MeeGo 1.2 Harmattan Developer Documentation Develop for the Nokia N9

QFont Class Reference

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

 #include <QFont>

Note: All functions in this class are reentrant.

Public Types

enum Capitalization { MixedCase, AllUppercase, AllLowercase, SmallCaps, Capitalize }
enum SpacingType { PercentageSpacing, AbsoluteSpacing }
enum Stretch { UltraCondensed, ExtraCondensed, Condensed, SemiCondensed, ..., UltraExpanded }
enum Style { StyleNormal, StyleItalic, StyleOblique }
enum StyleHint { AnyStyle, SansSerif, Helvetica, Serif, ..., System }
enum StyleStrategy { PreferDefault, PreferBitmap, PreferDevice, PreferOutline, ..., ForceIntegerMetrics }
enum Weight { Light, Normal, DemiBold, Bold, Black }

Public Functions

QFont ()
QFont ( const QString & family, int pointSize = -1, int weight = -1, bool italic = false )
QFont ( const QFont & font, QPaintDevice * pd )
QFont ( const QFont & font )
~QFont ()
bool bold () const
Capitalization capitalization () const
QString defaultFamily () const
bool exactMatch () const
QString family () const
bool fixedPitch () const
FT_Face freetypeFace () const
bool fromString ( const QString & descrip )
HFONT handle () const
bool isCopyOf ( const QFont & f ) const
bool italic () const
bool kerning () const
QString key () const
QString lastResortFamily () const
QString lastResortFont () const
qreal letterSpacing () const
SpacingType letterSpacingType () const
quint32 macFontID () const
bool overline () const
int pixelSize () const
int pointSize () const
qreal pointSizeF () const
bool rawMode () const
QString rawName () const
QFont resolve ( const QFont & other ) const
void setBold ( bool enable )
void setCapitalization ( Capitalization caps )
void setFamily ( const QString & family )
void setFixedPitch ( bool enable )
void setItalic ( bool enable )
void setKerning ( bool enable )
void setLetterSpacing ( SpacingType type, qreal spacing )
void setOverline ( bool enable )
void setPixelSize ( int pixelSize )
void setPointSize ( int pointSize )
void setPointSizeF ( qreal pointSize )
void setRawMode ( bool enable )
void setRawName ( const QString & name )
void setStretch ( int factor )
void setStrikeOut ( bool enable )
void setStyle ( Style style )
void setStyleHint ( StyleHint hint, StyleStrategy strategy = PreferDefault )
void setStyleStrategy ( StyleStrategy s )
void setUnderline ( bool enable )
void setWeight ( int weight )
void setWordSpacing ( qreal spacing )
int stretch () const
bool strikeOut () const
Style style () const
StyleHint styleHint () const
StyleStrategy styleStrategy () const
QString toString () const
bool underline () const
int weight () const
qreal wordSpacing () const
operator QVariant () const
bool operator!= ( const QFont & f ) const
bool operator< ( const QFont & f ) const
QFont & operator= ( const QFont & font )
bool operator== ( const QFont & f ) const

Static Public Members

void insertSubstitution ( const QString & familyName, const QString & substituteName )
void insertSubstitutions ( const QString & familyName, const QStringList & substituteNames )
void removeSubstitution ( const QString & familyName )
QString substitute ( const QString & familyName )
QStringList substitutes ( const QString & familyName )
QStringList substitutions ()

Related Non-Members

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

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().

Note that a QApplication instance must exist before a QFont can be used. You can set the application's default font with QApplication::setFont().

If a chosen 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, QFont::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(), setOverline(), 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.

In X11 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.

Note that the actual font matching algorithm varies from platform to platform.

In Windows a request for the "Courier" font is automatically changed to "Courier New", an improved version of Courier that allows for smooth scaling. The older "Courier" bitmap font can be selected by setting the PreferBitmap style strategy (see setStyleStrategy()).

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

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

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 f("Helvetica [Cronyx]");

You can specify the foundry you want in the family name. The font f 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 textWidthInPixels = fm.width("How many pixels wide is this text?");
 int textHeightInPixels = 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 QFontComboBox, QFontMetrics, QFontInfo, QFontDatabase, and Character Map Example.

Member Type Documentation

enum QFont::Capitalization

Rendering option for text this font applies to.

Constant Value Description
QFont::MixedCase 0 This is the normal text rendering option where no capitalization change is applied.
QFont::AllUppercase 1 This alters the text to be rendered in all uppercase type.
QFont::AllLowercase 2 This alters the text to be rendered in all lowercase type.
QFont::SmallCaps 3 This alters the text to be rendered in small-caps type.
QFont::Capitalize 4 This alters the text to be rendered with the first character of each word as an uppercase character.

This enum was introduced or modified in Qt 4.4.

enum QFont::SpacingType

Constant Value Description
QFont::PercentageSpacing 0 A value of 100 will keep the spacing unchanged; a value of 200 will enlarge the spacing after a character by the width of the character itself.
QFont::AbsoluteSpacing 1 A positive value increases the letter spacing by the corresponding pixels; a negative value decreases the spacing.

This enum was introduced or modified in Qt 4.4.

enum QFont::Stretch

Predefined stretch values that follow the CSS naming convention. The higher the value, the more stretched the text is.

Constant Value Description
QFont::UltraCondensed 50 50
QFont::ExtraCondensed 62 62
QFont::Condensed 75 75
QFont::SemiCondensed 87 87
QFont::Unstretched 100 100
QFont::SemiExpanded 112 112
QFont::Expanded 125 125
QFont::ExtraExpanded 150 150
QFont::UltraExpanded 200 200

See also setStretch() and stretch().

enum QFont::Style

This enum describes the different styles of glyphs that are used to display text.

Constant Value Description
QFont::StyleNormal 0 Normal glyphs used in unstyled text.
QFont::StyleItalic 1 Italic glyphs that are specifically designed for the purpose of representing italicized text.
QFont::StyleOblique 2 Glyphs with an italic appearance that are typically based on the unstyled glyphs, but are not fine-tuned for the purpose of representing italicized text.

See also Weight.

enum 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.

Constant Value Description
QFont::AnyStyle ? leaves the font matching algorithm to choose the family. This is the default.
QFont::SansSerif Helvetica the font matcher prefer sans serif fonts.
QFont::Helvetica 0 is a synonym for SansSerif.
QFont::Serif Times the font matcher prefers serif fonts.
QFont::Times ? is a synonym for Serif.
QFont::TypeWriter Courier the font matcher prefers fixed pitch fonts.
QFont::Courier ? a synonym for TypeWriter.
QFont::OldEnglish ? the font matcher prefers decorative fonts.
QFont::Decorative OldEnglish is a synonym for OldEnglish.
QFont::Monospace ? the font matcher prefers fonts that map to the CSS generic font-family 'monospace'.
QFont::Fantasy ? the font matcher prefers fonts that map to the CSS generic font-family 'fantasy'.
QFont::Cursive ? the font matcher prefers fonts that map to the CSS generic font-family 'cursive'.
QFont::System ? the font matcher prefers system fonts.

enum 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:

Constant Value Description
QFont::PreferDefault 0x0001 the default style strategy. It does not prefer any type of font.
QFont::PreferBitmap 0x0002 prefers bitmap fonts (as opposed to outline fonts).
QFont::PreferDevice 0x0004 prefers device fonts.
QFont::PreferOutline 0x0008 prefers outline fonts (as opposed to bitmap fonts).
QFont::ForceOutline 0x0010 forces the use of outline fonts.
QFont::NoAntialias 0x0100 don't antialias the fonts.
QFont::PreferAntialias 0x0080 antialias if possible.
QFont::OpenGLCompatible 0x0200 forces the use of OpenGL compatible fonts.
QFont::NoFontMerging 0x8000 If the font selected for a certain writing system does not contain a character requested to draw, then Qt automatically chooses a similar looking font that contains the character. The NoFontMerging flag disables this feature. Please note that enabling this flag will not prevent Qt from automatically picking a suitable font when the selected font does not support the writing system of the text.

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

Constant Value Description
QFont::PreferMatch 0x0020 prefer an exact match. The font matcher will try to use the exact font size that has been specified.
QFont::PreferQuality 0x0040 prefer the best quality font. The font matcher will use the nearest standard point size that the font supports.
QFont::ForceIntegerMetrics 0x0400 forces the use of integer values in font engines that support fractional font metrics.

enum 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:

Constant Value Description
QFont::Light 25 25
QFont::Normal 50 50
QFont::DemiBold 63 63
QFont::Bold 75 75
QFont::Black 87 87

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 = -1, int weight = -1, bool italic = false )

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

If pointSize is zero or negative, the point size of the font is set to a system-dependent default value. Generally, this is 12 points, except on Symbian where it is 7 points.

The family name may optionally also include a foundry name, e.g. "Helvetica [Cronyx]". 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, QPaintDevice * pd )

Constructs a font from font for use on the paint device pd.

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().

Capitalization QFont::capitalization () const

Returns the current capitalization type of the font.

This function was introduced in Qt 4.4.

See also setCapitalization().

QString QFont::defaultFamily () const

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

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

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().

bool QFont::