QFontMetrics Class▲

  • Header: QFontMetrics

  • CMake:

    find_package(Qt6 REQUIRED COMPONENTS Gui)

    target_link_libraries(mytarget PRIVATE Qt6::Gui)

  • qmake: QT += gui

  • 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:

  1. 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.)

  2. 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.

  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 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:

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

See Also▲