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/*************************************************************************
* Copyright (c) 2011 AT&T Intellectual Property
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-v10.html
*
* Contributors: Details at https://graphviz.org
*************************************************************************/
/*
* Force the vertices of a polygon to be in CW order.
*
* Works for polygons with concavities.
* Does not work for twisted polygons.
*
* ellson@graphviz.org October 2nd, 1996
*/
#include "makecw.h"
#include <pathplan/pathutil.h>
#include <stddef.h>
void make_CW(Ppoly_t * poly)
{
Ppoint_t *P;
Ppoint_t tP;
double area = 0.0;
P = poly->ps;
const size_t n = poly->pn;
/* points or lines don't have a rotation */
if (n > 2) {
/* check CW or CCW by computing (twice the) area of poly */
for (size_t i = 1; i < n - 1; i++) {
area += area2(P[0], P[i + 1], P[i]);
}
/* if the area is -ve then the rotation needs to be reversed */
/* the starting point is left unchanged */
if (area < 0.0) {
for (size_t i = 1, j = n - 1; i < 1 + n / 2; i++, j--) {
tP = P[i];
P[i] = P[j];
P[j] = tP;
}
}
}
}
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