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Add API to disable text shaping on fonts

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In the past, we had an undocumented text flag that worked with
one of the QPainter::drawText() overloads. This was never intended
as public API and served a specific cause in Qt WebKit at one point.

But there is a general need for such API, as disabling shaping features
easily gives 25% performance improvement on text rendering even for
fairly short strings.

This patch adds a new style strategy flag to disable shaping and
will just uses the CMAP and HDMX tables to get glyph indices and advances
for the characters. In Qt 6, the TextBypassShaping flag can be removed
completely and be replaced by the style strategy.

[ChangeLog][QtGui][Text] Added QFont::PreferNoShaping style strategy to support
improvements to performance at the expense of some cosmetic font features.

Task-number: QTBUG-56728
Change-Id: I48e025dcc06afe02824bf5b5011702a7e0036f6d
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
This commit is contained in:
Eskil Abrahamsen Blomfeldt 2017-07-03 11:30:43 +02:00
parent 8719660416
commit 73176d2922
10 changed files with 144 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
src/corelib/global/qnamespace.h
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@ -241,8 +241,11 @@ public:
TextForceRightToLeft = 0x40000,
// Ensures that the longest variant is always used when computing the
// size of a multi-variant string.
TextLongestVariant = 0x80000,
TextBypassShaping = 0x100000
TextLongestVariant = 0x80000
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
, TextBypassShaping = 0x100000
#endif
};
enum TextElideMode {

2
src/gui/painting/qpainter.cpp
View File

@ -5850,6 +5850,7 @@ void QPainter::drawText(const QPointF &p, const QString &str, int tf, int justif
if (!d->engine || str.isEmpty() || pen().style() == Qt::NoPen)
return;
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
if (tf & Qt::TextBypassShaping) {
// Skip complex shaping, shape using glyph advances only
int len = str.length();
@ -5863,6 +5864,7 @@ void QPainter::drawText(const QPointF &p, const QString &str, int tf, int justif
drawTextItem(p, gf);
return;
}
#endif
QStackTextEngine engine(str, d->state->font);
engine.option.setTextDirection(d->state->layoutDirection);

5
src/gui/text/qfont.cpp
View File

@ -1312,6 +1312,11 @@ QFont::StyleHint QFont::styleHint() const
looking font that contains the character. The NoFontMerging flag disables this feature.
Please note that enabling this flag will not prevent Qt from automatically picking a
suitable font when the selected font does not support the writing system of the text.
\value PreferNoShaping Sometimes, a font will apply complex rules to a set of characters in
order to display them correctly. In some writing systems, such as Brahmic scripts, this is
required in order for the text to be legible, but in e.g. Latin script, it is merely
a cosmetic feature. The PreferNoShaping flag will disable all such features when they
are not required, which will improve performance in most cases.
Any of these may be OR-ed with one of these flags:

1
src/gui/text/qfont.h
View File

@ -83,6 +83,7 @@ public:
OpenGLCompatible = 0x0200,
ForceIntegerMetrics = 0x0400,
NoSubpixelAntialias = 0x0800,
PreferNoShaping = 0x1000,
NoFontMerging = 0x8000
};
Q_ENUM(StyleStrategy)

4
src/gui/text/qfontengine.cpp
View File

@ -359,10 +359,8 @@ bool QFontEngine::supportsScript(QChar::Script script) const
// ### TODO: This only works for scripts that require OpenType. More generally
// for scripts that do not require OpenType we should just look at the list of
// supported writing systems in the font's OS/2 table.
if (!((script >= QChar::Script_Syriac && script <= QChar::Script_Sinhala)
|| script == QChar::Script_Khmer || script == QChar::Script_Nko)) {
if (!scriptRequiresOpenType(script))
return true;
}
#if QT_CONFIG(harfbuzz)
if (qt_useHarfbuzzNG()) {

6
src/gui/text/qfontengine_p.h
View File

@ -242,6 +242,12 @@ public:
void *harfbuzzFace() const;
bool supportsScript(QChar::Script script) const;
inline static bool scriptRequiresOpenType(QChar::Script script)
{
return ((script >= QChar::Script_Syriac && script <= QChar::Script_Sinhala)
|| script == QChar::Script_Khmer || script == QChar::Script_Nko);
}
virtual int getPointInOutline(glyph_t glyph, int flags, quint32 point, QFixed *xpos, QFixed *ypos, quint32 *nPoints);
void clearGlyphCache(const void *key);

2
src/gui/text/qfontmetrics.cpp
View File

@ -541,6 +541,7 @@ int QFontMetrics::width(const QString &text, int len, int flags) const
if (len == 0)
return 0;
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
if (flags & Qt::TextBypassShaping) {
// Skip complex shaping, only use advances
int numGlyphs = len;
@ -554,6 +555,7 @@ int QFontMetrics::width(const QString &text, int len, int flags) const
width += glyphs.advances[i];
return qRound(width);
}
#endif
QStackTextEngine layout(text, QFont(d.data()));
return qRound(layout.width(0, len));

85
src/gui/text/qtextengine.cpp
View File

@ -1005,20 +1005,53 @@ void QTextEngine::shapeText(int item) const
QFontEngine *fontEngine = this->fontEngine(si, &si.ascent, &si.descent, &si.leading);
bool kerningEnabled;
bool letterSpacingIsAbsolute;
bool shapingEnabled;
QFixed letterSpacing, wordSpacing;
#ifndef QT_NO_RAWFONT
if (useRawFont) {
QTextCharFormat f = format(&si);
kerningEnabled = f.fontKerning();
shapingEnabled = QFontEngine::scriptRequiresOpenType(QChar::Script(si.analysis.script))
|| (f.fontStyleStrategy() & QFont::PreferNoShaping) == 0;
wordSpacing = QFixed::fromReal(f.fontWordSpacing());
letterSpacing = QFixed::fromReal(f.fontLetterSpacing());
letterSpacingIsAbsolute = true;
} else
#endif
{
QFont font = this->font(si);
kerningEnabled = font.d->kerning;
shapingEnabled = QFontEngine::scriptRequiresOpenType(QChar::Script(si.analysis.script))
|| (font.d->request.styleStrategy & QFont::PreferNoShaping) == 0;
letterSpacingIsAbsolute = font.d->letterSpacingIsAbsolute;
letterSpacing = font.d->letterSpacing;
wordSpacing = font.d->wordSpacing;
if (letterSpacingIsAbsolute && letterSpacing.value())
letterSpacing *= font.d->dpi / qt_defaultDpiY();
}
// split up the item into parts that come from different font engines
// k * 3 entries, array[k] == index in string, array[k + 1] == index in glyphs, array[k + 2] == engine index
QVector<uint> itemBoundaries;
itemBoundaries.reserve(24);
if (fontEngine->type() == QFontEngine::Multi) {
QGlyphLayout initialGlyphs = availableGlyphs(&si);
int nGlyphs = initialGlyphs.numGlyphs;
if (fontEngine->type() == QFontEngine::Multi || !shapingEnabled) {
// ask the font engine to find out which glyphs (as an index in the specific font)
// to use for the text in one item.
QGlyphLayout initialGlyphs = availableGlyphs(&si);
int nGlyphs = initialGlyphs.numGlyphs;
QFontEngine::ShaperFlags shaperFlags(QFontEngine::GlyphIndicesOnly);
QFontEngine::ShaperFlags shaperFlags =
shapingEnabled
? QFontEngine::GlyphIndicesOnly
: QFontEngine::ShaperFlag(0);
if (!fontEngine->stringToCMap(reinterpret_cast<const QChar *>(string), itemLength, &initialGlyphs, &nGlyphs, shaperFlags))
Q_UNREACHABLE();
}
if (fontEngine->type() == QFontEngine::Multi) {
uint lastEngine = ~0u;
for (int i = 0, glyph_pos = 0; i < itemLength; ++i, ++glyph_pos) {
const uint engineIdx = initialGlyphs.glyphs[glyph_pos] >> 24;
@ -1046,35 +1079,29 @@ void QTextEngine::shapeText(int item) const
itemBoundaries.append(0);
}
bool kerningEnabled;
bool letterSpacingIsAbsolute;
QFixed letterSpacing, wordSpacing;
#ifndef QT_NO_RAWFONT
if (useRawFont) {
QTextCharFormat f = format(&si);
kerningEnabled = f.fontKerning();
wordSpacing = QFixed::fromReal(f.fontWordSpacing());
letterSpacing = QFixed::fromReal(f.fontLetterSpacing());
letterSpacingIsAbsolute = true;
} else
#endif
{
QFont font = this->font(si);
kerningEnabled = font.d->kerning;
letterSpacingIsAbsolute = font.d->letterSpacingIsAbsolute;
letterSpacing = font.d->letterSpacing;
wordSpacing = font.d->wordSpacing;
if (Q_UNLIKELY(!shapingEnabled)) {
ushort *log_clusters = logClusters(&si);
if (letterSpacingIsAbsolute && letterSpacing.value())
letterSpacing *= font.d->dpi / qt_defaultDpiY();
}
int glyph_pos = 0;
for (int i = 0; i < itemLength; ++i, ++glyph_pos) {
log_clusters[i] = glyph_pos;
initialGlyphs.attributes[glyph_pos].clusterStart = true;
if (QChar::isHighSurrogate(string[i])
&& i + 1 < itemLength
&& QChar::isLowSurrogate(string[i + 1])) {
++i;
log_clusters[i] = glyph_pos;
}
}
si.num_glyphs = glyph_pos;
#if QT_CONFIG(harfbuzz)
if (Q_LIKELY(qt_useHarfbuzzNG()))
} else if (Q_LIKELY(qt_useHarfbuzzNG())) {
si.num_glyphs = shapeTextWithHarfbuzzNG(si, string, itemLength, fontEngine, itemBoundaries, kerningEnabled, letterSpacing != 0);
else
#endif
si.num_glyphs = shapeTextWithHarfbuzz(si, string, itemLength, fontEngine, itemBoundaries, kerningEnabled);
} else {
si.num_glyphs = shapeTextWithHarfbuzz(si, string, itemLength, fontEngine, itemBoundaries, kerningEnabled);
}
if (Q_UNLIKELY(si.num_glyphs == 0)) {
Q_UNREACHABLE(); // ### report shaping errors somehow
return;

6
tests/auto/gui/text/qfontmetrics/tst_qfontmetrics.cpp
View File

@ -47,7 +47,11 @@ private slots:
void elidedText();
void veryNarrowElidedText();
void averageCharWidth();
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
void bypassShaping();
#endif
void elidedMultiLength();
void elidedMultiLengthF();
void inFontUcs4();
@ -187,6 +191,7 @@ void tst_QFontMetrics::averageCharWidth()
QVERIFY(fmf.averageCharWidth() != 0);
}
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
void tst_QFontMetrics::bypassShaping()
{
QFont f;
@ -201,6 +206,7 @@ void tst_QFontMetrics::bypassShaping()
// This assertion is needed in Qt WebKit's WebCore::Font::offsetForPositionForSimpleText
QCOMPARE(textWidth, charsWidth);
}
#endif
template<class FontMetrics, typename PrimitiveType> void elidedMultiLength_helper()
{

60
tests/auto/gui/text/qtextscriptengine/tst_qtextscriptengine.cpp
View File

@ -78,6 +78,9 @@ private slots:
void thaiIsolatedSaraAm();
void thaiWithZWJ();
void thaiMultipleVowels();
void shapingDisabledDevanagari();
void shapingDisabledLatin();
private:
bool haveTestFonts;
};
@ -1280,5 +1283,62 @@ void tst_QTextScriptEngine::thaiMultipleVowels()
// If we haven't crashed at this point, then the test has passed.
}
void tst_QTextScriptEngine::shapingDisabledLatin()
{
QString s("fi");
QFont font("Calibri");
font.setStyleStrategy(QFont::PreferNoShaping);
QTextLayout layout(s);
layout.setFont(font);
layout.beginLayout();
layout.createLine();
layout.endLayout();
QList<QGlyphRun> runs = layout.glyphRuns();
QCOMPARE(runs.size(), 1);
QCOMPARE(runs.first().glyphIndexes().size(), 2);
}
void tst_QTextScriptEngine::shapingDisabledDevanagari()
{
QString s;
s += QChar(0x0915); // KA
s += QChar(0x094D); // VIRAMA
s += QChar(0x0915); // KA
QList<QGlyphRun> normalRuns;
{
QTextLayout layout(s);
layout.beginLayout();
layout.createLine();
layout.endLayout();
normalRuns = layout.glyphRuns();
}
QFont font;
font.setStyleStrategy(QFont::PreferNoShaping);
QList<QGlyphRun> noShapingRuns;
{
QTextLayout layout(s);
layout.setFont(font);
layout.beginLayout();
layout.createLine();
layout.endLayout();
noShapingRuns = layout.glyphRuns();
}
// Even though shaping is disabled, Devanagari requires it, so the flag should be ignored.
QCOMPARE(normalRuns.size(), 1);
QCOMPARE(noShapingRuns.size(), 1);
QCOMPARE(noShapingRuns.first().glyphIndexes().size(), normalRuns.first().glyphIndexes().size());
}
QTEST_MAIN(tst_QTextScriptEngine)
#include "tst_qtextscriptengine.moc"