src/rt/glass.c

/* Copyright (c) 1986 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 transmission (tn) from transmissivity (Tn) use:
 *
 *      tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn
 *
 *  The transmission of standard 88% transmissivity glass is 0.96.
 *  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;
{
        double  sqrt(), pow();
        COLOR  mcolor;
        double  pdot;
        FVECT  pnorm;
        double  cos2;
        COLOR  trans, refl;
        double  transbright;
        double  d, r1;
        RAY  p;
        register int  i;

        if (m->oargs.nfargs != 3)
                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);
                                                /* 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 */
        r1 = (pdot - RINDEX*cos2) / (pdot + RINDEX*cos2);
        d = (1.0/pdot - RINDEX/cos2) / (1.0/pdot + RINDEX/cos2);
        r1 = (r1*r1 + d*d) / 2.0;
                                                /* compute transmittance */
        for (i = 0; i < 3; i++) {
                d = colval(mcolor, i);
                colval(trans,i) = (1.0-r1)*(1.0-r1)*d / (1.0 - r1*r1*d*d);
        }
        transbright = -FTINY;
                                                /* transmitted ray */
        if (rayorigin(&p, r, TRANS, bright(trans)) == 0) {
                VCOPY(p.rdir, r->rdir);
                rayvalue(&p);
                multcolor(p.rcol, r->pcol);     /* modify */
                multcolor(p.rcol, trans);
                addcolor(r->rcol, p.rcol);
                transbright = bright(p.rcol);
                r->rt = 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) = r1 * (1.0 + (1.0-2.0*r1)*d) / (1.0 - r1*r1*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 (bright(p.rcol) > transbright)
                        r->rt = r->rot + p.rt;
        }
}
Revision:	1.4
Committed:	Wed May 30 19:57:01 1990 UTC (33 years, 11 months ago) by greg
Content type:	text/plain
Branch:	MAIN
Changes since 1.3:	+4 -1 lines
Log Message:	improved computation of r->rt using brightness comparison
#	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			* 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+.0072522239TnTn)-.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	greg	1.4	double transbright;
53	greg	1.1	double d, r1;
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			/* get modifiers */
65			raytexture(r, m->omod);
66			pdot = raynormal(pnorm, r);
67			/* angular transmission */
68			cos2 = sqrt( (1.0-1.0/RINDEX/RINDEX) +
69			pdotpdot/(RINDEXRINDEX) );
70			setcolor(mcolor, pow(colval(mcolor,RED), 1.0/cos2),
71			pow(colval(mcolor,GRN), 1.0/cos2),
72			pow(colval(mcolor,BLU), 1.0/cos2));
73
74			/* compute reflection */
75			r1 = (pdot - RINDEXcos2) / (pdot + RINDEXcos2);
76			d = (1.0/pdot - RINDEX/cos2) / (1.0/pdot + RINDEX/cos2);
77			r1 = (r1r1 + dd) / 2.0;
78			/* compute transmittance */
79			for (i = 0; i < 3; i++) {
80			d = colval(mcolor, i);
81			colval(trans,i) = (1.0-r1)(1.0-r1)d / (1.0 - r1r1d*d);
82			}
83	greg	1.4	transbright = -FTINY;
84	greg	1.1	/* transmitted ray */
85	greg	1.2	if (rayorigin(&p, r, TRANS, bright(trans)) == 0) {
86	greg	1.1	VCOPY(p.rdir, r->rdir);
87			rayvalue(&p);
88			multcolor(p.rcol, r->pcol); /* modify */
89			multcolor(p.rcol, trans);
90			addcolor(r->rcol, p.rcol);
91	greg	1.4	transbright = bright(p.rcol);
92	greg	1.3	r->rt = r->rot + p.rt;
93	greg	1.1	}
94	greg	1.3
95	greg	1.1	if (r->crtype & SHADOW) /* skip reflected ray */
96			return;
97			/* compute reflectance */
98			for (i = 0; i < 3; i++) {
99			d = colval(mcolor, i);
100			d *= d;
101			colval(refl,i) = r1 * (1.0 + (1.0-2.0r1)d) / (1.0 - r1r1d);
102			}
103			/* reflected ray */
104	greg	1.2	if (rayorigin(&p, r, REFLECTED, bright(refl)) == 0) {
105	greg	1.1	for (i = 0; i < 3; i++)
106			p.rdir[i] = r->rdir[i] + 2.0pdotpnorm[i];
107			rayvalue(&p);
108			multcolor(p.rcol, refl);
109			addcolor(r->rcol, p.rcol);
110	greg	1.4	if (bright(p.rcol) > transbright)
111	greg	1.3	r->rt = r->rot + p.rt;
112	greg	1.1	}
113			}