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<span id="Particles"></span><div class="header">
<p>
Next: <a href="Tile-Maps.html" accesskey="n" rel="next">Tile Maps</a>, Previous: <a href="Vector-Paths.html" accesskey="p" rel="prev">Vector Paths</a>, Up: <a href="Graphics.html" accesskey="u" rel="up">Graphics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p>
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<hr />
<span id="Particles-1"></span><h4 class="subsection">5.3.6 Particles</h4>
<p>Effects like smoke, fire, sparks, etc. are often achieved by animating
lots of little, short-lived sprites known as “particles”. In fact,
all of these effects, and more, can be accomplished by turning a few
configuration knobs in a “particle system”. A particle system takes
care of managing the many miniscule moving morsels so the developer
can quickly produce an effect and move on with their life. The
<code>(chickadee graphics particles)</code> module provides an API for
manipulating particle systems.
</p>
<p>Below is an example of a very simple particle system that utilizes
nearly all of the default configuration settings:
</p>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">use-modules</span> <span class="syntax-open">(</span><span class="syntax-symbol">chickadee</span> <span class="syntax-symbol">graphics</span> <span class="syntax-symbol">particles</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-special">define</span> <span class="syntax-symbol">texture</span> <span class="syntax-open">(</span><span class="syntax-symbol">load-image</span> <span class="syntax-string">"particle.png"</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-special">define</span> <span class="syntax-symbol">particles</span> <span class="syntax-open">(</span><span class="syntax-symbol">make-particles</span> <span class="syntax-symbol">2000</span> <span class="syntax-keyword">#:texture</span> <span class="syntax-symbol">texture</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
</pre></div>
<p>In order to put particles into a particle system, a particle
“emitter” is needed. Emitters know where to spawn new particles,
how many of them to spawn, and for how long they should do it.
</p>
<p>Below is an example of an emitter that spawns 16 particles per frame
at the coordinates <code>(320, 240)</code>:
</p>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">use-modules</span> <span class="syntax-open">(</span><span class="syntax-symbol">chickadee</span> <span class="syntax-symbol">math</span> <span class="syntax-symbol">rect</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-special">define</span> <span class="syntax-symbol">emitter</span> <span class="syntax-open">(</span><span class="syntax-symbol">make-particle-emitter</span> <span class="syntax-open">(</span><span class="syntax-symbol">make-rect</span> <span class="syntax-symbol">0.0</span> <span class="syntax-symbol">0.0</span> <span class="syntax-symbol">320.0</span> <span class="syntax-symbol">240.0</span><span class="syntax-close">)</span> <span class="syntax-symbol">16</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">add-particle-emitter</span> <span class="syntax-symbol">particles</span> <span class="syntax-symbol">emitter</span><span class="syntax-close">)</span>
</pre></div>
<p>To see all of the tweakable knobs and switches, read on!
</p>
<dl>
<dt id="index-make_002dparticles">Procedure: <strong>make-particles</strong> <em>capacity [#:blend-mode] [#:color white] [#:end-color transparent] [#:texture] [#:animation-rows 1] [#:animation-columns 1] [#:width] [#:height] [#:speed-range (vec2 0.1 1.0)] [#:acceleration-range (vec2 0.0 0.1)] [#:direction-range (vec2 0 (* 2 pi))] [#:lifetime 30] [#:sort]</em></dt>
<dd>
<p>Return a new particle system that may contain up to <var>capacity</var>
particles. Achieving the desired particle effect involves tweaking
the following keyword arguments as needed:
</p>
<p>- <var>blend-mode</var>: Pixel blending mode. Alpha blending is used by
default. (see <a href="Render-Settings.html">Render Settings</a> for more about blend modes).
</p>
<p>- <var>start-color</var>: The tint color of the particle at the beginning of its
life. White by default.
</p>
<p>- <var>end-color</var>: The tint color of the particle at the end of of its
life. Completely transparent by default for a fade-out effect. The
color in the middle of a particle’s life will be an interpolation of
<var>start-color</var> and <var>end-color</var>.
</p>
<p>- <var>texture</var>: The texture applied to the particles. The texture
may be subdivided into many animation frames.
</p>
<p>- <var>animation-rows</var>: How many animation frame rows there are in the
texture. Default is 1.
</p>
<p>- <var>animation-columns</var>: How many animation frame columns there are
in the texture. Default is 1.
</p>
<p>- <var>width</var>: The width of each particle. By default, the width of
an animation frame (in pixels) is used.
</p>
<p>- <var>height</var>: The height of each particle. By default, the height
of an animation frame (in pixels) is used.
</p>
<p>- <var>speed-range</var>: A 2D vector containing the min and max particle
speed. Each particle will have a speed chosen at random from this
range. By default, speed ranges from 0.1 to 1.0.
</p>
<p>- <var>acceleration-range</var>: A 2D vector containing the min and max
particle acceleration. Each particle will have an acceleration chosen
at random from this range. By default, acceleration ranges from 0.0
to 0.1.
</p>
<p>- <var>direction-range</var>: A 2D vector containing the min and max
particle direction as an angle in radians. Each particle will have a
direction chosen at random from this range. By default, the range
covers all possible angles.
</p>
<p>- <var>lifetime</var>: How long each particle lives, measured in
updates. 30 by default.
</p>
<p>- <var>sort</var>: <code>youngest</code> if youngest particle should be drawn
last or <code>oldest</code> for the reverse. By default, no sorting is
applied at all.
</p></dd></dl>
<dl>
<dt id="index-particles_003f">Procedure: <strong>particles?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a particle system.
</p></dd></dl>
<dl>
<dt id="index-update_002dparticles">Procedure: <strong>update-particles</strong> <em>particles</em></dt>
<dd><p>Advance the simulation of <var>particles</var>.
</p></dd></dl>
<dl>
<dt id="index-draw_002dparticles">Procedure: <strong>draw-particles</strong> <em>particles</em></dt>
<dd><p>Render <var>particles</var>.
</p></dd></dl>
<dl>
<dt id="index-draw_002dparticles_002a">Procedure: <strong>draw-particles*</strong> <em>particles matrix</em></dt>
<dd><p>Render <var>particles</var> with <var>matrix</var> applied.
</p></dd></dl>
<dl>
<dt id="index-make_002dparticle_002demitter">Procedure: <strong>make-particle-emitter</strong> <em>spawn-area rate [duration]</em></dt>
<dd>
<p>Return a new particle emitter that spawns <var>rate</var> particles per
frame within <var>spawn-area</var> (a rectangle or 2D vector) for
<var>duration</var> frames. If <var>duration</var> is not specified, the
emitter will spawn particles indefinitely.
</p></dd></dl>
<dl>
<dt id="index-particle_002demitter_003f">Procedure: <strong>particle-emitter?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a particle emitter.
</p></dd></dl>
<dl>
<dt id="index-particle_002demitter_002dspawn_002darea">Procedure: <strong>particle-emitter-spawn-area</strong> <em>emitter</em></dt>
<dd><p>Return the spawn area for <var>emitter</var>.
</p></dd></dl>
<dl>
<dt id="index-particle_002demitter_002drate">Procedure: <strong>particle-emitter-rate</strong> <em>emitter</em></dt>
<dd><p>Return the number of particles that <var>emitter</var> will spawn per
frame.
</p></dd></dl>
<dl>
<dt id="index-particle_002demitter_002dlife">Procedure: <strong>particle-emitter-life</strong> <em>emitter</em></dt>
<dd><p>Return the number of frames remaining in <var>emitter</var>’s lifespan.
</p></dd></dl>
<dl>
<dt id="index-particle_002demitter_002ddone_003f">Procedure: <strong>particle-emitter-done?</strong> <em>emitter</em></dt>
<dd><p>Return <code>#t</code> if <var>emitter</var> has finished spawning particlces.
</p></dd></dl>
<dl>
<dt id="index-add_002dparticle_002demitter">Procedure: <strong>add-particle-emitter</strong> <em>particles emitter</em></dt>
<dd><p>Add <var>emitter</var> to <var>particles</var>.
</p></dd></dl>
<dl>
<dt id="index-remove_002dparticle_002demitter">Procedure: <strong>remove-particle-emitter</strong> <em>particles emitter</em></dt>
<dd><p>Remove <var>emitter</var> from <var>particles</var>
</p></dd></dl>
<hr />
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