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<title>Qt 4.6: The VNC Protocol and Qt for Embedded Linux</title>
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<td align="left" valign="top" width="32"><a href="http://qt.nokia.com/"><img src="images/qt-logo.png" align="left" border="0" /></a></td>
<td width="1"> </td><td class="postheader" valign="center"><a href="index.html"><font color="#004faf">Home</font></a> · <a href="classes.html"><font color="#004faf">All Classes</font></a> · <a href="functions.html"><font color="#004faf">All Functions</font></a> · <a href="overviews.html"><font color="#004faf">Overviews</font></a></td></tr></table><h1 class="title">The VNC Protocol and Qt for Embedded Linux<br /><span class="subtitle"></span>
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<p>VNC (Virtual Network Computing) software makes it possible to view and interact with one computer (the "server") from any other computer or mobile device (the "viewer") anywhere on a network.</p>
<p align="center"><img src="images/qt-embedded-vnc-screen.png" /></p><p>VNC clients are available for a vast array of display systems, including X11, Mac OS X and Windows.</p>
<a name="configuring-qt-with-vnc-capabilities"></a>
<h3>Configuring Qt with VNC Capabilities</h3>
<p>To run a <a href="qt-embedded-linux.html">Qt for Embedded Linux</a> application using the VNC protocol, the <a href="qt-embedded-linux.html">Qt for Embedded Linux</a> library must be configured and compiled with the <tt>-qt-gfx-vnc</tt> option:</p>
<pre> cd path/to/QtEmbedded
./configure -qt-gfx-vnc
make</pre>
<a name="running-a-server-application"></a>
<h3>Running a Server Application</h3>
<p>Start a server application by specifying the <tt>-qws</tt> command line option when running the application. (This can also be specified in the application's source code.) Use the <tt>-display</tt> command line option to specify the VNC server's driver and the virtual screen to use. For example:</p>
<pre> cd path/to/QtEmbedded/examples/widgets/analogclock
./analogclock -qws -display VNC:0</pre>
<p>The application will act as a VNC server which can be accessed using an ordinary VNC client, either on the development machine or from a different machine on a network.</p>
<p>For example, using the X11 VNC client to view the application from the same machine:</p>
<pre> vncviewer localhost:0</pre>
<p>To interact with the application from another machine on the network, run a VNC client pointing to the machine that is running the server application.</p>
<p><a href="qt-embedded-linux.html">Qt for Embedded Linux</a> will create a 640 by 480 pixel display by default. Alternatively, the <tt>QWS_SIZE</tt> environment variable can be used to set another size; e.g., <tt>QWS_SIZE=240x320</tt>.</p>
<a name="running-client-applications"></a>
<h3>Running Client Applications</h3>
<p>If you want to run more than one application on the same display, you only need to start the first one as a server application, using the <tt>-qws</tt> command line option to indicate that it will manage other windows.</p>
<pre> analogclock -qws -display VNC:0</pre>
<p>Subsequent client applications can be started <i>without</i> the <tt>-qws</tt> option, but will each require the same <tt>-display</tt> option and argument as those used for the server.</p>
<pre> calculator -display VNC:0
scribble -display VNC:0
imageviewer -display VNC:0</pre>
<p>However, for the clients, this option will not cause a new VNC server to be started, but only indicates that their windows will appear on the virtual screen managed by the server application.</p>
<a name="related-resources"></a>
<h3>Related Resources</h3>
<p>It is not always necessary to specify the <tt>-qws</tt> command line option when running a server application as long as the <a href="qapplication.html">QApplication</a> object used by the application has been constructed with the <a href="qapplication.html#Type-enum">QApplication::GuiServer</a> flag.</p>
<p>See the <a href="qt-embedded-running.html">running applications</a> documentation for more details about server and client applications.</p>
<p><table class="generic" align="center" cellpadding="2" cellspacing="1" border="0">
<tr valign="top" class="odd"><td><b>The Virtual Framebuffer</b><p>The <a href="qvfb.html">virtual framebuffer</a> is an alternative technique recommended for development and debugging purposes.</p>
<p>The virtual framebuffer emulates a framebuffer using a shared memory region and the <tt>qvfb</tt> tool to display the framebuffer in a window.</p>
<p>Its use of shared memory makes the virtual framebuffer much faster and smoother than using the VNC protocol, but it does not operate over a network.</p>
</td><td><img src="images/qt-embedded-virtualframebuffer.png" /></td></tr>
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