Detailed Description
The QFontMetrics 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 a
QFontMetrics object:
- 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.
- 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.
- QPainter::fontMetrics() returns the font metrics for a
painter's current font. If the widget's font is changed later, the
font metrics object is not updated.
* 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.
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 width(), 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 width(), 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.width( "What's the width of this text?" );
int pixelsHigh = fm.height();
See also QFont, QFontInfo, QFontDatabase, Graphics Classes, and Implicitly and Explicitly Shared Classes.
Member Function Documentation
QFontMetrics::QFontMetrics ( const QFont & font )
Constructs a font metrics object for font.
The font must be screen-compatible, i.e. a font you use when
drawing text in widgets or pixmaps, not 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.
Use QPainter::fontMetrics() to get the font metrics when painting.
This will give correct results also when painting on paint device
that is not screen-compatible.
QFontMetrics::QFontMetrics ( const QFont & font, QFont::Script script )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Constructs a font metrics object for font using the given script.
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 an unusual character in
an exotic language, so it is possible (though rare) that this
value will be too small.
See also descent().
Examples: drawdemo/drawdemo.cpp and scrollview/scrollview.cpp.
QRect QFontMetrics::boundingRect ( QChar ch ) const
Returns the bounding rectangle of the character ch relative to
the left-most point on the base line.
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.
Note that the rectangle usually extends both above and below the
base line.
See also width().
Example: xform/xform.cpp.
QRect QFontMetrics::boundingRect ( const QString & str, int len = -1 ) const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns the bounding rectangle that contains the first len
characters of string str.
QRect QFontMetrics::boundingRect ( int x, int y, int w, int h, int flgs, const QString & str, int len = -1, int tabstops = 0, int * tabarray = 0, QTextParag ** intern = 0 ) const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns the bounding rectangle of the first len characters of
str, 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 (x, y, w, h).
If len is negative (which is the default), the entire string is
used.
The flgs argument is the bitwise OR of the following flags:
- AlignAuto aligns to the left border for all languages except
Arabic and Hebrew where it aligns to the right.
- AlignLeft aligns to the left border.
- AlignRight aligns to the right border.
- AlignJustify produces justified text.
- AlignHCenter aligns horizontally centered.
- AlignTop aligns to the top border.
- AlignBottom aligns to the bottom border.
- AlignVCenter aligns vertically centered
- AlignCenter (== AlignHCenter | AlignVCenter)
- SingleLine ignores newline characters in the text.
- ExpandTabs expands tabs (see below)
- ShowPrefix interprets "&x" as "x", i.e. underlined.
- WordBreak breaks the text to fit the rectangle.
Horizontal alignment defaults to AlignAuto and vertical
alignment defaults to AlignTop.
If several of the horizontal or several of the vertical alignment
flags are set, the resulting alignment is undefined.
These flags are defined in qnamespace.h.
If ExpandTabs is set in flgs, 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 given 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.
The intern argument should not be used.
See also width(), QPainter::boundingRect(), and Qt::AlignmentFlags.
int QFontMetrics::charWidth ( const QString & str, int pos ) const
Returns the width of the character at position pos in the
string str.
The whole string is needed, as the glyph drawn may change
depending on the context (the letter before and after the current
one) for some languages (e.g. Arabic).
This function also takes non spacing marks and ligatures into
account.
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. (Note that this is different from X, which
adds 1 pixel.) 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 also ascent().
Examples: drawdemo/drawdemo.cpp and hello/hello.cpp.
int QFontMetrics::height () const
Returns the height of the font.
This is always equal to ascent()+descent()+1 (the 1 is for the
base line).
See also leading() and lineSpacing().
Examples: grapher/grapher.cpp, hello/hello.cpp, and qfd/fontdisplayer.cpp.
bool QFontMetrics::inFont ( QChar ch ) const
Returns TRUE if character ch is a valid character in the font;
otherwise returns FALSE.
Example: qfd/fontdisplayer.cpp.
int QFontMetrics::leading () const
Returns the leading of the font.
This is the natural inter-line spacing.
See also height() and 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 width(QChar) for a graphical description of this metric.
See also rightBearing(), minLeftBearing(), and width().
Example: qfd/fontdisplayer.cpp.
int QFontMetrics::lineSpacing () const
Returns the distance from one base line to the next.
This value is always equal to leading()+height().
See also height() and leading().
Examples: qfd/fontdisplayer.cpp, qwerty/qwerty.cpp, and scrollview/scrollview.cpp.
int QFontMetrics::lineWidth () const
Returns the width of the underline and strikeout lines, adjusted
for the point size of the font.
See also underlinePos(), overlinePos(), and strikeOutPos().
int QFontMetrics::maxWidth () const
Returns the width of the widest character in the font.
Example: qfd/fontdisplayer.cpp.
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 minRightBearing() and leftBearing().
Example: qfd/fontdisplayer.cpp.
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 minLeftBearing() and rightBearing().
Example: qfd/fontdisplayer.cpp.
Assigns the font metrics fm.
int QFontMetrics::overlinePos () const
Returns the distance from the base line to where an overline
should be drawn.
See also underlinePos(), strikeOutPos(), and 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 width() of the character.
See width() for a graphical description of this metric.
See also leftBearing(), minRightBearing(), and width().
Example: qfd/fontdisplayer.cpp.
QSize QFontMetrics::size ( int flgs, const QString & str, int len = -1, int tabstops = 0, int * tabarray = 0, QTextParag ** intern = 0 ) const
Returns the size in pixels of the first len characters of str.
If len is negative (the default), the entire string is used.
The flgs argument is the bitwise OR of the following flags:
- SingleLine ignores newline characters.
- ExpandTabs expands tabs (see below)
- ShowPrefix interprets "&x" as "x", i.e. underlined.
- WordBreak breaks the text to fit the rectangle.
These flags are defined in qnamespace.h.
If ExpandTabs is set in flgs, 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.
The intern argument should not be used.
See also boundingRect().
int QFontMetrics::strikeOutPos () const
Returns the distance from the base line to where the strikeout
line should be drawn.
See also underlinePos(), overlinePos(), and lineWidth().
int QFontMetrics::underlinePos () const
Returns the distance from the base line to where an underscore
should be drawn.
See also overlinePos(), strikeOutPos(), and lineWidth().
int QFontMetrics::width ( QChar ch ) const
Returns the logical width 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 to the right. The
central dark rectangles cover the logical width() 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.
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. Use charWidth()
instead if you aren't looking for the width of isolated
characters.
See also boundingRect() and charWidth().
Examples: drawdemo/drawdemo.cpp, hello/hello.cpp, movies/main.cpp, qfd/fontdisplayer.cpp, and scrollview/scrollview.cpp.
int QFontMetrics::width ( const QString & str, int len = -1 ) const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns the width of the first len characters of string str.
int QFontMetrics::width ( char c ) const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.
Provided to aid porting from Qt 1.x.
This file is part of the Qt toolkit.
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