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#ifndef lint
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static const char RCSid[] = "$Id: glass.c,v 2.16 2005/04/19 01:15:06 greg Exp $";
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#endif
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/*
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* glass.c - simpler shading function for thin glass surfaces.
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*/
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#include "copyright.h"
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#include "ray.h"
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#include "otypes.h"
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#include "rtotypes.h"
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/*
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* This definition of glass provides for a quick calculation
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* using a single surface where two closely spaced parallel
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* dielectric surfaces would otherwise be used. The chief
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* advantage to using this material is speed, since internal
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* reflections are avoided.
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*
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* The specification for glass is as follows:
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*
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* modifier glass id
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* 0
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* 0
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* 3+ red grn blu [refractive_index]
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*
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* The color is used for the transmission at normal incidence.
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* To compute transmissivity (tn) from transmittance (Tn) use:
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*
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* tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn
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*
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* The transmissivity of standard 88% transmittance glass is 0.96.
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* A refractive index other than the default can be used by giving
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* it as the fourth real argument. The above formula no longer applies.
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*
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* If we appear to hit the back side of the surface, then we
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* turn the normal around.
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*/
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#define RINDEX 1.52 /* refractive index of glass */
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extern int
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m_glass( /* color a ray which hit a thin glass surface */
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OBJREC *m,
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register RAY *r
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)
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{
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COLOR mcolor;
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double pdot;
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FVECT pnorm;
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double rindex, cos2;
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COLOR trans, refl;
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int hastexture, hastrans;
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double d, r1e, r1m;
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double transtest, transdist;
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double mirtest, mirdist;
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RAY p;
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register int i;
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/* check arguments */
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if (m->oargs.nfargs == 3)
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rindex = RINDEX; /* default value of n */
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else if (m->oargs.nfargs == 4)
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rindex = m->oargs.farg[3]; /* use their value */
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else
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objerror(m, USER, "bad arguments");
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/* check transmission */
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setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]);
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if ((hastrans = (intens(mcolor) > 1e-15))) {
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for (i = 0; i < 3; i++)
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if (colval(mcolor,i) < 1e-15)
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colval(mcolor,i) = 1e-15;
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} else if (r->crtype & SHADOW)
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return(1);
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/* get modifiers */
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raytexture(r, m->omod);
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if (r->rod < 0.0) /* reorient if necessary */
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flipsurface(r);
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mirtest = transtest = 0;
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mirdist = transdist = r->rot;
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/* perturb normal */
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if ( (hastexture = (DOT(r->pert,r->pert) > FTINY*FTINY)) ) {
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pdot = raynormal(pnorm, r);
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} else {
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VCOPY(pnorm, r->ron);
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pdot = r->rod;
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}
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/* angular transmission */
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cos2 = sqrt( (1.0-1.0/(rindex*rindex)) +
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pdot*pdot/(rindex*rindex) );
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if (hastrans)
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setcolor(mcolor, pow(colval(mcolor,RED), 1.0/cos2),
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pow(colval(mcolor,GRN), 1.0/cos2),
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pow(colval(mcolor,BLU), 1.0/cos2));
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/* compute reflection */
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r1e = (pdot - rindex*cos2) / (pdot + rindex*cos2);
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r1e *= r1e;
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r1m = (1.0/pdot - rindex/cos2) / (1.0/pdot + rindex/cos2);
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r1m *= r1m;
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/* compute transmission */
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if (hastrans) {
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for (i = 0; i < 3; i++) {
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d = colval(mcolor, i);
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colval(trans,i) = .5*(1.0-r1e)*(1.0-r1e)*d /
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(1.0-r1e*r1e*d*d);
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colval(trans,i) += .5*(1.0-r1m)*(1.0-r1m)*d /
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(1.0-r1m*r1m*d*d);
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}
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multcolor(trans, r->pcol); /* modify by pattern */
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/* transmitted ray */
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if (rayorigin(&p, TRANS, r, trans) == 0) {
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if (!(r->crtype & SHADOW) && hastexture) {
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for (i = 0; i < 3; i++) /* perturb direction */
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p.rdir[i] = r->rdir[i] +
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2.*(1.-rindex)*r->pert[i];
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if (normalize(p.rdir) == 0.0) {
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objerror(m, WARNING, "bad perturbation");
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VCOPY(p.rdir, r->rdir);
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}
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} else {
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VCOPY(p.rdir, r->rdir);
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transtest = 2;
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}
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rayvalue(&p);
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multcolor(p.rcol, p.rcoef);
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addcolor(r->rcol, p.rcol);
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transtest *= bright(p.rcol);
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transdist = r->rot + p.rt;
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}
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}
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if (r->crtype & SHADOW) { /* skip reflected ray */
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r->rt = transdist;
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return(1);
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}
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/* compute reflectance */
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for (i = 0; i < 3; i++) {
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d = colval(mcolor, i);
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d *= d;
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colval(refl,i) = .5*r1e*(1.0+(1.0-2.0*r1e)*d)/(1.0-r1e*r1e*d);
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colval(refl,i) += .5*r1m*(1.0+(1.0-2.0*r1m)*d)/(1.0-r1m*r1m*d);
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}
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/* reflected ray */
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if (rayorigin(&p, REFLECTED, r, refl) == 0) {
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for (i = 0; i < 3; i++)
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p.rdir[i] = r->rdir[i] + 2.0*pdot*pnorm[i];
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rayvalue(&p);
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multcolor(p.rcol, p.rcoef);
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addcolor(r->rcol, p.rcol);
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if (!hastexture && r->ro != NULL && isflat(r->ro->otype)) {
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mirtest = 2.0*bright(p.rcol);
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mirdist = r->rot + p.rt;
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}
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}
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/* check distance */
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d = bright(r->rcol);
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if (transtest > d)
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r->rt = transdist;
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else if (mirtest > d)
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r->rt = mirdist;
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return(1);
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}
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