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QFont Class Reference

The QFont class specifies a font used for drawing text. More...

#include <qfont.h>

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Detailed Description

The QFont class specifies a font used for drawing text.

When you create a QFont object you specify various attributes that you want the font to have. Qt will use the font with the specified attributes, or if no matching font exists, Qt will use the closest matching installed font. The attributes of the font that is actually used are retrievable from a QFontInfo object. If the window system provides an exact match exactMatch() returns TRUE. Use QFontMetrics to get measurements, e.g. the pixel length of a string using QFontMetrics::width().

Use QApplication::setFont() to set the application's default font.

If a choosen X11 font does not include all the characters that need to be displayed, QFont will try to find the characters in the nearest equivalent fonts. When a QPainter draws a character from a font the QFont will report whether or not it has the character; if it does not, QPainter will draw an unfilled square.

Create QFonts like this: 

    QFont serifFont( "Times", 10, Bold );
    QFont sansFont( "Helvetica [Cronyx]", 12 );

The attributes set in the constructor can also be set later, e.g. setFamily(), setPointSize(), setPointSizeFloat(), setWeight() and setItalic(). The remaining attributes must be set after contstruction, e.g. setBold(), setUnderline(), setStrikeOut() and setFixedPitch(). QFontInfo objects should be created after the font's attributes have been set. A QFontInfo object will not change, even if you change the font's attributes. The corresponding "get" functions, e.g. family(), pointSize(), etc., return the values that were set, even though the values used may differ. The actual values are available from a QFontInfo object.

If the requested font family is unavailable you can influence the font matching algorithm by choosing a particular QFont::StyleHint and QFont::StyleStrategy with setStyleHint(). The default family (corresponding to the current style hint) is returned by defaultFamily().

The font-matching algorithm has a lastResortFamily() and lastResortFont() in cases where a suitable match cannot be found. You can provide substitutions for font family names using insertSubstitution() and insertSubstitutions(). Substitutions can be removed with removeSubstitution(). Use substitute() to retrieve a family's first substitute, or the family name itself if it has no substitutes. Use substitutes() to retrieve a list of a family's substitutes (which may be empty).

Every QFont has a key() which you can use, for example, as the key in a cache or dictionary. If you want to store a user's font preferences you could use QSettings, writing the font information with toString() and reading it back with fromString(). The operator<<() and operator>>() functions are also available, but they work on a data stream.

It is possible to set the height of characters shown on the screen to a specified number of pixels with setPixelSize(); however using setPointSize() has a similar effect and provides device independence.

Under the X Window System you can set a font using its system specific name with setRawName().

Loading fonts can be expensive, especially on X11. QFont contains extensive optimizations to make the copying of QFont objects fast, and to cache the results of the slow window system functions it depends upon.

The font matching algorithm works as follows:

  1. The specified font family is searched for.
  2. If not found, the styleHint() is used to select a replacement family.
  3. Each replacement font family is searched for.
  4. If none of these are found or there was no styleHint(), "helvetica" will be searched for.
  5. If "helvetica" isn't found Qt will try the lastResortFamily().
  6. If the lastResortFamily() isn't found Qt will try the lastResortFont() which will always return a name of some kind.

Once a font is found, the remaining attributes are matched in order of priority:

  1. fixedPitch()
  2. pointSize() (see below)
  3. weight()
  4. italic()

If you have a font which matches on family, even if none of the other attributes match, this font will be chosen in preference to a font which doesn't match on family but which does match on the other attributes. This is because font family is the dominant search criteria.

The point size is defined to match if it is within 20% of the requested point size. When several fonts match and are only distinguished by point size, the font with the closest point size to the one requested will be chosen.

The actual family, font size, weight and other font attributes used for drawing text will depend on what's available for the chosen family under the window system. A QFontInfo object can be used to determine the actual values used for drawing the text.

Examples: 

    QFont f("Helvetica");
If you had both an Adobe and a Cronyx Helvetica, you might get either. 

    QFont f1( "Helvetica [Cronyx]" );  // Qt 3.x
    QFont f2( "Cronyx-Helvetica" );    // Qt 2.x compatibility
You can specify the foundry you want in the family name. Both fonts, f1 and f2, in the above example will be set to "Helvetica [Cronyx]".

To determine the attributes of the font actually used in the window system, use a QFontInfo object, e.g. 

    QFontInfo info( f1 );
    QString family = info.family();

To find out font metrics use a QFontMetrics object, e.g. 

    QFontMetrics fm( f1 );
    int pixelWidth = fm.width( "How many pixels wide is this text?" );
    int pixelHeight = fm.height();

For more general information on fonts, see the comp.fonts FAQ. Information on encodings can be found from Roman Czyborra's page.

See also QFontMetrics, QFontInfo, QFontDatabase, QApplication::setFont(), QWidget::font, QPainter::setFont(), QFont::StyleHint, QFont::Weight, Widget Appearance and Style, Graphics Classes and Implicitly and Explicitly Shared Classes.

Member Type Documentation

QFont::Script

This enum represents Unicode allocated scripts. For exhaustive coverage see The Unicode Standard Version 3.0. The following scripts are supported:

Modern European alphabetic scripts (left to right):

Middle Eastern scripts (right to left):

South and Southeast Asian scripts (left to right with few historical exceptions):

East Asian scripts (traditionally top-down, right to left, modern often horizontal left to right):

Additional scripts that do not fit well into the script categories above:

Symbols:

The values below are provided for completeness and must not be used in user programs.

QFont::StyleHint

Style hints are used by the font matching algorithm to find an appropriate default family if a selected font family is not available.

QFont::StyleStrategy

The style strategy tells the font matching algorithm what type of fonts should be used to find an appropriate default family.

The following strategies are available:

Any of these may be OR-ed with one of these flags:

QFont::Weight

Qt uses a weighting scale from 0 to 99 similar to, but not the same as, the scales used in Windows or CSS. A weight of 0 is ultralight, whilst 99 will be an extremely black.

This enum contains the predefined font weights:

Member Function Documentation

QFont::QFont ()

Constructs a font object that uses the application's default font.

See also QApplication::setFont() and QApplication::font().

QFont::QFont ( const QString & family, int pointSize = 12, int weight = Normal, bool italic = FALSE )

Constructs a font object with the specified family, pointSize, weight and italic settings.

If pointSize is <= 0 it is set to 1.

The family name may optionally also include a foundry name, e.g. "Helvetica [Cronyx]". (The Qt 2.x syntax, i.e. "Cronyx-Helvetica", is also supported.) If the family is available from more than one foundry and the foundry isn't specified, an arbitrary foundry is chosen. If the family isn't available a family will be set using the font matching algorithm.

See also Weight, setFamily(), setPointSize(), setWeight(), setItalic(), setStyleHint() and QApplication::font().

QFont::QFont ( const QFont & font )

Constructs a font that is a copy of font.

QFont::~QFont ()

Destroys the font object and frees all allocated resources.

bool QFont::bold () const

Returns TRUE if weight() is a value greater than QFont::Normal; otherwise returns FALSE.

See also weight(), setBold() and QFontInfo::bold().

int QFont::deciPointSize () const [protected]

Returns the point size in 1/10ths of a point.

The returned value will be -1 if the font size has been specified in pixels.

See also pointSize() and pointSizeFloat().

QString QFont::defaultFamily () const

Returns the family name that corresponds to the current style hint.

See also StyleHint, styleHint() and setStyleHint().

QFont QFont::defaultFont () [static]

This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.

Please use QApplication::font() instead.

bool QFont::dirty () const [protected]

Returns TRUE if the font attributes have been changed and the font has to be (re)loaded; otherwise returns FALSE.

bool QFont::exactMatch () const

Returns TRUE if a window system font exactly matching the settings of this font is available.

See also QFontInfo.

QString QFont::family () const

Returns the requested font family name, i.e. the name set in the constructor or the last setFont() call.

See also setFamily(), substitutes() and substitute().

Example: fonts/simple-qfont-demo/viewer.cpp.

bool QFont::fixedPitch () const

Returns TRUE if fixed pitch has been set; otherwise returns FALSE.

See also setFixedPitch() and QFontInfo::fixedPitch().

bool QFont::fromString ( const QString & descrip )

Sets this font to match the description descrip. The description is a comma-separated list of the font attributes, as returned by toString().

See also toString() and operator>>().

HFONT QFont::handle () const

Returns the window system handle to the font, for low-level access. Using this function is not portable.

void QFont::insertSubstitution ( const QString & familyName, const QString & substituteName ) [static]

Inserts the family name substituteName into the substitution table for familyName.

See also insertSubstitutions(), removeSubstitution(), substitutions(), substitute() and substitutes().

Example: fonts/simple-qfont-demo/viewer.cpp.

void QFont::insertSubstitutions ( const QString & familyName, const QStringList & substituteNames ) [static]

Inserts the list of families substituteNames into the substitution list for familyName.

See also insertSubstitution(), removeSubstitution(), substitutions() and substitute().

Example: fonts/simple-qfont-demo/viewer.cpp.

bool QFont::isCopyOf ( const QFont & f ) const

Returns TRUE if this font and f are copies of each other, i.e. one of them was created as a copy of the other and neither has been modified since. This is much stricter than equality.

See also operator=() and operator==().

bool QFont::italic () const

Returns TRUE if italic has been set; otherwise returns FALSE.

See also setItalic().

QString QFont::key () const

Returns the font's key, a textual representation of a font. It is typically used as the key for a cache or dictionary of fonts.

See also QMap.

QString QFont::lastResortFamily () const

Returns the "last resort" font family name.

The current implementation tries a wide variety of common fonts, returning the first one it finds. Is is possible that no family is found in which case a null string is returned.

See also lastResortFont().

QString QFont::lastResortFont () const

Returns a "last resort" font name for the font matching algorithm. This is used if the last resort family is not available. It will always return a name, if necessary returning something like "fixed" or "system".

The current implementation tries a wide variety of common fonts, returning the first one it finds. This implementation may change at any time, but this function will always return a string containing something.

It is theoretically possible that there really isn't a lastResortFont() in which case Qt will abort with an error message. We have not been able to identify a case where this happens. Please report it as a bug if it does, preferably with a list of the fonts you have installed.

See also lastResortFamily() and rawName().

bool QFont::operator!= ( const QFont & f ) const

Returns TRUE if this font is different from f; otherwise returns FALSE.

Two QFonts are considered to be different if their font attributes are different. If rawMode() is enabled for both fonts, only the family fields are compared.

See also operator==().

QFont & QFont::operator= ( const QFont & font )

Assigns font to this font and returns a reference to it.

bool QFont::operator== ( const QFont & f ) const

Returns TRUE if this font is equal to f; otherwise returns FALSE.

Two QFonts are considered equal if their font attributes are equal. If rawMode() is enabled for both fonts, only the family fields are compared.

See also operator!=() and isCopyOf().

int QFont::pixelSize () const

Returns the pixel size of the font if it was set with setPixelSize(). Returns -1 if the size was set with setPointSize() or setPointSizeFloat().

See also setPixelSize(), pointSize(), QFontInfo::pointSize() and QFontInfo::pixelSize().

int QFont::pointSize () const

Returns the point size of the font. Returns -1 if the font size was specified in pixels.

See also setPointSize(), deciPointSize() and pointSizeFloat().

Example: fonts/simple-qfont-demo/viewer.cpp.

float QFont::pointSizeFloat () const

Returns the point size of the font. Returns -1 if the font size was specified in pixels.

See also pointSize(), setPointSizeFloat(), pixelSize(), QFontInfo::pointSize() and QFontInfo::pixelSize().

void QFont::qwsRenderToDisk ( bool all = TRUE )

Saves the glyphs in the font that have previously been accessed as a QPF file. If all is TRUE (the default), then before saving, all glyphs are marked as used.

If the font is large and you are sure that only a subset of characters will ever be required on the target device, passing FALSE for the all parameter can save significant disk space.

Note that this function is only applicable on Qt/Embedded.

bool QFont::rawMode () const

Returns TRUE if raw mode is used for font name matching; otherwise returns FALSE.

See also setRawMode() and rawName().

QString QFont::rawName () const

Returns the name of the font within the underlying window system. On Windows, this is usually just the family name of a truetype font. Under X, it is an XLFD (X Logical Font Description). Using the return value of this function is usually not portable.

See also setRawName().

void QFont::removeSubstitution ( const QString & familyName ) [static]

Removes all the substitutions for familyName.

See also insertSubstitutions(), insertSubstitution(), substitutions() and substitute().

void QFont::setBold ( bool enable )

If enable is true sets the font's weight to QFont::Bold; otherwise sets the weight to QFont::Normal.

For finer boldness control use setWeight().

See also bold() and setWeight().

Examples: menu/menu.cpp and themes/metal.cpp.

void QFont::setDefaultFont ( const QFont & f ) [static]

This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.

Please use QApplication::setFont() instead.

void QFont::setFamily ( const QString & family )

Sets the family name of the font. The name is case insensitive and may include a foundry name.

The family name may optionally also include a foundry name, e.g. "Helvetica [Cronyx]". (The Qt 2.x syntax, i.e. "Cronyx-Helvetica", is also supported.) If the family is available from more than one foundry and the foundry isn't specified, an arbitrary foundry is chosen. If the family isn't available a family will be set using the font matching algorithm.

See also family(), setStyleHint() and QFontInfo.

void QFont::setFixedPitch ( bool enable )

If enable is TRUE, sets fixed pitch on; otherwise sets fixed pitch off.

See also fixedPitch() and QFontInfo.

void QFont::setItalic ( bool enable )

If enable is TRUE, italic is set on; otherwise italic is set off.

See also italic() and QFontInfo.

Examples: fileiconview/qfileiconview.cpp, fonts/simple-qfont-demo/viewer.cpp and themes/metal.cpp.

void QFont::setPixelSize ( int pixelSize )

Sets the font size to pixelSize pixels.

Using this function makes the font device dependent. Use setPointSize() or setPointSizeFloat() to set the size of the font in a device independent manner.

See also pixelSize().

Example: qwerty/qwerty.cpp.

void QFont::setPixelSizeFloat ( float pixelSize )

This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.

Sets the logical pixel height of font characters when shown on the screen to pixelSize.

void QFont::setPointSize ( int pointSize )

Sets the point size to pointSize. The point size must be greater than zero.

See also pointSize() and setPointSizeFloat().

Example: fonts/simple-qfont-demo/viewer.cpp.

void QFont::setPointSizeFloat ( float pointSize )

Sets the point size to pointSize. The point size must be greater than zero. The requested precision may not be achieved on all platforms.

See also pointSizeFloat(), setPointSize() and setPixelSize().

void QFont::setRawMode ( bool enable )

If enable is TRUE, turns raw mode on; otherwise turns raw mode off. This function only has an affect under X11.

If raw mode is enabled, Qt will search for an X font with a complete font name matching the family name, ignoring all other values set for the QFont. If the font name matches several fonts, Qt will use the first font returned by X. QFontInfo cannot be used to fetch information about a QFont using raw mode (it will return the values set in the QFont for all parameters, including the family name).

Warning: Do not use raw mode unless you really, really need it! In most (if not all) cases, setRawName() is a much better choice.

See also rawMode() and setRawName().

void QFont::setRawName ( const QString & name )

Sets a font by its system specific name. The function is in particular useful under X, where system font settings (for example X resources) are usually available in XLFD (X Logical Font Description) form only. You can pass an XLFD as name to this function.

In Qt 2.0 and later, a font set with setRawName() is still a full-featured QFont. It can be queried (for example with italic()) or modified (for example with setItalic() ) and is therefore also suitable for rendering rich text.

If Qt's internal font database cannot resolve the raw name, the font becomes a raw font with name as its family.

Note that the present implementation does not handle wildcards in XLFDs well, and that font aliases (file fonts.alias in the font directory on X11) are not supported.

See also rawName(), setRawMode() and setFamily().

void QFont::setStrikeOut ( bool enable )

If enable is TRUE, sets strikeout on; otherwise sets strikeout off.

See also strikeOut() and QFontInfo.

void QFont::setStyleHint ( StyleHint hint, StyleStrategy strategy = PreferDefault )

Sets the style hint and strategy to hint and strategy, respectively.

If these aren't set explicitly the style hint will default to AnyStyle and the style strategy to PreferDefault.

See also StyleHint, styleHint(), StyleStrategy, styleStrategy() and QFontInfo.

Examples: desktop/desktop.cpp and fonts/simple-qfont-demo/viewer.cpp.

void QFont::setStyleStrategy ( StyleStrategy s )

Sets the style strategy for the font to s.

See also QFont::StyleStrategy.

void QFont::setUnderline ( bool enable )

If enable is TRUE, sets underline on; otherwise sets underline off.

See also underline() and QFontInfo.

Examples: fonts/simple-qfont-demo/viewer.cpp and menu/menu.cpp.

void QFont::setWeight ( int weight )

Sets the weight the font to weight, which should be a value from the QFont::Weight enumeration.

See also weight() and QFontInfo.

Example: fonts/simple-qfont-demo/viewer.cpp.

bool QFont::strikeOut () const

Returns TRUE if strikeout has been set; otherwise returns FALSE.

See also setStrikeOut() and QFontInfo::strikeOut().

StyleHint QFont::styleHint () const

Returns the StyleHint.

The style hint affects the font matching algorithm. See QFont::StyleHint for the list of strategies.

See also setStyleHint(), QFont::StyleStrategy and QFontInfo::styleHint().

StyleStrategy QFont::styleStrategy () const

Returns the StyleStrategy.

The style strategy affects the font matching algorithm. See QFont::StyleStrategy for the list of strategies.

See also setStyleHint() and QFont::StyleHint.

QString QFont::substitute ( const QString & familyName ) [static]

Returns the first family name to be used whenever familyName is specified. The lookup is case insensitive.

If there is no substitution for familyName, familyName is returned.

To obtain a list of substitutions use substitutes().

See also setFamily(), insertSubstitutions(), insertSubstitution() and removeSubstitution().

QStringList QFont::substitutes ( const QString & familyName ) [static]

Returns a list of family names to be used whenever familyName is specified. The lookup is case insensitive.

If there is no substitution for familyName, an empty list is returned.

See also substitute(), insertSubstitutions(), insertSubstitution() and removeSubstitution().

Example: fonts/simple-qfont-demo/viewer.cpp.

QStringList QFont::substitutions () [static]

Returns a sorted list of substituted family names.

See also insertSubstitution(), removeSubstitution() and substitute().

QString QFont::toString () const

Returns a description of the font. The description is a comma-separated list of the attributes, perfectly suited for use in QSettings.

See also fromString() and operator<<().

bool QFont::underline () const

Returns TRUE if underline has been set; otherwise returns FALSE.

See also setUnderline() and QFontInfo::underline().

int QFont::weight () const

Returns the weight of the font which is one of the enumerated values from QFont::Weight.

See also setWeight(), Weight and QFontInfo.

Related Functions

QDataStream & operator<< ( QDataStream & s, const QFont & font )

Writes the font font to the data stream s. (toString() writes to a text stream.)

See also Format of the QDataStream operators.

QDataStream & operator>> ( QDataStream & s, QFont & font )

Reads the font font from the data stream s. (fromString() reads from a text stream.)

See also Format of the QDataStream operators.

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