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Viewing changes to tclpathplan/makecw.c

  • Committer: Bazaar Package Importer
  • Author(s): Stephen M Moraco
  • Date: 2002-02-05 18:52:12 UTC
  • Revision ID: james.westby@ubuntu.com-20020205185212-8i04c70te00rc40y
Tags: upstream-1.7.16
Import upstream version 1.7.16

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tclpathplan/makecw.c
 
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/* 
 
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 * Force the vertices of a polygon to be in CW order.
 
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 * 
 
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 * Works for polygons with concavities.
 
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 * Does not work for twisted polygons.
 
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 *
 
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 * ellson@lucent.com    October 2nd, 1996
 
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 */
 
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#include <pathutil.h>
 
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void
 
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make_CW (Ppoly_t *poly)
 
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{
 
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    int                 i, j, n;
 
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        Ppoint_t        *P;
 
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    Ppoint_t    tP;
 
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    double      area=0.0;
 
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        P = poly->ps;
 
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        n = poly->pn;
 
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    /* points or lines don't have a rotation */
 
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    if (n > 2) {
 
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        /* check CW or CCW by computing (twice the) area of poly */
 
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        for (i=1; i < n-1; i++) {
 
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            area += area2(P[0], P[i+1], P[i]);
 
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        }
 
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        /* if the area is -ve then the rotation needs to be reversed */
 
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        /* the starting point is left unchanged */
 
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        if (area < 0.0) {
 
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                        for (i = 1, j = n-1; i < 1+n/2; i++, j--) {
 
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                                tP = P[i];
 
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                                P[i] = P[j];
 
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                                P[j] = tP;
 
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                        }
 
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        }
 
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    }
 
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}