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<td >Qt 5.9</td><td ><a href="qtquick-index.html">Qt Quick</a></td><td >Qt Quick Particles Examples - Emitters</td></tr></table><table class="buildversion"><tr>
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<h1 class="title">Qt Quick Particles Examples - Emitters</h1>
<span class="subtitle"></span>
<!-- $$$particles/emitters-description -->
<div class="descr"> <a name="details"></a>
<p class="centerAlign"><img src="images/qml-emitters-example.png" alt="" /></p><p>This is a collection of small QML examples relating to using Emitters in the particle system. Each example is a small QML file emphasizing a particular type or feature.</p>
<p>Velocity from motion gives the effect of strong particle motion through primarily moving the emitters:</p>
<pre class="qml">

  <span class="type"><a href="qml-qtquick-particles-emitter.html">Emitter</a></span> {
      <span class="name">id</span>: <span class="name">trailsNormal</span>
      <span class="name">system</span>: <span class="name">sys1</span>

      <span class="name">emitRate</span>: <span class="number">500</span>
      <span class="name">lifeSpan</span>: <span class="number">2000</span>

      <span class="name">y</span>: <span class="name">mouseArea</span>.<span class="name">pressed</span> ? <span class="name">mouseArea</span>.<span class="name">mouseY</span> : <span class="name">circle</span>.<span class="name">cy</span>
      <span class="name">x</span>: <span class="name">mouseArea</span>.<span class="name">pressed</span> ? <span class="name">mouseArea</span>.<span class="name">mouseX</span> : <span class="name">circle</span>.<span class="name">cx</span>

      <span class="name">velocity</span>: <span class="name">PointDirection</span> {<span class="name">xVariation</span>: <span class="number">4</span>; <span class="name">yVariation</span>: <span class="number">4</span>;}
      <span class="name">acceleration</span>: <span class="name">PointDirection</span> {<span class="name">xVariation</span>: <span class="number">10</span>; <span class="name">yVariation</span>: <span class="number">10</span>;}
      <span class="name">velocityFromMovement</span>: <span class="number">8</span>

      <span class="name">size</span>: <span class="number">8</span>
      <span class="name">sizeVariation</span>: <span class="number">4</span>
  }

</pre>
<p>Burst and pulse calls the burst and pulse methods on two idential emitters.</p>
<pre class="qml">

      <span class="keyword">if</span> (<span class="name">lastWasPulse</span>) {
          <span class="name">burstEmitter</span>.<span class="name">burst</span>(<span class="number">500</span>);
          <span class="name">lastWasPulse</span> <span class="operator">=</span> <span class="number">false</span>;
      } <span class="keyword">else</span> {
          <span class="name">pulseEmitter</span>.<span class="name">pulse</span>(<span class="number">500</span>);
          <span class="name">lastWasPulse</span> <span class="operator">=</span> <span class="number">true</span>;
      }

</pre>
<p>Note how burst takes an argument of number of particles to emit, and pulse takes an argument of number of milliseconds to emit for. This gives a slightly different behaviour, which is easy to see in this example.</p>
<p>Custom Emitter connects to the emitParticles signal to set arbitrary values on particle data as they're emitted;</p>
<pre class="qml">

  <span class="name">onEmitParticles</span>: {
      <span class="keyword">for</span> (<span class="keyword">var</span> <span class="name">i</span>=<span class="number">0</span>; <span class="name">i</span><span class="operator">&lt;</span><span class="name">particles</span>.<span class="name">length</span>; i++) {
          var <span class="name">particle</span> = <span class="name">particles</span>[<span class="name">i</span>];
          <span class="name">particle</span>.<span class="name">startSize</span> <span class="operator">=</span> <span class="name">Math</span>.<span class="name">max</span>(<span class="number">02</span>,<span class="name">Math</span>.<span class="name">min</span>(<span class="number">492</span>,<span class="name">Math</span>.<span class="name">tan</span>(<span class="name">particle</span>.<span class="name">t</span><span class="operator">/</span><span class="number">2</span>)<span class="operator">*</span><span class="number">24</span>));
          var <span class="name">theta</span> = <span class="name">Math</span>.<span class="name">floor</span>(<span class="name">Math</span>.<span class="name">random</span>() <span class="operator">*</span> <span class="number">6.0</span>);
          <span class="name">particle</span>.<span class="name">red</span> <span class="operator">=</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">0</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">1</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">2</span> ? <span class="number">0.2</span> : <span class="number">1</span>;
          <span class="name">particle</span>.<span class="name">green</span> <span class="operator">=</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">2</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">3</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">4</span> ? <span class="number">0.2</span> : <span class="number">1</span>;
          <span class="name">particle</span>.<span class="name">blue</span> <span class="operator">=</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">4</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">5</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">0</span> ? <span class="number">0.2</span> : <span class="number">1</span>;
          <span class="name">theta</span> <span class="operator">/=</span> <span class="number">6.0</span>;
          <span class="name">theta</span> <span class="operator">*=</span> <span class="number">2.0</span><span class="operator">*</span><span class="name">Math</span>.<span class="name">PI</span>;
          <span class="name">theta</span> <span class="operator">+=</span> <span class="name">sys</span>.<span class="name">convert</span>(<span class="name">sys</span>.<span class="name">petalRotation</span>);<span class="comment">//Convert from degrees to radians</span>
          <span class="name">particle</span>.<span class="name">initialVX</span> <span class="operator">=</span> <span class="name">petalLength</span> <span class="operator">*</span> <span class="name">Math</span>.<span class="name">cos</span>(<span class="name">theta</span>);
          <span class="name">particle</span>.<span class="name">initialVY</span> <span class="operator">=</span> <span class="name">petalLength</span> <span class="operator">*</span> <span class="name">Math</span>.<span class="name">sin</span>(<span class="name">theta</span>);
          <span class="name">particle</span>.<span class="name">initialAX</span> <span class="operator">=</span> <span class="name">particle</span>.<span class="name">initialVX</span> <span class="operator">*</span> -<span class="number">0.5</span>;
          <span class="name">particle</span>.<span class="name">initialAY</span> <span class="operator">=</span> <span class="name">particle</span>.<span class="name">initialVY</span> <span class="operator">*</span> -<span class="number">0.5</span>;
      }
  }

</pre>
<p>This is used to emit curving particles in six rotating spokes.</p>
<p>Emit mask sets an image mask on the Emitter, to emit out of an arbitrary shape.</p>
<pre class="qml">

  <span class="name">shape</span>: <span class="name">MaskShape</span> {
      <span class="name">source</span>: <span class="string">&quot;../../images/starfish_mask.png&quot;</span>
  }

</pre>
<p>Maximum emitted emits no more than a certain number of particles at a time. This example makes it easy to see what happens when the limit is reached.</p>
<p>Shape and Direction emits particles out of an unfilled Ellipse shape, using a <a href="qml-qtquick-particles-targetdirection.html">TargetDirection</a></p>
<pre class="qml">

  <span class="name">shape</span>: <span class="name">EllipseShape</span> {<span class="name">fill</span>: <span class="number">false</span>}
  <span class="name">velocity</span>: <span class="name">TargetDirection</span> {
      <span class="name">targetX</span>: <span class="name">root</span>.<span class="name">width</span><span class="operator">/</span><span class="number">2</span>
      <span class="name">targetY</span>: <span class="name">root</span>.<span class="name">height</span><span class="operator">/</span><span class="number">2</span>
      <span class="name">proportionalMagnitude</span>: <span class="number">true</span>
      <span class="name">magnitude</span>: <span class="number">0.5</span>
  }

</pre>
<p>This sends the particles towards the center of the ellipse with proportional speed, keeping the ellipse outline as they move to the center.</p>
<p><a href="qml-qtquick-particles-trailemitter.html">TrailEmitter</a> uses that type to add smoke particles to trail the fire particles in the scene.</p>
<pre class="qml">

  <span class="name">onEmitParticles</span>: {
      <span class="keyword">for</span> (<span class="keyword">var</span> <span class="name">i</span>=<span class="number">0</span>; <span class="name">i</span><span class="operator">&lt;</span><span class="name">particles</span>.<span class="name">length</span>; i++) {
          var <span class="name">particle</span> = <span class="name">particles</span>[<span class="name">i</span>];
          <span class="name">particle</span>.<span class="name">startSize</span> <span class="operator">=</span> <span class="name">Math</span>.<span class="name">max</span>(<span class="number">02</span>,<span class="name">Math</span>.<span class="name">min</span>(<span class="number">492</span>,<span class="name">Math</span>.<span class="name">tan</span>(<span class="name">particle</span>.<span class="name">t</span><span class="operator">/</span><span class="number">2</span>)<span class="operator">*</span><span class="number">24</span>));
          var <span class="name">theta</span> = <span class="name">Math</span>.<span class="name">floor</span>(<span class="name">Math</span>.<span class="name">random</span>() <span class="operator">*</span> <span class="number">6.0</span>);
          <span class="name">particle</span>.<span class="name">red</span> <span class="operator">=</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">0</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">1</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">2</span> ? <span class="number">0.2</span> : <span class="number">1</span>;
          <span class="name">particle</span>.<span class="name">green</span> <span class="operator">=</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">2</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">3</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">4</span> ? <span class="number">0.2</span> : <span class="number">1</span>;
          <span class="name">particle</span>.<span class="name">blue</span> <span class="operator">=</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">4</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">5</span> <span class="operator">||</span> <span class="name">theta</span> <span class="operator">==</span> <span class="number">0</span> ? <span class="number">0.2</span> : <span class="number">1</span>;
          <span class="name">theta</span> <span class="operator">/=</span> <span class="number">6.0</span>;
          <span class="name">theta</span> <span class="operator">*=</span> <span class="number">2.0</span><span class="operator">*</span><span class="name">Math</span>.<span class="name">PI</span>;
          <span class="name">theta</span> <span class="operator">+=</span> <span class="name">sys</span>.<span class="name">convert</span>(<span class="name">sys</span>.<span class="name">petalRotation</span>);<span class="comment">//Convert from degrees to radians</span>
          <span class="name">particle</span>.<span class="name">initialVX</span> <span class="operator">=</span> <span class="name">petalLength</span> <span class="operator">*</span> <span class="name">Math</span>.<span class="name">cos</span>(<span class="name">theta</span>);
          <span class="name">particle</span>.<span class="name">initialVY</span> <span class="operator">=</span> <span class="name">petalLength</span> <span class="operator">*</span> <span class="name">Math</span>.<span class="name">sin</span>(<span class="name">theta</span>);
          <span class="name">particle</span>.<span class="name">initialAX</span> <span class="operator">=</span> <span class="name">particle</span>.<span class="name">initialVX</span> <span class="operator">*</span> -<span class="number">0.5</span>;
          <span class="name">particle</span>.<span class="name">initialAY</span> <span class="operator">=</span> <span class="name">particle</span>.<span class="name">initialVY</span> <span class="operator">*</span> -<span class="number">0.5</span>;
      }
  }

</pre>
<p>Files:</p>
<ul>
<li><a href="qtquick-particles-emitters-emitters-qml.html">particles/emitters/emitters.qml</a></li>
<li><a href="qtquick-particles-emitters-content-burstandpulse-qml.html">particles/emitters/content/burstandpulse.qml</a></li>
<li><a href="qtquick-particles-emitters-content-customemitter-qml.html">particles/emitters/content/customemitter.qml</a></li>
<li><a href="qtquick-particles-emitters-content-emitmask-qml.html">particles/emitters/content/emitmask.qml</a></li>
<li><a href="qtquick-particles-emitters-content-maximumemitted-qml.html">particles/emitters/content/maximumemitted.qml</a></li>
<li><a href="qtquick-particles-emitters-content-shapeanddirection-qml.html">particles/emitters/content/shapeanddirection.qml</a></li>
<li><a href="qtquick-particles-emitters-content-trailemitter-qml.html">particles/emitters/content/trailemitter.qml</a></li>
<li><a href="qtquick-particles-emitters-content-velocityfrommotion-qml.html">particles/emitters/content/velocityfrommotion.qml</a></li>
<li><a href="qtquick-particles-emitters-main-cpp.html">particles/emitters/main.cpp</a></li>
<li><a href="qtquick-particles-emitters-emitters-pro.html">particles/emitters/emitters.pro</a></li>
<li><a href="qtquick-particles-emitters-emitters-qmlproject.html">particles/emitters/emitters.qmlproject</a></li>
<li><a href="qtquick-particles-emitters-emitters-qrc.html">particles/emitters/emitters.qrc</a></li>
</ul>
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