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<td >Qt 5.12</td><td ><a href="qtbluetooth-index.html">Qt Bluetooth</a></td><td >Bluetooth QML Ping Pong example</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right"><a href="qtbluetooth-index.html">Qt 5.12.6 Reference Documentation</a></td>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#running-the-example">Running the Example</a></li>
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<h1 class="title">Bluetooth QML Ping Pong example</h1>
<span class="subtitle"></span>
<!-- $$$pingpong-brief -->
<p>A QML example showing Bluetooth communication.</p>
<!-- @@@pingpong -->
<!-- $$$pingpong-description -->
<div class="descr"> <a name="details"></a>
<p>The Bluetooth QML Ping Pong example presents the socket communication between two Bluetooth devices. The basic concept is the ping pong game where two players communicate via sockets.</p>
<p class="centerAlign"><img src="images/intro.png" alt="" /></p><a name="running-the-example"></a>
<h2 id="running-the-example">Running the Example</h2>
<p>To run the example from Qt Creator, open the <b>Welcome</b> mode and select the example from <b>Examples</b>. For more information, visit Building and Running an Example.</p>
<p>At the beginning, the user selects the role. One device acts as a server and the second one as a client. After selecting the role, adjustments to the screen size are done (two devices might have different screen sizes). The server side starts a service named "PingPong server".</p>
<pre class="cpp">
m_serverInfo <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qbluetoothserver.html">QBluetoothServer</a></span>(<span class="type"><a href="qbluetoothserviceinfo.html">QBluetoothServiceInfo</a></span><span class="operator">::</span>RfcommProtocol<span class="operator">,</span> <span class="keyword">this</span>);
connect(m_serverInfo<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbluetoothserver.html">QBluetoothServer</a></span><span class="operator">::</span>newConnection<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>clientConnected);
connect(m_serverInfo<span class="operator">,</span> <span class="type">QOverload</span><span class="operator"><</span><span class="type"><a href="qbluetoothserver.html">QBluetoothServer</a></span><span class="operator">::</span>Error<span class="operator">></span><span class="operator">::</span>of(<span class="operator">&</span><span class="type"><a href="qbluetoothserver.html">QBluetoothServer</a></span><span class="operator">::</span>error)<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>serverError);
<span class="keyword">const</span> <span class="type"><a href="qbluetoothuuid.html">QBluetoothUuid</a></span> uuid(serviceUuid);
m_serverInfo<span class="operator">-</span><span class="operator">></span>listen(uuid<span class="operator">,</span> <span class="type">QStringLiteral</span>(<span class="string">"PingPong server"</span>));
</pre>
<p>On the client side, the full service discovery on the nearby Bluetooth devices is done.</p>
<pre class="cpp">
discoveryAgent <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qbluetoothservicediscoveryagent.html">QBluetoothServiceDiscoveryAgent</a></span>(<span class="type"><a href="qbluetoothaddress.html">QBluetoothAddress</a></span>());
connect(discoveryAgent<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbluetoothservicediscoveryagent.html">QBluetoothServiceDiscoveryAgent</a></span><span class="operator">::</span>serviceDiscovered<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>addService);
connect(discoveryAgent<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbluetoothservicediscoveryagent.html">QBluetoothServiceDiscoveryAgent</a></span><span class="operator">::</span>finished<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>done);
connect(discoveryAgent<span class="operator">,</span> <span class="type">QOverload</span><span class="operator"><</span><span class="type"><a href="qbluetoothservicediscoveryagent.html">QBluetoothServiceDiscoveryAgent</a></span><span class="operator">::</span>Error<span class="operator">></span><span class="operator">::</span>of(<span class="operator">&</span><span class="type"><a href="qbluetoothservicediscoveryagent.html">QBluetoothServiceDiscoveryAgent</a></span><span class="operator">::</span>error)<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>serviceScanError);
<span class="preprocessor">#ifdef Q_OS_ANDROID //see QTBUG-61392</span>
<span class="keyword">if</span> (<span class="type">QtAndroid</span><span class="operator">::</span>androidSdkVersion() <span class="operator">></span><span class="operator">=</span> <span class="number">23</span>)
discoveryAgent<span class="operator">-</span><span class="operator">></span>setUuidFilter(<span class="type"><a href="qbluetoothuuid.html">QBluetoothUuid</a></span>(androidUuid));
<span class="keyword">else</span>
discoveryAgent<span class="operator">-</span><span class="operator">></span>setUuidFilter(<span class="type"><a href="qbluetoothuuid.html">QBluetoothUuid</a></span>(serviceUuid));
<span class="preprocessor">#else</span>
discoveryAgent<span class="operator">-</span><span class="operator">></span>setUuidFilter(<span class="type"><a href="qbluetoothuuid.html">QBluetoothUuid</a></span>(serviceUuid));
<span class="preprocessor">#endif</span>
discoveryAgent<span class="operator">-</span><span class="operator">></span>start(<span class="type"><a href="qbluetoothservicediscoveryagent.html">QBluetoothServiceDiscoveryAgent</a></span><span class="operator">::</span>FullDiscovery);
</pre>
<p>When the ping pong service is discovered, the client connects to the server using the socket.</p>
<pre class="cpp">
socket <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qbluetoothsocket.html">QBluetoothSocket</a></span>(<span class="type"><a href="qbluetoothserviceinfo.html">QBluetoothServiceInfo</a></span><span class="operator">::</span>RfcommProtocol);
socket<span class="operator">-</span><span class="operator">></span>connectToService(service);
connect(socket<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbluetoothsocket.html">QBluetoothSocket</a></span><span class="operator">::</span>readyRead<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>readSocket);
connect(socket<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbluetoothsocket.html">QBluetoothSocket</a></span><span class="operator">::</span>connected<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>serverConnected);
connect(socket<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbluetoothsocket.html">QBluetoothSocket</a></span><span class="operator">::</span>disconnected<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>serverDisconnected);
</pre>
<p>On the server side, the connected signal is emitted initiating that the client is connected. The necessary signals and slots on the server side are connected.</p>
<pre class="cpp">
<span class="keyword">if</span> (<span class="operator">!</span>m_serverInfo<span class="operator">-</span><span class="operator">></span>hasPendingConnections()) {
setMessage(<span class="string">"FAIL: expected pending server connection"</span>);
<span class="keyword">return</span>;
}
socket <span class="operator">=</span> m_serverInfo<span class="operator">-</span><span class="operator">></span>nextPendingConnection();
<span class="keyword">if</span> (<span class="operator">!</span>socket)
<span class="keyword">return</span>;
socket<span class="operator">-</span><span class="operator">></span>setParent(<span class="keyword">this</span>);
connect(socket<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbluetoothsocket.html">QBluetoothSocket</a></span><span class="operator">::</span>readyRead<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>readSocket);
connect(socket<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbluetoothsocket.html">QBluetoothSocket</a></span><span class="operator">::</span>disconnected<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>clientDisconnected);
connect(socket<span class="operator">,</span> <span class="type">QOverload</span><span class="operator"><</span><span class="type"><a href="qbluetoothsocket.html">QBluetoothSocket</a></span><span class="operator">::</span>SocketError<span class="operator">></span><span class="operator">::</span>of(<span class="operator">&</span><span class="type"><a href="qbluetoothsocket.html">QBluetoothSocket</a></span><span class="operator">::</span>error)<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> <span class="operator">&</span>PingPong<span class="operator">::</span>socketError);
</pre>
<p>The game starts after the devices are connected and the screen is adjusted.</p>
<pre class="cpp">
<span class="keyword">if</span> (m_role <span class="operator">=</span><span class="operator">=</span> <span class="number">1</span>)
updateDirection();
m_timer<span class="operator">-</span><span class="operator">></span>start(<span class="number">50</span>);
</pre>
<p>The server updates the ball direction and coordinates. The coordinates of pedals are sent to each other every 50ms.</p>
<pre class="cpp">
<span class="keyword">if</span> (m_role <span class="operator">=</span><span class="operator">=</span> <span class="number">1</span>) {
checkBoundaries();
m_ballPreviousX <span class="operator">=</span> m_ballX;
m_ballPreviousY <span class="operator">=</span> m_ballY;
m_ballY <span class="operator">=</span> m_direction<span class="operator">*</span>(m_ballX<span class="operator">+</span>interval) <span class="operator">-</span> m_direction<span class="operator">*</span>m_ballX <span class="operator">+</span> m_ballY;
m_ballX <span class="operator">=</span> m_ballX <span class="operator">+</span> interval;
size<span class="operator">.</span>setNum(m_ballX);
size<span class="operator">.</span>append(<span class="char">' '</span>);
<span class="type">QByteArray</span> size1;
size1<span class="operator">.</span>setNum(m_ballY);
size<span class="operator">.</span>append(size1);
size<span class="operator">.</span>append(<span class="char">' '</span>);
size1<span class="operator">.</span>setNum(m_leftBlockY);
size<span class="operator">.</span>append(size1);
size<span class="operator">.</span>append(<span class="string">" \n"</span>);
socket<span class="operator">-</span><span class="operator">></span>write(size<span class="operator">.</span>constData());
<span class="keyword">emit</span> ballChanged();
}
<span class="keyword">else</span> <span class="keyword">if</span> (m_role <span class="operator">=</span><span class="operator">=</span> <span class="number">2</span>) {
size<span class="operator">.</span>setNum(m_rightBlockY);
size<span class="operator">.</span>append(<span class="string">" \n"</span>);
socket<span class="operator">-</span><span class="operator">></span>write(size<span class="operator">.</span>constData());
}
</pre>
<p>The coordinates are updated and exchanged via sockets. As presented, the server sends its pedal's y coordinate and the ball coordinates whereas, the client sends only its pedal y coordinate.</p>
<pre class="cpp">
<span class="keyword">if</span> (((m_ballX <span class="operator">+</span> ballWidth) <span class="operator">></span> (m_boardWidth <span class="operator">-</span> blockSize)) <span class="operator">&</span><span class="operator">&</span> ((m_ballY <span class="operator">+</span> ballWidth) <span class="operator"><</span> (m_rightBlockY <span class="operator">+</span> blockHeight))
<span class="operator">&</span><span class="operator">&</span> (m_ballY <span class="operator">></span> m_rightBlockY)) {
m_targetY <span class="operator">=</span> <span class="number">2</span> <span class="operator">*</span> m_ballY <span class="operator">-</span> m_ballPreviousY;
m_targetX <span class="operator">=</span> m_ballPreviousX;
interval <span class="operator">=</span> <span class="operator">-</span><span class="number">5</span>;
updateDirection();
}
<span class="keyword">else</span> <span class="keyword">if</span> ((m_ballX <span class="operator"><</span> blockSize) <span class="operator">&</span><span class="operator">&</span> ((m_ballY <span class="operator">+</span> ballWidth) <span class="operator"><</span> (m_leftBlockY <span class="operator">+</span> blockHeight))
<span class="operator">&</span><span class="operator">&</span> (m_ballY <span class="operator">></span> m_leftBlockY)) {
m_targetY <span class="operator">=</span> <span class="number">2</span> <span class="operator">*</span> m_ballY <span class="operator">-</span> m_ballPreviousY;
m_targetX <span class="operator">=</span> m_ballPreviousX;
interval <span class="operator">=</span> <span class="number">5</span>;
updateDirection();
}
<span class="keyword">else</span> <span class="keyword">if</span> (m_ballY <span class="operator"><</span> <span class="number">0</span> <span class="operator">|</span><span class="operator">|</span> (m_ballY <span class="operator">+</span> ballWidth <span class="operator">></span> m_boardHeight)) {
m_targetY <span class="operator">=</span> m_ballPreviousY;
m_targetX <span class="operator">=</span> m_ballX <span class="operator">+</span> interval;
updateDirection();
}
</pre>
<p>In the code above, it was shown how the server checks whether the ball has reached the boundaries of the board. In the case of the goal, the server updates the results via its socket.</p>
<p class="centerAlign"><img src="images/intro1.png" alt="" /></p><p>Files:</p>
<ul>
<li><a href="qtbluetooth-pingpong-assets-board-qml.html">pingpong/assets/Board.qml</a></li>
<li><a href="qtbluetooth-pingpong-assets-dialog-qml.html">pingpong/assets/Dialog.qml</a></li>
<li><a href="qtbluetooth-pingpong-assets-menu-qml.html">pingpong/assets/Menu.qml</a></li>
<li><a href="qtbluetooth-pingpong-assets-main-qml.html">pingpong/assets/main.qml</a></li>
<li><a href="qtbluetooth-pingpong-main-cpp.html">pingpong/main.cpp</a></li>
<li><a href="qtbluetooth-pingpong-pingpong-cpp.html">pingpong/pingpong.cpp</a></li>
<li><a href="qtbluetooth-pingpong-pingpong-h.html">pingpong/pingpong.h</a></li>
<li><a href="qtbluetooth-pingpong-pingpong-pro.html">pingpong/pingpong.pro</a></li>
<li><a href="qtbluetooth-pingpong-resource-qrc.html">pingpong/resource.qrc</a></li>
</ul>
</div>
<!-- @@@pingpong -->
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