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root/radiance/ray/src/rt/glass.c
Revision: 2.15
Committed: Tue Mar 30 16:13:01 2004 UTC (20 years ago) by schorsch
Content type: text/plain
Branch: MAIN
CVS Tags: rad3R6, rad3R6P1
Changes since 2.14: +7 -5 lines
Log Message:
Continued ANSIfication. There are only bits and pieces left now.

File Contents

# Content
1 #ifndef lint
2 static const char RCSid[] = "$Id: glass.c,v 2.14 2003/07/27 22:12:03 schorsch Exp $";
3 #endif
4 /*
5 * glass.c - simpler shading function for thin glass surfaces.
6 */
7
8 #include "copyright.h"
9
10 #include "ray.h"
11 #include "otypes.h"
12 #include "rtotypes.h"
13
14 /*
15 * This definition of glass provides for a quick calculation
16 * using a single surface where two closely spaced parallel
17 * dielectric surfaces would otherwise be used. The chief
18 * advantage to using this material is speed, since internal
19 * reflections are avoided.
20 *
21 * The specification for glass is as follows:
22 *
23 * modifier glass id
24 * 0
25 * 0
26 * 3+ red grn blu [refractive_index]
27 *
28 * The color is used for the transmission at normal incidence.
29 * To compute transmissivity (tn) from transmittance (Tn) use:
30 *
31 * tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn
32 *
33 * The transmissivity of standard 88% transmittance glass is 0.96.
34 * A refractive index other than the default can be used by giving
35 * it as the fourth real argument. The above formula no longer applies.
36 *
37 * If we appear to hit the back side of the surface, then we
38 * turn the normal around.
39 */
40
41 #define RINDEX 1.52 /* refractive index of glass */
42
43
44 extern int
45 m_glass( /* color a ray which hit a thin glass surface */
46 OBJREC *m,
47 register RAY *r
48 )
49 {
50 COLOR mcolor;
51 double pdot;
52 FVECT pnorm;
53 double rindex, cos2;
54 COLOR trans, refl;
55 int hastexture;
56 double d, r1e, r1m;
57 double transtest, transdist;
58 double mirtest, mirdist;
59 RAY p;
60 register int i;
61 /* check arguments */
62 if (m->oargs.nfargs == 3)
63 rindex = RINDEX; /* default value of n */
64 else if (m->oargs.nfargs == 4)
65 rindex = m->oargs.farg[3]; /* use their value */
66 else
67 objerror(m, USER, "bad arguments");
68
69 setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]);
70
71 /* get modifiers */
72 raytexture(r, m->omod);
73 if (r->rod < 0.0) /* reorient if necessary */
74 flipsurface(r);
75 mirtest = transtest = 0;
76 mirdist = transdist = r->rot;
77 /* perturb normal */
78 if ( (hastexture = (DOT(r->pert,r->pert) > FTINY*FTINY)) ) {
79 pdot = raynormal(pnorm, r);
80 } else {
81 VCOPY(pnorm, r->ron);
82 pdot = r->rod;
83 }
84 /* angular transmission */
85 cos2 = sqrt( (1.0-1.0/(rindex*rindex)) +
86 pdot*pdot/(rindex*rindex) );
87 setcolor(mcolor, pow(colval(mcolor,RED), 1.0/cos2),
88 pow(colval(mcolor,GRN), 1.0/cos2),
89 pow(colval(mcolor,BLU), 1.0/cos2));
90
91 /* compute reflection */
92 r1e = (pdot - rindex*cos2) / (pdot + rindex*cos2);
93 r1e *= r1e;
94 r1m = (1.0/pdot - rindex/cos2) / (1.0/pdot + rindex/cos2);
95 r1m *= r1m;
96 /* compute transmittance */
97 for (i = 0; i < 3; i++) {
98 d = colval(mcolor, i);
99 colval(trans,i) = .5*(1.0-r1e)*(1.0-r1e)*d/(1.0-r1e*r1e*d*d);
100 colval(trans,i) += .5*(1.0-r1m)*(1.0-r1m)*d/(1.0-r1m*r1m*d*d);
101 }
102 /* transmitted ray */
103 if (rayorigin(&p, r, TRANS, bright(trans)) == 0) {
104 if (!(r->crtype & SHADOW) && hastexture) {
105 for (i = 0; i < 3; i++) /* perturb direction */
106 p.rdir[i] = r->rdir[i] +
107 2.*(1.-rindex)*r->pert[i];
108 if (normalize(p.rdir) == 0.0) {
109 objerror(m, WARNING, "bad perturbation");
110 VCOPY(p.rdir, r->rdir);
111 }
112 } else {
113 VCOPY(p.rdir, r->rdir);
114 transtest = 2;
115 }
116 rayvalue(&p);
117 multcolor(p.rcol, r->pcol); /* modify */
118 multcolor(p.rcol, trans);
119 addcolor(r->rcol, p.rcol);
120 transtest *= bright(p.rcol);
121 transdist = r->rot + p.rt;
122 }
123
124 if (r->crtype & SHADOW) { /* skip reflected ray */
125 r->rt = transdist;
126 return(1);
127 }
128 /* compute reflectance */
129 for (i = 0; i < 3; i++) {
130 d = colval(mcolor, i);
131 d *= d;
132 colval(refl,i) = .5*r1e*(1.0+(1.0-2.0*r1e)*d)/(1.0-r1e*r1e*d);
133 colval(refl,i) += .5*r1m*(1.0+(1.0-2.0*r1m)*d)/(1.0-r1m*r1m*d);
134 }
135 /* reflected ray */
136 if (rayorigin(&p, r, REFLECTED, bright(refl)) == 0) {
137 for (i = 0; i < 3; i++)
138 p.rdir[i] = r->rdir[i] + 2.0*pdot*pnorm[i];
139 rayvalue(&p);
140 multcolor(p.rcol, refl);
141 addcolor(r->rcol, p.rcol);
142 if (!hastexture && r->ro != NULL && isflat(r->ro->otype)) {
143 mirtest = 2.0*bright(p.rcol);
144 mirdist = r->rot + p.rt;
145 }
146 }
147 /* check distance */
148 d = bright(r->rcol);
149 if (transtest > d)
150 r->rt = transdist;
151 else if (mirtest > d)
152 r->rt = mirdist;
153 return(1);
154 }