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<a name="Tweening-1"></a>
<h4 class="subsection">2.4.3 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="example">
<pre class="example">(define x 0)
(script
;; 0 to 100 in 60 ticks of the agenda.
(tween 60 0 100 (lambda (y) (set! x y))))
</pre></div>
<dl>
<dt><a name="index-tween"></a>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
“easing” 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">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 (“lerp”
for short) is used.
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