1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
|
/****************************************************************************
**
** Copyright (C) 2017 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\example svggenerator
\title SVG Generator Example
The SVG Generator example shows how to add SVG file export to applications.
\image svggenerator-example.png
Scalable Vector Graphics (SVG) is an XML-based language for describing
two-dimensional vector graphics. Qt provides classes for rendering and
generating SVG drawings. This example allows the user to create a simple
picture and save it to an SVG file.
The example consists of two classes: \c Window and \c DisplayWidget.
The \c Window class contains the application logic and constructs the user
interface from a Qt Designer UI file as described in the
\l{Using a Designer UI File in Your C++ Application#The Multiple Inheritance Approach}{Qt Designer manual}.
It also contains the code to write an SVG file.
The \c DisplayWidget class performs all the work of painting a picture on
screen. Since we want the SVG to resemble this picture as closely as
possible, we make this code available to the \c Window class so that it can
be used to generate SVG files.
\section1 The DisplayWidget Class
The \c DisplayWidget class displays a drawing consisting of a selection of
elements chosen by the user. These are defined using \c Shape and
\c Background enums that are included within the class definition:
\snippet svggenerator/displaywidget.h DisplayWidget class definition
Much of this class is used to configure the appearance of the drawing. The
\c paintEvent() and \c paint() functions are most relevant to the purpose
of this example, so we will describe these here and leave the reader to
look at the source code for the example to see how shapes and colors are
handled.
We reimplement the QWidget::paintEvent() function to display the drawing
on screen:
\snippet svggenerator/displaywidget.cpp paint event
Here, we only construct a QPainter object, begin painting on the device
and set a render hint for improved output quality before calling the
\c paint() function to perform the painting itself. When this returns,
we close the painter and return.
The \c paint() function is designed to be used for different painting
tasks. In this example, we use it to draw on a \c DisplayWidget instance
and on a QSvgGenerator object. We show how the painting is performed to
demonstrate that there is nothing device-specific about the process:
\snippet svggenerator/displaywidget.cpp paint function
\section1 The Window Class
The \c Window class represents the example's window, containing the user
interface, which has been created using Qt Designer:
\snippet svggenerator/window.h Window class definition
As with the \c DisplayWidget class, we concentrate on the parts of the code
which are concerned with painting and SVG generation. In the \c Window
class, the \c saveSvg() function is called whenever the \b{Save As...}
button is clicked; this connection was defined in the \c{window.ui} file
using Qt Designer.
The start of the \c saveSvg() function performs the task of showing a file
dialog so that the user can specify a SVG file to save the drawing to.
\snippet svggenerator/window.cpp save SVG
In the rest of the function, we set up the generator and configure it to
generate output with the appropriate dimensions and write to the
user-specified file. We paint on the QSvgGenerator object in the same way
that we paint on a widget, calling the \c DisplayWidget::paint() function
so that we use exactly the same code that we used to display the drawing.
The generation process itself begins with the call to the painter's
\l{QPainter::}{begin()} function and ends with call to its
\l{QPainter::}{end()} function. The QSvgGenerator paint device relies on
the explicit use of these functions to ensure that output is written to
the file.
\section1 Further Reading
The \l{SVG Viewer Example} shows how to display SVG drawings in an
application, and can be used to show the contents of SVG files created
by this example.
See the Qt SVG module documentation for more information about SVG and Qt's
SVG classes.
*/
|
