source: trunk/doc/src/platforms/emb-displaymanagement.qdoc@ 651

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/*!
    \page qt-embedded-displaymanagement.html

    \title Qt for Embedded Linux Display Management
    \ingroup qt-embedded-linux

    When rendering, the default behavior for each Qt for Embedded Linux
    client is to render its widgets into memory, while the server is
    responsible for putting the contents of the memory onto the
    screen. The server uses the screen driver to copy the content of
    the memory to the display.

    The screen driver is loaded by the server application when it
    starts running, using Qt's \l {How to Create Qt Plugins}{plugin
    system}.

    Contents:

    \tableofcontents

    \section1 Available Drivers

    \l{Qt for Embedded Linux} provides drivers for the Linux framebuffer, the
    virtual framebuffer, transformed screens, VNC servers and multi
    screens. Run the \c configure script to list the available
    drivers:

    \if defined(QTOPIA_DOCS)
    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 0
    \else
    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 1
    \endif

    \if defined(QTOPIA_DOCS)
    In the default Qt Extended configuration, only an unaccelerated Linux
    framebuffer driver (\c /dev/fb0) is enabled. The various drivers
    can be enabled and disabled using the \c configure script. For
    example:

    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 2
    \else
    In the default Qt configuration, only an unaccelerated Linux
    framebuffer driver (\c /dev/fb0) is enabled. The various drivers
    can be enabled and disabled using the \c configure script. For
    example:

    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 3
    \endif

    Custom screen drivers can be implemented by subclassing the
    QScreen class and creating a screen driver plugin (derived from
    the QScreenDriverPlugin class). The default implementation
    of the QScreenDriverFactory class will automatically detect the
    plugin, loading the driver into the server application at run-time.

    \section1 Specifying a Driver

    To specify which driver to use, set the QWS_DISPLAY environment
    variable. For example (if the current shell is bash, ksh, zsh or
    sh):

    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 4

    The valid values for the \c <driver> argument are \c LinuxFb, \c
    QVFb, \c VNC, \c Transformed, \c Multi and \l
    {QScreenDriverPlugin::keys()}{keys} identifying custom drivers,
    and the \c {<display num>} argument is used to separate screens
    that are using the same screen driver and to enable multiple
    displays (see the \l {Running Qt for Embedded Linux Applications}
    documentation for more details). The driver specific options are
    described in the table below.

    \table
    \header
        \o Driver Specific Option \o Available For  \o Description
    \row
        \o \c tty=<device>
        \o LinuxFb
        \o Passes the device file to the console the application is
        running on.
    \row
        \o \c nographicsmodeswitch
        \o LinuxFb
        \o Ensures that the application is not in graphics mode.
    \row
        \o \c littleendian
        \o LinuxFb
        \o Tells the driver it must handle a little-endian frame 
        buffer in a big-endian system.
    \row
        \o \c mmWidth=<value> \target mmWidth
        \o LinuxFb, QVFb
        \o The screen's physical width (used to calculate DPI).
    \row
        \o \c mmHeight=<value> \target mmHeight
        \o LinuxFb, QVFb
        \o The screen's physical height (used to calculate DPI).
    \row
        \o \c <device>
        \o LinuxFb
        \o
    \row
        \o \c <subdriver>
        \o VNC, Transformed, Multi
        \o Specifies a subdriver.
    \row
        \o \c <RotX>
        \o Transformed
        \o Specifies the rotation of the screen. The valid values of
        \c X are 90, 180 and 270.
    \row
        \o \c offset=<x,y>
        \o Multi
        \o Specifies the coordinates of a subscreen's top-left corner
        (by default 0,0).

    \endtable

    The QWS_DISPLAY environment variable can also be set using the \c
    -display option when running an application. For example:

    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 5

    \section1 Subdrivers and Multiple Drivers

    The VNC, Transformed and Multi screen drivers depend on
    subdrivers. The general syntax for specifying a driver is as
    follows:

    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 6

    In the case of subdrivers, it is important to add a space between
    each subdriver and before the display number to separate the
    various drivers and displays. Note that \c Multi screen drivers
    can have several subdrivers. For example:

    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 7

    Note also that the VNC screen driver defaults to a virtual screen
    driver if no subdriver is specified. In this case the VNC driver accepts a
    few additional (optional) arguments specifying the size and depth
    of the default virtual screen:

    \list
        \o \c {size=<width x height>}
        \o \c {depth=<value>}
        \o \c {mmHeight=<physical height in millimeters>}
        \o \c {mmWidth=<physical width in millimeters>}
    \endlist

    Example running the VNC screen driver with a virtual screen of size 
    720x480 with 32 bits per pixel:

    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 8

    Example running the VNC screen driver on top of the Linux framebuffer
    driver:

    \snippet doc/src/snippets/code/doc_src_qt-embedded-displaymanagement.qdoc 9

    In this last example, Qt is using two screen drivers simultaneously,
    displaying output on both the device's screen and across a network on
    VNC client displays.
*/