qfontmetrics.cpp

奇趣公司比较新的qt/emd版本

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#include "qfont.h"
#include "qpaintdevice.h"
#include "qfontmetrics.h"

#include "qfont_p.h"
#include "qfontengine_p.h"
#include <private/qunicodetables_p.h>

#include <math.h>

#ifdef Q_WS_X11
#include "qx11info_x11.h"
extern const QX11Info *qt_x11Info(const QPaintDevice *pd);
#endif

extern void qt_format_text(const QFont& font, const QRectF &_r,
                           int tf, const QString &text, QRectF *brect,
                           int tabStops, int *tabArray, int tabArrayLen,
                           QPainter *painter);
extern int qt_defaultDpi();

/*****************************************************************************
  QFontMetrics member functions
 *****************************************************************************/

/*!
    \class QFontMetrics
    \brief The QFontMetrics class provides font metrics information.

    \ingroup multimedia
    \ingroup shared
    \ingroup text

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

    \list 1
    \o 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 \e 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.)

    \o 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 \e not
    updated.

    \o 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 \e not updated.
    \endlist

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

    \sa QFont, QFontInfo, QFontDatabase, QFontComboBox, {Character Map Example}
*/

/*!
    \fn QRect QFontMetrics::boundingRect(int x, int y, int width, int height,
        int flags, const QString &text, int tabStops, int *tabArray) const
    \overload

    Returns the bounding rectangle for the given \a text within the
    rectangle specified by the \a x and \a y coordinates, \a width, and
    \a height.

    If Qt::TextExpandTabs is set in \a flags and \a tabArray is
    non-null, it specifies a 0-terminated sequence of pixel-positions
    for tabs; otherwise, if \a tabStops is non-zero, it is used as the
    tab spacing (in pixels).
*/

/*!
    Constructs a font metrics object for \a font.

    The font metrics will be compatible with the paintdevice used to
    create \a 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.
*/
QFontMetrics::QFontMetrics(const QFont &font)
    : d(font.d)
{
    d->ref.ref();
}

/*!
    Constructs a font metrics object for \a font and \a paintdevice.

    The font metrics will be compatible with the paintdevice passed.
    If the \a paintdevice is 0, the metrics will be screen-compatible,
    ie. the metrics you get if you use the font for drawing text on a
    \link QWidget widgets\endlink or \link QPixmap pixmaps\endlink,
    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.
*/
QFontMetrics::QFontMetrics(const QFont &font, QPaintDevice *paintdevice)
{
    int dpi = paintdevice ? paintdevice->logicalDpiY() : qt_defaultDpi();
#ifdef Q_WS_X11
    const QX11Info *info = qt_x11Info(paintdevice);
    int screen = info ? info->screen() : 0;
#else
    const int screen = 0;
#endif
    if (font.d->dpi != dpi || font.d->screen != screen ) {
        d = new QFontPrivate(*font.d);
        d->dpi = dpi;
        d->screen = screen;
    } else {
        d = font.d;
        d->ref.ref();
    }

}

/*!
    Constructs a copy of \a fm.
*/
QFontMetrics::QFontMetrics(const QFontMetrics &fm)
    : d(fm.d)
{ d->ref.ref(); }

/*!
    Destroys the font metrics object and frees all allocated
    resources.
*/
QFontMetrics::~QFontMetrics()
{
    if (!d->ref.deref())
        delete d;
}

/*!
    Assigns the font metrics \a fm.
*/
QFontMetrics &QFontMetrics::operator=(const QFontMetrics &fm)
{
    qAtomicAssign(d, fm.d);
    return *this;
}

/*!
    \overload
    Returns true if \a 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.

    \sa operator!=()
*/
bool QFontMetrics::operator ==(const QFontMetrics &other) const
{
    return d == other.d;
}

/*!
    Returns true if \a 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.

    \sa operator!=()
*/
bool QFontMetrics::operator ==(const QFontMetrics &other)
{
    return d == other.d;
}

/*!
    \fn bool QFontMetrics::operator!=(const QFontMetrics &other)

    Returns true if \a 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.

    \sa operator==()
*/

/*!
    \fn bool QFontMetrics::operator !=(const QFontMetrics &other) const

    Returns true if \a 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.

    \sa operator==()
*/

/*!
    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.

    \sa descent()
*/
int QFontMetrics::ascent() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->ascent());
}


/*!
    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.

    \sa ascent()
*/
int QFontMetrics::descent() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->descent());
}

/*!
    Returns the height of the font.

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

    \sa leading(), lineSpacing()
*/
int QFontMetrics::height() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->ascent() + engine->descent()) + 1;
}

/*!
    Returns the leading of the font.

    This is the natural inter-line spacing.

    \sa height(), lineSpacing()
*/
int QFontMetrics::leading() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->leading());
}

/*!
    Returns the distance from one base line to the next.

    This value is always equal to leading()+height().

    \sa height(), leading()
*/
int QFontMetrics::lineSpacing() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->leading() + engine->ascent() + engine->descent()) + 1;
}

/*!
    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.

    \sa minRightBearing(), leftBearing()
*/
int QFontMetrics::minLeftBearing() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->minLeftBearing());
}

/*!
    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.

    \sa minLeftBearing(), rightBearing()
*/
int QFontMetrics::minRightBearing() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->minRightBearing());
}

/*!
    Returns the width of the widest character in the font.
*/
int QFontMetrics::maxWidth() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->maxCharWidth());
}

/*!
    Returns the 'x' height of the font. This is often but not always
    the same as the height of the character 'x'.
*/
int QFontMetrics::xHeight() const
{
    QFontEngine *engine = d->engineForScript(QUnicodeTables::Common);
    Q_ASSERT(engine != 0);
    return qRound(engine->xHeight());
}

/*!
    \since 4.2

    Returns the average width of glyphs in the font.
*/