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Improve hinted rendering quality on Windows

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When rendering hinted text on Windows with DirectWrite, the goal was
to keep the rendering and metrics as close to GDI as possible,
minimizing the impact of changing the default font backend.

Therefore, the DWRITE_RENDERING_MODE_GDI_CLASSIC was always preferred
when hinting was on.

However, DWRITE_RENDERING_MODE_GDI_CLASSIC only applies antialiasing
in the horizontal direction, but GDI applies vertical antialiasing
as well. The result is that text will look more aliased with
DirectWrite than it did with GDI, which arguably looks ugly
especially at large sizes and can be perceived as a regression.

Microsoft documentation recommends using symmetric antialiasing
when the pixel size exceeds 16, so this patch enables
DWRITE_RENDERING_MODE_NATURAL_SYMMETRIC for fonts larger than
16px regardless of whether hinting is on.

It's worth noting that for fonts with heavy hinting, such as
Times New Roman, the rendering using
DWRITE_RENDERING_MODE_NATURAL_SYMMETRIC is different from
GDI, although more similar to Freetype. However, the impact
of not having vertical antialiasing is worse and as native apps
are moving towards using DirectWrite, the GDI rendering is not
going to be the definition of a "native" look anymore.

A second thing to note in this patch is that we always pass in false
for the useGdiNatural argument in GetGdiCompatibleGlyphMetrics().
According to the documentation, we should be passing in true for text
rendered with CLEARTYPE_NATURAL_QUALITY. However, doing this causes
wider kerning in certain cases. Since the tighter kerning matches
the layouts we get in native apps, as well as when using Freetype,
I've chosen to pass false for now, to be consistent.

This change also adds a manual test which can be used to switch
between DirectWrite, GDI and Freetype rendering on Windows, so
that it's easy to compare.

[ChangeLog][Windows] Improved hinted text rendering at font sizes
larger than 16px.

Pick-to: 6.8 6.9
Fixes: QTBUG-131946
Change-Id: Iebbe5c7affe7df6266ade6b161c31bde3d2caa84
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>
This commit is contained in:
Eskil Abrahamsen Blomfeldt 2024-12-09 13:27:10 +01:00
parent eb03784510
commit 407a98d94f
6 changed files with 479 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

51
src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
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@ -163,27 +163,39 @@ static DWRITE_MEASURING_MODE renderModeToMeasureMode(DWRITE_RENDERING_MODE rende
}
}
static QFont::HintingPreference determineHinting(const QFontDef &fontDef)
{
QFont::HintingPreference hintingPreference = QFont::HintingPreference(fontDef.hintingPreference);
if (hintingPreference == QFont::PreferDefaultHinting) {
if (!qFuzzyCompare(qApp->devicePixelRatio(), 1.0)) {
// Microsoft documentation recommends using asymmetric rendering for small fonts
// at pixel size 16 and less, and symmetric for larger fonts.
hintingPreference = fontDef.pixelSize > 16.0
? QFont::PreferNoHinting
: QFont::PreferVerticalHinting;
} else {
hintingPreference = QFont::PreferFullHinting;
}
}
return hintingPreference;
}
DWRITE_RENDERING_MODE QWindowsFontEngineDirectWrite::hintingPreferenceToRenderingMode(const QFontDef &fontDef) const
{
if ((fontDef.styleStrategy & QFont::NoAntialias) && glyphFormat != QFontEngine::Format_ARGB)
return DWRITE_RENDERING_MODE_ALIASED;
QFont::HintingPreference hintingPreference = QFont::HintingPreference(fontDef.hintingPreference);
if (!qFuzzyCompare(qApp->devicePixelRatio(), 1.0) && hintingPreference == QFont::PreferDefaultHinting) {
// Microsoft documentation recommends using asymmetric rendering for small fonts
// at pixel size 16 and less, and symmetric for larger fonts.
hintingPreference = fontDef.pixelSize > 16.0
? QFont::PreferNoHinting
: QFont::PreferVerticalHinting;
}
QFont::HintingPreference hintingPreference = determineHinting(fontDef);
switch (hintingPreference) {
case QFont::PreferNoHinting:
return DWRITE_RENDERING_MODE_CLEARTYPE_NATURAL_SYMMETRIC;
case QFont::PreferVerticalHinting:
return DWRITE_RENDERING_MODE_CLEARTYPE_NATURAL;
default:
return DWRITE_RENDERING_MODE_CLEARTYPE_GDI_CLASSIC;
return fontDef.pixelSize > 16.0
? DWRITE_RENDERING_MODE_NATURAL_SYMMETRIC
: DWRITE_RENDERING_MODE_GDI_CLASSIC;
}
}
@ -558,15 +570,17 @@ void QWindowsFontEngineDirectWrite::recalcAdvances(QGlyphLayout *glyphs, QFontEn
QVarLengthArray<DWRITE_GLYPH_METRICS> glyphMetrics(glyphIndices.size());
HRESULT hr;
DWRITE_RENDERING_MODE renderMode = hintingPreferenceToRenderingMode(fontDef);
QFont::HintingPreference hint = determineHinting(fontDef);
bool needsDesignMetrics = shaperFlags & QFontEngine::DesignMetrics;
if (!needsDesignMetrics && (renderMode == DWRITE_RENDERING_MODE_GDI_CLASSIC
|| renderMode == DWRITE_RENDERING_MODE_GDI_NATURAL
|| renderMode == DWRITE_RENDERING_MODE_ALIASED)) {
if (!needsDesignMetrics && hint == QFont::PreferFullHinting) {
const DWRITE_RENDERING_MODE renderMode = hintingPreferenceToRenderingMode(fontDef);
const bool needsNaturalMetrics = renderMode == DWRITE_RENDERING_MODE_NATURAL
|| renderMode == DWRITE_RENDERING_MODE_NATURAL_SYMMETRIC;
hr = m_directWriteFontFace->GetGdiCompatibleGlyphMetrics(float(fontDef.pixelSize),
1.0f,
NULL,
renderMode == DWRITE_RENDERING_MODE_GDI_NATURAL,
needsNaturalMetrics,
glyphIndices.data(),
glyphIndices.size(),
glyphMetrics.data());
@ -763,11 +777,10 @@ QImage QWindowsFontEngineDirectWrite::alphaMapForGlyph(glyph_t glyph,
bool QWindowsFontEngineDirectWrite::supportsHorizontalSubPixelPositions() const
{
DWRITE_RENDERING_MODE renderMode = hintingPreferenceToRenderingMode(fontDef);
QFont::HintingPreference hinting = determineHinting(fontDef);
return (!isColorFont()
&& renderMode != DWRITE_RENDERING_MODE_GDI_CLASSIC
&& renderMode != DWRITE_RENDERING_MODE_GDI_NATURAL
&& renderMode != DWRITE_RENDERING_MODE_ALIASED);
&& hinting != QFont::PreferFullHinting
&& !(fontDef.styleStrategy & QFont::NoAntialias));
}
QFontEngine::Properties QWindowsFontEngineDirectWrite::properties() const

21
tests/manual/textrendering/fontenginecomparison/CMakeLists.txt Normal file
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@ -0,0 +1,21 @@
# Copyright (C) 2025 The Qt Company Ltd.
# SPDX-License-Identifier: BSD-3-Clause
if(NOT QT_BUILD_STANDALONE_TESTS AND NOT QT_BUILDING_QT)
cmake_minimum_required(VERSION 3.16)
project(vrs LANGUAGES CXX)
find_package(Qt6BuildInternals REQUIRED COMPONENTS STANDALONE_TEST)
endif()
qt_internal_add_manual_test(fontenginecomparison
GUI
SOURCES
main.cpp
mainwindow.cpp mainwindow.h mainwindow.ui
LIBRARIES
Qt::Gui
Qt::Widgets
ENABLE_AUTOGEN_TOOLS
uic
)

51
tests/manual/textrendering/fontenginecomparison/main.cpp Normal file
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@ -0,0 +1,51 @@
// Copyright (C) 2025 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
#include "mainwindow.h"
#include <QtGui>
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
if (a.arguments().size() > 5) {
QString fontFamily = a.arguments().at(1);
int fontSize = a.arguments().at(2).toInt();
QString example = a.arguments().at(3);
int weight = a.arguments().at(4).toInt();
bool isItalic = a.arguments().at(5).toInt();
QFont font(fontFamily);
font.setPixelSize(fontSize);
font.setWeight(QFont::Weight(weight));
font.setItalic(isItalic);
QTextLayout layout;
layout.setFont(font);
layout.setText(example);
layout.beginLayout();
layout.createLine();
layout.endLayout();
QRect brect = layout.boundingRect().toAlignedRect();
QImage image(brect.size(), QImage::Format_RGB32);
image.fill(Qt::white);
image.setDevicePixelRatio(1.0);
QPainter p;
p.begin(&image);
layout.draw(&p, -brect.topLeft());
p.end();
image.save(QStringLiteral("output.png"));
return 0;
} else {
MainWindow w;
w.show();
return a.exec();
}
}

86
tests/manual/textrendering/fontenginecomparison/mainwindow.cpp Normal file
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@ -0,0 +1,86 @@
// Copyright (C) 2025 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QProcess>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
ui->cbWeight->addItem(QStringLiteral("Thin"), QFont::Thin);
ui->cbWeight->addItem(QStringLiteral("ExtraLight"), QFont::ExtraLight);
ui->cbWeight->addItem(QStringLiteral("Light"), QFont::Light);
ui->cbWeight->addItem(QStringLiteral("Normal"), QFont::Normal);
ui->cbWeight->addItem(QStringLiteral("Medium"), QFont::Medium);
ui->cbWeight->addItem(QStringLiteral("DemiBold"), QFont::DemiBold);
ui->cbWeight->addItem(QStringLiteral("Bold"), QFont::Bold);
ui->cbWeight->addItem(QStringLiteral("ExtraBold"), QFont::ExtraBold);
ui->cbWeight->addItem(QStringLiteral("Black"), QFont::Black);
ui->cbWeight->setCurrentIndex(3);
updateFont();
connect(ui->sbPixelSize, &QSpinBox::valueChanged, this, &MainWindow::updateFont);
connect(ui->fontComboBox, &QFontComboBox::currentFontChanged, this, &MainWindow::updateFont);
connect(ui->rbDefault, &QRadioButton::toggled, this, &MainWindow::updateFont);
connect(ui->rbGdi, &QRadioButton::toggled, this, &MainWindow::updateFont);
connect(ui->rbFreetype, &QRadioButton::toggled, this, &MainWindow::updateFont);
connect(ui->leText, &QLineEdit::textChanged, this, &MainWindow::updateFont);
connect(ui->cbWeight, &QComboBox::currentIndexChanged, this, &MainWindow::updateFont);
connect(ui->cbItalic, &QCheckBox::toggled, this, &MainWindow::updateFont);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::updateImage()
{
if (m_process == nullptr)
return;
QImage img(QStringLiteral("output.png"));
if (!img.isNull())
ui->lImage->setPixmap(QPixmap::fromImage(img));
}
void MainWindow::updateFont()
{
if (m_process == nullptr) {
m_process = new QProcess;
connect(m_process, &QProcess::finished, this, &MainWindow::updateImage);
}
if (m_process->isOpen())
m_process->close();
QString fontEngineName = QStringLiteral("directwrite");
if (ui->rbGdi->isChecked())
fontEngineName = QStringLiteral("gdi");
else if (ui->rbFreetype->isChecked())
fontEngineName = QStringLiteral("freetype");
QProcessEnvironment env;
env.insert(QStringLiteral("QT_QPA_PLATFORM"), QStringLiteral("windows:fontengine=%1").arg(fontEngineName));
env.insert(QStringLiteral("windir"), qgetenv("windir"));
m_process->setProcessEnvironment(env);
QStringList args;
args.append(ui->fontComboBox->currentFont().family());
args.append(QString::number(ui->sbPixelSize->value()));
args.append(ui->leText->text().isEmpty()
? QStringLiteral("The quick brown fox jumps over the lazy dog")
: ui->leText->text());
args.append(QString::number(ui->cbWeight->currentData().toInt()));
args.append(QString::number(int(ui->cbItalic->isChecked())));
m_process->start(qApp->arguments().first(), args);
m_process->waitForFinished();
}

35
tests/manual/textrendering/fontenginecomparison/mainwindow.h Normal file
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@ -0,0 +1,35 @@
// Copyright (C) 2025 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QProcess>
QT_BEGIN_NAMESPACE
namespace Ui {
class MainWindow;
}
QT_END_NAMESPACE
class FontEngineRenderer;
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
public slots:
void updateFont();
void updateImage();
private:
Ui::MainWindow *ui;
FontEngineRenderer *m_renderer = nullptr;
QProcess *m_process = nullptr;
};
#endif // MAINWINDOW_H

254
tests/manual/textrendering/fontenginecomparison/mainwindow.ui Normal file
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@ -0,0 +1,254 @@
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>800</width>
<height>600</height>
</rect>
</property>
<property name="palette">
<palette>
<active>
<colorrole role="Window">
<brush brushstyle="SolidPattern">
<color alpha="255">
<red>255</red>
<green>255</green>
<blue>255</blue>
</color>
</brush>
</colorrole>
</active>
<inactive>
<colorrole role="Window">
<brush brushstyle="SolidPattern">
<color alpha="255">
<red>255</red>
<green>255</green>
<blue>255</blue>
</color>
</brush>
</colorrole>
</inactive>
<disabled>
<colorrole role="Base">
<brush brushstyle="SolidPattern">
<color alpha="255">
<red>255</red>
<green>255</green>
<blue>255</blue>
</color>
</brush>
</colorrole>
<colorrole role="Window">
<brush brushstyle="SolidPattern">
<color alpha="255">
<red>255</red>
<green>255</green>
<blue>255</blue>
</color>
</brush>
</colorrole>
</disabled>
</palette>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<widget class="QWidget" name="centralwidget">
<layout class="QVBoxLayout" name="verticalLayout_2">
<item>
<widget class="QGroupBox" name="gbExamples">
<property name="palette">
<palette>
<active>
<colorrole role="Window">
<brush brushstyle="SolidPattern">
<color alpha="255">
<red>255</red>
<green>255</green>
<blue>255</blue>
</color>
</brush>
</colorrole>
</active>
<inactive>
<colorrole role="Window">
<brush brushstyle="SolidPattern">
<color alpha="255">
<red>255</red>
<green>255</green>
<blue>255</blue>
</color>
</brush>
</colorrole>
</inactive>
<disabled>
<colorrole role="Base">
<brush brushstyle="SolidPattern">
<color alpha="255">
<red>255</red>
<green>255</green>
<blue>255</blue>
</color>
</brush>
</colorrole>
<colorrole role="Window">
<brush brushstyle="SolidPattern">
<color alpha="255">
<red>255</red>
<green>255</green>
<blue>255</blue>
</color>
</brush>
</colorrole>
</disabled>
</palette>
</property>
<property name="title">
<string>Examples</string>
</property>
<layout class="QVBoxLayout" name="verticalLayout_3">
<item>
<widget class="QLabel" name="lImage">
<property name="text">
<string/>
</property>
</widget>
</item>
</layout>
</widget>
</item>
<item>
<widget class="QGroupBox" name="groupBox_2">
<property name="title">
<string>Text settings</string>
</property>
<layout class="QVBoxLayout" name="verticalLayout">
<item>
<widget class="QLineEdit" name="leText">
<property name="text">
<string>The quick brown fox jumps over the lazy dog</string>
</property>
</widget>
</item>
<item>
<widget class="QFontComboBox" name="fontComboBox"/>
</item>
<item>
<layout class="QHBoxLayout" name="horizontalLayout_3">
<item>
<widget class="QComboBox" name="cbWeight"/>
</item>
<item>
<widget class="QCheckBox" name="cbItalic">
<property name="sizePolicy">
<sizepolicy hsizetype="MinimumExpanding" vsizetype="Fixed">
<horstretch>0</horstretch>
<verstretch>0</verstretch>
</sizepolicy>
</property>
<property name="text">
<string>Italic</string>
</property>
</widget>
</item>
</layout>
</item>
<item>
<layout class="QHBoxLayout" name="horizontalLayout_2">
<item>
<widget class="QLabel" name="label">
<property name="text">
<string>Pixel size:</string>
</property>
</widget>
</item>
<item>
<widget class="QSpinBox" name="sbPixelSize">
<property name="minimum">
<number>1</number>
</property>
<property name="value">
<number>30</number>
</property>
</widget>
</item>
<item>
<spacer name="horizontalSpacer">
<property name="orientation">
<enum>Qt::Orientation::Horizontal</enum>
</property>
<property name="sizeHint" stdset="0">
<size>
<width>40</width>
<height>20</height>
</size>
</property>
</spacer>
</item>
</layout>
</item>
</layout>
</widget>
</item>
<item>
<widget class="QGroupBox" name="groupBox">
<property name="title">
<string>Font engines</string>
</property>
<layout class="QHBoxLayout" name="horizontalLayout">
<item>
<widget class="QRadioButton" name="rbDefault">
<property name="text">
<string>Default</string>
</property>
<property name="checked">
<bool>true</bool>
</property>
</widget>
</item>
<item>
<widget class="QRadioButton" name="rbGdi">
<property name="text">
<string>GDI</string>
</property>
</widget>
</item>
<item>
<widget class="QRadioButton" name="rbFreetype">
<property name="enabled">
<bool>true</bool>
</property>
<property name="text">
<string>Freetype</string>
</property>
<property name="checked">
<bool>false</bool>
</property>
</widget>
</item>
</layout>
</widget>
</item>
</layout>
</widget>
<widget class="QMenuBar" name="menubar">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>800</width>
<height>22</height>
</rect>
</property>
</widget>
<widget class="QStatusBar" name="statusbar"/>
</widget>
<resources/>
<connections/>
</ui>