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root/radiance/ray/src/ot/o_face.c
Revision: 1.1
Committed: Thu Feb 2 10:33:03 1989 UTC (35 years, 9 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     * o_face.c - routines for creating octrees for polygonal faces.
9     *
10     * 8/27/85
11     */
12    
13     #include "standard.h"
14    
15     #include "octree.h"
16    
17     #include "object.h"
18    
19     #include "face.h"
20    
21     #include "plocate.h"
22    
23     /*
24     * The algorithm for determining a face's intersection
25     * with a cube is relatively straightforward:
26     *
27     * 1) Check to see if any vertices are inside the cube
28     * (intersection).
29     *
30     * 2) Check to see if all vertices are to one side of
31     * cube (no intersection).
32     *
33     * 3) Check to see if any portion of any edge is inside
34     * cube (intersection).
35     *
36     * 4) Check to see if the cube cuts the plane of the
37     * face and one of its edges passes through
38     * the face (intersection).
39     *
40     * 5) If test 4 fails, we have no intersection.
41     */
42    
43    
44     o_face(o, cu) /* determine if face intersects cube */
45     OBJREC *o;
46     CUBE *cu;
47     {
48     FVECT cumin, cumax;
49     FVECT v1, v2;
50     double d1, d2;
51     int vloc;
52     register FACE *f;
53     register int i, j;
54     /* get face arguments */
55     f = getface(o);
56     if (f->area == 0.0) /* empty face */
57     return(0);
58     /* compute cube boundaries */
59     for (j = 0; j < 3; j++)
60     cumax[j] = (cumin[j] = cu->cuorg[j]) + cu->cusize;
61    
62     vloc = ABOVE | BELOW; /* check vertices */
63     for (i = 0; i < f->nv; i++)
64     if (j = plocate(VERTEX(f,i), cumin, cumax))
65     vloc &= j;
66     else
67     return(1); /* vertex inside */
68    
69     if (vloc) /* all to one side */
70     return(0);
71    
72     for (i = 0; i < f->nv; i++) { /* check edges */
73     if ((j = i + 1) >= f->nv)
74     j = 0; /* wrap around */
75     VCOPY(v1, VERTEX(f,i)); /* clip modifies */
76     VCOPY(v2, VERTEX(f,j)); /* the vertices! */
77     if (clip(v1, v2, cumin, cumax))
78     return(1); /* edge inside */
79     }
80     /* see if cube cuts plane */
81     for (j = 0; j < 3; j++)
82     if (f->norm[j] > 0.0) {
83     v1[j] = cumin[j];
84     v2[j] = cumax[j];
85     } else {
86     v1[j] = cumax[j];
87     v2[j] = cumin[j];
88     }
89     if ((d1 = DOT(v1, f->norm) - f->const) > FTINY)
90     return(0);
91     if ((d2 = DOT(v2, f->norm) - f->const) < -FTINY)
92     return(0);
93     /* intersect face */
94     for (j = 0; j < 3; j++)
95     v1[j] = (v1[j]*d2 - v2[j]*d1)/(d2 - d1);
96     if (inface(v1, f))
97     return(1);
98    
99     return(0); /* no intersection */
100     }