#ifndef lint
static const char	RCSid[] = "$Id: clip.c,v 2.3 2003/02/22 02:07:21 greg Exp $";
#endif
/*
 *  clip.c - routine to clip 3D line segments to a box.
 */

/* ====================================================================
 * The Radiance Software License, Version 1.0
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 * through Lawrence Berkeley National Laboratory.   All rights reserved.
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 * 1. Redistributions of source code must retain the above copyright
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 *           if any, must include the following acknowledgment:
 *             "This product includes Radiance software
 *                 (http://radsite.lbl.gov/)
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 *               (http://www.lbl.gov/)."
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 * 4. The names "Radiance," "Lawrence Berkeley National Laboratory"
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#include  "fvect.h"

#include  "plocate.h"

#define MAXITER		6	/* maximum possible number of iterations */


int
clip(ep1, ep2, min, max)	/* clip a line segment to a box */
FLOAT  *ep1, *ep2;
FVECT  min, max;
{
	int  itlim = MAXITER;
	int  loc1, loc2;
	int  accept;
	FLOAT  *dp;
	double  d;
	register int  i, j;

	/*
	 *	The Cohen-Sutherland algorithm is used to determine
	 *  what part (if any) of the given line segment is contained
	 *  in the box specified by the min and max vectors.
	 *	The routine returns non-zero if any segment is left.
	 */
	
	loc1 = plocate(ep1, min, max);
	loc2 = plocate(ep2, min, max);

			/* check for trivial accept and reject */
			/* trivial accept is both points inside */
			/* trivial reject is both points to one side */
	
	while (!((accept = !(loc1 | loc2)) || (loc1 & loc2))) {
	
		if (itlim-- <= 0)	/* past theoretical limit? */
			return(0);	/* quit fooling around */

		if (!loc1) {		/* make sure first point is outside */
			dp = ep1; ep1 = ep2; ep2 = dp;
			i = loc1; loc1 = loc2; loc2 = i;
		}
		
		for (i = 0; i < 3; i++) {		/* chop segment */
			
			if (loc1 & position(i) & BELOW) {
				d = (min[i] - ep1[i])/(ep2[i] - ep1[i]);
				ep1[i] = min[i];
			} else if (loc1 & position(i) & ABOVE) {
				d = (max[i] - ep1[i])/(ep2[i] - ep1[i]);
				ep1[i] = max[i];
			} else
				continue;
			
			for (j = 0; j < 3; j++)
				if (j != i)
					ep1[j] += (ep2[j] - ep1[j])*d;
			break;
		}
		loc1 = plocate(ep1, min, max);
	}
	return(accept);
}