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/* Copyright (c) 1991 Regents of the University of California */ |
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|
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#ifndef lint |
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static char SCCSid[] = "$SunId$ LBL"; |
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#endif |
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|
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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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* 11/14/86 |
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*/ |
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|
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#include "ray.h" |
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|
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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 |
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* |
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* The color is used for the transmission at normal incidence. |
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* To compute transmission (tn) from transmissivity (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 transmission of standard 88% transmissivity 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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|
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#define RINDEX 1.52 /* refractive index of glass */ |
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|
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|
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m_glass(m, r) /* 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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double sqrt(), pow(); |
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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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double d, r1e, r1m; |
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double transtest, transdist; |
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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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|
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setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]); |
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|
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if (r->rod < 0.0) /* reorient if necessary */ |
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flipsurface(r); |
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transtest = 0; |
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/* get modifiers */ |
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raytexture(r, m->omod); |
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pdot = raynormal(pnorm, r); |
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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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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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|
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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 transmittance */ |
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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/(1.0-r1e*r1e*d*d); |
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colval(trans,i) += .5*(1.0-r1m)*(1.0-r1m)*d/(1.0-r1m*r1m*d*d); |
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} |
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/* transmitted ray */ |
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if (rayorigin(&p, r, TRANS, bright(trans)) == 0) { |
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if (!(r->crtype & SHADOW) && |
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DOT(r->pert,r->pert) > FTINY*FTINY) { |
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for (i = 0; i < 3; i++) /* perturb direction */ |
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p.rdir[i] = r->rdir[i] - r->pert[i]/rindex; |
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normalize(p.rdir); |
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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, r->pcol); /* modify */ |
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multcolor(p.rcol, trans); |
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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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return; |
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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, r, REFLECTED, bright(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, refl); |
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addcolor(r->rcol, p.rcol); |
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} |
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if (transtest > bright(r->rcol)) |
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r->rt = transdist; |
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} |
