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root/radiance/ray/src/ot/sphere.c
Revision: 1.3
Committed: Wed May 22 17:01:43 1991 UTC (33 years, 5 months ago) by greg
Content type: text/plain
Branch: MAIN
Changes since 1.2: +9 -2 lines
Log Message:
change sphere with negative radii into bubbles

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 greg 1.3 if (o->oargs.nfargs != 4)
68     objerror(o, USER, "bad # arguments");
69 greg 1.1 fa = o->oargs.farg;
70 greg 1.3 if (rad < -FTINY) {
71     objerror(o, WARNING, "negative radius");
72     o->otype = o->otype == OBJ_SPHERE ?
73     OBJ_BUBBLE : OBJ_SPHERE;
74     rad = -rad;
75     } else if (rad <= FTINY)
76     objerror(o, USER, "zero radius");
77 greg 1.1
78     d1 = ROOT3/2.0 * cu->cusize; /* bounding radius for cube */
79    
80     d2 = cu->cusize * 0.5; /* get distance between centers */
81     for (i = 0; i < 3; i++)
82     v1[i] = cu->cuorg[i] + d2 - cent[i];
83     d2 = DOT(v1,v1);
84    
85     if (d2 > (rad+d1+FTINY)*(rad+d1+FTINY)) /* quick test */
86 greg 1.2 return(O_MISS); /* cube outside */
87 greg 1.1
88     /* check sphere interior */
89     if (d1 < rad) {
90     if (d2 < (rad-d1-FTINY)*(rad-d1-FTINY))
91 greg 1.2 return(O_MISS); /* cube inside sphere */
92 greg 1.1 if (d2 < (rad+FTINY)*(rad+FTINY))
93 greg 1.2 return(O_HIT); /* cube center inside */
94 greg 1.1 }
95     /* find closest distance */
96     for (i = 0; i < 3; i++)
97     if (cent[i] < cu->cuorg[i])
98     v1[i] = cu->cuorg[i] - cent[i];
99     else if (cent[i] > cu->cuorg[i] + cu->cusize)
100     v1[i] = cent[i] - (cu->cuorg[i] + cu->cusize);
101     else
102     v1[i] = 0;
103     /* final intersection check */
104     if (DOT(v1,v1) <= (rad+FTINY)*(rad+FTINY))
105 greg 1.2 return(O_HIT);
106 greg 1.1 else
107 greg 1.2 return(O_MISS);
108 greg 1.1 }