source: trunk/src/gui/painting/qpaintdevice.qdoc@ 758

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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 physical resolution differ, the corresponding
    QPaintEngine must handle the mapping. Finally, the colorCount()
    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().