| 1 |
/* Copyright (c) 1991 Regents of the University of California */ |
| 2 |
|
| 3 |
#ifndef lint |
| 4 |
static char SCCSid[] = "$SunId$ LBL"; |
| 5 |
#endif |
| 6 |
|
| 7 |
/* |
| 8 |
* glass.c - simpler shading function for thin glass surfaces. |
| 9 |
* |
| 10 |
* 11/14/86 |
| 11 |
*/ |
| 12 |
|
| 13 |
#include "ray.h" |
| 14 |
|
| 15 |
/* |
| 16 |
* This definition of glass provides for a quick calculation |
| 17 |
* using a single surface where two closely spaced parallel |
| 18 |
* dielectric surfaces would otherwise be used. The chief |
| 19 |
* advantage to using this material is speed, since internal |
| 20 |
* reflections are avoided. |
| 21 |
* |
| 22 |
* The specification for glass is as follows: |
| 23 |
* |
| 24 |
* modifier glass id |
| 25 |
* 0 |
| 26 |
* 0 |
| 27 |
* 3 red grn blu |
| 28 |
* |
| 29 |
* The color is used for the transmission at normal incidence. |
| 30 |
* To compute transmission (tn) from transmissivity (Tn) use: |
| 31 |
* |
| 32 |
* tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn |
| 33 |
* |
| 34 |
* The transmission of standard 88% transmissivity glass is 0.96. |
| 35 |
* If we appear to hit the back side of the surface, then we |
| 36 |
* turn the normal around. |
| 37 |
*/ |
| 38 |
|
| 39 |
#define RINDEX 1.52 /* refractive index of glass */ |
| 40 |
|
| 41 |
|
| 42 |
m_glass(m, r) /* color a ray which hit a thin glass surface */ |
| 43 |
OBJREC *m; |
| 44 |
register RAY *r; |
| 45 |
{ |
| 46 |
double sqrt(), pow(); |
| 47 |
COLOR mcolor; |
| 48 |
double pdot; |
| 49 |
FVECT pnorm; |
| 50 |
double cos2; |
| 51 |
COLOR trans, refl; |
| 52 |
double d, r1; |
| 53 |
double transtest, transdist; |
| 54 |
RAY p; |
| 55 |
register int i; |
| 56 |
|
| 57 |
if (m->oargs.nfargs != 3) |
| 58 |
objerror(m, USER, "bad arguments"); |
| 59 |
|
| 60 |
setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]); |
| 61 |
|
| 62 |
if (r->rod < 0.0) /* reorient if necessary */ |
| 63 |
flipsurface(r); |
| 64 |
r->rt = r->rot; /* default ray length */ |
| 65 |
transtest = 0; |
| 66 |
/* get modifiers */ |
| 67 |
raytexture(r, m->omod); |
| 68 |
pdot = raynormal(pnorm, r); |
| 69 |
/* angular transmission */ |
| 70 |
cos2 = sqrt( (1.0-1.0/RINDEX/RINDEX) + |
| 71 |
pdot*pdot/(RINDEX*RINDEX) ); |
| 72 |
setcolor(mcolor, pow(colval(mcolor,RED), 1.0/cos2), |
| 73 |
pow(colval(mcolor,GRN), 1.0/cos2), |
| 74 |
pow(colval(mcolor,BLU), 1.0/cos2)); |
| 75 |
|
| 76 |
/* compute reflection */ |
| 77 |
r1 = (pdot - RINDEX*cos2) / (pdot + RINDEX*cos2); |
| 78 |
d = (1.0/pdot - RINDEX/cos2) / (1.0/pdot + RINDEX/cos2); |
| 79 |
r1 = (r1*r1 + d*d) / 2.0; |
| 80 |
/* compute transmittance */ |
| 81 |
for (i = 0; i < 3; i++) { |
| 82 |
d = colval(mcolor, i); |
| 83 |
colval(trans,i) = (1.0-r1)*(1.0-r1)*d / (1.0 - r1*r1*d*d); |
| 84 |
} |
| 85 |
/* transmitted ray */ |
| 86 |
if (rayorigin(&p, r, TRANS, bright(trans)) == 0) { |
| 87 |
if (DOT(r->pert,r->pert) > FTINY*FTINY) { |
| 88 |
for (i = 0; i < 3; i++) /* perturb direction */ |
| 89 |
p.rdir[i] = r->rdir[i] - r->pert[i]/RINDEX; |
| 90 |
normalize(p.rdir); |
| 91 |
} else |
| 92 |
transtest = 2; |
| 93 |
rayvalue(&p); |
| 94 |
multcolor(p.rcol, r->pcol); /* modify */ |
| 95 |
multcolor(p.rcol, trans); |
| 96 |
addcolor(r->rcol, p.rcol); |
| 97 |
transtest *= bright(p.rcol); |
| 98 |
transdist = r->rot + p.rt; |
| 99 |
} |
| 100 |
|
| 101 |
if (r->crtype & SHADOW) /* skip reflected ray */ |
| 102 |
return; |
| 103 |
/* compute reflectance */ |
| 104 |
for (i = 0; i < 3; i++) { |
| 105 |
d = colval(mcolor, i); |
| 106 |
d *= d; |
| 107 |
colval(refl,i) = r1 * (1.0 + (1.0-2.0*r1)*d) / (1.0 - r1*r1*d); |
| 108 |
} |
| 109 |
/* reflected ray */ |
| 110 |
if (rayorigin(&p, r, REFLECTED, bright(refl)) == 0) { |
| 111 |
for (i = 0; i < 3; i++) |
| 112 |
p.rdir[i] = r->rdir[i] + 2.0*pdot*pnorm[i]; |
| 113 |
rayvalue(&p); |
| 114 |
multcolor(p.rcol, refl); |
| 115 |
addcolor(r->rcol, p.rcol); |
| 116 |
} |
| 117 |
if (transtest > bright(r->rcol)) |
| 118 |
r->rt = transdist; |
| 119 |
} |
