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<li class="level1"><a href="#the-main-program">The Main Program</a></li>
<li class="level1"><a href="#calibration-class-definition">Calibration Class Definition</a></li>
<li class="level1"><a href="#calibration-class-implementation">Calibration Class Implementation</a></li>
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<h1 class="title">Mouse Calibration Example</h1>
<span class="subtitle"></span>
<!-- $$$qws/mousecalibration-description -->
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<p>Files:</p>
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<li><a href="qws-mousecalibration-calibration-cpp.html">qws/mousecalibration/calibration.cpp</a></li>
<li><a href="qws-mousecalibration-calibration-h.html">qws/mousecalibration/calibration.h</a></li>
<li><a href="qws-mousecalibration-scribblewidget-cpp.html">qws/mousecalibration/scribblewidget.cpp</a></li>
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<li><a href="qws-mousecalibration-mousecalibration-pro.html">qws/mousecalibration/mousecalibration.pro</a></li>
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<p>The Mouse Calibration example demonstrates how to write a simple program using the mechanisms provided by the <a href="qwsmousehandler.html">QWSMouseHandler</a> class to calibrate the mouse handler in <a href="qt-embedded-linux.html">Qt for Embedded Linux</a>.<p>Calibration is the process of mapping between physical (i.e. device) coordinates and logical coordinates.</p>
<p>The example consists of two classes in addition to the main program:</p>
<ul>
<li><tt>Calibration</tt> is a dialog widget that retrieves the device coordinates.</li>
<li><tt>ScribbleWidget</tt> is a minimal drawing program used to let the user test the new mouse settings.</li>
</ul>
<p>First we will review the main program, then we will take a look at the <tt>Calibration</tt> class. The <tt>ScribbleWidget</tt> class is only a help tool in this context, and will not be covered here.</p>
<a name="the-main-program"></a>
<h2>The Main Program</h2>
<p>The program starts by presenting a message box informing the user of what is going to happen:</p>
<pre class="cpp"> <span class="type">int</span> main(<span class="type">int</span> argc<span class="operator">,</span> <span class="type">char</span> <span class="operator">*</span><span class="operator">*</span>argv)
{
<span class="type"><a href="qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv<span class="operator">,</span> <span class="type"><a href="qapplication.html">QApplication</a></span><span class="operator">::</span>GuiServer);
<span class="keyword">if</span> (<span class="operator">!</span><span class="type"><a href="qwsserver.html">QWSServer</a></span><span class="operator">::</span>mouseHandler())
<a href="qtglobal.html#qFatal">qFatal</a>(<span class="string">"No mouse handler installed"</span>);
{
<span class="type"><a href="qmessagebox.html">QMessageBox</a></span> message;
message<span class="operator">.</span>setText(<span class="string">"<p>Please press once at each of the marks "</span>
<span class="string">"shown in the next screen.</p>"</span>
<span class="string">"<p>This messagebox will timout after 10 seconds "</span>
<span class="string">"if you are unable to close it.</p>"</span>);
<span class="type"><a href="qtimer.html">QTimer</a></span><span class="operator">::</span>singleShot(<span class="number">10</span> <span class="operator">*</span> <span class="number">1000</span><span class="operator">,</span> <span class="operator">&</span>message<span class="operator">,</span> SLOT(accept()));
message<span class="operator">.</span>exec();
}</pre>
<p>The <a href="qmessagebox.html">QMessageBox</a> class provides a modal dialog with a range of different messages, roughly arranged along two axes: severity and complexity. The message box has a different icon for each of the severity levels, but the icon must be specified explicitly. In our case we use the default <a href="qmessagebox.html#Icon-enum">QMessageBox::NoIcon</a> value. In addition we use the default complexity, i.e. a message box showing the given text and an <b>OK</b> button.</p>
<p>At this stage in the program, the mouse could be completely uncalibrated, making the user unable to press the <b>OK</b> button. For that reason we use the static <a href="qtimer.html#singleShot">QTimer::singleShot</a>() function to make the message box disappear after 10 seconds. The <a href="qtimer.html">QTimer</a> class provides repetitive and single-shot timers: The single shot function calls the given slot after the specified interval.</p>
<pre class="cpp"> Calibration cal;
cal<span class="operator">.</span>exec();</pre>
<p>Next, we create an instance of the <tt>Calibration</tt> class which is a dialog widget retrieving the required sample coordinates: The dialog sequentially presents five marks for the user to press, storing the device coordinates for the mouse press events.</p>
<pre class="cpp"> {
<span class="type"><a href="qmessagebox.html">QMessageBox</a></span> message;
message<span class="operator">.</span>setText(<span class="string">"<p>The next screen will let you test the calibration "</span>
<span class="string">"by drawing into a widget.</p><p>This program will "</span>
<span class="string">"automatically close after 20 seconds.<p>"</span>);
<span class="type"><a href="qtimer.html">QTimer</a></span><span class="operator">::</span>singleShot(<span class="number">10</span> <span class="operator">*</span> <span class="number">1000</span><span class="operator">,</span> <span class="operator">&</span>message<span class="operator">,</span> SLOT(accept()));
message<span class="operator">.</span>exec();
}
ScribbleWidget scribble;
scribble<span class="operator">.</span>showMaximized();
scribble<span class="operator">.</span>show();
app<span class="operator">.</span>setActiveWindow(<span class="operator">&</span>scribble);
<span class="type"><a href="qtimer.html">QTimer</a></span><span class="operator">::</span>singleShot(<span class="number">20</span> <span class="operator">*</span> <span class="number">1000</span><span class="operator">,</span> <span class="operator">&</span>app<span class="operator">,</span> SLOT(quit()));
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
<p>When the calibration dialog returns, we let the user test the new mouse settings by drawing onto a <tt>ScribbleWidget</tt> object. Since the mouse still can be uncalibrated, we continue to use the <a href="qmessagebox.html">QMessageBox</a> and <a href="qtimer.html">QTimer</a> classes to inform the user about the program's progress.</p>
<p>An improved calibration tool would let the user choose between accepting the new calibration, reverting to the old one, and restarting the calibration.</p>
<a name="calibration-class-definition"></a>
<h2>Calibration Class Definition</h2>
<p>The <tt>Calibration</tt> class inherits from <a href="qdialog.html">QDialog</a> and is responsible for retrieving the device coordinates from the user.</p>
<pre class="cpp"> <span class="keyword">class</span> Calibration : <span class="keyword">public</span> <span class="type"><a href="qdialog.html">QDialog</a></span>
{
<span class="keyword">public</span>:
Calibration();
<span class="operator">~</span>Calibration();
<span class="type">int</span> exec();
<span class="keyword">protected</span>:
<span class="type">void</span> paintEvent(<span class="type"><a href="qpaintevent.html">QPaintEvent</a></span><span class="operator">*</span>);
<span class="type">void</span> mouseReleaseEvent(<span class="type"><a href="qmouseevent.html">QMouseEvent</a></span><span class="operator">*</span>);
<span class="type">void</span> accept();
<span class="keyword">private</span>:
<span class="type"><a href="qwspointercalibrationdata.html">QWSPointerCalibrationData</a></span> data;
<span class="type">int</span> pressCount;
};</pre>
<p>We reimplement <a href="qdialog.html">QDialog</a>'s <a href="qdialog.html#exec">exec()</a> and <a href="qdialog.html#accept">accept()</a> slots, and <a href="qwidget.html">QWidget</a>'s <a href="qwidget.html#paintEvent">paintEvent()</a> and <a href="qwidget.html#mouseReleaseEvent">mouseReleaseEvent()</a> functions.</p>
<p>In addition, we declare a couple of private variables, <tt>data</tt> and <tt>pressCount</tt>, holding the <tt>Calibration</tt> object's number of mouse press events and current calibration data. The <tt>pressCount</tt> variable is a convenience variable, while the <tt>data</tt> is a <a href="qwspointercalibrationdata.html">QWSPointerCalibrationData</a> object (storing the physical and logical coordinates) that is passed to the mouse handler. The <a href="qwspointercalibrationdata.html">QWSPointerCalibrationData</a> class is simply a container for calibration data.</p>
<a name="calibration-class-implementation"></a>
<h2>Calibration Class Implementation</h2>
<p>In the constructor we first ensure that the <tt>Calibration</tt> dialog fills up the entire screen, has focus and will receive mouse events (the latter by making the dialog modal):</p>
<pre class="cpp"> Calibration<span class="operator">::</span>Calibration()
{
<span class="type"><a href="qrect.html">QRect</a></span> desktop <span class="operator">=</span> <span class="type"><a href="qapplication.html">QApplication</a></span><span class="operator">::</span>desktop()<span class="operator">-</span><span class="operator">></span>geometry();
desktop<span class="operator">.</span>moveTo(<span class="type"><a href="qpoint.html">QPoint</a></span>(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span>));
setGeometry(desktop);
setFocusPolicy(<span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>StrongFocus);
setFocus();
setModal(<span class="keyword">true</span>);</pre>
<p>Then we initialize the <a href="qwspointercalibrationdata.html#screenPoints-var">screenPoints</a> array:</p>
<pre class="cpp"> <span class="type">int</span> width <span class="operator">=</span> qt_screen<span class="operator">-</span><span class="operator">></span>deviceWidth();
<span class="type">int</span> height <span class="operator">=</span> qt_screen<span class="operator">-</span><span class="operator">></span>deviceHeight();
<span class="type">int</span> dx <span class="operator">=</span> width <span class="operator">/</span> <span class="number">10</span>;
<span class="type">int</span> dy <span class="operator">=</span> height <span class="operator">/</span> <span class="number">10</span>;
<span class="type"><a href="qpoint.html">QPoint</a></span> <span class="operator">*</span>points <span class="operator">=</span> data<span class="operator">.</span>screenPoints;
points<span class="operator">[</span><span class="type"><a href="qwspointercalibrationdata.html">QWSPointerCalibrationData</a></span><span class="operator">::</span>TopLeft<span class="operator">]</span> <span class="operator">=</span> <span class="type"><a href="qpoint.html">QPoint</a></span>(dx<span class="operator">,</span> dy);
points<span class="operator">[</span><span class="type"><a href="qwspointercalibrationdata.html">QWSPointerCalibrationData</a></span><span class="operator">::</span>BottomLeft<span class="operator">]</span> <span class="operator">=</span> <span class="type"><a href="qpoint.html">QPoint</a></span>(dx<span class="operator">,</span> height <span class="operator">-</span> dy);
points<span class="operator">[</span><span class="type"><a href="qwspointercalibrationdata.html">QWSPointerCalibrationData</a></span><span class="operator">::</span>BottomRight<span class="operator">]</span> <span class="operator">=</span> <span class="type"><a href="qpoint.html">QPoint</a></span>(width <span class="operator">-</span> dx<span class="operator">,</span> height <span class="operator">-</span> dy);
points<span class="operator">[</span><span class="type"><a href="qwspointercalibrationdata.html">QWSPointerCalibrationData</a></span><span class="operator">::</span>TopRight<span class="operator">]</span> <span class="operator">=</span> <span class="type"><a href="qpoint.html">QPoint</a></span>(width <span class="operator">-</span> dx<span class="operator">,</span> dy);
points<span class="operator">[</span><span class="type"><a href="qwspointercalibrationdata.html">QWSPointerCalibrationData</a></span><span class="operator">::</span>Center<span class="operator">]</span> <span class="operator">=</span> <span class="type"><a href="qpoint.html">QPoint</a></span>(width <span class="operator">/</span> <span class="number">2</span><span class="operator">,</span> height <span class="operator">/</span> <span class="number">2</span>);</pre>
<p>In order to specify the calibration, the <a href="qwspointercalibrationdata.html#screenPoints-var">screenPoints</a> array must contain the screen coordinates for the logical positions represented by the <a href="qwspointercalibrationdata.html#Location-enum">QWSPointerCalibrationData::Location</a> enum (e.g. <a href="qwspointercalibrationdata.html#Location-enum">QWSPointerCalibrationData::TopLeft</a>). Since non-linearity is expected to increase on the edge of the screen, all points are kept 10 percent within the screen. The <tt>qt_screen</tt> pointer is a reference to the screen device. There can only be one screen device per application.</p>
<pre class="cpp"> pressCount <span class="operator">=</span> <span class="number">0</span>;
}</pre>
<p>Finally, we initialize the variable which keeps track of the number of mouse press events we have received.</p>
<pre class="cpp"> Calibration<span class="operator">::</span><span class="operator">~</span>Calibration()
{
}</pre>
<p>The destructor is trivial.</p>
<pre class="cpp"> <span class="type">int</span> Calibration<span class="operator">::</span>exec()
{
<span class="type"><a href="qwsserver.html">QWSServer</a></span><span class="operator">::</span>mouseHandler()<span class="operator">-</span><span class="operator">></span>clearCalibration();
grabMouse();
activateWindow();
<span class="type">int</span> ret <span class="operator">=</span> <span class="type"><a href="qdialog.html">QDialog</a></span><span class="operator">::</span>exec();
releaseMouse();
<span class="keyword">return</span> ret;
}</pre>
<p>The reimplementation of the <a href="qdialog.html#exec">QDialog::exec</a>() slot is called from the main program.</p>
<p>First we clear the current calibration making the following mouse event delivered in raw device coordinates. Then we call the <a href="qwidget.html#grabMouse">QWidget::grabMouse</a>() function to make sure no mouse events are lost, and the <a href="qwidget.html#activateWindow">QWidget::activateWindow</a>() function to make the top-level widget containing this dialog, the active window. When the call to the <a href="qdialog.html#exec">QDialog::exec</a>() base function returns, we call <a href="qwidget.html#releaseMouse">QWidget::releaseMouse</a>() to release the mouse grab before the function returns.</p>
<pre class="cpp"> <span class="type">void</span> Calibration<span class="operator">::</span>paintEvent(<span class="type"><a href="qpaintevent.html">QPaintEvent</a></span><span class="operator">*</span>)
{
<span class="type"><a href="qpainter.html">QPainter</a></span> p(<span class="keyword">this</span>);
p<span class="operator">.</span>fillRect(rect()<span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>white);
<span class="type"><a href="qpoint.html">QPoint</a></span> point <span class="operator">=</span> data<span class="operator">.</span>screenPoints<span class="operator">[</span>pressCount<span class="operator">]</span>;
<span class="comment">// Map to logical coordinates in case the screen is transformed</span>
<span class="type"><a href="qsize.html">QSize</a></span> screenSize(qt_screen<span class="operator">-</span><span class="operator">></span>deviceWidth()<span class="operator">,</span> qt_screen<span class="operator">-</span><span class="operator">></span>deviceHeight());
point <span class="operator">=</span> qt_screen<span class="operator">-</span><span class="operator">></span>mapFromDevice(point<span class="operator">,</span> screenSize);
p<span class="operator">.</span>fillRect(point<span class="operator">.</span>x() <span class="operator">-</span> <span class="number">6</span><span class="operator">,</span> point<span class="operator">.</span>y() <span class="operator">-</span> <span class="number">1</span><span class="operator">,</span> <span class="number">13</span><span class="operator">,</span> <span class="number">3</span><span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>black);
p<span class="operator">.</span>fillRect(point<span class="operator">.</span>x() <span class="operator">-</span> <span class="number">1</span><span class="operator">,</span> point<span class="operator">.</span>y() <span class="operator">-</span> <span class="number">6</span><span class="operator">,</span> <span class="number">3</span><span class="operator">,</span> <span class="number">13</span><span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>black);
}</pre>
<p>The <a href="qwidget.html#paintEvent">QWidget::paintEvent</a>() function is reimplemented to receive the widget's paint events. A paint event is a request to repaint all or parts of the widget. It can happen as a result of <a href="qwidget.html#repaint">QWidget::repaint</a>() or <a href="qwidget.html#update">QWidget::update</a>(), or because the widget was obscured and has now been uncovered, or for many other reasons. In our reimplementation of the function we simply draw a cross at the next point the user should press.</p>
<pre class="cpp"> <span class="type">void</span> Calibration<span class="operator">::</span>mouseReleaseEvent(<span class="type"><a href="qmouseevent.html">QMouseEvent</a></span> <span class="operator">*</span>event)
{
<span class="comment">// Map from device coordinates in case the screen is transformed</span>
<span class="type"><a href="qsize.html">QSize</a></span> screenSize(qt_screen<span class="operator">-</span><span class="operator">></span>width()<span class="operator">,</span> qt_screen<span class="operator">-</span><span class="operator">></span>height());
<span class="type"><a href="qpoint.html">QPoint</a></span> p <span class="operator">=</span> qt_screen<span class="operator">-</span><span class="operator">></span>mapToDevice(event<span class="operator">-</span><span class="operator">></span>pos()<span class="operator">,</span> screenSize);
data<span class="operator">.</span>devPoints<span class="operator">[</span>pressCount<span class="operator">]</span> <span class="operator">=</span> p;
<span class="keyword">if</span> (<span class="operator">+</span><span class="operator">+</span>pressCount <span class="operator"><</span> <span class="number">5</span>)
repaint();
<span class="keyword">else</span>
accept();
}</pre>
<p>We then reimplement the <a href="qwidget.html#mouseReleaseEvent">QWidget::mouseReleaseEvent</a>() function to receive the widget's move events, using the <a href="qmouseevent.html">QMouseEvent</a> object passed as parameter to find the coordinates the user pressed, and update the <a href="qwspointercalibrationdata.html#devPoints-var">QWSPointerCalibrationData::devPoints</a> array.</p>
<p>In order to complete the mapping between logical and physical coordinates, the <a href="qwspointercalibrationdata.html#devPoints-var">devPoints</a> array must contain the raw device coordinates for the logical positions represented by the <a href="qwspointercalibrationdata.html#Location-enum">QWSPointerCalibrationData::Location</a> enum (e.g. <a href="qwspointercalibrationdata.html#Location-enum">QWSPointerCalibrationData::TopLeft</a>)</p>
<p>We continue by drawing the next cross, or close the dialog by calling the <a href="qdialog.html#accept">QDialog::accept</a>() slot if we have collected all the required coordinate samples.</p>
<pre class="cpp"> <span class="type">void</span> Calibration<span class="operator">::</span>accept()
{
Q_ASSERT(pressCount <span class="operator">=</span><span class="operator">=</span> <span class="number">5</span>);
<span class="type"><a href="qwsserver.html">QWSServer</a></span><span class="operator">::</span>mouseHandler()<span class="operator">-</span><span class="operator">></span>calibrate(<span class="operator">&</span>data);
<span class="type"><a href="qdialog.html">QDialog</a></span><span class="operator">::</span>accept();
}</pre>
<p>Our reimplementation of the <a href="qdialog.html#accept">QDialog::accept</a>() slot simply activate the new calibration data using the <a href="qwsmousehandler.html#calibrate">QWSMouseHandler::calibrate</a>() function. We also use the <a href="qtglobal.html#Q_ASSERT">Q_ASSERT</a>() macro to ensure that the number of required samples are present.</p>
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