QRawFont Class Reference

The QRawFont class provides access to a single physical instance of a font. More...

 #include <QRawFont>

This class was introduced in Qt 4.8.

Public Types

enum AntialiasingType { PixelAntialiasing, SubPixelAntialiasing }

Public Functions

QRawFont ()
QRawFont ( const QString & fileName, qreal pixelSize, QFont::HintingPreference hintingPreference = QFont::PreferDefaultHinting )
QRawFont ( const QByteArray & fontData, qreal pixelSize, QFont::HintingPreference hintingPreference = QFont::PreferDefaultHinting )
QRawFont ( const QRawFont & other )
~QRawFont ()
QVector<QPointF> advancesForGlyphIndexes ( const QVector<quint32> & glyphIndexes ) const
bool advancesForGlyphIndexes ( const quint32 * glyphIndexes, QPointF * advances, int numGlyphs ) const
QImage alphaMapForGlyph ( quint32 glyphIndex, AntialiasingType antialiasingType = SubPixelAntialiasing, const QTransform & transform = QTransform() ) const
qreal ascent () const
qreal averageCharWidth () const
qreal descent () const
QString familyName () const
QByteArray fontTable ( const char * tagName ) const
bool glyphIndexesForChars ( const QChar * chars, int numChars, quint32 * glyphIndexes, int * numGlyphs ) const
QVector<quint32> glyphIndexesForString ( const QString & text ) const
QFont::HintingPreference hintingPreference () const
bool isValid () const
qreal leading () const
void loadFromData ( const QByteArray & fontData, qreal pixelSize, QFont::HintingPreference hintingPreference )
void loadFromFile ( const QString & fileName, qreal pixelSize, QFont::HintingPreference hintingPreference )
qreal maxCharWidth () const
QPainterPath pathForGlyph ( quint32 glyphIndex ) const
qreal pixelSize () const
void setPixelSize ( qreal pixelSize )
QFont::Style style () const
QString styleName () const
QList<QFontDatabase::WritingSystem> supportedWritingSystems () const
bool supportsCharacter ( QChar character ) const
bool supportsCharacter ( quint32 ucs4 ) const
qreal unitsPerEm () const
int weight () const
qreal xHeight () const
bool operator!= ( const QRawFont & other ) const
QRawFont & operator= ( const QRawFont & other )
bool operator== ( const QRawFont & other ) const

Static Public Members

QRawFont fromFont ( const QFont & font, QFontDatabase::WritingSystem writingSystem = QFontDatabase::Any )

Detailed Description

The QRawFont class provides access to a single physical instance of a font.

Note: QRawFont is a low level class. For most purposes QFont is a more appropriate class.

Most commonly, when presenting text in a user interface, the exact fonts used to render the characters is to some extent unknown. This can be the case for several reasons: For instance, the actual, physical fonts present on the target system could be unexpected to the developers, or the text could contain user selected styles, sizes or writing systems that are not supported by font chosen in the code.

Therefore, Qt's QFont class really represents a query for fonts. When text is interpreted, Qt will do its best to match the text to the query, but depending on the support, different fonts can be used behind the scenes.

For most use cases, this is both expected and necessary, as it minimizes the possibility of text in the user interface being undisplayable. In some cases, however, more direct control over the process might be useful. It is for these use cases the QRawFont class exists.

A QRawFont object represents a single, physical instance of a given font in a given pixel size. I.e. in the typical case it represents a set of TrueType or OpenType font tables and uses a user specified pixel size to convert metrics into logical pixel units. It can be used in combination with the QGlyphRun class to draw specific glyph indexes at specific positions, and also have accessors to some relevant data in the physical font.

QRawFont only provides support for the main font technologies: GDI and DirectWrite on Windows platforms, FreeType on Symbian and Linux platforms and CoreText on Mac OS X. For other font back-ends, the APIs will be disabled.

QRawFont can be constructed in a number of ways:

  • It can be constructed by calling QTextLayout::glyphs() or QTextFragment::glyphs(). The returned QGlyphs objects will contain QRawFont objects which represent the actual fonts used to render each portion of the text.
  • It can be constructed by passing a QFont object to QRawFont::fromFont(). The function will return a QRawFont object representing the font that will be selected as response to the QFont query and the selected writing system.
  • It can be constructed by passing a file name or QByteArray directly to the QRawFont constructor, or by calling loadFromFile() or loadFromData(). In this case, the font will not be registered in QFontDatabase, and it will not be available as part of regular font selection.

QRawFont is considered local to the thread in which it is constructed (either using a constructor, or by calling loadFromData() or loadFromFile()). The QRawFont cannot be moved to a different thread, but will have to be recreated in the thread in question.

Note: For the requirement of caching glyph indexes and font selections for static text to avoid reshaping and relayouting in the inner loop of an application, a better choice is the QStaticText class, since it optimizes the memory cost of the cache and also provides the possibility of paint engine specific caches for an additional speed-up.

Member Type Documentation

enum QRawFont::AntialiasingType

This enum represents the different ways a glyph can be rasterized in the function alphaMapForGlyph().

ConstantValueDescription
QRawFont::PixelAntialiasing0Will rasterize by measuring the coverage of the shape on whole pixels. The returned image contains the alpha values of each pixel based on the coverage of the glyph shape.
QRawFont::SubPixelAntialiasing1Will rasterize by measuring the coverage of each subpixel, returning a separate alpha value for each of the red, green and blue components of each pixel.

Member Function Documentation

QRawFont::QRawFont ()

Constructs an invalid QRawFont.

QRawFont::QRawFont ( const QString & fileName, qreal pixelSize, QFont::HintingPreference hintingPreference = QFont::PreferDefaultHinting )

Constructs a QRawFont representing the font contained in the file referenced by fileName for the size (in pixels) given by pixelSize, and using the hinting preference specified by hintingPreference.

Note: The referenced file must contain a TrueType or OpenType font.

QRawFont::QRawFont ( const QByteArray & fontData, qreal pixelSize, QFont::HintingPreference hintingPreference = QFont::PreferDefaultHinting )

Constructs a QRawFont representing the font contained in the supplied fontData for the size (in pixels) given by pixelSize, and using the hinting preference specified by hintingPreference.

Note: The data must contain a TrueType or OpenType font.

QRawFont::QRawFont ( const QRawFont & other )

Creates a QRawFont which is a copy of other.

QRawFont::~QRawFont ()

Destroys the QRawFont

QVector<QPointF> QRawFont::advancesForGlyphIndexes ( const QVector<quint32> & glyphIndexes ) const

Returns the QRawFont's advances for each of the glyphIndexes in pixel units. The advances give the distance from the position of a given glyph to where the next glyph should be drawn to make it appear as if the two glyphs are unspaced.

See also QTextLine::horizontalAdvance() and QFontMetricsF::width().

bool QRawFont::advancesForGlyphIndexes ( const quint32 * glyphIndexes, QPointF * advances, int numGlyphs ) const

Returns the QRawFont's advances for each of the glyphIndexes in pixel units. The advances give the distance from the position of a given glyph to where the next glyph should be drawn to make it appear as if the two glyphs are unspaced. The glyph indexes are given with the array glyphIndexes while the results are returned through advances, both of them must have numGlyphs elements.

See also QTextLine::horizontalAdvance() and QFontMetricsF::width().

QImage QRawFont::alphaMapForGlyph ( quint32 glyphIndex, AntialiasingType antialiasingType = SubPixelAntialiasing, const QTransform & transform = QTransform() ) const

This function returns a rasterized image of the glyph at the given glyphIndex in the underlying font, using the transform specified. If the QRawFont is not valid, this function will return an invalid QImage.

If antialiasingType is set to QRawFont::SubPixelAntialiasing, then the resulting image will be in QImage::Format_RGB32 and the RGB values of each pixel will represent the subpixel opacities of the pixel in the rasterization of the glyph. Otherwise, the image will be in the format of QImage::Format_Indexed8 and each pixel will contain the opacity of the pixel in the rasterization.

See also pathForGlyph() and QPainter::drawGlyphRun().

qreal QRawFont::ascent () const

Returns the ascent of this QRawFont in pixel units.

See also QFontMetricsF::ascent().

qreal QRawFont::averageCharWidth () const

Returns the average character width of this QRawFont in pixel units.

See also QFontMetricsF::averageCharWidth().

qreal QRawFont::descent () const

Returns the descent of this QRawFont in pixel units.

See also QFontMetricsF::descent().

QString QRawFont::familyName () const

Returns the family name of this QRawFont.

QByteArray QRawFont::fontTable ( const char * tagName ) const

Retrieves the sfnt table named tagName from the underlying physical font, or an empty byte array if no such table was found. The returned font table's byte order is Big Endian, like the sfnt format specifies. The tagName must be four characters long and should be formatted in the default endianness of the current platform.

QRawFont QRawFont::fromFont ( const QFont & font, QFontDatabase::WritingSystem writingSystem = QFontDatabase::Any ) [static]

Fetches the physical representation based on a font query. The physical font returned is the font that will be preferred by Qt in order to display text in the selected writingSystem.

bool QRawFont::glyphIndexesForChars ( const QChar * chars, int numChars, quint32 * glyphIndexes, int * numGlyphs ) const

Converts a string of unicode points to glyph indexes using the CMAP table in the underlying font. The function works like glyphIndexesForString() except it take an array (chars), the results will be returned though glyphIndexes array and number of glyphs will be set in numGlyphs. The size of glyphIndexes array must be at least numChars, if that's still not enough, this function will return false, then you can resize glyphIndexes from the size returned in numGlyphs.

See also glyphIndexesForString(), advancesForGlyphIndexes(), QGlyphRun, QTextLayout::glyphRuns(), and QTextFragment::glyphRuns().

QVector<quint32> QRawFont::glyphIndexesForString ( const QString & text ) const

Converts the string of unicode points given by text to glyph indexes using the CMAP table in the underlying font, and returns a vector containing the result.

Note that, in cases where there are other tables in the font that affect the shaping of the text, the returned glyph indexes will not correctly represent the rendering of the text. To get the correctly shaped text, you can use QTextLayout to lay out and shape the text, then call QTextLayout::glyphs() to get the set of glyph index list and QRawFont pairs.

See also advancesForGlyphIndexes(), glyphIndexesForChars(), QGlyphRun, QTextLayout::glyphRuns(), and QTextFragment::glyphRuns().

QFont::HintingPreference QRawFont::hintingPreference () const

Returns the hinting preference used to construct this QRawFont.

See also QFont::hintingPreference().

bool QRawFont::isValid () const

Returns true if the QRawFont is valid and false otherwise.

qreal QRawFont::leading () const

Returns the leading of this QRawFont in pixel units.

See also QFontMetricsF::leading().

void QRawFont::loadFromData ( const QByteArray & fontData, qreal pixelSize, QFont::HintingPreference hintingPreference )

Replaces the current QRawFont with the font contained in the supplied fontData for the size (in pixels) given by pixelSize, and using the hinting preference specified by hintingPreference.

The fontData must contain a TrueType or OpenType font.

See also loadFromFile().

void QRawFont::loadFromFile ( const QString & fileName, qreal pixelSize, QFont::HintingPreference hintingPreference )

Replaces the current QRawFont with the contents of the file referenced by fileName for the size (in pixels) given by pixelSize, and using the hinting preference specified by hintingPreference.

The file must reference a TrueType or OpenType font.

See also loadFromData().

qreal QRawFont::maxCharWidth () const

Returns the width of the widest character in the font.

See also QFontMetricsF::maxWidth().

QPainterPath QRawFont::pathForGlyph ( quint32 glyphIndex ) const

This function returns the shape of the glyph at a given glyphIndex in the underlying font if the QRawFont is valid. Otherwise, it returns an empty QPainterPath.

The returned glyph will always be unhinted.

See also alphaMapForGlyph() and QPainterPath::addText().

qreal QRawFont::pixelSize () const

Returns the pixel size set for this QRawFont. The pixel size affects how glyphs are rasterized, the size of glyphs returned by pathForGlyph(), and is used to convert internal metrics from design units to logical pixel units.

See also setPixelSize().

void QRawFont::setPixelSize ( qreal pixelSize )

Sets the pixel size with which this font should be rendered to pixelSize.

See also pixelSize().

QFont::Style QRawFont::style () const

Returns the style of this QRawFont.

See also QFont::style().

QString QRawFont::styleName () const

Returns the style name of this QRawFont.

See also QFont::styleName().

QList<QFontDatabase::WritingSystem> QRawFont::supportedWritingSystems () const

Returns a list of writing systems supported by the font according to designer supplied information in the font file. Please note that this does not guarantee support for a specific unicode point in the font. You can use the supportsCharacter() to check support for a single, specific character.

Note: The list is determined based on the unicode ranges and codepage ranges set in the font's OS/2 table and requires such a table to be present in the underlying font file.

See also supportsCharacter().

bool QRawFont::supportsCharacter ( QChar character ) const

Returns true if the font has a glyph that corresponds to the given character.

See also supportedWritingSystems().

bool QRawFont::supportsCharacter ( quint32 ucs4 ) const

This is an overloaded function.

Returns true if the font has a glyph that corresponds to the UCS-4 encoded character ucs4.

See also supportedWritingSystems().

qreal QRawFont::unitsPerEm () const

Returns the number of design units define the width and height of the em square for this QRawFont. This value is used together with the pixel size when converting design metrics to pixel units, as the internal metrics are specified in design units and the pixel size gives the size of 1 em in pixels.

See also pixelSize() and setPixelSize().

int QRawFont::weight () const

Returns the weight of this QRawFont.

See also QFont::weight().

qreal QRawFont::xHeight () const

Returns the xHeight of this QRawFont in pixel units.

See also QFontMetricsF::xHeight().

bool QRawFont::operator!= ( const QRawFont & other ) const

Returns true if this QRawFont is not equal to other. Otherwise, returns false.

QRawFont & QRawFont::operator= ( const QRawFont & other )

Assigns other to this QRawFont.

bool QRawFont::operator== ( const QRawFont & other ) const

Returns true if this QRawFont is equal to other. Otherwise, returns false.

Notes provided by the Qt Community

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