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<td >Qt 5.9</td><td ><a href="qtdatavisualization-index.html">Qt Data Visualization</a></td><td >Qt Quick 2 Spectrogram Example</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right">Qt 5.9.4 Reference Documentation</td>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#running-the-example">Running the Example</a></li>
<li class="level1"><a href="#creating-a-spectrogram">Creating a Spectrogram</a></li>
<li class="level1"><a href="#polar-spectrogram">Polar Spectrogram</a></li>
<li class="level1"><a href="#example-contents">Example Contents</a></li>
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<h1 class="title">Qt Quick 2 Spectrogram Example</h1>
<span class="subtitle"></span>
<!-- $$$qmlspectrogram-description -->
<div class="descr"> <a name="details"></a>
<p>The Qt Quick 2 Spectrogram example demonstrates how to show a polar and cartesian spectrograms and how to utilize orthographic projection to show them in 2D.</p>
<p class="centerAlign"><img src="images/qmlspectrogram-example.png" alt="" /></p><p>Spectrogram is simply a surface graph with a range gradient used to emphasize the different values. Typically spectrograms are shown with two dimensional surfaces, which we simulate with a top down orthographic view of the graph. To enforce the 2D effect, we disable the graph rotation via mouse or touch when in the orthographic mode.</p>
<p>The focus in this example is on showing how to display spectrograms, so the basic functionality is not explained. For more detailed QML example documentation, see <a href="qtdatavisualization-qmlscatter-example.html">Qt Quick 2 Scatter Example</a>.</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>
<a name="creating-a-spectrogram"></a>
<h2 id="creating-a-spectrogram">Creating a Spectrogram</h2>
<p>To create a 2D spectrogram, we define a <a href="qml-qtdatavisualization-surface3d.html">Surface3D</a> item:</p>
<pre class="qml">
<span class="type"><a href="qml-qtdatavisualization-surface3d.html">Surface3D</a></span> {
<span class="name">id</span>: <span class="name">surfaceGraph</span>
<span class="name">width</span>: <span class="name">surfaceView</span>.<span class="name">width</span>
<span class="name">height</span>: <span class="name">surfaceView</span>.<span class="name">height</span>
<span class="name">shadowQuality</span>: <span class="name">AbstractGraph3D</span>.<span class="name">ShadowQualityNone</span>
<span class="name">selectionMode</span>: <span class="name">AbstractGraph3D</span>.<span class="name">SelectionSlice</span> <span class="operator">|</span> <span class="name">AbstractGraph3D</span>.<span class="name">SelectionItemAndColumn</span>
<span class="name">axisX</span>: <span class="name">xAxis</span>
<span class="name">axisY</span>: <span class="name">yAxis</span>
<span class="name">axisZ</span>: <span class="name">zAxis</span>
<span class="name">theme</span>: <span class="name">customTheme</span>
<span class="name">inputHandler</span>: <span class="name">customInputHandler</span>
<span class="comment">// Remove the perspective and view the graph from top down to achieve 2D effect</span>
<span class="name">orthoProjection</span>: <span class="number">true</span>
<span class="name">scene</span>.activeCamera.cameraPreset: <span class="name">Camera3D</span>.<span class="name">CameraPresetDirectlyAbove</span>
<span class="name">flipHorizontalGrid</span>: <span class="number">true</span>
<span class="name">radialLabelOffset</span>: <span class="number">0.01</span>
<span class="name">horizontalAspectRatio</span>: <span class="number">1</span>
<span class="name">scene</span>.activeCamera.zoomLevel: <span class="number">85</span>
<span class="type"><a href="qml-qtdatavisualization-surface3dseries.html">Surface3DSeries</a></span> {
<span class="name">id</span>: <span class="name">surfaceSeries</span>
<span class="name">flatShadingEnabled</span>: <span class="number">false</span>
<span class="name">drawMode</span>: <span class="name">Surface3DSeries</span>.<span class="name">DrawSurface</span>
<span class="name">baseGradient</span>: <span class="name">surfaceGradient</span>
<span class="name">colorStyle</span>: <span class="name">Theme3D</span>.<span class="name">ColorStyleRangeGradient</span>
<span class="name">itemLabelFormat</span>: <span class="string">"(@xLabel, @zLabel): @yLabel"</span>
<span class="type"><a href="qml-qtdatavisualization-itemmodelsurfacedataproxy.html">ItemModelSurfaceDataProxy</a></span> {
<span class="name">itemModel</span>: <span class="name">surfaceData</span>.<span class="name">model</span>
<span class="name">rowRole</span>: <span class="string">"radius"</span>
<span class="name">columnRole</span>: <span class="string">"angle"</span>
<span class="name">yPosRole</span>: <span class="string">"value"</span>
}
}
}
</pre>
<p>The key properties for enabling the 2D effect are <a href="qml-qtdatavisualization-abstractgraph3d.html#orthoProjection-prop">orthoProjection</a> and <a href="qml-qtdatavisualization-camera3d.html#cameraPreset-prop">scene.activeCamera.cameraPreset</a>. We remove the perspective by enabling orthographic projection for the graph, and then we eliminate the Y-dimension by viewing the graph directly from above:</p>
<pre class="qml">
<span class="name">orthoProjection</span>: <span class="number">true</span>
<span class="name">scene</span>.activeCamera.cameraPreset: <span class="name">Camera3D</span>.<span class="name">CameraPresetDirectlyAbove</span>
</pre>
<p>Since this viewpoint causes the horizontal axis grid to be mostly obscured by the surface, we also specify that the horizontal grid should be drawn on top of the graph:</p>
<pre class="qml">
<span class="name">flipHorizontalGrid</span>: <span class="number">true</span>
</pre>
<a name="polar-spectrogram"></a>
<h2 id="polar-spectrogram">Polar Spectrogram</h2>
<p>Depending on the data, it is sometimes more natural to use a polar graph instead of a cartesian one. Qt Data Visualization supports this via <a href="qml-qtdatavisualization-abstractgraph3d.html#polar-prop">polar</a> property. In this example we provide a button to switch between polar and cartesian modes:</p>
<pre class="qml">
<span class="type">NewButton</span> {
<span class="name">id</span>: <span class="name">polarToggle</span>
<span class="name">Layout</span>.fillWidth: <span class="number">true</span>
<span class="name">Layout</span>.fillHeight: <span class="number">true</span>
<span class="name">text</span>: <span class="string">"Switch to polar"</span>
<span class="name">onClicked</span>: {
<span class="keyword">if</span> (<span class="name">surfaceGraph</span>.<span class="name">polar</span> <span class="operator">===</span> <span class="number">false</span>) {
<span class="name">surfaceGraph</span>.<span class="name">polar</span> <span class="operator">=</span> <span class="number">true</span>
<span class="name">text</span> <span class="operator">=</span> <span class="string">"Switch to cartesian"</span>
} <span class="keyword">else</span> {
<span class="name">surfaceGraph</span>.<span class="name">polar</span> <span class="operator">=</span> <span class="number">false</span>
<span class="name">text</span> <span class="operator">=</span> <span class="string">"Switch to polar"</span>
}
}
}
</pre>
<p>In the polar mode, the X-axis is converted into the angular polar axis, and the Z-axis is converted into the radial polar axis. The surface points are recalculated according to new axes.</p>
<p>The radial axis labels are drawn outside the graph by default, but in this example we want to draw them right next to the 0 degree angular axis inside the graph, so we define only a tiny offset for them:</p>
<pre class="qml">
<span class="name">radialLabelOffset</span>: <span class="number">0.01</span>
</pre>
<p>To enforce the 2D effect, graph rotation via user input is disabled when in orthographic mode. We do this by specifying a new input handler:</p>
<pre class="qml">
<span class="type"><a href="qml-qtdatavisualization-touchinputhandler3d.html">TouchInputHandler3D</a></span> {
<span class="name">id</span>: <span class="name">customInputHandler</span>
<span class="name">rotationEnabled</span>: <span class="number">false</span>
}
<span class="type"><a href="qml-qtdatavisualization-surface3d.html">Surface3D</a></span> {
...
<span class="name">inputHandler</span>: <span class="name">customInputHandler</span>
...
</pre>
<p>When the projection mode changes, we adjust the value of the <a href="qml-qtdatavisualization-inputhandler3d.html#rotationEnabled-prop">rotationEnabled</a> property of the <code>customInputHandler</code> to control the rotation.</p>
<a name="example-contents"></a>
<h2 id="example-contents">Example Contents</h2>
<p>Files:</p>
<ul>
<li><a href="qtdatavisualization-qmlspectrogram-qml-qmlspectrogram-data-qml.html">qmlspectrogram/qml/qmlspectrogram/Data.qml</a></li>
<li><a href="qtdatavisualization-qmlspectrogram-qml-qmlspectrogram-newbutton-qml.html">qmlspectrogram/qml/qmlspectrogram/NewButton.qml</a></li>
<li><a href="qtdatavisualization-qmlspectrogram-qml-qmlspectrogram-main-qml.html">qmlspectrogram/qml/qmlspectrogram/main.qml</a></li>
<li><a href="qtdatavisualization-qmlspectrogram-main-cpp.html">qmlspectrogram/main.cpp</a></li>
<li><a href="qtdatavisualization-qmlspectrogram-qmlspectrogram-pro.html">qmlspectrogram/qmlspectrogram.pro</a></li>
<li><a href="qtdatavisualization-qmlspectrogram-qmlspectrogram-qrc.html">qmlspectrogram/qmlspectrogram.qrc</a></li>
</ul>
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