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QRawFont Class Reference
[QtGui module]

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

Types

Methods

Static Methods

Special Methods


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:

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.


Type Documentation

QRawFont.AntialiasingType

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

Constant Value Description
QRawFont.PixelAntialiasing 0 Will 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.SubPixelAntialiasing 1 Will 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.

Method Documentation

QRawFont.__init__ (self)

Constructs an invalid QRawFont.

QRawFont.__init__ (self, QString fileName, float 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.__init__ (self, QByteArray fontData, float 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.__init__ (self, QRawFont other)

Creates a QRawFont which is a copy of other.

list-of-QPointF QRawFont.advancesForGlyphIndexes (self, list-of-int glyphIndexes)

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().

QImage QRawFont.alphaMapForGlyph (self, int glyphIndex, AntialiasingType antialiasingType = QRawFont.SubPixelAntialiasing, QTransform transform = QTransform())

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().

float QRawFont.ascent (self)

Returns the ascent of this QRawFont in pixel units.

See also QFontMetricsF.ascent().

float QRawFont.averageCharWidth (self)

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

See also QFontMetricsF.averageCharWidth().

float QRawFont.descent (self)

Returns the descent of this QRawFont in pixel units.

See also QFontMetricsF.descent().

QString QRawFont.familyName (self)

Returns the family name of this QRawFont.

QByteArray QRawFont.fontTable (self, str tagName)

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 (QFont font, QFontDatabase.WritingSystem writingSystem = QFontDatabase.Any)

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.

list-of-int QRawFont.glyphIndexesForString (self, QString text)

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 (self)

Returns the hinting preference used to construct this QRawFont.

See also QFont.hintingPreference().

bool QRawFont.isValid (self)

Returns true if the QRawFont is valid and false otherwise.

float QRawFont.leading (self)

Returns the leading of this QRawFont in pixel units.

See also QFontMetricsF.leading().

QRawFont.loadFromData (self, QByteArray fontData, float 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().

QRawFont.loadFromFile (self, QString fileName, float 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().

float QRawFont.maxCharWidth (self)

Returns the width of the widest character in the font.

See also QFontMetricsF.maxWidth().

QPainterPath QRawFont.pathForGlyph (self, int glyphIndex)

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().

float QRawFont.pixelSize (self)

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().

QRawFont.setPixelSize (self, float pixelSize)

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

See also pixelSize().

QFont.Style QRawFont.style (self)

Returns the style of this QRawFont.

See also QFont.style().

QString QRawFont.styleName (self)

Returns the style name of this QRawFont.

See also QFont.styleName().

list-of-QFontDatabase.WritingSystem QRawFont.supportedWritingSystems (self)

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 (self, int ucs4)

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

See also supportedWritingSystems().

bool QRawFont.supportsCharacter (self, QChar character)

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().

float QRawFont.unitsPerEm (self)

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 (self)

Returns the weight of this QRawFont.

See also QFont.weight().

float QRawFont.xHeight (self)

Returns the xHeight of this QRawFont in pixel units.

See also QFontMetricsF.xHeight().

bool QRawFont.__eq__ (self, QRawFont other)

bool QRawFont.__ne__ (self, QRawFont other)


PyQt 4.9.4 for WindowsCopyright © Riverbank Computing Ltd and Nokia 2012Qt 4.8.2