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/****************************************************************************
**
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in a
** written agreement between you and Nokia.
**
** GNU Free Documentation License
** 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.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\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.
*/
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