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* Chickadee: (chickadee).     Game programming toolkit for Guile.

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<span id="Tweening"></span><div class="header">
<p>
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<hr />
<span id="Tweening-1"></span><h4 class="subsection">5.5.3 Tweening</h4>

<p>Tweening is the process of transitioning something from an initial
state to a final state over a pre-determined period of time.  In other
words, tweening is a way to create animation.  The <code>tween</code>
procedure can be used within any script like so:
</p>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-special">define</span> <span class="syntax-symbol">x</span> <span class="syntax-symbol">0</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">script</span>
  <span class="syntax-comment">;; 0 to 100 in 60 ticks of the agenda.
</span>  <span class="syntax-open">(</span><span class="syntax-symbol">tween</span> <span class="syntax-symbol">60</span> <span class="syntax-symbol">0</span> <span class="syntax-symbol">100</span> <span class="syntax-open">(</span><span class="syntax-special">lambda</span> <span class="syntax-open">(</span><span class="syntax-symbol">y</span><span class="syntax-close">)</span> <span class="syntax-open">(</span><span class="syntax-symbol">set!</span> <span class="syntax-symbol">x</span> <span class="syntax-symbol">y</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span><span class="syntax-close">)</span>
</pre></div>

<dl>
<dt id="index-tween">Procedure: <strong>tween</strong> <em>duration start end proc                          [#:step <code>1</code>] [#:ease <code>smoothstep</code>]                          #:interpolate <code>lerp</code>]</em></dt>
<dd><p>Transition a value from <var>start</var> to <var>end</var> over <var>duration</var>,
sending each succesive value to <var>proc</var>.  <var>step</var> controls the
amount of time between each update of the animation.
</p>
<p>To control how the animation goes from the initial to final state, an
&ldquo;easing&rdquo; procedure may be specified.  By default, the
<code>smoothstep</code> easing is used, which is a more pleasing default
than a simplistic linear function.  See <a href="Easings.html">Easings</a> for a complete list
of available easing procedures.
</p>
<p>The <var>interpolate</var> procedure computes the values in between
<var>start</var> and <var>end</var>.  By default, linear interpolation (&ldquo;lerp&rdquo;
for short) is used.
</p></dd></dl>




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