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/*!

    \class QPaintDevice

    \brief The QPaintDevice class is the base class of objects that

    can be painted.

    \ingroup painting

    A paint device is an abstraction of a two-dimensional space that

    can be drawn using a QPainter.  Its default coordinate system has

    its origin located at the top-left position. X increases to the

    right and Y increases downwards. The unit is one pixel.

    The drawing capabilities of QPaintDevice are currently implemented

    by the QWidget, QImage, QPixmap, QGLPixelBuffer, QPicture, and

    QPrinter subclasses.

    To implement support for a new backend, you must derive from

    QPaintDevice and reimplement the virtual paintEngine() function to

    tell QPainter which paint engine should be used to draw on this

    particular device. Note that you also must create a corresponding

    paint engine to be able to draw on the device, i.e derive from

    QPaintEngine and reimplement its virtual functions.

    \warning Qt requires that a QApplication object exists before

    any paint devices can be created. Paint devices access window

    system resources, and these resources are not initialized before

    an application object is created.

    The QPaintDevice class provides several functions returning the

    various device metrics: The depth() function returns its bit depth

    (number of bit planes). The height() function returns its height

    in default coordinate system units (e.g. pixels for QPixmap and

    QWidget) while heightMM() returns the height of the device in

    millimeters. Similiarily, the width() and widthMM() functions

    return the width of the device in default coordinate system units

    and in millimeters, respectively. Alternatively, the protected

    metric() function can be used to retrieve the metric information

    by specifying the desired PaintDeviceMetric as argument.

    The logicalDpiX() and logicalDpiY() functions return the

    horizontal and vertical resolution of the device in dots per

    inch. The physicalDpiX() and physicalDpiY() functions also return

    the resolution of the device in dots per inch, but note that if

    the logical and vertical resolution differ, the corresponding

    QPaintEngine must handle the mapping. Finally, the numColors()

    function returns the number of different colors available for the

    paint device.

    \sa QPaintEngine, QPainter, {The Coordinate System}, {The Paint

    System}

*/

/*!

    \enum QPaintDevice::PaintDeviceMetric

    Describes the various metrics of a paint device.

    \value PdmWidth The width of the paint device in default

    coordinate system units (e.g. pixels for QPixmap and QWidget). See

    also width().

    \value PdmHeight The height of the paint device in default

    coordinate system units (e.g. pixels for QPixmap and QWidget). See

    also height().

    \value PdmWidthMM The width of the paint device in millimeters. See

    also widthMM().

    \value PdmHeightMM  The height of the paint device in millimeters. See

    also heightMM().

    \value PdmNumColors The number of different colors available for

    the paint device. See also numColors().

    \value PdmDepth The bit depth (number of bit planes) of the paint

    device. See also depth().

    \value PdmDpiX The horizontal resolution of the device in dots per

    inch. See also logicalDpiX().

    \value PdmDpiY  The vertical resolution of the device in dots per inch. See

    also logicalDpiY().

    \value PdmPhysicalDpiX The horizontal resolution of the device in

    dots per inch. See also physicalDpiX().

    \value PdmPhysicalDpiY The vertical resolution of the device in

    dots per inch. See also physicalDpiY().

    \sa metric()

*/

/*!

    \fn QPaintDevice::QPaintDevice()

    Constructs a paint device. This constructor can be invoked only from

    subclasses of QPaintDevice.

*/

/*!

    \fn QPaintDevice::~QPaintDevice()

    Destroys the paint device and frees window system resources.

*/

/*!

    \fn int QPaintDevice::devType() const

    \internal

    Returns the device type identifier, which is QInternal::Widget

    if the device is a QWidget, QInternal::Pixmap if it's a

    QPixmap, QInternal::Printer if it's a QPrinter,

    QInternal::Picture if it's a QPicture, or

    QInternal::UnknownDevice in other cases.

*/

/*!

    \fn bool QPaintDevice::paintingActive() const

    Returns true if the device is currently being painted on, i.e. someone has

    called QPainter::begin() but not yet called QPainter::end() for

    this device; otherwise returns false.

    \sa QPainter::isActive()

*/

/*!

    \fn QPaintEngine *QPaintDevice::paintEngine() const

    Returns a pointer to the paint engine used for drawing on the

    device.

*/

/*!

    \fn int QPaintDevice::metric(PaintDeviceMetric metric) const

    Returns the metric information for  the given paint device \a metric.

    \sa PaintDeviceMetric

*/

/*!

    \fn int QPaintDevice::width() const

    Returns the width of the paint device in default coordinate system

    units (e.g. pixels for QPixmap and QWidget).

    \sa widthMM()

*/

/*!

    \fn int QPaintDevice::height() const

    Returns the height of the paint device in default coordinate

    system units (e.g. pixels for QPixmap and QWidget).

    \sa heightMM()

*/

/*!

    \fn int QPaintDevice::widthMM() const

    Returns the width of the paint device in millimeters. Due to platform

    limitations it may not be possible to use this function to determine

    the actual physical size of a widget on the screen.

    \sa width()

*/

/*!

    \fn int QPaintDevice::heightMM() const

    Returns the height of the paint device in millimeters. Due to platform

    limitations it may not be possible to use this function to determine

    the actual physical size of a widget on the screen.

    \sa height()

*/

/*!

    \fn int QPaintDevice::numColors() const

    Returns the number of different colors available for the paint

    device. Since this value is an int, it will not be sufficient to represent

    the number of colors on 32 bit displays, in this case INT_MAX is

    returned instead.

*/

/*!

    \fn int QPaintDevice::depth() const

    Returns the bit depth (number of bit planes) of the paint device.

*/

/*!

    \fn int QPaintDevice::logicalDpiX() const

    Returns the horizontal resolution of the device in dots per inch,

    which is used when computing font sizes. For X11, this is usually

    the same as could be computed from widthMM().

    Note that if the logicalDpiX() doesn't equal the physicalDpiX(),

    the corresponding QPaintEngine must handle the resolution mapping.

    \sa logicalDpiY(), physicalDpiX()

*/

/*!

    \fn int QPaintDevice::logicalDpiY() const

    Returns the vertical resolution of the device in dots per inch,

    which is used when computing font sizes. For X11, this is usually

    the same as could be computed from heightMM().

    Note that if the logicalDpiY() doesn't equal the physicalDpiY(),

    the corresponding QPaintEngine must handle the resolution mapping.

    \sa  logicalDpiX(), physicalDpiY()

*/

/*!

    \fn int QPaintDevice::physicalDpiX() const

    Returns the horizontal resolution of the device in dots per inch.

    For example, when printing, this resolution refers to the physical

    printer's resolution. The logical DPI on the other hand, refers to

    the resolution used by the actual paint engine.

    Note that if the physicalDpiX() doesn't equal the logicalDpiX(),

    the corresponding QPaintEngine must handle the resolution mapping.

    \sa  physicalDpiY(),  logicalDpiX()

*/

/*!

    \fn int QPaintDevice::physicalDpiY() const

    Returns the horizontal resolution of the device in dots per inch.

    For example, when printing, this resolution refers to the physical

    printer's resolution. The logical DPI on the other hand, refers to

    the resolution used by the actual paint engine.

    Note that if the physicalDpiY() doesn't equal the logicalDpiY(),

    the corresponding QPaintEngine must handle the resolution mapping.

    \sa  physicalDpiX(),  logicalDpiY()

*/