little_helpers/tikz/sketch-0.2.161/Doc/sketch/Polyline-sweeps-with-closure.html

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  56 <h4 class="subsection">2.7.5 Polyline sweeps with closure</h4>
  57
  58 <p>A polyline sweep with a closure tag
  59 <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
  60 surface.  First, the polyline segments are connected by faces, just as
  61 without the closure tag.  Then, each set of end points is joined to
  62 make a polygon, one for each end.  A code for several views of a
  63 cylindrical prism follows.
  64 <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>
  65 <pre class="verbatim">
  66   def n_cyl_segs 20  def n_views 5  def I [1,0,0]
  67   def endopts [fillcolor=lightgray]
  68   repeat { n_views, rotate(180/n_views, [I]) then translate([I] * 2.1) }
  69     sweep[endopts]{ n_cyl_segs&lt;>, rotate(360/n_cyl_segs, [0,1,0]) }
  70       line[fillcolor=white](1,-1)(1,1)
  71 </pre>
  72 It produces this drawing.
  73
  74 <div align="center"><img src="ex110.png" alt="ex110.png"></div>
  75
  76 <p class="noindent">The options of the swept line, if any, are applied to the faces
  77 produced by sweeping the line, but not the end polygons.  Otherwise,
  78 the sweep options are applied throughout.
  79 <a name="index-options_002c-swept-object-146"></a>The <tt>def</tt> in this example is an <dfn>option</dfn> definition.
  80 <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.&nbsp;<!-- /@w -->
  81 <tt>[foo]</tt>.
  82 <a name="index-reference_002c-options-149"></a><a name="index-_005bfoo_005d_0040r_007b_002c-options-reference_007d-150"></a>You can concatenate several sets of options with a single
  83 reference, e.g.&nbsp;<!-- /@w -->
  84 <tt>[color, size, style]</tt>
  85 would cause the option definitions for <code>color</code>, <code>size</code>,
  86 and <code>style</code> to appear in sequence in the output
  87 created by the <code>sketch</code> command containing the reference.
  88 Happily, the syntax of <code>sketch</code> is such that
  89 options references can never be confused with vector references.  While
  90 not apparent in this example, options references are useful when
  91 defining many objects with a similar appearance.
  92
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