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44 \brief The QPaintDevice class is the base class of objects that
49 A paint device is an abstraction of a two-dimensional space that
50 can be drawn using a QPainter. Its default coordinate system has
51 its origin located at the top-left position. X increases to the
52 right and Y increases downwards. The unit is one pixel.
54 The drawing capabilities of QPaintDevice are currently implemented
55 by the QWidget, QImage, QPixmap, QGLPixelBuffer, QPicture, and
58 To implement support for a new backend, you must derive from
59 QPaintDevice and reimplement the virtual paintEngine() function to
60 tell QPainter which paint engine should be used to draw on this
61 particular device. Note that you also must create a corresponding
62 paint engine to be able to draw on the device, i.e derive from
63 QPaintEngine and reimplement its virtual functions.
65 \warning Qt requires that a QApplication object exists before
66 any paint devices can be created. Paint devices access window
67 system resources, and these resources are not initialized before
68 an application object is created.
70 The QPaintDevice class provides several functions returning the
71 various device metrics: The depth() function returns its bit depth
72 (number of bit planes). The height() function returns its height
73 in default coordinate system units (e.g. pixels for QPixmap and
74 QWidget) while heightMM() returns the height of the device in
75 millimeters. Similiarily, the width() and widthMM() functions
76 return the width of the device in default coordinate system units
77 and in millimeters, respectively. Alternatively, the protected
78 metric() function can be used to retrieve the metric information
79 by specifying the desired PaintDeviceMetric as argument.
81 The logicalDpiX() and logicalDpiY() functions return the
82 horizontal and vertical resolution of the device in dots per
83 inch. The physicalDpiX() and physicalDpiY() functions also return
84 the resolution of the device in dots per inch, but note that if
85 the logical and vertical resolution differ, the corresponding
86 QPaintEngine must handle the mapping. Finally, the numColors()
87 function returns the number of different colors available for the
90 \sa QPaintEngine, QPainter, {The Coordinate System}, {The Paint
95 \enum QPaintDevice::PaintDeviceMetric
97 Describes the various metrics of a paint device.
99 \value PdmWidth The width of the paint device in default
100 coordinate system units (e.g. pixels for QPixmap and QWidget). See
103 \value PdmHeight The height of the paint device in default
104 coordinate system units (e.g. pixels for QPixmap and QWidget). See
107 \value PdmWidthMM The width of the paint device in millimeters. See
110 \value PdmHeightMM The height of the paint device in millimeters. See
113 \value PdmNumColors The number of different colors available for
114 the paint device. See also numColors().
116 \value PdmDepth The bit depth (number of bit planes) of the paint
117 device. See also depth().
119 \value PdmDpiX The horizontal resolution of the device in dots per
120 inch. See also logicalDpiX().
122 \value PdmDpiY The vertical resolution of the device in dots per inch. See
125 \value PdmPhysicalDpiX The horizontal resolution of the device in
126 dots per inch. See also physicalDpiX().
128 \value PdmPhysicalDpiY The vertical resolution of the device in
129 dots per inch. See also physicalDpiY().
135 \fn QPaintDevice::QPaintDevice()
137 Constructs a paint device. This constructor can be invoked only from
138 subclasses of QPaintDevice.
142 \fn QPaintDevice::~QPaintDevice()
144 Destroys the paint device and frees window system resources.
148 \fn int QPaintDevice::devType() const
152 Returns the device type identifier, which is QInternal::Widget
153 if the device is a QWidget, QInternal::Pixmap if it's a
154 QPixmap, QInternal::Printer if it's a QPrinter,
155 QInternal::Picture if it's a QPicture, or
156 QInternal::UnknownDevice in other cases.
160 \fn bool QPaintDevice::paintingActive() const
162 Returns true if the device is currently being painted on, i.e. someone has
163 called QPainter::begin() but not yet called QPainter::end() for
164 this device; otherwise returns false.
166 \sa QPainter::isActive()
170 \fn QPaintEngine *QPaintDevice::paintEngine() const
172 Returns a pointer to the paint engine used for drawing on the
177 \fn int QPaintDevice::metric(PaintDeviceMetric metric) const
179 Returns the metric information for the given paint device \a metric.
181 \sa PaintDeviceMetric
185 \fn int QPaintDevice::width() const
187 Returns the width of the paint device in default coordinate system
188 units (e.g. pixels for QPixmap and QWidget).
194 \fn int QPaintDevice::height() const
196 Returns the height of the paint device in default coordinate
197 system units (e.g. pixels for QPixmap and QWidget).
203 \fn int QPaintDevice::widthMM() const
205 Returns the width of the paint device in millimeters. Due to platform
206 limitations it may not be possible to use this function to determine
207 the actual physical size of a widget on the screen.
213 \fn int QPaintDevice::heightMM() const
215 Returns the height of the paint device in millimeters. Due to platform
216 limitations it may not be possible to use this function to determine
217 the actual physical size of a widget on the screen.
223 \fn int QPaintDevice::numColors() const
225 Returns the number of different colors available for the paint
226 device. Since this value is an int, it will not be sufficient to represent
227 the number of colors on 32 bit displays, in this case INT_MAX is
232 \fn int QPaintDevice::depth() const
234 Returns the bit depth (number of bit planes) of the paint device.
238 \fn int QPaintDevice::logicalDpiX() const
240 Returns the horizontal resolution of the device in dots per inch,
241 which is used when computing font sizes. For X11, this is usually
242 the same as could be computed from widthMM().
244 Note that if the logicalDpiX() doesn't equal the physicalDpiX(),
245 the corresponding QPaintEngine must handle the resolution mapping.
247 \sa logicalDpiY(), physicalDpiX()
251 \fn int QPaintDevice::logicalDpiY() const
253 Returns the vertical resolution of the device in dots per inch,
254 which is used when computing font sizes. For X11, this is usually
255 the same as could be computed from heightMM().
257 Note that if the logicalDpiY() doesn't equal the physicalDpiY(),
258 the corresponding QPaintEngine must handle the resolution mapping.
260 \sa logicalDpiX(), physicalDpiY()
264 \fn int QPaintDevice::physicalDpiX() const
266 Returns the horizontal resolution of the device in dots per inch.
267 For example, when printing, this resolution refers to the physical
268 printer's resolution. The logical DPI on the other hand, refers to
269 the resolution used by the actual paint engine.
271 Note that if the physicalDpiX() doesn't equal the logicalDpiX(),
272 the corresponding QPaintEngine must handle the resolution mapping.
274 \sa physicalDpiY(), logicalDpiX()
278 \fn int QPaintDevice::physicalDpiY() const
280 Returns the horizontal resolution of the device in dots per inch.
281 For example, when printing, this resolution refers to the physical
282 printer's resolution. The logical DPI on the other hand, refers to
283 the resolution used by the actual paint engine.
285 Note that if the physicalDpiY() doesn't equal the logicalDpiY(),
286 the corresponding QPaintEngine must handle the resolution mapping.
288 \sa physicalDpiX(), logicalDpiY()