src/rt/glass.c

/* Copyright (c) 1991 Regents of the University of California */

#ifndef lint
static char SCCSid[] = "$SunId$ LBL";
#endif

/*
 *  glass.c - simpler shading function for thin glass surfaces.
 *
 *     11/14/86
 */

#include  "ray.h"

/*
 *  This definition of glass provides for a quick calculation
 *  using a single surface where two closely spaced parallel
 *  dielectric surfaces would otherwise be used.  The chief
 *  advantage to using this material is speed, since internal
 *  reflections are avoided.
 *
 *  The specification for glass is as follows:
 *
 *      modifier glass id
 *      0
 *      0
 *      3 red grn blu
 *
 *  The color is used for the transmission at normal incidence.
 *  To compute transmissivity (tn) from transmittance (Tn) use:
 *
 *      tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn
 *
 *  The transmissivity of standard 88% transmittance glass is 0.96.
 *  A refractive index other than the default can be used by giving
 *  it as the fourth real argument.  The above formula no longer applies.
 *
 *  If we appear to hit the back side of the surface, then we
 *  turn the normal around.
 */

#define  RINDEX         1.52            /* refractive index of glass */


m_glass(m, r)           /* color a ray which hit a thin glass surface */
OBJREC  *m;
register RAY  *r;
{
        COLOR  mcolor;
        double  pdot;
        FVECT  pnorm;
        double  rindex, cos2;
        COLOR  trans, refl;
        double  d, r1e, r1m;
        double  transtest, transdist;
        RAY  p;
        register int  i;
                                                /* check arguments */
        if (m->oargs.nfargs == 3)
                rindex = RINDEX;                /* default value of n */
        else if (m->oargs.nfargs == 4)
                rindex = m->oargs.farg[3];      /* use their value */
        else
                objerror(m, USER, "bad arguments");

        setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]);

        if (r->rod < 0.0)                       /* reorient if necessary */
                flipsurface(r);
        transtest = 0;
                                                /* get modifiers */
        raytexture(r, m->omod);
        pdot = raynormal(pnorm, r);
                                                /* angular transmission */
        cos2 = sqrt( (1.0-1.0/(rindex*rindex)) +
                     pdot*pdot/(rindex*rindex) );
        setcolor(mcolor, pow(colval(mcolor,RED), 1.0/cos2),
                         pow(colval(mcolor,GRN), 1.0/cos2),
                         pow(colval(mcolor,BLU), 1.0/cos2));

                                                /* compute reflection */
        r1e = (pdot - rindex*cos2) / (pdot + rindex*cos2);
        r1e *= r1e;
        r1m = (1.0/pdot - rindex/cos2) / (1.0/pdot + rindex/cos2);
        r1m *= r1m;
                                                /* compute transmittance */
        for (i = 0; i < 3; i++) {
                d = colval(mcolor, i);
                colval(trans,i) = .5*(1.0-r1e)*(1.0-r1e)*d/(1.0-r1e*r1e*d*d);
                colval(trans,i) += .5*(1.0-r1m)*(1.0-r1m)*d/(1.0-r1m*r1m*d*d);
        }
                                                /* transmitted ray */
        if (rayorigin(&p, r, TRANS, bright(trans)) == 0) {
                if (!(r->crtype & SHADOW) &&
                                DOT(r->pert,r->pert) > FTINY*FTINY) {
                        for (i = 0; i < 3; i++)         /* perturb direction */
                                p.rdir[i] = r->rdir[i] +
                                                2.*(1.-rindex)*r->pert[i];
                        if (normalize(p.rdir) == 0.0) {
                                objerror(m, WARNING, "bad perturbation");
                                VCOPY(p.rdir, r->rdir);
                        }
                } else {
                        VCOPY(p.rdir, r->rdir);
                        transtest = 2;
                }
                rayvalue(&p);
                multcolor(p.rcol, r->pcol);     /* modify */
                multcolor(p.rcol, trans);
                addcolor(r->rcol, p.rcol);
                transtest *= bright(p.rcol);
                transdist = r->rot + p.rt;
        }

        if (r->crtype & SHADOW)                 /* skip reflected ray */
                return;
                                                /* compute reflectance */
        for (i = 0; i < 3; i++) {
                d = colval(mcolor, i);
                d *= d;
                colval(refl,i) = .5*r1e*(1.0+(1.0-2.0*r1e)*d)/(1.0-r1e*r1e*d);
                colval(refl,i) += .5*r1m*(1.0+(1.0-2.0*r1m)*d)/(1.0-r1m*r1m*d);
        }
                                                /* reflected ray */
        if (rayorigin(&p, r, REFLECTED, bright(refl)) == 0) {
                for (i = 0; i < 3; i++)
                        p.rdir[i] = r->rdir[i] + 2.0*pdot*pnorm[i];
                rayvalue(&p);
                multcolor(p.rcol, refl);
                addcolor(r->rcol, p.rcol);
        }
        if (transtest > bright(r->rcol))
                r->rt = transdist;
}
Revision:	2.5
Committed:	Mon Nov 30 12:02:54 1992 UTC (31 years, 5 months ago) by greg
Content type:	text/plain
Branch:	MAIN
Changes since 2.4:	+2 -2 lines
Log Message:	fixed comment terminology
#	User	Rev	Content
1	greg	1.7	/* Copyright (c) 1991 Regents of the University of California */
2	greg	1.1
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	greg	2.5	* To compute transmissivity (tn) from transmittance (Tn) use:
31	greg	1.1	*
32			* tn = (sqrt(.8402528435+.0072522239TnTn)-.9166530661)/.0036261119/Tn
33			*
34	greg	2.5	* The transmissivity of standard 88% transmittance glass is 0.96.
35	greg	1.12	* A refractive index other than the default can be used by giving
36			* it as the fourth real argument. The above formula no longer applies.
37			*
38	greg	1.1	* If we appear to hit the back side of the surface, then we
39			* turn the normal around.
40			*/
41
42			#define RINDEX 1.52 /* refractive index of glass */
43
44
45			m_glass(m, r) /* color a ray which hit a thin glass surface */
46			OBJREC *m;
47			register RAY *r;
48			{
49			COLOR mcolor;
50			double pdot;
51			FVECT pnorm;
52	greg	1.12	double rindex, cos2;
53	greg	1.1	COLOR trans, refl;
54	greg	1.11	double d, r1e, r1m;
55	greg	1.7	double transtest, transdist;
56	greg	1.1	RAY p;
57			register int i;
58	greg	1.12	/* check arguments */
59			if (m->oargs.nfargs == 3)
60			rindex = RINDEX; /* default value of n */
61			else if (m->oargs.nfargs == 4)
62			rindex = m->oargs.farg[3]; /* use their value */
63			else
64	greg	1.1	objerror(m, USER, "bad arguments");
65
66			setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]);
67
68			if (r->rod < 0.0) /* reorient if necessary */
69			flipsurface(r);
70	greg	1.7	transtest = 0;
71	greg	1.1	/* get modifiers */
72			raytexture(r, m->omod);
73			pdot = raynormal(pnorm, r);
74			/* angular transmission */
75	greg	1.12	cos2 = sqrt( (1.0-1.0/(rindex*rindex)) +
76			pdotpdot/(rindexrindex) );
77	greg	1.1	setcolor(mcolor, pow(colval(mcolor,RED), 1.0/cos2),
78			pow(colval(mcolor,GRN), 1.0/cos2),
79			pow(colval(mcolor,BLU), 1.0/cos2));
80
81			/* compute reflection */
82	greg	1.12	r1e = (pdot - rindexcos2) / (pdot + rindexcos2);
83	greg	1.11	r1e *= r1e;
84	greg	1.12	r1m = (1.0/pdot - rindex/cos2) / (1.0/pdot + rindex/cos2);
85	greg	1.11	r1m *= r1m;
86	greg	1.1	/* compute transmittance */
87			for (i = 0; i < 3; i++) {
88			d = colval(mcolor, i);
89	greg	1.11	colval(trans,i) = .5(1.0-r1e)(1.0-r1e)d/(1.0-r1er1edd);
90			colval(trans,i) += .5(1.0-r1m)(1.0-r1m)d/(1.0-r1mr1mdd);
91	greg	1.1	}
92			/* transmitted ray */
93	greg	1.2	if (rayorigin(&p, r, TRANS, bright(trans)) == 0) {
94	greg	1.10	if (!(r->crtype & SHADOW) &&
95			DOT(r->pert,r->pert) > FTINY*FTINY) {
96	greg	1.7	for (i = 0; i < 3; i++) /* perturb direction */
97	greg	2.2	p.rdir[i] = r->rdir[i] +
98			2.(1.-rindex)r->pert[i];
99	greg	2.4	if (normalize(p.rdir) == 0.0) {
100			objerror(m, WARNING, "bad perturbation");
101			VCOPY(p.rdir, r->rdir);
102			}
103	greg	1.8	} else {
104			VCOPY(p.rdir, r->rdir);
105	greg	1.7	transtest = 2;
106	greg	1.8	}
107	greg	1.1	rayvalue(&p);
108			multcolor(p.rcol, r->pcol); /* modify */
109			multcolor(p.rcol, trans);
110			addcolor(r->rcol, p.rcol);
111	greg	1.7	transtest *= bright(p.rcol);
112			transdist = r->rot + p.rt;
113	greg	1.1	}
114	greg	1.3
115	greg	1.1	if (r->crtype & SHADOW) /* skip reflected ray */
116			return;
117			/* compute reflectance */
118			for (i = 0; i < 3; i++) {
119			d = colval(mcolor, i);
120			d *= d;
121	greg	1.11	colval(refl,i) = .5r1e(1.0+(1.0-2.0r1e)d)/(1.0-r1er1ed);
122			colval(refl,i) += .5r1m(1.0+(1.0-2.0r1m)d)/(1.0-r1mr1md);
123	greg	1.1	}
124			/* reflected ray */
125	greg	1.2	if (rayorigin(&p, r, REFLECTED, bright(refl)) == 0) {
126	greg	1.1	for (i = 0; i < 3; i++)
127			p.rdir[i] = r->rdir[i] + 2.0pdotpnorm[i];
128			rayvalue(&p);
129			multcolor(p.rcol, refl);
130			addcolor(r->rcol, p.rcol);
131			}
132	greg	1.7	if (transtest > bright(r->rcol))
133			r->rt = transdist;
134	greg	1.1	}