src/ot/sphere.c

/* Copyright (c) 1986 Regents of the University of California */

#ifndef lint
static char SCCSid[] = "$SunId$ LBL";
#endif

/*
 *  sphere.c - routines for creating octrees for spheres.
 *
 *     7/28/85
 */

#include  "standard.h"

#include  "octree.h"

#include  "object.h"

#include  "otypes.h"

#define  ROOT3          1.732050808

/*
 *      Regrettably, the algorithm for determining a cube's location
 *  with respect to a sphere is not simple.  First, a quick test is 
 *  made to determine if the sphere and the bounding sphere of the cube 
 *  are disjoint.  This of course means no intersection.  Failing this,
 *  we determine if the cube lies inside the sphere.  The cube is
 *  entirely inside if the bounding sphere on the cube is
 *  contained within our sphere.  This means no intersection.  Otherwise,
 *  if the cube radius is smaller than the sphere's and the cube center is
 *  inside the sphere, we assume intersection.  If these tests fail,
 *  we proceed as follows.
 *      The sphere center is located in relation to the 6 cube faces,
 *  and one of four things is done depending on the number of
 *  planes the center lies between:
 *
 *      0:  The sphere is closest to a cube corner, find the
 *              distance to that corner.
 *
 *      1:  The sphere is closest to a cube edge, find this
 *              distance.
 *
 *      2:  The sphere is closest to a cube face, find the distance.
 *
 *      3:  The sphere has its center inside the cube.
 *
 *      In cases 0-2, if the closest part of the cube is within
 *  the radius distance from the sphere center, we have intersection.
 *  If it is not, the cube must be outside the sphere.
 *      In case 3, there must be intersection, and no further
 *  tests are necessary.
 */


o_sphere(o, cu)                 /* determine if sphere intersects cube */
OBJREC  *o;
register CUBE  *cu;
{
        FVECT  v1;
        double  d1, d2;
        register double  *fa;
        register int  i;
#define  cent           fa
#define  rad            fa[3]
                                        /* get arguments */
        fa = o->oargs.farg;
        if (o->oargs.nfargs != 4 || rad <= FTINY)
                objerror(o, USER, "bad arguments");

        d1 = ROOT3/2.0 * cu->cusize;    /* bounding radius for cube */

        d2 = cu->cusize * 0.5;          /* get distance between centers */
        for (i = 0; i < 3; i++)
                v1[i] = cu->cuorg[i] + d2 - cent[i];
        d2 = DOT(v1,v1);

        if (d2 > (rad+d1+FTINY)*(rad+d1+FTINY)) /* quick test */
                return(O_MISS);                 /* cube outside */
        
                                        /* check sphere interior */
        if (d1 < rad) {
                if (d2 < (rad-d1-FTINY)*(rad-d1-FTINY))
                        return(O_MISS);         /* cube inside sphere */
                if (d2 < (rad+FTINY)*(rad+FTINY))
                        return(O_HIT);          /* cube center inside */
        }
                                        /* find closest distance */
        for (i = 0; i < 3; i++)
                if (cent[i] < cu->cuorg[i])
                        v1[i] = cu->cuorg[i] - cent[i];
                else if (cent[i] > cu->cuorg[i] + cu->cusize)
                        v1[i] = cent[i] - (cu->cuorg[i] + cu->cusize);
                else
                        v1[i] = 0;
                                        /* final intersection check */
        if (DOT(v1,v1) <= (rad+FTINY)*(rad+FTINY))
                return(O_HIT);
        else
                return(O_MISS);
}
Revision:	1.2
Committed:	Sat Oct 14 11:19:36 1989 UTC (35 years, 2 months ago) by greg
Content type:	text/plain
Branch:	MAIN
Changes since 1.1:	+5 -5 lines
Log Message:	Defined return values for intersection functions. Changed order of call to addobject to rotate O_IN objects.
#	User	Rev	Content
1	greg	1.1	/* Copyright (c) 1986 Regents of the University of California */
2
3			#ifndef lint
4			static char SCCSid[] = "$SunId$ LBL";
5			#endif
6
7			/*
8			* sphere.c - routines for creating octrees for spheres.
9			*
10			* 7/28/85
11			*/
12
13			#include "standard.h"
14
15			#include "octree.h"
16
17			#include "object.h"
18
19			#include "otypes.h"
20
21			#define ROOT3 1.732050808
22
23			/*
24			* Regrettably, the algorithm for determining a cube's location
25			* with respect to a sphere is not simple. First, a quick test is
26			* made to determine if the sphere and the bounding sphere of the cube
27			* are disjoint. This of course means no intersection. Failing this,
28			* we determine if the cube lies inside the sphere. The cube is
29			* entirely inside if the bounding sphere on the cube is
30			* contained within our sphere. This means no intersection. Otherwise,
31			* if the cube radius is smaller than the sphere's and the cube center is
32			* inside the sphere, we assume intersection. If these tests fail,
33			* we proceed as follows.
34			* The sphere center is located in relation to the 6 cube faces,
35			* and one of four things is done depending on the number of
36			* planes the center lies between:
37			*
38			* 0: The sphere is closest to a cube corner, find the
39			* distance to that corner.
40			*
41			* 1: The sphere is closest to a cube edge, find this
42			* distance.
43			*
44			* 2: The sphere is closest to a cube face, find the distance.
45			*
46			* 3: The sphere has its center inside the cube.
47			*
48			* In cases 0-2, if the closest part of the cube is within
49			* the radius distance from the sphere center, we have intersection.
50			* If it is not, the cube must be outside the sphere.
51			* In case 3, there must be intersection, and no further
52			* tests are necessary.
53			*/
54
55
56			o_sphere(o, cu) /* determine if sphere intersects cube */
57			OBJREC *o;
58			register CUBE *cu;
59			{
60			FVECT v1;
61			double d1, d2;
62			register double *fa;
63			register int i;
64			#define cent fa
65			#define rad fa[3]
66			/* get arguments */
67			fa = o->oargs.farg;
68			if (o->oargs.nfargs != 4 \|\| rad <= FTINY)
69			objerror(o, USER, "bad arguments");
70
71			d1 = ROOT3/2.0 * cu->cusize; /* bounding radius for cube */
72
73			d2 = cu->cusize * 0.5; /* get distance between centers */
74			for (i = 0; i < 3; i++)
75			v1[i] = cu->cuorg[i] + d2 - cent[i];
76			d2 = DOT(v1,v1);
77
78			if (d2 > (rad+d1+FTINY)(rad+d1+FTINY)) / quick test */
79	greg	1.2	return(O_MISS); /* cube outside */
80	greg	1.1
81			/* check sphere interior */
82			if (d1 < rad) {
83			if (d2 < (rad-d1-FTINY)*(rad-d1-FTINY))
84	greg	1.2	return(O_MISS); /* cube inside sphere */
85	greg	1.1	if (d2 < (rad+FTINY)*(rad+FTINY))
86	greg	1.2	return(O_HIT); /* cube center inside */
87	greg	1.1	}
88			/* find closest distance */
89			for (i = 0; i < 3; i++)
90			if (cent[i] < cu->cuorg[i])
91			v1[i] = cu->cuorg[i] - cent[i];
92			else if (cent[i] > cu->cuorg[i] + cu->cusize)
93			v1[i] = cent[i] - (cu->cuorg[i] + cu->cusize);
94			else
95			v1[i] = 0;
96			/* final intersection check */
97			if (DOT(v1,v1) <= (rad+FTINY)*(rad+FTINY))
98	greg	1.2	return(O_HIT);
99	greg	1.1	else
100	greg	1.2	return(O_MISS);
101	greg	1.1	}