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         xml:id="howto.transparent_particles" xmlns="http://docbook.org/ns/docbook"
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  <title>Semi-transparent particles</title>

  <para>
     <figure>
      <title>Semi-transparent particles</title>
      <screenshot><mediaobject><imageobject>
            <imagedata fileref="images/howtos/semitransparent_particles.png" format="png" />
       </imageobject></mediaobject></screenshot>
    </figure> 
    Particles can be made semi-transparent by setting the <literal>Transparency</literal> particle property.
    A <literal>Transparency</literal> value of 0 lets a particle appear fully opaque, while any value between
    0 and 1 lets it appear translucent.
  </para>
  
  <para>
    The easiest method of setting the <literal>Transparency</literal> property is by using the 
    <link linkend="particles.modifiers.compute_property">Compute property</link> modifier.
    In the example here, a simple math formula was used to set the <literal>Transparency</literal> property
    of particles depending on their position:
    <screen>   ReducedPosition.X</screen>
    The expression <literal>ReducedPosition.X</literal> evaluates to a particle's X position in reduced coordinates,
    which varies between 0 to 1 from one side of the simulation box to the other. When assigning the computed values
    to the <literal>Transparency</literal> property, particles on the left appear fully opaque while particles
    on the right side of the simulation box become fully transparent.
  </para>
  
  <para>
    You can make just the selected particles transparent by checking the <emphasis>Compute only for selected particles</emphasis> option in the
    <link linkend="particles.modifiers.compute_property">Compute property</link> modifier.
  </para>
  
  <para>
    Note: The current program version cannot display particles with <link linkend="howto.aspherical_particles">cylindrical or spherocylindrical shape</link> 
    that are semi-transparent. These aspherical particles will always appear fully opaque.
  </para>

</section>
