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glass.c
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Tue, Jun 25, 16:15

glass.c
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#ifndef lint
static const char RCSid[] = "$Id: glass.c,v 2.28 2019/04/19 19:01:32 greg Exp $";
#endif
/*
* glass.c - simpler shading function for thin glass surfaces.
*/
#include "copyright.h"
#include "ray.h"
#include "otypes.h"
#include "rtotypes.h"
#include "pmapmat.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 [refractive_index]
*
* 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 */
int
m_glass( /* color a ray which hit a thin glass surface */
OBJREC *m,
RAY *r
)
{
COLOR mcolor;
double pdot;
FVECT pnorm;
double rindex=0, cos2;
COLOR trans, refl;
int hastexture, hastrans;
double d, r1e, r1m;
RAY p;
int i;
/* PMAP: skip refracted shadow or ambient ray if accounted for in
photon map */
if (shadowRayInPmap(r) || ambRayInPmap(r))
return(1);
/* 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");
/* check back face visibility */
if (!backvis && r->rod <= 0.0) {
raytrans(r);
return(1);
}
/* check transmission */
setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]);
if ((hastrans = (intens(mcolor) > 1e-15))) {
for (i = 0; i < 3; i++)
if (colval(mcolor,i) < 1e-15)
colval(mcolor,i) = 1e-15;
} else if (r->crtype & SHADOW)
return(1);
/* get modifiers */
raytexture(r, m->omod);
if (r->rod < 0.0) /* reorient if necessary */
flipsurface(r);
/* perturb normal */
if ( (hastexture = (DOT(r->pert,r->pert) > FTINY*FTINY)) ) {
pdot = raynormal(pnorm, r);
} else {
VCOPY(pnorm, r->ron);
pdot = r->rod;
}
/* angular transmission */
cos2 = sqrt( (1.0-1.0/(rindex*rindex)) +
pdot*pdot/(rindex*rindex) );
if (hastrans)
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 transmission */
if (hastrans) {
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);
}
multcolor(trans, r->pcol); /* modify by pattern */
/* transmitted ray */
if (rayorigin(&p, TRANS, r, trans) == 0) {
if (!(r->crtype & (SHADOW|AMBIENT)) && hastexture) {
VSUM(p.rdir, r->rdir, r->pert, 2.*(1.-rindex));
if (normalize(p.rdir) == 0.0) {
objerror(m, WARNING, "bad perturbation");
VCOPY(p.rdir, r->rdir);
}
} else {
VCOPY(p.rdir, r->rdir);
}
rayvalue(&p);
multcolor(p.rcol, p.rcoef);
addcolor(r->rcol, p.rcol);
if (!hastexture || r->crtype & (SHADOW|AMBIENT))
r->rxt = r->rot + raydistance(&p);
}
}
if (r->crtype & SHADOW) /* skip reflected ray */
return(1);
/* 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, REFLECTED, r, refl) == 0) {
VSUM(p.rdir, r->rdir, pnorm, 2.*pdot);
checknorm(p.rdir);
rayvalue(&p);
multcolor(p.rcol, p.rcoef);
copycolor(r->mcol, p.rcol);
addcolor(r->rcol, p.rcol);
r->rmt = r->rot;
if (r->ro != NULL && isflat(r->ro->otype) &&
!hastexture | (r->crtype & AMBIENT))
r->rmt += raydistance(&p);
}
return(1);
}

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