source: trunk/doc/src/examples/svgalib.qdoc

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/*!
    \example qws/svgalib
    \title Accelerated Graphics Driver Example

    The Accelerated Graphics Driver example shows how you can write
    your own accelerated graphics driver and \l {add your graphics
    driver to Qt for Embedded Linux}.  In \l{Qt for Embedded Linux},
    painting is a pure software implementation and is normally performed
    in two steps:
    The clients render each window onto a corresponding surface
    (stored in memory) using a paint engine, and then the server uses
    the graphics driver to compose the surface images and copy them to
    the screen. (See the \l{Qt for Embedded Linux Architecture} documentation
    for details.)

    The rendering can be accelerated in two ways: Either by
    accelerating the copying of pixels to the screen, or by
    accelerating the explicit painting operations. The first is done
    in the graphics driver implementation, the latter is performed by
    the paint engine implementation. Typically, both the pixel copying
    and the painting operations are accelerated using the following
    approach:

    \list 1
        \o \l {Step 1: Creating a Custom Graphics Driver}
        {Creating a Custom Graphics Driver}

        \o \l {Step 2: Implementing a Custom Raster Paint Engine}
        {Implementing a Custom Paint Engine}

        \o \l {Step 3: Making the Widgets Aware of the Custom Paint
        Engine}{Making the Widgets Aware of the Custom Paint Engine}

    \endlist

    After compiling the example code, install the graphics driver
    plugin with the command \c {make install}. To start an application
    using the graphics driver, you can either set the environment
    variable \l QWS_DISPLAY and then run the application, or you can
    just run the application using the \c -display switch:

    \snippet doc/src/snippets/code/doc_src_examples_svgalib.qdoc 0

    \table
    \header \o SVGAlib
    \row \o

    Instead of interfacing the graphics hardware directly, this
    example relies on \l {http://www.svgalib.org}{SVGAlib} being
    installed on your system.  \l {http://www.svgalib.org}{SVGAlib} is
    a small graphics library which provides acceleration for many
    common graphics cards used on desktop computers. It should work on
    most workstations and has a small and simple API.

    \endtable

    \section1 Step 1: Creating a Custom Graphics Driver

    The custom graphics driver is created by deriving from the QScreen
    class. QScreen is the base class for implementing screen/graphics
    drivers in Qt for Embedded Linux.

    \snippet examples/qws/svgalib/svgalibscreen.h 0
    \codeline
    \snippet examples/qws/svgalib/svgalibscreen.h 1

    The \l {QScreen::}{connect()}, \l {QScreen::}{disconnect()}, \l
    {QScreen::}{initDevice()} and \l {QScreen::}{shutdownDevice()}
    functions are declared as pure virtual functions in QScreen and
    must be implemented. They are used to configure the hardware, or
    query its configuration: \l {QScreen::}{connect()} and \l
    {QScreen::}{disconnect()} are called by both the server and client
    processes, while the \l {QScreen::}{initDevice()} and \l
    {QScreen::}{shutdownDevice()} functions are only called by the
    server process.

    QScreen's \l {QScreen::}{setMode()} and \l {QScreen::}{blank()}
    functions are also pure virtual, but our driver's implementations
    are trivial. The last two functions (\l {QScreen::}{blit()} and \l
    {QScreen::}{solidFill()}) are the ones involved in putting pixels
    on the screen, i.e., we reimplement these functions to perform the
    pixel copying acceleration.

    Finally, the \c context variable is a pointer to a \l
    {http://www.svgalib.org}{SVGAlib} specific type. Note that the
    details of using the \l {http://www.svgalib.org}{SVGAlib} library
    is beyond the scope of this example.

    \section2 SvgalibScreen Class Implementation

    The \l {QScreen::}{connect()} function is the first function that