QFont Class | Qt GUI 5.15.18 (original) (raw)

Detailed Description

QFont can be regarded as a query for one or more fonts on the system.

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 QFontMetricsF to get measurements, e.g. the pixel length of a string using QFontMetrics::width().

Attributes which are not specifically set will not affect the font selection algorithm, and default values will be preferred instead.

To load a specific physical font, typically represented by a single file, use QRawFont instead.

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

You can provide substitutions for font family names using insertSubstitution() and insertSubstitutions(). Substitutions can be removed with removeSubstitutions(). 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). After substituting a font, you must trigger the updating of the font by destroying and re-creating all QFont objects.

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.

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 families (set by setFamilies()) are searched for.
  2. If not found, then if set the specified font family exists and can be used to represent the writing system in use, it will be selected.
  3. If not, a replacement font that supports the writing system is selected. The font matching algorithm will try to find the best match for all the properties set in the QFont. How this is done varies from platform to platform.
  4. If no font exists on the system that can support the text, then special "missing character" boxes will be shown in its place.

Note: If the selected font, though supporting the writing system in general, is missing glyphs for one or more specific characters, then Qt will try to find a fallback font for this or these particular characters. This feature can be disabled using QFont::NoFontMerging style strategy.

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:

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.

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

QFontMetrics fm(f1); int textWidthInPixels = fm.horizontalAdvance("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.

Member Function Documentation

QFont::QFont(const QFont &font)

Constructs a font that is a copy of font.

QFont::QFont(const QFont &font, const QPaintDevice *pd)

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

This function was introduced in Qt 5.13.

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.

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 QGuiApplication::font().

QFont::QFont()

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

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

QFont &QFont::operator=(QFont &&other)

Move-assigns other to this QFont instance.

This function was introduced in Qt 5.2.

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

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

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::Medium; otherwise returns false.

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

QFont::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.

QStringList QFont::families() const

Returns the requested font family names, i.e. the names set in the last setFamilies() call or via the constructor. Otherwise it returns an empty list.

This function was introduced in Qt 5.13.

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

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::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().

QFont::HintingPreference QFont::hintingPreference() const

Returns the currently preferred hinting level for glyphs rendered with this font.

This function was introduced in Qt 4.8.

See also setHintingPreference().

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

Inserts substituteName into the substitution table for the family familyName.

After substituting a font, trigger the updating of the font by destroying and re-creating all QFont objects.

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

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

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

After substituting a font, trigger the updating of the font by destroying and re-creating all QFont objects.

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

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 the style() of the font is not QFont::StyleNormal

See also setItalic() and style().

bool QFont::kerning() const

Returns true if kerning should be used when drawing text with this font.

See also setKerning().

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.

qreal QFont::letterSpacing() const

Returns the letter spacing for the font.

This function was introduced in Qt 4.4.

See also setLetterSpacing(), letterSpacingType(), and setWordSpacing().

QFont::SpacingType QFont::letterSpacingType() const

Returns the spacing type used for letter spacing.

This function was introduced in Qt 4.4.

See also letterSpacing(), setLetterSpacing(), and setWordSpacing().

bool QFont::overline() const

Returns true if overline has been set; otherwise returns false.

See also setOverline().

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 setPointSizeF().

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() and pointSizeF().

qreal QFont::pointSizeF() const

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

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

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

Removes all the substitutions for familyName.

This function was introduced in Qt 5.0.

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

QFont QFont::resolve(const QFont &other) const

Returns a new QFont that has attributes copied from other that have not been previously set on this font.

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().

Note: If styleName() is set, this value may be ignored, or if supported on the platform, the font artificially embolded.

See also bold() and setWeight().

void QFont::setCapitalization(QFont::Capitalization caps)

Sets the capitalization of the text in this font to caps.

A font's capitalization makes the text appear in the selected capitalization mode.

This function was introduced in Qt 4.4.

See also capitalization().

void QFont::setFamilies(const QStringList &families)

Sets the list of family names for the font. The names are case insensitive and may include a foundry name. The first family in families will be set as the main family for the font.

Each family name entry in families 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.

This function was introduced in Qt 5.13.

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

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]". 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::setHintingPreference(QFont::HintingPreference hintingPreference)

Set the preference for the hinting level of the glyphs to hintingPreference. This is a hint to the underlying font rendering system to use a certain level of hinting, and has varying support across platforms. See the table in the documentation for QFont::HintingPreference for more details.

The default hinting preference is QFont::PreferDefaultHinting.

This function was introduced in Qt 4.8.

See also hintingPreference().

void QFont::setItalic(bool enable)

Sets the style() of the font to QFont::StyleItalic if enable is true; otherwise the style is set to QFont::StyleNormal.

Note: If styleName() is set, this value may be ignored, or if supported on the platform, the font may be rendered tilted instead of picking a designed italic font-variant.

See also italic() and QFontInfo.

void QFont::setKerning(bool enable)

Enables kerning for this font if enable is true; otherwise disables it. By default, kerning is enabled.

When kerning is enabled, glyph metrics do not add up anymore, even for Latin text. In other words, the assumption that width('a') + width('b') is equal to width("ab") is not necessarily true.

See also kerning() and QFontMetrics.

void QFont::setLetterSpacing(QFont::SpacingType type, qreal spacing)

Sets the letter spacing for the font to spacing and the type of spacing to type.

Letter spacing changes the default spacing between individual letters in the font. The spacing between the letters can be made smaller as well as larger either in percentage of the character width or in pixels, depending on the selected spacing type.

This function was introduced in Qt 4.4.

See also letterSpacing(), letterSpacingType(), and setWordSpacing().

void QFont::setOverline(bool enable)

If enable is true, sets overline on; otherwise sets overline off.

See also overline() and QFontInfo.

void QFont::setPixelSize(int pixelSize)

Sets the font size to pixelSize pixels.

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

See also pixelSize().

void QFont::setPointSize(int pointSize)

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

See also pointSize() and setPointSizeF().

void QFont::setPointSizeF(qreal 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 pointSizeF(), setPointSize(), and setPixelSize().

void QFont::setStretch(int factor)

Sets the stretch factor for the font.

The stretch factor matches a condensed or expanded version of the font or applies a stretch transform that changes the width of all characters in the font by factor percent. For example, setting factor to 150 results in all characters in the font being 1.5 times (ie. 150%) wider. The minimum stretch factor is 1, and the maximum stretch factor is 4000. The default stretch factor is AnyStretch, which will accept any stretch factor and not apply any transform on the font.

The stretch factor is only applied to outline fonts. The stretch factor is ignored for bitmap fonts.

Note: When matching a font with a native non-default stretch factor, requesting a stretch of 100 will stretch it back to a medium width font.

See also stretch() and QFont::Stretch.

void QFont::setStrikeOut(bool enable)

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

See also strikeOut() and QFontInfo.

void QFont::setStyle(QFont::Style style)

Sets the style of the font to style.

See also style(), italic(), and QFontInfo.

void QFont::setStyleHint(QFont::StyleHint hint, QFont::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.

Qt does not support style hints on X11 since this information is not provided by the window system.

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

void QFont::setStyleName(const QString &styleName)

Sets the style name of the font to styleName. When set, other style properties like style() and weight() will be ignored for font matching, though they may be simulated afterwards if supported by the platform's font engine.

Due to the lower quality of artificially simulated styles, and the lack of full cross platform support, it is not recommended to use matching by style name together with matching by style properties

This function was introduced in Qt 4.8.

See also styleName().

void QFont::setStyleStrategy(QFont::StyleStrategy s)

Sets the style strategy for the font to s.

See also styleStrategy() and QFont::StyleStrategy.

void QFont::setUnderline(bool enable)

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

See also underline() and QFontInfo.

void QFont::setWeight(int weight)

Sets the weight of the font to weight, using the scale defined by QFont::Weight enumeration.

Note: If styleName() is set, this value may be ignored for font selection.

See also weight() and QFontInfo.

void QFont::setWordSpacing(qreal spacing)

Sets the word spacing for the font to spacing.

Word spacing changes the default spacing between individual words. A positive value increases the word spacing by a corresponding amount of pixels, while a negative value decreases the inter-word spacing accordingly.

Word spacing will not apply to writing systems, where indiviaul words are not separated by white space.

This function was introduced in Qt 4.4.

See also wordSpacing() and setLetterSpacing().

int QFont::stretch() const

Returns the stretch factor for the font.

See also setStretch().

bool QFont::strikeOut() const

Returns true if strikeout has been set; otherwise returns false.

See also setStrikeOut().

QFont::Style QFont::style() const

Returns the style of the font.

See also setStyle().

QFont::StyleHint QFont::styleHint() const

Returns the StyleHint.

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

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

QString QFont::styleName() const

Returns the requested font style name. This can be used to match the font with irregular styles (that can't be normalized in other style properties).

This function was introduced in Qt 4.8.

See also setStyleName(), setFamily(), and setStyle().

QFont::StyleStrategy QFont::styleStrategy() const

Returns the StyleStrategy.

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

See also setStyleStrategy(), setStyleHint(), and QFont::StyleHint.

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

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 removeSubstitutions().

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

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 removeSubstitutions().

[static] QStringList QFont::substitutions()

Returns a sorted list of substituted family names.

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

void QFont::swap(QFont &other)

Swaps this font instance with other. This function is very fast and never fails.

This function was introduced in Qt 5.0.

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, and consists of the following:

See also fromString().

bool QFont::underline() const

Returns true if underline has been set; otherwise returns false.

See also setUnderline().

int QFont::weight() const

Returns the weight of the font, using the same scale as the QFont::Weight enumeration.

See also setWeight(), Weight, and QFontInfo.

qreal QFont::wordSpacing() const

Returns the word spacing for the font.

This function was introduced in Qt 4.4.

See also setWordSpacing() and setLetterSpacing().

QVariant QFont::operator QVariant() const

Returns the font as a QVariant

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.

See also operator==().

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

Provides an arbitrary comparison of this font and font f. All that is guaranteed is that the operator returns false if both fonts are equal and that (f1 < f2) == !(f2 < f1) if the fonts are not equal.

This function is useful in some circumstances, for example if you want to use QFont objects as keys in a QMap.

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

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.

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