = emSquareSize();
m_ascent = QFixed::fromReal(ascent * fontDef.pixelSize) / unitsPerEm;
m_descent = -QFixed::fromReal(descent * fontDef.pixelSize) / unitsPerEm;
m_leading = QFixed::fromReal(leading * fontDef.pixelSize) / unitsPerEm;
return true;
}
return false;
}
void QFontEngine::initializeHeightMetrics() const
{
if (!processHheaTable()) {
qWarning() << "Cannot determine metrics for font" << fontDef.family;
m_ascent = m_descent = m_leading = 1;
}
// Allow OS/2 metrics to override if present
processOS2Table();
m_heightMetricsQueried = true;
}
bool QFontEngine::processOS2Table() const
{
QByteArray os2 = getSfntTable(MAKE_TAG('O', 'S', '/', '2'));
if (os2.size() >= 78) {
quint16 fsSelection = qFromBigEndian<quint16>(os2.constData() + 62);
qint16 typoAscent = qFromBigEndian<qint16>(os2.constData() + 68);
qint16 typoDescent = qFromBigEndian<qint16>(os2.constData() + 70);
qint16 typoLineGap = qFromBigEndian<qint16>(os2.constData() + 72);
quint16 winAscent = qFromBigEndian<quint16>(os2.constData() + 74);
quint16 winDescent = qFromBigEndian<quint16>(os2.constData() + 76);
enum { USE_TYPO_METRICS = 0x80 };
QFixed unitsPerEm = emSquareSize();
if (fsSelection & USE_TYPO_METRICS) {
m_ascent = QFixed::fromReal(typoAscent * fontDef.pixelSize) / unitsPerEm;
m_descent = -QFixed::fromReal(typoDescent * fontDef.pixelSize) / unitsPerEm;
m_leading = QFixed::fromReal(typoLineGap * fontDef.pixelSize) / unitsPerEm;
} else {
m_ascent = QFixed::fromReal(winAscent * fontDef.pixelSize) / unitsPerEm;
m_descent = QFixed::fromReal(winDescent * fontDef.pixelSize) / unitsPerEm;
}
return true;
}
return false;
}
QFixed QFontEngine::leading() const
{
if (!m_heightMetricsQueried)
initializeHeightMetrics();
return (fontDef.styleStrategy & QFont::ForceIntegerMetrics) ? m_leading.round() : m_leading;
}
QFixed QFontEngine::ascent() const
{
if (!m_heightMetricsQueried)
initializeHeightMetrics();
return (fontDef.styleStrategy & QFont::ForceIntegerMetrics) ? m_ascent.round() : m_ascent;
}
QFixed QFontEngine::descent() const
{
if (!m_heightMetricsQueried)
initializeHeightMetrics();
return (fontDef.styleStrategy & QFont::ForceIntegerMetrics) ? m_descent.round() : m_descent;
}
qreal QFontEngine::minLeftBearing() const
{
if (m_minLeftBearing == kBearingNotInitialized)

16
src/gui/text/qfontengine_p.h
View File

@ -221,10 +221,10 @@ public:
virtual glyph_metrics_t boundingBox(glyph_t glyph, const QTransform &matrix);
glyph_metrics_t tightBoundingBox(const QGlyphLayout &glyphs);
virtual QFixed ascent() const = 0;
virtual QFixed ascent() const;
virtual QFixed capHeight() const = 0;
virtual QFixed descent() const = 0;
virtual QFixed leading() const = 0;
virtual QFixed descent() const;
virtual QFixed leading() const;
virtual QFixed xHeight() const;
virtual QFixed averageCharWidth() const;
@ -369,6 +369,15 @@ protected:
inline void setUserData(const QVariant &userData) { m_userData = userData; }
QFixed calculatedCapHeight() const;
mutable QFixed m_ascent;
mutable QFixed m_descent;
mutable QFixed m_leading;
mutable bool m_heightMetricsQueried;
virtual void initializeHeightMetrics() const;
virtual bool processHheaTable() const;
virtual bool processOS2Table() const;
private:
struct GlyphCacheEntry {
GlyphCacheEntry();
@ -388,7 +397,6 @@ private:
mutable qreal m_minLeftBearing;
mutable qreal m_minRightBearing;
};
Q_DECLARE_TYPEINFO(QFontEngine::KernPair, Q_PRIMITIVE_TYPE);

40
src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp
View File

@ -1241,12 +1241,26 @@ int QFontEngineFT::synthesized() const
return s;
}
QFixed QFontEngineFT::ascent() const
void QFontEngineFT::initializeHeightMetrics() const
{
QFixed v = QFixed::fromFixed(metrics.ascender);
if (scalableBitmapScaleFactor != 1)
v *= scalableBitmapScaleFactor;
return v;
QFontEngine::initializeHeightMetrics();
if (scalableBitmapScaleFactor != 1) {
m_ascent *= scalableBitmapScaleFactor;
m_descent *= scalableBitmapScaleFactor;
m_leading *= scalableBitmapScaleFactor;
}
}
bool QFontEngineFT::processHheaTable() const
{
if (!QFontEngine::processHheaTable()) {
m_ascent = QFixed::fromFixed(metrics.ascender);
m_descent = QFixed::fromFixed(-metrics.descender);
m_leading = QFixed::fromFixed(metrics.height - metrics.ascender + metrics.descender);
}
return true;
}
QFixed QFontEngineFT::capHeight() const
@ -1261,22 +1275,6 @@ QFixed QFontEngineFT::capHeight() const
return calculatedCapHeight();
}
QFixed QFontEngineFT::descent() const
{
QFixed v = QFixed::fromFixed(-metrics.descender);
if (scalableBitmapScaleFactor != 1)
v *= scalableBitmapScaleFactor;
return v;
}
QFixed QFontEngineFT::leading() const
{
QFixed v = QFixed::fromFixed(metrics.height - metrics.ascender + metrics.descender);
if (scalableBitmapScaleFactor != 1)
v *= scalableBitmapScaleFactor;
return v;
}
QFixed QFontEngineFT::xHeight() const
{
TT_OS2 *os2 = (TT_OS2 *)FT_Get_Sfnt_Table(freetype->face, ft_sfnt_os2);

5
src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h
View File

@ -191,10 +191,9 @@ private:
bool getSfntTableData(uint tag, uchar *buffer, uint *length) const override;
int synthesized() const override;
QFixed ascent() const override;
void initializeHeightMetrics() const override;
bool processHheaTable() const override;
QFixed capHeight() const override;
QFixed descent() const override;
QFixed leading() const override;
QFixed xHeight() const override;
QFixed averageCharWidth() const override;

35
src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm
View File

@ -381,14 +381,15 @@ QT_WARNING_POP
return ret;
}
QFixed QCoreTextFontEngine::ascent() const
bool QCoreTextFontEngine::processHheaTable() const
{
QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
return (fontDef.styleStrategy & QFont::ForceIntegerMetrics)
? QFixed::fromReal(CTFontGetAscent(ctfont)).round()
: QFixed::fromReal(CTFontGetAscent(ctfont));
QT_WARNING_POP
if (!QFontEngine::processHheaTable()) {
m_ascent = QFixed::fromReal(CTFontGetAscent(ctfont));
m_descent = QFixed::fromReal(CTFontGetDescent(ctfont));
m_leading = QFixed::fromReal(CTFontGetLeading(ctfont));
}
return true;
}
QFixed QCoreTextFontEngine::capHeight() const
@ -406,26 +407,6 @@ QT_WARNING_POP
return c;
}
QFixed QCoreTextFontEngine::descent() const
{
QFixed d = QFixed::fromReal(CTFontGetDescent(ctfont));
QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
if (fontDef.styleStrategy & QFont::ForceIntegerMetrics)
QT_WARNING_POP
d = d.round();
return d;
}
QFixed QCoreTextFontEngine::leading() const
{
QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
return (fontDef.styleStrategy & QFont::ForceIntegerMetrics)
? QFixed::fromReal(CTFontGetLeading(ctfont)).round()
: QFixed::fromReal(CTFontGetLeading(ctfont));
QT_WARNING_POP
}
QFixed QCoreTextFontEngine::xHeight() const
{
QT_WARNING_PUSH

4
src/platformsupport/fontdatabases/mac/qfontengine_coretext_p.h
View File

@ -82,10 +82,7 @@ public:
glyph_metrics_t boundingBox(const QGlyphLayout &glyphs) override;
glyph_metrics_t boundingBox(glyph_t glyph) override;
QFixed ascent() const override;
QFixed capHeight() const override;
QFixed descent() const override;
QFixed leading() const override;
QFixed xHeight() const override;
qreal maxCharWidth() const override;
QFixed averageCharWidth() const override;
@ -142,6 +139,7 @@ protected:
bool hasColorGlyphs() const;
bool shouldAntialias() const;
bool shouldSmoothFont() const;
bool processHheaTable() const override;
QCFType<CTFontRef> ctfont;
QCFType<CGFontRef> cgFont;

26
src/platformsupport/fontdatabases/windows/qwindowsfontengine.cpp
View File

@ -492,21 +492,6 @@ glyph_metrics_t QWindowsFontEngine::boundingBox(glyph_t glyph, const QTransform
return glyphMetrics;
}
QFixed QWindowsFontEngine::ascent() const
{
return tm.tmAscent;
}
QFixed QWindowsFontEngine::descent() const
{
return tm.tmDescent;
}
QFixed QWindowsFontEngine::leading() const
{
return tm.tmExternalLeading;
}
namespace {
# pragma pack(1)
@ -625,6 +610,17 @@ void QWindowsFontEngine::getGlyphBearings(glyph_t glyph, qreal *leftBearing, qre
}
#endif // Q_CC_MINGW
bool QWindowsFontEngine::processHheaTable() const
{
if (!QFontEngine::processHheaTable()) {
m_ascent = tm.tmAscent;
m_descent = tm.tmDescent;
m_leading = tm.tmExternalLeading;
}
return true;
}
bool QWindowsFontEngine::hasUnreliableGlyphOutline() const
{
return hasUnreliableOutline || QFontEngine::hasUnreliableGlyphOutline();

6
src/platformsupport/fontdatabases/windows/qwindowsfontengine_p.h
View File

@ -98,9 +98,6 @@ public:
glyph_metrics_t boundingBox(glyph_t g, const QTransform &t) override;
QFixed ascent() const override;
QFixed descent() const override;
QFixed leading() const override;
QFixed xHeight() const override;
QFixed capHeight() const override;
QFixed averageCharWidth() const override;
@ -132,6 +129,9 @@ public:
void setUniqueFamilyName(const QString &newName) { uniqueFamilyName = newName; }
protected:
bool processHheaTable() const override;
private:
QWindowsNativeImage *drawGDIGlyph(HFONT font, glyph_t, int margin, const QTransform &xform,
QImage::Format mask_format);

52
src/platformsupport/fontdatabases/windows/qwindowsfontenginedirectwrite.cpp
View File

@ -236,11 +236,8 @@ QWindowsFontEngineDirectWrite::QWindowsFontEngineDirectWrite(IDWriteFontFace *di
, m_directWriteBitmapRenderTarget(0)
, m_lineThickness(-1)
, m_unitsPerEm(-1)
, m_ascent(-1)
, m_capHeight(-1)
, m_descent(-1)
, m_xHeight(-1)
, m_lineGap(-1)
{
qCDebug(lcQpaFonts) << __FUNCTION__ << pixelSize;
@ -346,6 +343,20 @@ QString QWindowsFontEngineDirectWrite::filenameFromFontFile(IDWriteFontFile *fon
return ret;
}
bool QWindowsFontEngineDirectWrite::processHheaTable() const
{
if (!QFontEngine::processHheaTable()) {
DWRITE_FONT_METRICS metrics;
m_directWriteFontFace->GetMetrics(&metrics);
m_ascent = DESIGN_TO_LOGICAL(metrics.ascent);
m_descent = DESIGN_TO_LOGICAL(metrics.descent);
m_leading = DESIGN_TO_LOGICAL(metrics.lineGap);
}
return true;
}
void QWindowsFontEngineDirectWrite::collectMetrics()
{
DWRITE_FONT_METRICS metrics;
@ -354,11 +365,8 @@ void QWindowsFontEngineDirectWrite::collectMetrics()
m_unitsPerEm = metrics.designUnitsPerEm;
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);
m_underlinePosition = DESIGN_TO_LOGICAL(metrics.underlinePosition);
IDWriteFontFile *fontFile = nullptr;
@ -567,7 +575,7 @@ QT_WARNING_POP
}
return glyph_metrics_t(0, -m_ascent, w - lastRightBearing(glyphs), m_ascent + m_descent, w, 0);
return glyph_metrics_t(0, -ascent(), w - lastRightBearing(glyphs), ascent() + descent(), w, 0);
}
glyph_metrics_t QWindowsFontEngineDirectWrite::boundingBox(glyph_t g)
@ -608,16 +616,6 @@ QT_WARNING_POP
return glyph_metrics_t();
}
QFixed QWindowsFontEngineDirectWrite::ascent() const
{
QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
return fontDef.styleStrategy & QFont::ForceIntegerMetrics
? m_ascent.round()
: m_ascent;
QT_WARNING_POP
}
QFixed QWindowsFontEngineDirectWrite::capHeight() const
{
if (m_capHeight <= 0)
@ -631,26 +629,6 @@ QT_WARNING_DISABLE_DEPRECATED
QT_WARNING_POP
}
QFixed QWindowsFontEngineDirectWrite::descent() const
{
QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
return fontDef.styleStrategy & QFont::ForceIntegerMetrics
? m_descent.round()
: m_descent;
QT_WARNING_POP
}
QFixed QWindowsFontEngineDirectWrite::leading() const
{
QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
return fontDef.styleStrategy & QFont::ForceIntegerMetrics
? m_lineGap.round()
: m_lineGap;
QT_WARNING_POP
}
QFixed QWindowsFontEngineDirectWrite::xHeight() const
{
QT_WARNING_PUSH

8
src/platformsupport/fontdatabases/windows/qwindowsfontenginedirectwrite_p.h
View File

@ -99,10 +99,7 @@ public:
glyph_metrics_t alphaMapBoundingBox(glyph_t glyph, QFixed,
const QTransform &matrix, GlyphFormat) override;
QFixed ascent() const override;
QFixed capHeight() const override;
QFixed descent() const override;
QFixed leading() const override;
QFixed xHeight() const override;
qreal maxCharWidth() const override;
FaceId faceId() const override;
@ -125,6 +122,8 @@ public:
void setUniqueFamilyName(const QString &newName) { m_uniqueFamilyName = newName; }
bool processHheaTable() const override;
private:
QImage imageForGlyph(glyph_t t, QFixed subPixelPosition, int margin, const QTransform &xform, const QColor &color = QColor());
void collectMetrics();
@ -139,11 +138,8 @@ private:
QFixed m_lineThickness;
QFixed m_underlinePosition;
int m_unitsPerEm;
QFixed m_ascent;
QFixed m_capHeight;
QFixed m_descent;
QFixed m_xHeight;
QFixed m_lineGap;
QFixed m_maxAdvanceWidth;
FaceId m_faceId;
QString m_uniqueFamilyName;