The QPlatformFontDatabase class makes it possible to customize how fonts are discovered and how they are rendered. More...

#include <qplatformfontdatabase.h>

Inheritance diagram for QPlatformFontDatabase:

Collaboration diagram for QPlatformFontDatabase:

Public Member Functions
virtual	~QPlatformFontDatabase ()

virtual void	populateFontDatabase ()
	This function is called once at startup by Qt's internal font database.

virtual bool	populateFamilyAliases (const QString &missingFamily)

virtual void	populateFamily (const QString &familyName)
	This function is called whenever a lazily populated family, populated through registerFontFamily(), needs full population.

virtual void	invalidate ()
	This function is called whenever the font database is invalidated.

virtual QStringList	fallbacksForFamily (const QString &family, QFont::Style style, QFont::StyleHint styleHint, QChar::Script script) const
	Returns a list of alternative fonts for the specified family and style and script using the styleHint given.

virtual QStringList	addApplicationFont (const QByteArray &fontData, const QString &fileName, QFontDatabasePrivate::ApplicationFont *font=nullptr)
	Adds an application font described by the font contained supplied fontData or using the font contained in the file referenced by fileName.

virtual QFontEngine *	fontEngine (const QFontDef &fontDef, void *handle)
	Returns the font engine that can be used to render the font described by the font definition, fontDef, in the specified script.

virtual QFontEngine *	fontEngine (const QByteArray &fontData, qreal pixelSize, QFont::HintingPreference hintingPreference)
	Returns the font engine that will be used to back a QRawFont, based on the given \fontData, pixelSize, and hintingPreference.

virtual QFontEngineMulti *	fontEngineMulti (QFontEngine *fontEngine, QChar::Script script)
	Returns a multi font engine in the specified script to encapsulate fontEngine with the option to fall back to the fonts given by fallbacks if fontEngine does not support a certain character.

virtual void	releaseHandle (void *handle)
	Releases the specified font handle.

virtual QString	fontDir () const
	Returns the directory containing the fonts used by the database.

virtual QFont	defaultFont () const
	Returns the default system font.

virtual bool	isPrivateFontFamily (const QString &family) const
	Returns true if the font family is private.

virtual QString	resolveFontFamilyAlias (const QString &family) const
	Resolve alias to actual font family names.

virtual bool	fontsAlwaysScalable () const
	Return true if all fonts are considered scalable when using this font database.

virtual QList< int >	standardSizes () const
	Return list of standard font sizes when using this font database.

virtual bool	supportsVariableApplicationFonts () const
	Returns true if this font database supports loading named instances from variable application fonts.

Static Public Member Functions
static QSupportedWritingSystems	writingSystemsFromTrueTypeBits (quint32 unicodeRange[4], quint32 codePageRange[2])
	Helper function that determines the writing systems support by a given unicodeRange and codePageRange.

static QSupportedWritingSystems	writingSystemsFromOS2Table (const char *os2Table, size_t length)
	Helper function that determines the writing system support based on the contents of the OS/2 table in the font.

static void	registerFont (const QString &familyname, const QString &stylename, const QString &foundryname, QFont::Weight weight, QFont::Style style, QFont::Stretch stretch, bool antialiased, bool scalable, int pixelSize, bool fixedPitch, const QSupportedWritingSystems &writingSystems, void *handle)
	Registers a font with the given set of attributes describing the font's foundry, family name, style and stretch information, pixel size, and supported writing systems.

static void	registerFontFamily (const QString &familyName)
	Registers a font family with the font database.

static void	registerAliasToFontFamily (const QString &familyName, const QString &alias)
	Helper function that register the alias for the familyName.

static void	repopulateFontDatabase ()
	Requests that the platform font database should be repopulated.

static bool	isFamilyPopulated (const QString &familyName)
	Helper function that returns true if the font family has already been registered and populated.

Detailed Description

The QPlatformFontDatabase class makes it possible to customize how fonts are discovered and how they are rendered.

Since: 5.0

\preliminary

QPlatformFontDatabase is the superclass which is intended to let platform implementations use native font handling.

Qt has its internal font database which it uses to discover available fonts on the user's system. To be able to populate this database subclass this class, and reimplement populateFontDatabase().

Use the function registerFont() to populate the internal font database.

Sometimes a specified font does not have the required glyphs; in such a case, the fallbackForFamily() function is called automatically to find alternative font families that can supply alternatives to the missing glyphs.

See also: QSupportedWritingSystems

Definition at line 66 of file qplatformfontdatabase.h.

Constructor & Destructor Documentation

◆ ~QPlatformFontDatabase()

QPlatformFontDatabase::~QPlatformFontDatabase ( )

virtual

Definition at line 227 of file qplatformfontdatabase.cpp.

Member Function Documentation

◆ addApplicationFont()

QStringList QPlatformFontDatabase::addApplicationFont	(	const QByteArray &	fontData,
		const QString &	fileName,
		QFontDatabasePrivate::ApplicationFont *	applicationFont = nullptr )

virtual

Adds an application font described by the font contained supplied fontData or using the font contained in the file referenced by fileName.

Returns a list of family names, or an empty list if the font could not be added.

If applicationFont is non-null, its properties list should be filled with information from the loaded fonts. This is exposed through FontLoader in Qt Quick where it is needed for disambiguating fonts in the same family. When the function exits, the applicationFont should contain an entry of properties per font in the file, or it should be empty if no font was loaded.

Note: The default implementation of this function does not add an application font. Subclasses should reimplement this function to perform the necessary loading and registration of fonts.

Reimplemented in QCoreTextFontDatabase, QFreeTypeFontDatabase, QFontconfigDatabase, QWindowsFontDatabase, and QWindowsDirectWriteFontDatabase.

Definition at line 334 of file qplatformfontdatabase.cpp.

References fileName, Q_UNUSED, and qWarning.

◆ defaultFont()

QFont QPlatformFontDatabase::defaultFont ( ) const

virtual

Returns the default system font.

See also: QGuiApplication::font()

Since: 5.0

Reimplemented in QCoreTextFontDatabase, QFontconfigDatabase, QWindowsDirectWriteFontDatabase, QWindowsFontDatabaseFT, QWindowsFontDatabase, QAndroidPlatformFontDatabase, and QWasmFontDatabase.

Definition at line 386 of file qplatformfontdatabase.cpp.

◆ fallbacksForFamily()

QStringList QPlatformFontDatabase::fallbacksForFamily	(	const QString &	family,
		QFont::Style	style,
		QFont::StyleHint	styleHint,
		QChar::Script	script ) const

virtual

Returns a list of alternative fonts for the specified family and style and script using the styleHint given.

Default implementation returns a list of fonts for which style and script support has been reported during the font database population.

Reimplemented in QCoreTextFontDatabase, QFontconfigDatabase, QWindowsDirectWriteFontDatabase, QWindowsFontDatabaseFT, QWindowsFontDatabase, QAndroidPlatformFontDatabase, and QWasmFontDatabase.

Definition at line 623 of file qfontdatabase.cpp.

References QFontDatabase::Any, QString::append(), QtFontFoundry::count, db, familySupportsWritingSystem(), i, QFontDatabasePrivate::instance(), QString::isEmpty(), j, QtFontStyle::key, QtFontFoundry::name, Q_UNUSED, qt_writing_system_for_script(), QtFontStyle::Key::style, QtFontFoundry::styles, and QFontDatabase::WritingSystemsCount.

Referenced by QWindowsDirectWriteFontDatabase::fallbacksForFamily(), QWindowsFontDatabaseFT::fallbacksForFamily(), QWindowsFontDatabase::fallbacksForFamily(), QAndroidPlatformFontDatabase::fallbacksForFamily(), and QWasmFontDatabase::fallbacksForFamily().

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◆ fontDir()

QString QPlatformFontDatabase::fontDir ( ) const

virtual

Returns the directory containing the fonts used by the database.

Reimplemented in QWindowsFontDatabaseFT, QWindowsFontDatabase, and QAndroidPlatformFontDatabase.

Definition at line 360 of file qplatformfontdatabase.cpp.

References QString::fromLocal8Bit(), QLibraryInfo::LibrariesPath, QLibraryInfo::path(), and qgetenv().

Referenced by QWindowsFontDatabase::fontDir(), and QFreeTypeFontDatabase::populateFontDatabase().

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◆ fontEngine() [1/2]

QFontEngine * QPlatformFontDatabase::fontEngine	(	const QByteArray &	fontData,
		qreal	pixelSize,
		QFont::HintingPreference	hintingPreference )

virtual

Returns the font engine that will be used to back a QRawFont, based on the given \fontData, pixelSize, and hintingPreference.

This function is called by QRawFont, and does not play a part in the normal operations of QFontDatabase.

Reimplemented in QCoreTextFontDatabaseEngineFactory< T >, QFreeTypeFontDatabase, QFontconfigDatabase, QWindowsDirectWriteFontDatabase, QWindowsFontDatabaseFT, QWindowsFontDatabase, and QWindowsFontDatabaseBase.

Definition at line 309 of file qplatformfontdatabase.cpp.

References Q_UNUSED, and qWarning.

◆ fontEngine() [2/2]

QFontEngine * QPlatformFontDatabase::fontEngine	(	const QFontDef &	fontDef,
		void *	handle )

virtual

Returns the font engine that can be used to render the font described by the font definition, fontDef, in the specified script.

This function is called by QFontDatabase both for system fonts provided by the platform font database, as well as for application fonts added by the application developer.

The handle is the QPlatformFontDatabase specific handle passed when registering the font family via QPlatformFontDatabase::registerFont.

The function is called for both fonts added via a filename as well as fonts added from QByteArray data. Subclasses will need to handle both cases via its platform specific handle.

Reimplemented in QCoreTextFontDatabaseEngineFactory< T >, QFreeTypeFontDatabase, QFontconfigDatabase, QWindowsDirectWriteFontDatabase, QWindowsFontDatabaseFT, QWindowsFontDatabase, QWindowsFontDatabaseBase, QWasmFontDatabase, QCoreTextFontDatabaseEngineFactory< T >, and QCoreTextFontDatabaseEngineFactory< T >.

Definition at line 294 of file qplatformfontdatabase.cpp.

References Q_UNUSED, and qWarning.

Referenced by QWindowsFontDatabaseBase::fontEngine(), and fontEngineMulti().

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◆ fontEngineMulti()

QFontEngineMulti * QPlatformFontDatabase::fontEngineMulti	(	QFontEngine *	fontEngine,
		QChar::Script	script )

virtual

Returns a multi font engine in the specified script to encapsulate fontEngine with the option to fall back to the fonts given by fallbacks if fontEngine does not support a certain character.

Reimplemented in QFontconfigDatabase.

Definition at line 274 of file qplatformfontdatabase.cpp.

References fontEngine().

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◆ fontsAlwaysScalable()

bool QPlatformFontDatabase::fontsAlwaysScalable ( ) const

virtual

Return true if all fonts are considered scalable when using this font database.

Defaults to false.

Since: 5.0

Reimplemented in QCoreTextFontDatabase, and QWindowsFontDatabase.

Definition at line 411 of file qplatformfontdatabase.cpp.

◆ invalidate()

void QPlatformFontDatabase::invalidate ( )

virtual

This function is called whenever the font database is invalidated.

Reimplement this function to clear any internal data structures that will need to be rebuilt at the next call to populateFontDatabase().

Reimplemented in QCoreTextFontDatabase, QFontconfigDatabase, QWindowsFontDatabase, and QWindowsFontDatabaseBase.

Definition at line 265 of file qplatformfontdatabase.cpp.

◆ isFamilyPopulated()

bool QPlatformFontDatabase::isFamilyPopulated ( const QString & familyName )

static

Helper function that returns true if the font family has already been registered and populated.

Since: 5.14

Definition at line 643 of file qplatformfontdatabase.cpp.

References qt_isFontFamilyPopulated().

Referenced by addFontToDatabase(), and QCoreTextFontDatabase::populateFamilyAliases().

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◆ isPrivateFontFamily()

bool QPlatformFontDatabase::isPrivateFontFamily ( const QString & family ) const

virtual

Returns true if the font family is private.

For any given family name, the result is platform dependent.

Reimplemented in QCoreTextFontDatabase, QWindowsDirectWriteFontDatabase, and QWindowsFontDatabase.

Definition at line 373 of file qplatformfontdatabase.cpp.

References Q_UNUSED.

Referenced by QCoreTextFontDatabase::isPrivateFontFamily(), and QWindowsFontDatabase::isPrivateFontFamily().

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◆ populateFamily()

void QPlatformFontDatabase::populateFamily ( const QString & familyName )

virtual

This function is called whenever a lazily populated family, populated through registerFontFamily(), needs full population.

You are expected to fully populate the family by calling registerFont() for each font that matches the family name.

Reimplemented in QCoreTextFontDatabase, QWindowsDirectWriteFontDatabase, QWindowsFontDatabaseFT, and QWindowsFontDatabase.

Definition at line 254 of file qplatformfontdatabase.cpp.

References Q_UNUSED.

◆ populateFamilyAliases()

virtual bool QPlatformFontDatabase::populateFamilyAliases ( const QString & missingFamily )

inlinevirtual

Reimplemented in QWindowsFontDatabaseFT, QCoreTextFontDatabase, QWindowsDirectWriteFontDatabase, and QWindowsFontDatabase.

Definition at line 71 of file qplatformfontdatabase.h.

References Q_UNUSED.

Referenced by QWindowsDirectWriteFontDatabase::populateFamilyAliases().

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◆ populateFontDatabase()

void QPlatformFontDatabase::populateFontDatabase ( )

virtual

This function is called once at startup by Qt's internal font database.

Reimplement this function in a subclass for a convenient place to initialize the internal font database.

You may lazily populate the database by calling registerFontFamily() instead of registerFont(), in which case you'll get a callback to populateFamily() when the required family needs population. You then call registerFont() to finish population of the family.

The default implementation does nothing.

Reimplemented in QCoreTextFontDatabase, QFreeTypeFontDatabase, QFontconfigDatabase, QWindowsDirectWriteFontDatabase, QWindowsFontDatabaseFT, QWindowsFontDatabase, QAndroidPlatformFontDatabase, DummyFontDatabase, and QWasmFontDatabase.

Definition at line 243 of file qplatformfontdatabase.cpp.

◆ registerAliasToFontFamily()

void QPlatformFontDatabase::registerAliasToFontFamily	(	const QString &	familyName,
		const QString &	alias )

static

Helper function that register the alias for the familyName.

Since: 5.2

Definition at line 615 of file qplatformfontdatabase.cpp.

References qt_registerAliasToFontFamily().

Referenced by addFontToDatabase(), addFontToDatabase(), QCoreTextFontDatabase::populateFamilyAliases(), populateFontFamilies(), populateFontFamilies(), and populateFromPattern().

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◆ registerFont()

void QPlatformFontDatabase::registerFont	(	const QString &	familyname,
		const QString &	stylename,
		const QString &	foundryname,
		QFont::Weight	weight,
		QFont::Style	style,
		QFont::Stretch	stretch,
		bool	antialiased,
		bool	scalable,
		int	pixelSize,
		bool	fixedPitch,
		const QSupportedWritingSystems &	writingSystems,
		void *	usrPtr )

static

Registers a font with the given set of attributes describing the font's foundry, family name, style and stretch information, pixel size, and supported writing systems.

Additional information about whether the font can be scaled and antialiased can also be provided.

The foundry name and font family are described by foundryName and familyName. The font weight (light, normal, bold, etc.), style (normal, oblique, italic) and stretch information (condensed, expanded, unstretched, etc.) are specified by weight, style and stretch.

Some fonts can be antialiased and scaled; scalable and antialiased can be set to true for fonts with these attributes. The intended pixel size of non-scalable fonts is specified by pixelSize; this value will be ignored for scalable fonts.

The writing systems supported by the font are specified by the writingSystems argument.