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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#setting-up-the-resource-file">Setting Up The Resource File</a></li>
<li class="level1"><a href="#imagecomposer-class-definition">ImageComposer Class Definition</a></li>
<li class="level1"><a href="#imagecomposer-class-implementation">ImageComposer Class Implementation</a></li>
<li class="level1"><a href="#the-function">The <tt>main()</tt> Function</a></li>
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<h1 class="title">Image Composition Example</h1>
<span class="subtitle"></span>
<!-- $$$painting/imagecomposition-description -->
<div class="descr"> <a name="details"></a>
<p>Files:</p>
<ul>
<li><a href="painting-imagecomposition-imagecomposer-cpp.html">painting/imagecomposition/imagecomposer.cpp</a></li>
<li><a href="painting-imagecomposition-imagecomposer-h.html">painting/imagecomposition/imagecomposer.h</a></li>
<li><a href="painting-imagecomposition-main-cpp.html">painting/imagecomposition/main.cpp</a></li>
<li><a href="painting-imagecomposition-imagecomposition-pro.html">painting/imagecomposition/imagecomposition.pro</a></li>
<li><a href="painting-imagecomposition-imagecomposition-qrc.html">painting/imagecomposition/imagecomposition.qrc</a></li>
</ul>
<p>Images:</p>
<ul>
<li><a href="images/used-in-examples/painting/imagecomposition/images/background.png">painting/imagecomposition/images/background.png</a></li>
<li><a href="images/used-in-examples/painting/imagecomposition/images/blackrectangle.png">painting/imagecomposition/images/blackrectangle.png</a></li>
<li><a href="images/used-in-examples/painting/imagecomposition/images/butterfly.png">painting/imagecomposition/images/butterfly.png</a></li>
<li><a href="images/used-in-examples/painting/imagecomposition/images/checker.png">painting/imagecomposition/images/checker.png</a></li>
</ul>
<p>The Image Composition example lets the user combine images together using any composition mode supported by <a href="qpainter.html">QPainter</a>, described in detail in <a href="qpainter.html#composition-modes">Composition Modes</a>.<p class="centerAlign"><img src="images/imagecomposition-example.png" alt="" /></p><a name="setting-up-the-resource-file"></a>
<h2>Setting Up The Resource File</h2>
<p>The Image Composition example requires two source images, <i>butterfly.png</i> and <i>checker.png</i> that are embedded within <i>imagecomposition.qrc</i>. The file contains the following code:</p>
<pre class="cpp"> <!DOCTYPE RCC><RCC version="1.0">
<qresource>
<file>images/butterfly.png</file>
<file>images/checker.png</file>
</qresource>
</RCC></pre>
<p>For more information on resource files, see <a href="resources.html">The Qt Resource System</a>.</p>
<a name="imagecomposer-class-definition"></a>
<h2>ImageComposer Class Definition</h2>
<p>The <tt>ImageComposer</tt> class is a subclass of <a href="qwidget.html">QWidget</a> that implements three private slots, <tt>chooseSource()</tt>, <tt>chooseDestination()</tt>, and <tt>recalculateResult()</tt>.</p>
<pre class="cpp"> <span class="keyword">class</span> ImageComposer : <span class="keyword">public</span> <span class="type"><a href="qwidget.html">QWidget</a></span>
{
Q_OBJECT
<span class="keyword">public</span>:
ImageComposer();
<span class="keyword">private</span> <span class="keyword">slots</span>:
<span class="type">void</span> chooseSource();
<span class="type">void</span> chooseDestination();
<span class="type">void</span> recalculateResult();</pre>
<p>In addition, <tt>ImageComposer</tt> consists of five private functions, <tt>addOp()</tt>, <tt>chooseImage()</tt>, <tt>loadImage()</tt>, <tt>currentMode()</tt>, and <tt>imagePos()</tt>, as well as private instances of <a href="qtoolbutton.html">QToolButton</a>, <a href="qcombobox.html">QComboBox</a>, <a href="qlabel.html">QLabel</a>, and <a href="qimage.html">QImage</a>.</p>
<pre class="cpp"> <span class="keyword">private</span>:
<span class="type">void</span> addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode mode<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>name);
<span class="type">void</span> chooseImage(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>title<span class="operator">,</span> <span class="type"><a href="qimage.html">QImage</a></span> <span class="operator">*</span>image<span class="operator">,</span> <span class="type"><a href="qtoolbutton.html">QToolButton</a></span> <span class="operator">*</span>button);
<span class="type">void</span> loadImage(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>fileName<span class="operator">,</span> <span class="type"><a href="qimage.html">QImage</a></span> <span class="operator">*</span>image<span class="operator">,</span> <span class="type"><a href="qtoolbutton.html">QToolButton</a></span> <span class="operator">*</span>button);
<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode currentMode() <span class="keyword">const</span>;
<span class="type"><a href="qpoint.html">QPoint</a></span> imagePos(<span class="keyword">const</span> <span class="type"><a href="qimage.html">QImage</a></span> <span class="operator">&</span>image) <span class="keyword">const</span>;
<span class="type"><a href="qtoolbutton.html">QToolButton</a></span> <span class="operator">*</span>sourceButton;
<span class="type"><a href="qtoolbutton.html">QToolButton</a></span> <span class="operator">*</span>destinationButton;
<span class="type"><a href="qcombobox.html">QComboBox</a></span> <span class="operator">*</span>operatorComboBox;
<span class="type"><a href="qlabel.html">QLabel</a></span> <span class="operator">*</span>equalLabel;
<span class="type"><a href="qlabel.html">QLabel</a></span> <span class="operator">*</span>resultLabel;
<span class="type"><a href="qimage.html">QImage</a></span> sourceImage;
<span class="type"><a href="qimage.html">QImage</a></span> destinationImage;
<span class="type"><a href="qimage.html">QImage</a></span> resultImage;
};</pre>
<a name="imagecomposer-class-implementation"></a>
<h2>ImageComposer Class Implementation</h2>
<p>We declare a <a href="qsize.html">QSize</a> object, <tt>resultSize</tt>, as a static constant with width and height equal to 200.</p>
<pre class="cpp"> <span class="preprocessor">#if defined(Q_OS_SYMBIAN) || defined(Q_WS_SIMULATOR)</span>
<span class="keyword">static</span> <span class="keyword">const</span> <span class="type"><a href="qsize.html">QSize</a></span> resultSize(<span class="number">50</span><span class="operator">,</span> <span class="number">50</span>);
<span class="preprocessor">#else</span>
<span class="keyword">static</span> <span class="keyword">const</span> <span class="type"><a href="qsize.html">QSize</a></span> resultSize(<span class="number">200</span><span class="operator">,</span> <span class="number">200</span>);
<span class="preprocessor">#endif</span></pre>
<p>Within the constructor, we instantiate a <a href="qtoolbutton.html">QToolButton</a> object, <tt>sourceButton</tt> and set its <a href="qabstractbutton.html#iconSize-prop">iconSize</a> property to <tt>resultSize</tt>. The <tt>operatorComboBox</tt> is instantiated and then populated using the <tt>addOp()</tt> function. This function accepts a <a href="qpainter.html#CompositionMode-enum">QPainter::CompositionMode</a>, <i>mode</i>, and a <a href="qstring.html">QString</a>, <i>name</i>, representing the name of the composition mode.</p>
<pre class="cpp"> ImageComposer<span class="operator">::</span>ImageComposer()
{
sourceButton <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtoolbutton.html">QToolButton</a></span>;
sourceButton<span class="operator">-</span><span class="operator">></span>setIconSize(resultSize);
operatorComboBox <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qcombobox.html">QComboBox</a></span>;
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_SourceOver<span class="operator">,</span> tr(<span class="string">"SourceOver"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_DestinationOver<span class="operator">,</span> tr(<span class="string">"DestinationOver"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Clear<span class="operator">,</span> tr(<span class="string">"Clear"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Source<span class="operator">,</span> tr(<span class="string">"Source"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Destination<span class="operator">,</span> tr(<span class="string">"Destination"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_SourceIn<span class="operator">,</span> tr(<span class="string">"SourceIn"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_DestinationIn<span class="operator">,</span> tr(<span class="string">"DestinationIn"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_SourceOut<span class="operator">,</span> tr(<span class="string">"SourceOut"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_DestinationOut<span class="operator">,</span> tr(<span class="string">"DestinationOut"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_SourceAtop<span class="operator">,</span> tr(<span class="string">"SourceAtop"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_DestinationAtop<span class="operator">,</span> tr(<span class="string">"DestinationAtop"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Xor<span class="operator">,</span> tr(<span class="string">"Xor"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Plus<span class="operator">,</span> tr(<span class="string">"Plus"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Multiply<span class="operator">,</span> tr(<span class="string">"Multiply"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Screen<span class="operator">,</span> tr(<span class="string">"Screen"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Overlay<span class="operator">,</span> tr(<span class="string">"Overlay"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Darken<span class="operator">,</span> tr(<span class="string">"Darken"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Lighten<span class="operator">,</span> tr(<span class="string">"Lighten"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_ColorDodge<span class="operator">,</span> tr(<span class="string">"ColorDodge"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_ColorBurn<span class="operator">,</span> tr(<span class="string">"ColorBurn"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_HardLight<span class="operator">,</span> tr(<span class="string">"HardLight"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_SoftLight<span class="operator">,</span> tr(<span class="string">"SoftLight"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Difference<span class="operator">,</span> tr(<span class="string">"Difference"</span>));
addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Exclusion<span class="operator">,</span> tr(<span class="string">"Exclusion"</span>));</pre>
<p>The <tt>destinationButton</tt> is instantiated and its <a href="qabstractbutton.html#iconSize-prop">iconSize</a> property is set to <tt>resultSize</tt> as well. The <a href="qlabel.html">QLabel</a>s <tt>equalLabel</tt> and <tt>resultLabel</tt> are created and <tt>resultLabel</tt>'s <a href="qwidget.html#minimumWidth-prop">minimumWidth</a> is set.</p>
<pre class="cpp"> destinationButton <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtoolbutton.html">QToolButton</a></span>;
destinationButton<span class="operator">-</span><span class="operator">></span>setIconSize(resultSize);
equalLabel <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qlabel.html">QLabel</a></span>(tr(<span class="string">"="</span>));
resultLabel <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qlabel.html">QLabel</a></span>;
resultLabel<span class="operator">-</span><span class="operator">></span>setMinimumWidth(resultSize<span class="operator">.</span>width());</pre>
<p>We connect the following signals to their corresponding slots:</p>
<ul>
<li><tt>sourceButton</tt>'s <a href="qabstractbutton.html#clicked">clicked()</a> signal is connected to <tt>chooseSource()</tt>,</li>
<li><tt>operatorComboBox</tt>'s <a href="qcombobox.html#activated">activated()</a> signal is connected to <tt>recalculateResult()</tt>, and</li>
<li><tt>destinationButton</tt>'s <a href="qabstractbutton.html#clicked">clicked()</a> signal is connected to <tt>chooseDestination()</tt>.</li>
</ul>
<pre class="cpp"> connect(sourceButton<span class="operator">,</span> SIGNAL(clicked())<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(chooseSource()));
connect(operatorComboBox<span class="operator">,</span> SIGNAL(activated(<span class="type">int</span>))<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> SLOT(recalculateResult()));
connect(destinationButton<span class="operator">,</span> SIGNAL(clicked())<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> SLOT(chooseDestination()));</pre>
<p>A <a href="qgridlayout.html">QGridLayout</a>, <tt>mainLayout</tt>, is used to place all the widgets. Note that <tt>mainLayout</tt>'s <a href="qlayout.html#sizeConstraint-prop">sizeConstraint</a> property is set to <a href="qlayout.html#SizeConstraint-enum">QLayout::SetFixedSize</a>, which means that <tt>ImageComposer</tt>'s size cannot be resized at all.</p>
<pre class="cpp"> <span class="type"><a href="qgridlayout.html">QGridLayout</a></span> <span class="operator">*</span>mainLayout <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qgridlayout.html">QGridLayout</a></span>;
mainLayout<span class="operator">-</span><span class="operator">></span>addWidget(sourceButton<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">3</span><span class="operator">,</span> <span class="number">1</span>);
mainLayout<span class="operator">-</span><span class="operator">></span>addWidget(operatorComboBox<span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">1</span>);
mainLayout<span class="operator">-</span><span class="operator">></span>addWidget(destinationButton<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">2</span><span class="operator">,</span> <span class="number">3</span><span class="operator">,</span> <span class="number">1</span>);
mainLayout<span class="operator">-</span><span class="operator">></span>addWidget(equalLabel<span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">3</span>);
mainLayout<span class="operator">-</span><span class="operator">></span>addWidget(resultLabel<span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="number">4</span><span class="operator">,</span> <span class="number">3</span><span class="operator">,</span> <span class="number">1</span>);
<span class="preprocessor">#if defined(Q_OS_SYMBIAN) || defined(Q_WS_MAEMO_5) || defined(Q_WS_SIMULATOR)</span>
<span class="preprocessor">#else</span>
mainLayout<span class="operator">-</span><span class="operator">></span>setSizeConstraint(<span class="type"><a href="qlayout.html">QLayout</a></span><span class="operator">::</span>SetFixedSize);
<span class="preprocessor">#endif</span>
setLayout(mainLayout);</pre>
<p>We create a <a href="qimage.html">QImage</a>, <tt>resultImage</tt>, and we invoke <tt>loadImage()</tt> twice to load both the image files in our <i>imagecomposition.qrc</i> file. Then, we set the <a href="qwidget.html#windowTitle-prop">windowTitle</a> property to "Image Composition".</p>
<pre class="cpp"> resultImage <span class="operator">=</span> <span class="type"><a href="qimage.html">QImage</a></span>(resultSize<span class="operator">,</span> <span class="type"><a href="qimage.html">QImage</a></span><span class="operator">::</span>Format_ARGB32_Premultiplied);
loadImage(<span class="string">":/images/butterfly.png"</span><span class="operator">,</span> <span class="operator">&</span>sourceImage<span class="operator">,</span> sourceButton);
loadImage(<span class="string">":/images/checker.png"</span><span class="operator">,</span> <span class="operator">&</span>destinationImage<span class="operator">,</span> destinationButton);
setWindowTitle(tr(<span class="string">"Image Composition"</span>));
}</pre>
<p>The <tt>chooseSource()</tt> and <tt>chooseDestination()</tt> functions are convenience functions that invoke <tt>chooseImage()</tt> with specific parameters.</p>
<pre class="cpp"> <span class="type">void</span> ImageComposer<span class="operator">::</span>chooseSource()
{
chooseImage(tr(<span class="string">"Choose Source Image"</span>)<span class="operator">,</span> <span class="operator">&</span>sourceImage<span class="operator">,</span> sourceButton);
}
<span class="type">void</span> ImageComposer<span class="operator">::</span>chooseDestination()
{
chooseImage(tr(<span class="string">"Choose Destination Image"</span>)<span class="operator">,</span> <span class="operator">&</span>destinationImage<span class="operator">,</span>
destinationButton);
}</pre>
<p>The <tt>chooseImage()</tt> function loads an image of the user's choice, depending on the <i>title</i>, <i>image</i>, and <i>button</i>.</p>
<pre class="cpp"> <span class="type">void</span> ImageComposer<span class="operator">::</span>chooseImage(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>title<span class="operator">,</span> <span class="type"><a href="qimage.html">QImage</a></span> <span class="operator">*</span>image<span class="operator">,</span>
<span class="type"><a href="qtoolbutton.html">QToolButton</a></span> <span class="operator">*</span>button)
{
<span class="type"><a href="qstring.html">QString</a></span> fileName <span class="operator">=</span> <span class="type"><a href="qfiledialog.html">QFileDialog</a></span><span class="operator">::</span>getOpenFileName(<span class="keyword">this</span><span class="operator">,</span> title);
<span class="keyword">if</span> (<span class="operator">!</span>fileName<span class="operator">.</span>isEmpty())
loadImage(fileName<span class="operator">,</span> image<span class="operator">,</span> button);
}</pre>
<p>The <tt>recalculateResult()</tt> function is used to calculate amd display the result of combining the two images together with the user's choice of composition mode.</p>
<pre class="cpp"> <span class="type">void</span> ImageComposer<span class="operator">::</span>recalculateResult()
{
<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode mode <span class="operator">=</span> currentMode();
<span class="type"><a href="qpainter.html">QPainter</a></span> painter(<span class="operator">&</span>resultImage);
painter<span class="operator">.</span>setCompositionMode(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Source);
painter<span class="operator">.</span>fillRect(resultImage<span class="operator">.</span>rect()<span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>transparent);
painter<span class="operator">.</span>setCompositionMode(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_SourceOver);
painter<span class="operator">.</span>drawImage(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> destinationImage);
painter<span class="operator">.</span>setCompositionMode(mode);
painter<span class="operator">.</span>drawImage(<span class="number">0</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> sourceImage);
painter<span class="operator">.</span>setCompositionMode(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_DestinationOver);
painter<span class="operator">.</span>fillRect(resultImage<span class="operator">.</span>rect()<span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>white);
painter<span class="operator">.</span>end();
resultLabel<span class="operator">-</span><span class="operator">></span>setPixmap(<span class="type"><a href="qpixmap.html">QPixmap</a></span><span class="operator">::</span>fromImage(resultImage));
}</pre>
<p>The <tt>addOp()</tt> function adds an item to the <tt>operatorComboBox</tt> using <a href="qcombobox.html">QComboBox</a>'s <a href="qcombobox.html#addItem">addItem</a> function. This function accepts a <a href="qpainter.html#CompositionMode-enum">QPainter::CompositionMode</a>, <i>mode</i>, and a <a href="qstring.html">QString</a>, <i>name</i>. The rectangle is filled with Qt::Transparent and both the <tt>sourceImage</tt> and <tt>destinationImage</tt> are painted, before displaying it on <tt>resultLabel</tt>.</p>
<pre class="cpp"> <span class="type">void</span> ImageComposer<span class="operator">::</span>addOp(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode mode<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>name)
{
operatorComboBox<span class="operator">-</span><span class="operator">></span>addItem(name<span class="operator">,</span> mode);
}</pre>
<p>The <tt>loadImage()</tt> function paints a transparent background using <a href="qpainter.html#fillRect">fillRect()</a> and draws <tt>image</tt> in a centralized position using <a href="qpainter.html#drawImage">drawImage()</a>. This <tt>image</tt> is then set as the <tt>button</tt>'s icon.</p>
<pre class="cpp"> <span class="type">void</span> ImageComposer<span class="operator">::</span>loadImage(<span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>fileName<span class="operator">,</span> <span class="type"><a href="qimage.html">QImage</a></span> <span class="operator">*</span>image<span class="operator">,</span>
<span class="type"><a href="qtoolbutton.html">QToolButton</a></span> <span class="operator">*</span>button)
{
image<span class="operator">-</span><span class="operator">></span>load(fileName);
<span class="comment">// Scale the image to given size</span>
<span class="operator">*</span>image <span class="operator">=</span> image<span class="operator">-</span><span class="operator">></span>scaled(resultSize<span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>KeepAspectRatio);
<span class="type"><a href="qimage.html">QImage</a></span> fixedImage(resultSize<span class="operator">,</span> <span class="type"><a href="qimage.html">QImage</a></span><span class="operator">::</span>Format_ARGB32_Premultiplied);
<span class="type"><a href="qpainter.html">QPainter</a></span> painter(<span class="operator">&</span>fixedImage);
painter<span class="operator">.</span>setCompositionMode(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_Source);
painter<span class="operator">.</span>fillRect(fixedImage<span class="operator">.</span>rect()<span class="operator">,</span> <span class="type"><a href="qt.html">Qt</a></span><span class="operator">::</span>transparent);
painter<span class="operator">.</span>setCompositionMode(<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode_SourceOver);
painter<span class="operator">.</span>drawImage(imagePos(<span class="operator">*</span>image)<span class="operator">,</span> <span class="operator">*</span>image);
painter<span class="operator">.</span>end();
button<span class="operator">-</span><span class="operator">></span>setIcon(<span class="type"><a href="qpixmap.html">QPixmap</a></span><span class="operator">::</span>fromImage(fixedImage));
<span class="operator">*</span>image <span class="operator">=</span> fixedImage;
recalculateResult();
}</pre>
<p>The <tt>currentMode()</tt> function returns the composition mode currently selected in <tt>operatorComboBox</tt>.</p>
<pre class="cpp"> <span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode ImageComposer<span class="operator">::</span>currentMode() <span class="keyword">const</span>
{
<span class="keyword">return</span> (<span class="type"><a href="qpainter.html">QPainter</a></span><span class="operator">::</span>CompositionMode)
operatorComboBox<span class="operator">-</span><span class="operator">></span>itemData(operatorComboBox<span class="operator">-</span><span class="operator">></span>currentIndex())<span class="operator">.</span>toInt();
}</pre>
<p>We use the <tt>imagePos()</tt> function to ensure that images loaded onto the <a href="qtoolbutton.html">QToolButton</a> objects, <tt>sourceButton</tt> and <tt>destinationButton</tt>, are centralized.</p>
<pre class="cpp"> <span class="type"><a href="qpoint.html">QPoint</a></span> ImageComposer<span class="operator">::</span>imagePos(<span class="keyword">const</span> <span class="type"><a href="qimage.html">QImage</a></span> <span class="operator">&</span>image) <span class="keyword">const</span>
{
<span class="keyword">return</span> <span class="type"><a href="qpoint.html">QPoint</a></span>((resultSize<span class="operator">.</span>width() <span class="operator">-</span> image<span class="operator">.</span>width()) <span class="operator">/</span> <span class="number">2</span><span class="operator">,</span>
(resultSize<span class="operator">.</span>height() <span class="operator">-</span> image<span class="operator">.</span>height()) <span class="operator">/</span> <span class="number">2</span>);
}</pre>
<a name="the-function"></a>
<h2>The <tt>main()</tt> Function</h2>
<p>The <tt>main()</tt> function instantiates <a href="qapplication.html">QApplication</a> and <tt>ImageComposer</tt> and invokes its <a href="qwidget.html#show">show()</a> function.</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>argv<span class="operator">[</span><span class="operator">]</span>)
{
Q_INIT_RESOURCE(imagecomposition);
<span class="type"><a href="qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv);
ImageComposer composer;
<span class="preprocessor">#if defined(Q_OS_SYMBIAN)</span>
composer<span class="operator">.</span>showMaximized();
<span class="preprocessor">#else</span>
composer<span class="operator">.</span>show();
<span class="preprocessor">#endif</span>
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}</pre>
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