QFontMetrics Class▲
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Header: QFontMetrics
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CMake:
find_package(Qt6 REQUIRED COMPONENTS Gui)
target_link_libraries(mytarget PRIVATE Qt6::Gui)
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qmake: QT += gui
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Group: QFontMetrics is part of Painting Classes, shared
Detailed Description▲
QFontMetrics functions calculate the size of characters and strings for a given font. There are three ways you can create a QFontMetrics object:
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Calling the QFontMetrics constructor with a QFont 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 is not 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.)
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QWidget::fontMetrics() returns the font metrics for a widget's font. This is equivalent to QFontMetrics(widget->font()). If the widget's font is changed later, the font metrics object is not updated.
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QPainter::fontMetrics() returns the font metrics for a painter's current font. If the painter's font is changed later, the font metrics object is not 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() and lineSpacing() return the basic size properties of the font. The underlinePos(), overlinePos(), strikeOutPos() and lineWidth() 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() and maxWidth(). These are by necessity slow, and we recommend avoiding them if possible.
For each character, you can get its horizontalAdvance(), leftBearing(), and rightBearing(), and find out whether it is in the font using inFont(). You can also treat the character as a string, and use the string functions on it.
The string functions include horizontalAdvance(), 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, and size(), to return the size of that rectangle.
Example:
QFont font("times", 24);
QFontMetrics fm(font);
int pixelsWide = fm.horizontalAdvance("What's the width of this text?");
int pixelsHigh = fm.height();See Also▲
See also QFont, QFontInfo, QFontDatabase, Character Map Example
Member Function Documentation▲
[explicit] QFontMetrics::QFontMetrics(const QFont &font)▲
Constructs a font metrics object for font.
The font metrics will be compatible with the paintdevice used to create font.
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.
Use QFontMetrics(const QFont &, QPaintDevice *) to get the font metrics that are compatible with a certain paint device.
[since 5.13] QFontMetrics::QFontMetrics(const QFont &font, const QPaintDevice *paintdevice)▲
Constructs a font metrics object for font and paintdevice.
The font metrics will be compatible with the paintdevice passed. If the paintdevice is nullptr, the metrics will be screen-compatible, ie. the metrics you get if you use the font for drawing text on a widgets or pixmaps, not on a QPicture or QPrinter.
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.
This function was introduced in Qt 5.13.
QFontMetrics::QFontMetrics(const QFontMetrics &fm)▲
Constructs a copy of fm.
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 a certain character, so it is possible (though rare) that this value will be too small.
See Also▲
See also descent()
int QFontMetrics::averageCharWidth() const▲
Returns the average width of glyphs in the font.
QRect QFontMetrics::boundingRect(QChar ch) const▲
Returns the rectangle that is covered by ink if character ch 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 cover all 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.
The width of the returned rectangle is not the advance width of the character. Use boundingRect(const QString &) or horizontalAdvance() instead.
See Also▲
See also horizontalAdvance()
QRect QFontMetrics::boundingRect(const QString &text) const▲
Returns the bounding rectangle of the characters in the string specified by text. 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 the horizontalAdvance() method returns.
If you want to know the advance width of the string (to lay out a set of strings next to each other), use horizontalAdvance() 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 by height().
See Also▲
See also horizontalAdvance(), height(), QPainter::boundingRect(), tightBoundingRect()
[since 6.3] QRect QFontMetrics::boundingRect(const QString &text, const QTextOption &option) const▲
Returns the bounding rectangle of the characters in the string specified by text laid out using option. 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 the horizontalAdvance() method returns.
If you want to know the advance width of the string (to lay out a set of strings next to each other), use horizontalAdvance() 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 by height().
This function was introduced in Qt 6.3.
See Also▲
See also horizontalAdvance(), height(), QPainter::boundingRect(), tightBoundingRect()
QRect QFontMetrics::boundingRect(const QRect &rect, int flags, const QString &text, int tabStops = 0, int *tabArray = nullptr) const▲
This is an overloaded function.
Returns the bounding rectangle of the characters in the string specified by text, 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 rectangle rect.
The flags argument is the bitwise OR of the following flags:
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Qt::AlignLeft aligns to the left border, except for Arabic and Hebrew where it aligns to the right.
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Qt::AlignRight aligns to the right border, except for Arabic and Hebrew where it aligns to the left.
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Qt::AlignJustify produces justified text.
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Qt::AlignHCenter aligns horizontally centered.
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Qt::AlignTop aligns to the top border.
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Qt::AlignBottom aligns to the bottom border.
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Qt::AlignVCenter aligns vertically centered
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Qt::AlignCenter (== Qt::AlignHCenter | Qt::AlignVCenter)
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Qt::TextSingleLine ignores newline characters in the text.
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Qt::TextExpandTabs expands tabs (see below)
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Qt::TextShowMnemonic interprets "&x" as x; i.e., underlined.
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Qt::TextWordWrap breaks the text to fit the rectangle.
Qt::Horizontal alignment defaults to Qt::AlignLeft and vertical alignment defaults to Qt::AlignTop.
If several of the horizontal or several of the vertical alignment flags are set, the resulting alignment is undefined.
If Qt::TextExpandTabs is set in flags, then: if tabArray is non-null, it specifies a 0-terminated sequence of pixel-positions for tabs; otherwise if tabStops 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 cover all 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 simpler boundingRect() function. This function uses the maximum left and right font bearings as is necessary for multi-line text to align correctly. Also, fontHeight() and lineSpacing() are used to calculate the height, rather than individual character heights.
See Also▲
See also horizontalAdvance(), QPainter::boundingRect(), Qt::Alignment
QRect QFontMetrics::boundingRect(int x, int y, int width, int height, int flags, const QString &text, int tabStops = 0, int *tabArray = nullptr) const▲
This is an overloaded function.
Returns the bounding rectangle for the given text within the rectangle specified by the x and y coordinates, width, and height.
If Qt::TextExpandTabs is set in flags and tabArray is non-null, it specifies a 0-terminated sequence of pixel-positions for tabs; otherwise, if tabStops is non-zero, it is used as the tab spacing (in pixels).
[since 5.8] int QFontMetrics::capHeight() const▲
Returns the cap height of the font.
The cap height of a font is the height of a capital letter above the baseline. It specifically is the height of capital letters that are flat - such as H or I - as opposed to round letters such as O, or pointed letters like A, both of which may display overshoot.
This function was introduced in Qt 5.8.
See Also▲
See also ascent()
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 a certain character, so it is possible (though rare) that this value will be too small.
See Also▲
See also ascent()
QString QFontMetrics::elidedText(const QString &text, Qt::TextElideMode mode, int width, int flags = 0) const▲
If the string text is wider than width, returns an elided version of the string (i.e., a string with "..." in it). Otherwise, returns the original string.
The mode 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...").
The width is specified in pixels, not characters.
The flags argument is optional and currently only supports Qt::TextShowMnemonic as value.
The elide mark follows the layoutdirection. For example, it will be on the right side of the text for right-to-left layouts if the mode is Qt::ElideLeft, and on the left side of the text if the mode is Qt::ElideRight.
[since 5.14] qreal QFontMetrics::fontDpi() const▲
Returns the font DPI.
This function was introduced in Qt 5.14.
int QFontMetrics::height() const▲
Returns the height of the font.
This is always equal to ascent()+descent().
See Also▲
See also leading(), lineSpacing()
[since 5.11] int QFontMetrics::horizontalAdvance(const QString &text, int len = -1) const▲
Returns the horizontal advance in pixels of the first len characters of text. If len is negative (the default), the entire string is used.
This is the distance appropriate for drawing a subsequent character after text.
This function was introduced in Qt 5.11.
See Also▲
See also boundingRect()
[since 6.3] int QFontMetrics::horizontalAdvance(const QString &text, const QTextOption &option) const▲
Returns the horizontal advance in pixels of text laid out using option.
The advance is the distance appropriate for drawing a subsequent character after text.
This function was introduced in Qt 6.3.
See Also▲
See also boundingRect()
[since 5.11] int QFontMetrics::horizontalAdvance(QChar ch) const▲
This is an overloaded function.
Returns the horizontal advance of character ch in pixels. This is a distance appropriate for drawing a subsequent character after ch.
Some of the metrics are described in the image. The central dark rectangles cover the logical horizontalAdvance() of each character. The outer pale rectangles cover the leftBearing() and rightBearing() of each character. Notice that the bearings of "f" in this particular font are both negative, while the bearings of "o" are both positive.
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, use QTextLayout instead.
This function was introduced in Qt 5.11.
See Also▲
See also boundingRect()
bool QFontMetrics::inFont(QChar ch) const▲
Returns true if character ch is a valid character in the font; otherwise returns false.
bool QFontMetrics::inFontUcs4(uint ucs4) const▲
Returns true if the character ucs4 encoded in UCS-4/UTF-32 is a valid character in the font; otherwise returns false.
int QFontMetrics::leading() const▲
Returns the leading of the font.
This is the natural inter-line spacing.
See Also▲
See also height(), lineSpacing()
int QFontMetrics::leftBearing(QChar ch) const▲
Returns the left bearing of character ch 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 horizontalAdvance() for a graphical description of this metric.
See Also▲
See also rightBearing(), minLeftBearing(), horizontalAdvance()
int QFontMetrics::lineSpacing() const▲
Returns the distance from one base line to the next.
This value is always equal to leading()+height().
See Also▲
int QFontMetrics::lineWidth() const▲
Returns the width of the underline and strikeout lines, adjusted for the point size of the font.
See Also▲
See also underlinePos(), overlinePos(), strikeOutPos()
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 smallest leftBearing(char) of all characters in the font.
Note that this function can be very slow if the font is large.
See Also▲
See also minRightBearing(), leftBearing()
int QFontMetrics::minRightBearing() const▲
Returns the minimum right bearing of the font.
This is the smallest rightBearing(char) of all characters in the font.
Note that this function can be very slow if the font is large.
See Also▲
See also minLeftBearing(), rightBearing()
int QFontMetrics::overlinePos() const▲
Returns the distance from the base line to where an overline should be drawn.
See Also▲
See also underlinePos(), strikeOutPos(), lineWidth()
int QFontMetrics::rightBearing(QChar ch) const▲
Returns the right bearing of character ch 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 the horizontalAdvance() of the character.
See horizontalAdvance() for a graphical description of this metric.
See Also▲
See also leftBearing(), minRightBearing(), horizontalAdvance()
QSize QFontMetrics::size(int flags, const QString &text, int tabStops = 0, int *tabArray = nullptr) const▲
Returns the size in pixels of text.
The flags argument is the bitwise OR of the following flags:
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Qt::TextSingleLine ignores newline characters.
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Qt::TextExpandTabs expands tabs (see below)
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Qt::TextShowMnemonic interprets "&x" as x; i.e., underlined.
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Qt::TextWordWrap breaks the text to fit the rectangle.
If Qt::TextExpandTabs is set in flags, then: if tabArray is non-null, it specifies a 0-terminated sequence of pixel-positions for tabs; otherwise if tabStops 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 Also▲
See also boundingRect()
int QFontMetrics::strikeOutPos() const▲
Returns the distance from the base line to where the strikeout line should be drawn.
See Also▲
See also underlinePos(), overlinePos(), lineWidth()
[since 5.0] void QFontMetrics::swap(QFontMetrics &other)▲
Swaps this font metrics instance with other. This function is very fast and never fails.
This function was introduced in Qt 5.0.
QRect QFontMetrics::tightBoundingRect(const QString &text) const▲
Returns a tight bounding rectangle around the characters in the string specified by text. 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 the horizontalAdvance() method returns.
If you want to know the advance width of the string (to lay out a set of strings next to each other), use horizontalAdvance() instead.
Newline characters are processed as normal characters, not as linebreaks.
See Also▲
See also horizontalAdvance(), height(), boundingRect()
[since 6.3] QRect QFontMetrics::tightBoundingRect(const QString &text, const QTextOption &option) const▲
Returns a tight bounding rectangle around the characters in the string specified by text laid out using option. 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 the horizontalAdvance() method returns.
If you want to know the advance width of the string (to lay out a set of strings next to each other), use horizontalAdvance() instead.
Newline characters are processed as normal characters, not as linebreaks.
This function was introduced in Qt 6.3.
See Also▲
See also horizontalAdvance(), height(), boundingRect()
int QFontMetrics::underlinePos() const▲
Returns the distance from the base line to where an underscore should be drawn.
See Also▲
See also overlinePos(), strikeOutPos(), lineWidth()
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!=(const QFontMetrics &other) const▲
Returns true if other is not equal to this object; otherwise returns false.
Two font metrics are considered equal if they were constructed from the same QFont and the paint devices they were constructed for are considered compatible.
See Also▲
See also operator==()
QFontMetrics &QFontMetrics::operator=(const QFontMetrics &fm)▲
Assigns the font metrics fm.
[since 5.2] QFontMetrics &QFontMetrics::operator=(QFontMetrics &&other)▲
Move-assigns other to this QFontMetrics instance.
This function was introduced in Qt 5.2.
bool QFontMetrics::operator==(const QFontMetrics &other) const▲
Returns true if other is equal to this object; otherwise returns false.
Two font metrics are considered equal if they were constructed from the same QFont and the paint devices they were constructed for are considered compatible.
See Also▲
See also operator!=()