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root/radiance/ray/src/ot/sphere.c
Revision: 1.1
Committed: Thu Feb 2 10:33:06 1989 UTC (35 years, 10 months ago) by greg
Content type: text/plain
Branch: MAIN
Log Message:
Initial revision

File Contents

# 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     return(0); /* cube outside */
80    
81     /* check sphere interior */
82     if (d1 < rad) {
83     if (d2 < (rad-d1-FTINY)*(rad-d1-FTINY))
84     return(0); /* cube inside sphere */
85     if (d2 < (rad+FTINY)*(rad+FTINY))
86     return(1); /* cube center inside */
87     }
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     return(1);
99     else
100     return(0);
101     }