source: branches/4.5.1/doc/src/examples/svggenerator.qdoc

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/*!
    \example painting/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 \c{.ui} file as described in the
    \l{Using a Designer .ui File in Your 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 examples/painting/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 examples/painting/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 examples/painting/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 examples/painting/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 \gui{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 examples/painting/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 QtSvg module documentation for more information about SVG and Qt's
    SVG classes.
*/