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30 \brief The QPaintDevice class is the base class of objects that
35 A paint device is an abstraction of a two-dimensional space that
36 can be drawn using a QPainter. Its default coordinate system has
37 its origin located at the top-left position. X increases to the
38 right and Y increases downwards. The unit is one pixel.
40 The drawing capabilities of QPaintDevice are currently implemented
41 by the QWidget, QImage, QPixmap, QGLPixelBuffer, QPicture, and
44 To implement support for a new backend, you must derive from
45 QPaintDevice and reimplement the virtual paintEngine() function to
46 tell QPainter which paint engine should be used to draw on this
47 particular device. Note that you also must create a corresponding
48 paint engine to be able to draw on the device, i.e derive from
49 QPaintEngine and reimplement its virtual functions.
51 \warning Qt requires that a QApplication object exists before
52 any paint devices can be created. Paint devices access window
53 system resources, and these resources are not initialized before
54 an application object is created.
56 The QPaintDevice class provides several functions returning the
57 various device metrics: The depth() function returns its bit depth
58 (number of bit planes). The height() function returns its height
59 in default coordinate system units (e.g. pixels for QPixmap and
60 QWidget) while heightMM() returns the height of the device in
61 millimeters. Similiarily, the width() and widthMM() functions
62 return the width of the device in default coordinate system units
63 and in millimeters, respectively. Alternatively, the protected
64 metric() function can be used to retrieve the metric information
65 by specifying the desired PaintDeviceMetric as argument.
67 The logicalDpiX() and logicalDpiY() functions return the
68 horizontal and vertical resolution of the device in dots per
69 inch. The physicalDpiX() and physicalDpiY() functions also return
70 the resolution of the device in dots per inch, but note that if
71 the logical and physical resolution differ, the corresponding
72 QPaintEngine must handle the mapping. Finally, the colorCount()
73 function returns the number of different colors available for the
76 \sa QPaintEngine, QPainter, {Coordinate System}, {Paint System}
80 \enum QPaintDevice::PaintDeviceMetric
82 Describes the various metrics of a paint device.
84 \value PdmWidth The width of the paint device in default
85 coordinate system units (e.g. pixels for QPixmap and QWidget). See
88 \value PdmHeight The height of the paint device in default
89 coordinate system units (e.g. pixels for QPixmap and QWidget). See
92 \value PdmWidthMM The width of the paint device in millimeters. See
95 \value PdmHeightMM The height of the paint device in millimeters. See
98 \value PdmNumColors The number of different colors available for
99 the paint device. See also colorCount().
101 \value PdmDepth The bit depth (number of bit planes) of the paint
102 device. See also depth().
104 \value PdmDpiX The horizontal resolution of the device in dots per
105 inch. See also logicalDpiX().
107 \value PdmDpiY The vertical resolution of the device in dots per inch. See
110 \value PdmPhysicalDpiX The horizontal resolution of the device in
111 dots per inch. See also physicalDpiX().
113 \value PdmPhysicalDpiY The vertical resolution of the device in
114 dots per inch. See also physicalDpiY().
120 \fn QPaintDevice::QPaintDevice()
122 Constructs a paint device. This constructor can be invoked only from
123 subclasses of QPaintDevice.
127 \fn QPaintDevice::~QPaintDevice()
129 Destroys the paint device and frees window system resources.
133 \fn int QPaintDevice::devType() const
137 Returns the device type identifier, which is QInternal::Widget
138 if the device is a QWidget, QInternal::Pixmap if it's a
139 QPixmap, QInternal::Printer if it's a QPrinter,
140 QInternal::Picture if it's a QPicture, or
141 QInternal::UnknownDevice in other cases.
145 \fn bool QPaintDevice::paintingActive() const
147 Returns true if the device is currently being painted on, i.e. someone has
148 called QPainter::begin() but not yet called QPainter::end() for
149 this device; otherwise returns false.
151 \sa QPainter::isActive()
155 \fn QPaintEngine *QPaintDevice::paintEngine() const
157 Returns a pointer to the paint engine used for drawing on the
162 \fn int QPaintDevice::metric(PaintDeviceMetric metric) const
164 Returns the metric information for the given paint device \a metric.
166 \sa PaintDeviceMetric
170 \fn int QPaintDevice::width() const
172 Returns the width of the paint device in default coordinate system
173 units (e.g. pixels for QPixmap and QWidget).
179 \fn int QPaintDevice::height() const
181 Returns the height of the paint device in default coordinate
182 system units (e.g. pixels for QPixmap and QWidget).
188 \fn int QPaintDevice::widthMM() const
190 Returns the width of the paint device in millimeters. Due to platform
191 limitations it may not be possible to use this function to determine
192 the actual physical size of a widget on the screen.
198 \fn int QPaintDevice::heightMM() const
200 Returns the height of the paint device in millimeters. Due to platform
201 limitations it may not be possible to use this function to determine
202 the actual physical size of a widget on the screen.
208 \fn int QPaintDevice::colorCount() const
210 Returns the number of different colors available for the paint
211 device. Since this value is an int, it will not be sufficient to
212 represent the number of colors on 32 bit displays, in this case
213 INT_MAX is returned instead.
217 \fn int QPaintDevice::depth() const
219 Returns the bit depth (number of bit planes) of the paint device.
223 \fn int QPaintDevice::logicalDpiX() const
225 Returns the horizontal resolution of the device in dots per inch,
226 which is used when computing font sizes. For X11, this is usually
227 the same as could be computed from widthMM().
229 Note that if the logicalDpiX() doesn't equal the physicalDpiX(),
230 the corresponding QPaintEngine must handle the resolution mapping.
232 \sa logicalDpiY(), physicalDpiX()
236 \fn int QPaintDevice::logicalDpiY() const
238 Returns the vertical resolution of the device in dots per inch,
239 which is used when computing font sizes. For X11, this is usually
240 the same as could be computed from heightMM().
242 Note that if the logicalDpiY() doesn't equal the physicalDpiY(),
243 the corresponding QPaintEngine must handle the resolution mapping.
245 \sa logicalDpiX(), physicalDpiY()
249 \fn int QPaintDevice::physicalDpiX() const
251 Returns the horizontal resolution of the device in dots per inch.
252 For example, when printing, this resolution refers to the physical
253 printer's resolution. The logical DPI on the other hand, refers to
254 the resolution used by the actual paint engine.
256 Note that if the physicalDpiX() doesn't equal the logicalDpiX(),
257 the corresponding QPaintEngine must handle the resolution mapping.
259 \sa physicalDpiY(), logicalDpiX()
263 \fn int QPaintDevice::physicalDpiY() const
265 Returns the horizontal resolution of the device in dots per inch.
266 For example, when printing, this resolution refers to the physical
267 printer's resolution. The logical DPI on the other hand, refers to
268 the resolution used by the actual paint engine.
270 Note that if the physicalDpiY() doesn't equal the logicalDpiY(),
271 the corresponding QPaintEngine must handle the resolution mapping.
273 \sa physicalDpiX(), logicalDpiY()