path: root/doc/src/emb-qvfb.qdoc

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/*!
    \page qvfb.html

    \title The Virtual Framebuffer
    \ingroup qt-embedded-linux

    \l{Qt for Embedded Linux} applications write directly to the
    framebuffer, eliminating the need for the X Window System and
    saving memory. For development and debugging purposes, a virtual
    framebuffer can be used, allowing \l{Qt for Embedded Linux}
    programs to be developed on a desktop machine, without switching
    between consoles and X11.

    QVFb is an X11 application supplied with Qt for X11 that provides
    a virtual framebuffer for Qt for Embedded Linux to use. To use it,
    you need to \l{Installing Qt on X11 Platforms}{configure and
    install Qt on X11 platforms} appropriately. Further requirements
    can be found in the \l{Qt for Embedded Linux Requirements}
    document.

    \image qt-embedded-virtualframebuffer.png

    The virtual framebuffer emulates a framebuffer using a shared
    memory region and the \c qvfb tool to display the framebuffer in a
    window. The \c qvfb tool also supports a feature known as a skin
    which can be used to change the look and feel of the display. The
    tool is located in Qt's \c tools/qvfb directory, and provides
    several additional features accessible through its \gui File and
    \gui View menus.

    Please note that the virtual framebuffer is a development tool
    only. No security issues have been considered in the virtual
    framebuffer design. It should be avoided in a production
    environment; i.e. do not configure production libraries with the
    \c -qvfb option.

    \tableofcontents

    \section1 Displaying the Virtual Framebuffer

    To run the \c qvfb tool displaying the virtual framebuffer, the
    \l{Qt for Embedded Linux} library must be configured and compiled
    with the \c -qvfb option:

    \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 0

    Ensure that you have all the
    \l{Qt for Embedded Linux Requirements#Additional X11 Libraries for QVFb}
    {necessary libraries} needed to build the tool, then compile and run the
    \c qvfb tool as a normal Qt for X11 application (i.e., do \e not compile
    it as a \l{Qt for Embedded Linux} application):

    \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 1

    The \c qvfb application supports the following command line
    options:

    \table
    \header \o Option \o Description
    \row
    \o \c {-width <value>}
    \o The width of the virtual framebuffer (default: 240).
    \row
    \o \c {-height <value>}
    \o The height of the virtual framebuffer (default: 320).
    \row
    \o \c {-depth <value>}
    \o The depth of the virtual framebuffer (1, 8 or 32; default: 8).
    \row
    \o \c -nocursor
    \o Do not display the X11 cursor in the framebuffer window.
    \row
    \o \c {-qwsdisplay <:id>}
    \o The \l{Qt for Embedded Linux} display ID (default: 0).
    \row
    \o \c {-skin <name>.skin}
    \o The preferred skin. Note that the skin must be located in Qt's
    \c /tools/qvfb/ directory.
    \row
    \o \c {-zoom <factor>}
    \o Scales the application view with the given factor.

    \endtable

    \section2 Skins

    A skin is a set of XML and pixmap files that tells the vitual
    framebuffer what it should look like and how it should behave; a
    skin can change the unrealistic default display into a display
    that is similar to the target device. To access the \c qvfb tool's
    menus when a skin is activated, right-click over the display.

    Note that a skin can have buttons which (when clicked) send
    signals to the Qt Extended application running inside the virtual
    framebuffer, just as would happen on a real device.

    \table 100%
    \row
        \o
        \bold {Target Device Environment}

        The \c qvfb tool provides various skins by default, allowing
        the user to view their application in an environment similar
        to their target device. The provided skins are:

        \list
            \o ClamshellPhone
            \o pda
            \o PDAPhone
            \o Qt ExtendedPDA
            \o Qt ExtendedPhone-Advanced
            \o Qt ExtendedPhone-Simple
            \o SmartPhone
            \o SmartPhone2
            \o SmartPhoneWithButtons
            \o TouchscreenPhone
            \o Trolltech-Keypad
            \o Trolltech-Touchscreen
        \endlist

        In addition, it is possible to create custom skins.

        \o \image qt-embedded-phone.png
        \o \image qt-embedded-pda.png
    \endtable

    \bold {Creating Custom Skins}

    The XML and pixmap files specifying a custom skin must be located
    in subdirectory of the Qt's \c /tools/qvfb directory, called \c
    /customskin.skin. See the ClamshellPhone skin for an example of the
    file structure:

    \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 2

    The \c /ClamshellPhone.skin directory contains the following files:

    \list
        \o \c ClamshellPhone.skin
        \o \c ClamshellPhone1-5.png
        \o \c ClamshellPhone1-5-pressed.png
        \o \c ClamshellPhone1-5-closed.png
        \o \c defaultbuttons.conf (only necessary for \l Qt Extended)
    \endlist

    Note that the \c defaultbuttons.conf file is only necessary if the
    skin is supposed to be used with \l Qt Extended (The file customizes
    the launch screen applications, orders the soft keys and provides
    input method hints). See the \l Qt Extended documentation for more
    information.

    \table 100%
    \header
    \o {3,1} The ClamshellPhone Skin
    \row
    \o {3,1}

    \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 3

    The \c ClamShellPhone.skin file quoted above, specifies three
    pixmaps: One for the normal skin (\c Up), one for the activated
    skin (\c Down) and one for the closed skin (\c Closed). In
    addition, it is possible to specify a pixmap for the cursor (using
    a \c Cursor variable).

    The file also specifies the screen size (\c Screen) and the number
    of available buttons (\c Areas). Then it describes the buttons
    themselves; each button is specified by its name, keycode and
    coordinates.

    The coordinates are a list of at least 2 points in clockwise order
    that define a shape for the button; a click inside this shape will
    be treated as a click on that button. While pressed, the pixels
    for the button are redrawn from the activated skin.

    \row
    \row
    \o
    \image qt-embedded-clamshellphone-closed.png The ClamshellPhone Skin (closed)
    \o
    \image qt-embedded-clamshellphone.png The ClamshellPhone Skin
    \o
    \image qt-embedded-clamshellphone-pressed.png The ClamshellPhone Skin (pressed)
    \row
    \o \c ClamshellPhone1-5-closed.png
    \o \c ClamshellPhone1-5.png
    \o \c ClamshellPhone1-5-pressed.png
    \endtable

    \section2 The File Menu

    \image qt-embedded-qvfbfilemenu.png

    The \gui File menu allows the user to configure the virtual
    framebuffer display (\gui File|Configure...), save a snapshot of
    the framebuffer contents (\gui {File|Save Image...}) and record
    the movements in the framebuffer (\gui File|Animation...).

    When choosing the \gui File|Configure menu item, the \c qvfb tool
    provides a configuration dialog allowing the user to customize the
    display of the virtual framebuffer. The user can modify the size
    and depth as well as the Gamma values, and also select the
    preferred skin (i.e. making the virtual framebuffer simulate the
    target device environment). In addition, it is possible to emulate
    a touch screen and a LCD screen.

    Note that when configuring (except when changing the Gamma values
    only), any applications using the virtual framebuffer will be
    terminated.

    \section2 The View Menu

    \image qt-embedded-qvfbviewmenu.png

    The \gui View menu allows the user to modify the target's refresh
    rate (\gui {View|Refresh Rate...}), making \c qvfb check for
    updated regions more or less frequently.

    The regions of the display that have changed are updated
    periodically, i.e. the virtual framebuffer is displaying discrete
    snapshots of the framebuffer rather than each individual drawing
    operation. For this reason drawing problems such as flickering may
    not be apparent until the program is run using a real framebuffer.
    If little drawing is being done, the framebuffer will not show any
    updates between drawing events. If an application is displaying an
    animation, the updates will be frequent, and the application and
    \c qvfb will compete for processor time.

    The \gui View menu also allows the user to zoom the view of the
    application  (\gui {View|Zoom *}).

    \section1 Running Applications Using the Virtual Framebuffer

    Once the virtual framebuffer (the \c qvfb application) is running,
    it is ready for use: Start a server application (i.e. construct a
    QApplication object with the QApplication::GuiServer flag or use
    the \c -qws command line parameter. See the
    \l {Running Qt for Embedded Linux Applications}{running applications}
    documentation for details). For example:

    \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 4

    Note that as long as the virtual framebuffer is running and the
    current \l{Qt for Embedded Linux} configuration supports \c qvfb,
    \l{Qt for Embedded Linux} will automatically detect it and use it by
    default. Alternatively, the \c -display option can be used to
    specify the virtual framebuffer driver. For example:

    \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 5

    \warning If \c qvfb is not running (or the current
    \l{Qt for Embedded Linux} configuration doesn't support it) and the
    driver is not explicitly specified, \l{Qt for Embedded Linux} will
    write to the real framebuffer and the X11 display will be corrupted.
*/