Contents

• Public Functions
• Detailed Description

Detailed Description

TheQFontMetrics class provides font metrics information.

QFontMetrics functions calculate the size of characters and strings for a given font. There are three ways you can create aQFontMetrics object:

1. Calling theQFontMetrics constructor with aQFont creates a font metrics object for a screen-compatible font, i.e. the font cannot be a printer font. If the font is changed later, the font metrics object isnot updated.

   (Note: If you use a printer font the values returned may be inaccurate. Printer fonts are not always accessible so the nearest screen font is used if a printer font is supplied.)

2. QWidget::fontMetrics() returns the font metrics for a widget's font. This is equivalent toQFontMetrics(widget->font()). If the widget's font is changed later, the font metrics object isnot updated.
3. QPainter::fontMetrics() returns the font metrics for a painter's current font. If the painter's font is changed later, the font metrics object isnot updated.

Once created, the object provides functions to access the individual metrics of the font, its characters, and for strings rendered in the font.

There are several functions that operate on the font:ascent(),descent(),height(),leading() andlineSpacing() return the basic size properties of the font. TheunderlinePos(),overlinePos(),strikeOutPos() andlineWidth() functions, return the properties of the line that underlines, overlines or strikes out the characters. These functions are all fast.

There are also some functions that operate on the set of glyphs in the font:minLeftBearing(),minRightBearing() andmaxWidth(). These are by necessity slow, and we recommend avoiding them if possible.

For each character, you can get itswidth(),leftBearing() andrightBearing() and find out whether it is in the font usinginFont(). You can also treat the character as a string, and use the string functions on it.

The string functions includewidth(), to return the width of a string in pixels (or points, for a printer),boundingRect(), to return a rectangle large enough to contain the rendered string, andsize(), to return the size of that rectangle.

Example:

QFont font("times",24);QFontMetrics fm(font);int pixelsWide= fm.width("What's the width of this text?");int pixelsHigh= fm.height();

Member Function Documentation

QFontMetrics::QFontMetrics(constQFont & font)

Constructs a font metrics object forfont.

The font metrics will be compatible with the paintdevice used to createfont.

The font metrics object holds the information for the font that is passed in the constructor at the time it is created, and is not updated if the font's attributes are changed later.

UseQFontMetrics(constQFont &,QPaintDevice *) to get the font metrics that are compatible with a certain paint device.

QFontMetrics::QFontMetrics(constQFont & font,QPaintDevice * paintdevice)

Constructs a font metrics object forfont andpaintdevice.

The font metrics will be compatible with the paintdevice passed. If thepaintdevice is 0, the metrics will be screen-compatible, ie. the metrics you get if you use the font for drawing text on awidgets orpixmaps, not on aQPicture orQPrinter.

The font metrics object holds the information for the font that is passed in the constructor at the time it is created, and is not updated if the font's attributes are changed later.

QFontMetrics::QFontMetrics(constQFontMetrics & fm)

Constructs a copy offm.

QFontMetrics::~QFontMetrics()

Destroys the font metrics object and frees all allocated resources.

int QFontMetrics::ascent() const

Returns the ascent of the font.

The ascent of a font is the distance from the baseline to the highest position characters extend to. In practice, some font designers break this rule, e.g. when they put more than one accent on top of a character, or to accommodate an unusual character in an exotic language, so it is possible (though rare) that this value will be too small.

See alsodescent().

int QFontMetrics::averageCharWidth() const

Returns the average width of glyphs in the font.

This function was introduced in Qt 4.2.

QRect QFontMetrics::boundingRect(QChar ch) const

Returns the rectangle that is covered by ink if characterch were to be drawn at the origin of the coordinate system.

Note that the bounding rectangle may extend to the left of (0, 0) (e.g., for italicized fonts), and that the text output may coverall pixels in the bounding rectangle. For a space character the rectangle will usually be empty.

Note that the rectangle usually extends both above and below the base line.

Warning: The width of the returned rectangle is not the advance width of the character. Use boundingRect(constQString &) orwidth() instead.

See alsowidth().

QRect QFontMetrics::boundingRect(constQString & text) const

Returns the bounding rectangle of the characters in the string specified bytext. The bounding rectangle always covers at least the set of pixels the text would cover if drawn at (0, 0).

Note that the bounding rectangle may extend to the left of (0, 0), e.g. for italicized fonts, and that the width of the returned rectangle might be different than what thewidth() method returns.

If you want to know the advance width of the string (to layout a set of strings next to each other), usewidth() instead.

Newline characters are processed as normal characters,not as linebreaks.

The height of the bounding rectangle is at least as large as the value returned byheight().

See alsowidth(),height(),QPainter::boundingRect(), andtightBoundingRect().

QRect QFontMetrics::boundingRect(int x,int y,int width,int height,int flags, constQString & text,int tabStops = 0,int * tabArray = 0) const

This is an overloaded function.

Returns the bounding rectangle for the giventext within the rectangle specified by thex andy coordinates,width, andheight.

IfQt::TextExpandTabs is set inflags andtabArray is non-null, it specifies a 0-terminated sequence of pixel-positions for tabs; otherwise, iftabStops is non-zero, it is used as the tab spacing (in pixels).

QRect QFontMetrics::boundingRect(constQRect & rect,int flags, constQString & text,int tabStops = 0,int * tabArray = 0) const

This is an overloaded function.

Returns the bounding rectangle of the characters in the string specified bytext, which is the set of pixels the text would cover if drawn at (0, 0). The drawing, and hence the bounding rectangle, is constrained to the rectanglerect.

Theflags argument is the bitwise OR of the following flags:

• Qt::AlignLeft aligns to the left border, except for Arabic and Hebrew where it aligns to the right.
• Qt::AlignRight aligns to the right border, except for Arabic and Hebrew where it aligns to the left.
• Qt::AlignJustify produces justified text.
• Qt::AlignHCenter aligns horizontally centered.
• Qt::AlignTop aligns to the top border.
• Qt::AlignBottom aligns to the bottom border.
• Qt::AlignVCenter aligns vertically centered
• Qt::AlignCenter (==Qt::AlignHCenter | Qt::AlignVCenter)
• Qt::TextSingleLine ignores newline characters in the text.
• Qt::TextExpandTabs expands tabs (see below)
• Qt::TextShowMnemonic interprets "&x" asx; i.e., underlined.
• Qt::TextWordWrap breaks the text to fit the rectangle.

Qt::Horizontal alignment defaults toQt::AlignLeft and vertical alignment defaults toQt::AlignTop.

If several of the horizontal or several of the vertical alignment flags are set, the resulting alignment is undefined.

IfQt::TextExpandTabs is set inflags, then: iftabArray is non-null, it specifies a 0-terminated sequence of pixel-positions for tabs; otherwise iftabStops is non-zero, it is used as the tab spacing (in pixels).

Note that the bounding rectangle may extend to the left of (0, 0), e.g. for italicized fonts, and that the text output may coverall pixels in the bounding rectangle.

Newline characters are processed as linebreaks.

Despite the different actual character heights, the heights of the bounding rectangles of "Yes" and "yes" are the same.

The bounding rectangle returned by this function is somewhat larger than that calculated by the simplerboundingRect() function. This function uses themaximum left andright font bearings as is necessary for multi-line text to align correctly. Also, fontHeight() andlineSpacing() are used to calculate the height, rather than individual character heights.

See alsowidth(),QPainter::boundingRect(), andQt::Alignment.

int QFontMetrics::descent() const

Returns the descent of the font.

The descent is the distance from the base line to the lowest point characters extend to. In practice, some font designers break this rule, e.g. to accommodate an unusual character in an exotic language, so it is possible (though rare) that this value will be too small.

See alsoascent().

QString QFontMetrics::elidedText(constQString & text,Qt::TextElideMode mode,int width,int flags = 0) const

If the stringtext is wider thanwidth, returns an elided version of the string (i.e., a string with "..." in it). Otherwise, returns the original string.

Themode parameter specifies whether the text is elided on the left (e.g., "...tech"), in the middle (e.g., "Tr...ch"), or on the right (e.g., "Trol...").

Thewidth is specified in pixels, not characters.

Theflags argument is optional and currently only supportsQt::TextShowMnemonic as value.

The elide mark will follow thelayout direction; it will be on the right side of the text for right-to-left layouts, and on the left side for right-to-left layouts. Note that this behavior is independent of the text language.

This function was introduced in Qt 4.2.

int QFontMetrics::height() const

Returns the height of the font.

This is always equal toascent()+descent()+1 (the 1 is for the base line).

See alsoleading() andlineSpacing().

bool QFontMetrics::inFont(QChar ch) const

Returns true if characterch is a valid character in the font; otherwise returns false.

bool QFontMetrics::inFontUcs4(uint character) const

Returns true if the givencharacter encoded in UCS-4/UTF-32 is a valid character in the font; otherwise returns false.

This function was introduced in Qt 4.8.

int QFontMetrics::leading() const

Returns the leading of the font.

This is the natural inter-line spacing.

See alsoheight() andlineSpacing().

int QFontMetrics::leftBearing(QChar ch) const

Returns the left bearing of characterch in the font.

The left bearing is the right-ward distance of the left-most pixel of the character from the logical origin of the character. This value is negative if the pixels of the character extend to the left of the logical origin.

See width(QChar) for a graphical description of this metric.

See alsorightBearing(),minLeftBearing(), andwidth().

int QFontMetrics::lineSpacing() const

Returns the distance from one base line to the next.

This value is always equal toleading()+height().

See alsoheight() andleading().

int QFontMetrics::lineWidth() const

Returns the width of the underline and strikeout lines, adjusted for the point size of the font.

See alsounderlinePos(),overlinePos(), andstrikeOutPos().

int QFontMetrics::maxWidth() const

Returns the width of the widest character in the font.

int QFontMetrics::minLeftBearing() const

Returns the minimum left bearing of the font.

This is the smallestleftBearing(char) of all characters in the font.

Note that this function can be very slow if the font is large.

See alsominRightBearing() andleftBearing().

int QFontMetrics::minRightBearing() const

Returns the minimum right bearing of the font.

This is the smallestrightBearing(char) of all characters in the font.

Note that this function can be very slow if the font is large.

See alsominLeftBearing() andrightBearing().

int QFontMetrics::overlinePos() const

Returns the distance from the base line to where an overline should be drawn.

See alsounderlinePos(),strikeOutPos(), andlineWidth().

int QFontMetrics::rightBearing(QChar ch) const

Returns the right bearing of characterch in the font.

The right bearing is the left-ward distance of the right-most pixel of the character from the logical origin of a subsequent character. This value is negative if the pixels of the character extend to the right of thewidth() of the character.

Seewidth() for a graphical description of this metric.

See alsoleftBearing(),minRightBearing(), andwidth().

QSize QFontMetrics::size(int flags, constQString & text,int tabStops = 0,int * tabArray = 0) const

Returns the size in pixels oftext.

Theflags argument is the bitwise OR of the following flags:

• Qt::TextSingleLine ignores newline characters.
• Qt::TextExpandTabs expands tabs (see below)
• Qt::TextShowMnemonic interprets "&x" asx; i.e., underlined.
• Qt::TextWordBreak breaks the text to fit the rectangle.

IfQt::TextExpandTabs is set inflags, then: iftabArray is non-null, it specifies a 0-terminated sequence of pixel-positions for tabs; otherwise iftabStops is non-zero, it is used as the tab spacing (in pixels).

Newline characters are processed as linebreaks.

Despite the different actual character heights, the heights of the bounding rectangles of "Yes" and "yes" are the same.

See alsoboundingRect().

int QFontMetrics::strikeOutPos() const

Returns the distance from the base line to where the strikeout line should be drawn.

See alsounderlinePos(),overlinePos(), andlineWidth().

QRect QFontMetrics::tightBoundingRect(constQString & text) const

Returns a tight bounding rectangle around the characters in the string specified bytext. The bounding rectangle always covers at least the set of pixels the text would cover if drawn at (0, 0).

Note that the bounding rectangle may extend to the left of (0, 0), e.g. for italicized fonts, and that the width of the returned rectangle might be different than what thewidth() method returns.

If you want to know the advance width of the string (to layout a set of strings next to each other), usewidth() instead.

Newline characters are processed as normal characters,not as linebreaks.

Warning: Calling this method is very slow on Windows.

This function was introduced in Qt 4.3.

See alsowidth(),height(), andboundingRect().

int QFontMetrics::underlinePos() const

Returns the distance from the base line to where an underscore should be drawn.

See alsooverlinePos(),strikeOutPos(), andlineWidth().

int QFontMetrics::width(constQString & text,int len = -1) const

Returns the width in pixels of the firstlen characters oftext. Iflen is negative (the default), the entire string is used.

Note that this value isnot equal toboundingRect().width();boundingRect() returns a rectangle describing the pixels this string will cover whereas width() returns the distance to where the next string should be drawn.

See alsoboundingRect().

int QFontMetrics::width(QChar ch) const

This is an overloaded function.

Returns the logical width of characterch in pixels. This is a distance appropriate for drawing a subsequent character afterch.

Some of the metrics are described in the image to the right. The central dark rectangles cover the logicalwidth() of each character. The outer pale rectangles cover theleftBearing() andrightBearing() of each character. Notice that the bearings of "f" in this particular font are both negative, while the bearings of "o" are both positive.

Warning: This function will produce incorrect results for Arabic characters or non-spacing marks in the middle of a string, as the glyph shaping and positioning of marks that happens when processing strings cannot be taken into account. When implementing an interactive text control, useQTextLayout instead.

See alsoboundingRect().

int QFontMetrics::xHeight() const

Returns the 'x' height of the font. This is often but not always the same as the height of the character 'x'.

bool QFontMetrics::operator!=(constQFontMetrics & other)

Returns true ifother is not equal to this object; otherwise returns false.

Two font metrics are considered equal if they were constructed from the sameQFont and the paint devices they were constructed for are considered compatible.

See alsooperator==().

bool QFontMetrics::operator!=(constQFontMetrics & other) const

Returns true ifother is not equal to this object; otherwise returns false.

Two font metrics are considered equal if they were constructed from the sameQFont and the paint devices they were constructed for are considered compatible.

See alsooperator==().

QFontMetrics & QFontMetrics::operator=(constQFontMetrics & fm)

Assigns the font metricsfm.

QFontMetrics & QFontMetrics::operator=(QFontMetrics && other)

bool QFontMetrics::operator==(constQFontMetrics & other)

Returns true ifother is equal to this object; otherwise returns false.

Two font metrics are considered equal if they were constructed from the sameQFont and the paint devices they were constructed for are considered compatible.

See alsooperator!=().

bool QFontMetrics::operator==(constQFontMetrics & other) const

This is an overloaded function.

Returns true ifother is equal to this object; otherwise returns false.

Two font metrics are considered equal if they were constructed from the sameQFont and the paint devices they were constructed for are considered compatible.

See alsooperator!=().