little_helpers/tikz/sketch-0.2.161/Doc/sketch/Sweep-face-splitting.html

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  54 <h5 class="subsubsection">3.2.6.5 Sweep face splitting</h5>
  55
  56 <p>Before sending each four-sided body polygon of a <code>sweep</code>
  57 to the output, <code>sketch</code> tests to see if it is roughly planar.
  58 <a name="index-polygon_002c-planar-323"></a><a name="index-planarity-of-polygons-324"></a>Since planarity is necessary for proper functioning of the hidden
  59 surface algorithm, &ldquo;warped&rdquo; polygons are automatically split into
  60 two triangles.
  61
  62    <p>Hole-filling polygons produced by closure-tagged
  63 <a name="index-_003c_003e_0040r_007b_002c-closure-tag_007d-325"></a><a name="index-closure-tag_002c-_0040code_007b_003c_003e_007d-326"></a>line sweeps are not
  64 split.  Nor are original polygons in polygon sweeps.  It is the user's
  65 responsibility to ensure these are planar.
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