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root/radiance/ray/src/rt/glass.c
Revision: 2.17
Committed: Tue Jun 21 15:06:50 2005 UTC (18 years, 9 months ago) by greg
Content type: text/plain
Branch: MAIN
CVS Tags: rad3R7P2, rad3R7P1, rad4R0, rad3R8, rad3R9
Changes since 2.16: +38 -29 lines
Log Message:
Fixed bugs in black glass transmission and source weight computation

File Contents

# Content
1 #ifndef lint
2 static const char RCSid[] = "$Id: glass.c,v 2.16 2005/04/19 01:15:06 greg 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, hastrans;
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 /* check transmission */
69 setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]);
70 if ((hastrans = (intens(mcolor) > 1e-15))) {
71 for (i = 0; i < 3; i++)
72 if (colval(mcolor,i) < 1e-15)
73 colval(mcolor,i) = 1e-15;
74 } else if (r->crtype & SHADOW)
75 return(1);
76 /* get modifiers */
77 raytexture(r, m->omod);
78 if (r->rod < 0.0) /* reorient if necessary */
79 flipsurface(r);
80 mirtest = transtest = 0;
81 mirdist = transdist = r->rot;
82 /* perturb normal */
83 if ( (hastexture = (DOT(r->pert,r->pert) > FTINY*FTINY)) ) {
84 pdot = raynormal(pnorm, r);
85 } else {
86 VCOPY(pnorm, r->ron);
87 pdot = r->rod;
88 }
89 /* angular transmission */
90 cos2 = sqrt( (1.0-1.0/(rindex*rindex)) +
91 pdot*pdot/(rindex*rindex) );
92 if (hastrans)
93 setcolor(mcolor, pow(colval(mcolor,RED), 1.0/cos2),
94 pow(colval(mcolor,GRN), 1.0/cos2),
95 pow(colval(mcolor,BLU), 1.0/cos2));
96
97 /* compute reflection */
98 r1e = (pdot - rindex*cos2) / (pdot + rindex*cos2);
99 r1e *= r1e;
100 r1m = (1.0/pdot - rindex/cos2) / (1.0/pdot + rindex/cos2);
101 r1m *= r1m;
102 /* compute transmission */
103 if (hastrans) {
104 for (i = 0; i < 3; i++) {
105 d = colval(mcolor, i);
106 colval(trans,i) = .5*(1.0-r1e)*(1.0-r1e)*d /
107 (1.0-r1e*r1e*d*d);
108 colval(trans,i) += .5*(1.0-r1m)*(1.0-r1m)*d /
109 (1.0-r1m*r1m*d*d);
110 }
111 multcolor(trans, r->pcol); /* modify by pattern */
112 /* transmitted ray */
113 if (rayorigin(&p, TRANS, r, trans) == 0) {
114 if (!(r->crtype & SHADOW) && hastexture) {
115 for (i = 0; i < 3; i++) /* perturb direction */
116 p.rdir[i] = r->rdir[i] +
117 2.*(1.-rindex)*r->pert[i];
118 if (normalize(p.rdir) == 0.0) {
119 objerror(m, WARNING, "bad perturbation");
120 VCOPY(p.rdir, r->rdir);
121 }
122 } else {
123 VCOPY(p.rdir, r->rdir);
124 transtest = 2;
125 }
126 rayvalue(&p);
127 multcolor(p.rcol, p.rcoef);
128 addcolor(r->rcol, p.rcol);
129 transtest *= bright(p.rcol);
130 transdist = r->rot + p.rt;
131 }
132 }
133 if (r->crtype & SHADOW) { /* skip reflected ray */
134 r->rt = transdist;
135 return(1);
136 }
137 /* compute reflectance */
138 for (i = 0; i < 3; i++) {
139 d = colval(mcolor, i);
140 d *= d;
141 colval(refl,i) = .5*r1e*(1.0+(1.0-2.0*r1e)*d)/(1.0-r1e*r1e*d);
142 colval(refl,i) += .5*r1m*(1.0+(1.0-2.0*r1m)*d)/(1.0-r1m*r1m*d);
143 }
144 /* reflected ray */
145 if (rayorigin(&p, REFLECTED, r, refl) == 0) {
146 for (i = 0; i < 3; i++)
147 p.rdir[i] = r->rdir[i] + 2.0*pdot*pnorm[i];
148 rayvalue(&p);
149 multcolor(p.rcol, p.rcoef);
150 addcolor(r->rcol, p.rcol);
151 if (!hastexture && r->ro != NULL && isflat(r->ro->otype)) {
152 mirtest = 2.0*bright(p.rcol);
153 mirdist = r->rot + p.rt;
154 }
155 }
156 /* check distance */
157 d = bright(r->rcol);
158 if (transtest > d)
159 r->rt = transdist;
160 else if (mirtest > d)
161 r->rt = mirdist;
162 return(1);
163 }