source: trunk/src/gui/painting/qpaintdevice.qdoc@ 1012

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[556]1/****************************************************************************
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[846]3** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
[556]4** All rights reserved.
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[556]15**
[846]16** GNU Free Documentation License
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27
28/*!
29 \class QPaintDevice
30 \brief The QPaintDevice class is the base class of objects that
31 can be painted.
32
33 \ingroup painting
34
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.
39
40 The drawing capabilities of QPaintDevice are currently implemented
41 by the QWidget, QImage, QPixmap, QGLPixelBuffer, QPicture, and
42 QPrinter subclasses.
43
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.
50
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.
55
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.
66
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
74 paint device.
75
[846]76 \sa QPaintEngine, QPainter, {Coordinate System}, {Paint System}
[556]77*/
78
79/*!
80 \enum QPaintDevice::PaintDeviceMetric
81
82 Describes the various metrics of a paint device.
83
84 \value PdmWidth The width of the paint device in default
85 coordinate system units (e.g. pixels for QPixmap and QWidget). See
86 also width().
87
88 \value PdmHeight The height of the paint device in default
89 coordinate system units (e.g. pixels for QPixmap and QWidget). See
90 also height().
91
92 \value PdmWidthMM The width of the paint device in millimeters. See
93 also widthMM().
94
95 \value PdmHeightMM The height of the paint device in millimeters. See
96 also heightMM().
97
98 \value PdmNumColors The number of different colors available for
99 the paint device. See also colorCount().
100
101 \value PdmDepth The bit depth (number of bit planes) of the paint
102 device. See also depth().
103
104 \value PdmDpiX The horizontal resolution of the device in dots per
105 inch. See also logicalDpiX().
106
107 \value PdmDpiY The vertical resolution of the device in dots per inch. See
108 also logicalDpiY().
109
110 \value PdmPhysicalDpiX The horizontal resolution of the device in
111 dots per inch. See also physicalDpiX().
112
113 \value PdmPhysicalDpiY The vertical resolution of the device in
114 dots per inch. See also physicalDpiY().
115
116 \sa metric()
117*/
118
119/*!
120 \fn QPaintDevice::QPaintDevice()
121
122 Constructs a paint device. This constructor can be invoked only from
123 subclasses of QPaintDevice.
124*/
125
126/*!
127 \fn QPaintDevice::~QPaintDevice()
128
129 Destroys the paint device and frees window system resources.
130*/
131