source: trunk/doc/src/examples/textobject.qdoc@ 560

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41
42/*!
43 \example richtext/textobject
44 \title Text Object Example
45
46 The Text Object example shows how to insert an SVG file into a
47 QTextDocument.
48
49 \image textobject-example.png
50
51 A QTextDocument consists of a hierarchy of elements, such as text blocks and
52 frames. A text object describes the structure or format of one or more of these
53 elements. For instance, images imported from HTML are implemented using text
54 objects. Text objects are used by the document's
55 \l{QAbstractTextDocumentLayout}{layout} to lay out and render (paint) the
56 document. Each object knows how to paint the elements they govern, and
57 calculates their size.
58
59 To be able to insert an SVG image into a text document, we create
60 a text object, and implement painting for that object. This object
61 can then be \l{QTextCharFormat::setObjectType()}{set} on a
62 QTextCharFormat. We also register the text object with the layout
63 of the document, enabling it to draw \l{QTextCharFormat}s governed
64 by our text object. We can summarize the procedure with the
65 following steps:
66
67 \list
68 \o Implement the text object.
69 \o Register the text object with the layout of the text
70 document.
71 \o Set the text object on a QTextCharFormat.
72 \o Insert a QChar::ObjectReplacementCharacter with that
73 text char format into the document.
74 \endlist
75
76 The example consists of the following classes:
77
78 \list
79 \o \c{SvgTextObject} implements the text object.
80 \o \c{Window} shows a QTextEdit into which SVG images can be
81 inserted.
82 \endlist
83
84 \section1 SvgTextObject Class Definition
85
86 Let's take a look at the header file of \c {SvgTextObject}:
87
88 \snippet examples/richtext/textobject/svgtextobject.h 0
89
90 A text object is a QObject that implements QTextObjectInterface.
91 Note that the first class inherited must be QObject, and that
92 you must use Q_INTERFACES to let Qt know that your class
93 implements QTextObjectInterface.
94
95 The document layout keeps a collection of text objects stored as
96 \l{QObject}s, each of which has an associated object type. The
97 layout casts the QObject for the associated object type into the
98 QTextObjectInterface.
99
100 The \l{QTextObjectInterface::}{intrinsicSize()} and
101 \l{QTextObjectInterface::}{drawObject()} functions are then used
102 to calculate the size of the text object and draw it.
103
104 \section1 SvgTextObject Class Implementation
105
106 We start of by taking a look at the
107 \l{QTextObjectInterface::}{intrinsicSize()} function:
108
109 \snippet examples/richtext/textobject/svgtextobject.cpp 0
110
111 \c intrinsicSize() is called by the layout to calculate the size
112 of the text object. Notice that we have drawn the SVG image on a
113 QImage. This is because SVG rendering is quite expensive. The
114 example would lag seriously for large images if we drew them
115 with a QSvgRenderer each time.
116
117 \snippet examples/richtext/textobject/svgtextobject.cpp 1
118
119 In \c drawObject(), we paint the SVG image using the QPainter
120 provided by the layout.
121
122 \section1 Window Class Definition
123
124 The \c Window class is a self-contained window that has a
125 QTextEdit in which SVG images can be inserted.
126