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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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* 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 cos2; |
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COLOR trans, refl; |
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double d, r1; |
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double transtest, transdist; |
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RAY p; |
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register int i; |
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|
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if (m->oargs.nfargs != 3) |
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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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r1 = (pdot - RINDEX*cos2) / (pdot + RINDEX*cos2); |
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d = (1.0/pdot - RINDEX/cos2) / (1.0/pdot + RINDEX/cos2); |
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r1 = (r1*r1 + d*d) / 2.0; |
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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) = (1.0-r1)*(1.0-r1)*d / (1.0 - r1*r1*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 (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) = r1 * (1.0 + (1.0-2.0*r1)*d) / (1.0 - r1*r1*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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} |
