src/common/clip.c

#ifndef lint
static const char       RCSid[] = "$Id$";
#endif
/*
 *  clip.c - routine to clip 3D line segments to a box.
 */

#include "copyright.h"

#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);
}
Revision:	2.4
Committed:	Tue Feb 25 02:47:21 2003 UTC (21 years, 2 months ago) by greg
Content type:	text/plain
Branch:	MAIN
CVS Tags:	rad3R5
Changes since 2.3:	+1 -56 lines
Log Message:	Replaced inline copyright notice with #include "copyright.h"
#	User	Rev	Content
1	greg	1.1	#ifndef lint
2	greg	2.3	static const char RCSid[] = "$Id$";
3	greg	1.1	#endif
4			/*
5			* clip.c - routine to clip 3D line segments to a box.
6	greg	2.3	*/
7
8	greg	2.4	#include "copyright.h"
9	greg	1.1
10	greg	1.2	#include "fvect.h"
11
12	greg	1.1	#include "plocate.h"
13
14	greg	2.2	#define MAXITER 6 /* maximum possible number of iterations */
15	greg	1.1
16	greg	2.2
17	greg	2.3	int
18	greg	1.1	clip(ep1, ep2, min, max) /* clip a line segment to a box */
19	greg	1.2	FLOAT ep1, ep2;
20			FVECT min, max;
21	greg	1.1	{
22	greg	2.2	int itlim = MAXITER;
23	greg	1.1	int loc1, loc2;
24			int accept;
25	greg	1.2	FLOAT *dp;
26	greg	1.1	double d;
27			register int i, j;
28
29			/*
30			* The Cohen-Sutherland algorithm is used to determine
31			* what part (if any) of the given line segment is contained
32			* in the box specified by the min and max vectors.
33			* The routine returns non-zero if any segment is left.
34			*/
35
36			loc1 = plocate(ep1, min, max);
37			loc2 = plocate(ep2, min, max);
38
39			/* check for trivial accept and reject */
40			/* trivial accept is both points inside */
41			/* trivial reject is both points to one side */
42
43			while (!((accept = !(loc1 \| loc2)) \|\| (loc1 & loc2))) {
44
45	greg	2.2	if (itlim-- <= 0) /* past theoretical limit? */
46			return(0); /* quit fooling around */
47
48	greg	1.1	if (!loc1) { /* make sure first point is outside */
49			dp = ep1; ep1 = ep2; ep2 = dp;
50			i = loc1; loc1 = loc2; loc2 = i;
51			}
52
53			for (i = 0; i < 3; i++) { /* chop segment */
54
55			if (loc1 & position(i) & BELOW) {
56			d = (min[i] - ep1[i])/(ep2[i] - ep1[i]);
57			ep1[i] = min[i];
58			} else if (loc1 & position(i) & ABOVE) {
59			d = (max[i] - ep1[i])/(ep2[i] - ep1[i]);
60			ep1[i] = max[i];
61			} else
62			continue;
63
64			for (j = 0; j < 3; j++)
65			if (j != i)
66			ep1[j] += (ep2[j] - ep1[j])*d;
67			break;
68			}
69			loc1 = plocate(ep1, min, max);
70			}
71			return(accept);
72			}