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<title>Polyline sweeps with closure - Sketch</title>
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<p>
<a name="Polyline-sweeps-with-closure"></a>Next: <a rel="next" accesskey="n" href="Affine-arithmetic.html#Affine-arithmetic">Affine arithmetic</a>,
Previous: <a rel="previous" accesskey="p" href="Polygon-sweeps.html#Polygon-sweeps">Polygon sweeps</a>,
Up: <a rel="up" accesskey="u" href="Swept-objects.html#Swept-objects">Swept objects</a>
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<h4 class="subsection">2.7.5 Polyline sweeps with closure</h4>
<p>A polyline sweep with a closure tag
<a name="index-_003c_003e_0040r_007b_002c-closure-tag_007d-136"></a><a name="index-closure-tag_002c-_0040code_007b_003c_003e_007d-137"></a>creates another kind of closed
surface. First, the polyline segments are connected by faces, just as
without the closure tag. Then, each set of end points is joined to
make a polygon, one for each end. A code for several views of a
cylindrical prism follows.
<a name="index-def-138"></a><a name="index-repeat-139"></a><a name="index-rotate-140"></a><a name="index-then-141"></a><a name="index-translate-142"></a><a name="index-sweep-143"></a><a name="index-line-144"></a><a name="index-fillcolor-145"></a>
<pre class="verbatim">
def n_cyl_segs 20 def n_views 5 def I [1,0,0]
def endopts [fillcolor=lightgray]
repeat { n_views, rotate(180/n_views, [I]) then translate([I] * 2.1) }
sweep[endopts]{ n_cyl_segs<>, rotate(360/n_cyl_segs, [0,1,0]) }
line[fillcolor=white](1,-1)(1,1)
</pre>
It produces this drawing.
<div align="center"><img src="ex110.png" alt="ex110.png"></div>
<p class="noindent">The options of the swept line, if any, are applied to the faces
produced by sweeping the line, but not the end polygons. Otherwise,
the sweep options are applied throughout.
<a name="index-options_002c-swept-object-146"></a>The <tt>def</tt> in this example is an <dfn>option</dfn> definition.
<a name="index-definition_002c-options-147"></a><a name="index-options-definition-148"></a>References to options must be enclosed in square brackets, e.g. <!-- /@w -->
<tt>[foo]</tt>.
<a name="index-reference_002c-options-149"></a><a name="index-_005bfoo_005d_0040r_007b_002c-options-reference_007d-150"></a>Happily, the syntax of <code>sketch</code> is such that
options references can never be confused with vector references. While
not apparent in this example, options references are useful when
defining many objects with a similar appearance.
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