unctions for drawing 
    X-splines to produce smooth lines or closed shapes with smooth
    boundaries.  The following code shows an example (used for the
    top X-spline in the diagram above).
  </p>
<div class="chunk" id="unnamed-chunk-3"><div class="rcode"><div class="source"><pre class="knitr r"><span class="hl kwd">library</span><span class="hl std">(grid)</span>
</pre></div>
</div></div>
<div class="chunk" id="x-spline-code"><div class="rcode"><div class="source"><pre class="knitr r"><span class="hl