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greg |
1.1 |
/* Copyright (c) 1986 Regents of the University of California */
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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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* dielectric.c - shading function for transparent materials.
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*
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* 9/6/85
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*/
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#include "ray.h"
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#include "otypes.h"
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#ifdef DISPERSE
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#include "source.h"
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#endif
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/*
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* Explicit calculations for Fresnel's equation are performed,
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* but only one square root computation is necessary.
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* The index of refraction is given as a Hartmann equation
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* with lambda0 equal to zero. If the slope of Hartmann's
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* equation is non-zero, the material disperses light upon
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* refraction. This condition is examined on rays traced to
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* light sources. If a ray is exiting a dielectric material, we
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* check the sources to see if any would cause bright color to be
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* directed to the viewer due to dispersion. This gives colorful
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* sparkle to crystals, etc. (Only if DISPERSE is defined!)
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*
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* Arguments for MAT_DIELECTRIC are:
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* red grn blu rndx Hartmann
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*
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* Arguments for MAT_INTERFACE are:
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* red1 grn1 blu1 rndx1 red2 grn2 blu2 rndx2
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*
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* The primaries are material transmission per unit length.
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* MAT_INTERFACE uses dielectric1 for inside and dielectric2 for
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* outside.
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*/
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#define MLAMBDA 500 /* mean lambda */
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#define MAXLAMBDA 779 /* maximum lambda */
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#define MINLAMBDA 380 /* minimum lambda */
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#define MINCOS 0.997 /* minimum dot product for dispersion */
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m_dielectric(m, r) /* color a ray which hit something transparent */
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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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double cos1, cos2, nratio;
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COLOR mcolor;
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double mabsorp;
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greg |
1.5 |
double refl, trans;
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greg |
1.1 |
FVECT dnorm;
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double d1, d2;
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RAY p;
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register int i;
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if (m->oargs.nfargs != (m->otype==MAT_DIELECTRIC ? 5 : 8))
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objerror(m, USER, "bad arguments");
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greg |
1.5 |
r->rt = r->rot; /* just use ray length */
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greg |
1.1 |
raytexture(r, m->omod); /* get modifiers */
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cos1 = raynormal(dnorm, r); /* cosine of theta1 */
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/* index of refraction */
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if (m->otype == MAT_DIELECTRIC)
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nratio = m->oargs.farg[3] + m->oargs.farg[4]/MLAMBDA;
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else
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nratio = m->oargs.farg[3] / m->oargs.farg[7];
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if (cos1 < 0.0) { /* inside */
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cos1 = -cos1;
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dnorm[0] = -dnorm[0];
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dnorm[1] = -dnorm[1];
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dnorm[2] = -dnorm[2];
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setcolor(mcolor, pow(m->oargs.farg[0], r->rot),
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pow(m->oargs.farg[1], r->rot),
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pow(m->oargs.farg[2], r->rot));
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} else { /* outside */
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nratio = 1.0 / nratio;
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if (m->otype == MAT_INTERFACE)
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setcolor(mcolor, pow(m->oargs.farg[4], r->rot),
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pow(m->oargs.farg[5], r->rot),
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pow(m->oargs.farg[6], r->rot));
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else
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setcolor(mcolor, 1.0, 1.0, 1.0);
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}
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greg |
1.2 |
mabsorp = bright(mcolor);
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greg |
1.1 |
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d2 = 1.0 - nratio*nratio*(1.0 - cos1*cos1); /* compute cos theta2 */
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if (d2 < FTINY) /* total reflection */
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refl = 1.0;
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else { /* refraction occurs */
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/* compute Fresnel's equations */
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cos2 = sqrt(d2);
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d1 = cos1;
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d2 = nratio*cos2;
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d1 = (d1 - d2) / (d1 + d2);
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refl = d1 * d1;
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d1 = 1.0 / cos1;
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d2 = nratio / cos2;
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d1 = (d1 - d2) / (d1 + d2);
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refl += d1 * d1;
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refl /= 2.0;
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trans = 1.0 - refl;
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if (rayorigin(&p, r, REFRACTED, mabsorp*trans) == 0) {
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/* compute refracted ray */
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d1 = nratio*cos1 - cos2;
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for (i = 0; i < 3; i++)
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p.rdir[i] = nratio*r->rdir[i] + d1*dnorm[i];
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#ifdef DISPERSE
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if (m->otype != MAT_DIELECTRIC
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|| r->rod > 0.0
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|| r->crtype & SHADOW
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greg |
1.6 |
|| directinvis
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greg |
1.1 |
|| m->oargs.farg[4] == 0.0
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|| !disperse(m, r, p.rdir, trans))
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#endif
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{
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rayvalue(&p);
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multcolor(mcolor, r->pcol); /* modify */
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scalecolor(p.rcol, trans);
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addcolor(r->rcol, p.rcol);
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}
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}
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}
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if (!(r->crtype & SHADOW) &&
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rayorigin(&p, r, REFLECTED, mabsorp*refl) == 0) {
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/* compute reflected ray */
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for (i = 0; i < 3; i++)
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p.rdir[i] = r->rdir[i] + 2.0*cos1*dnorm[i];
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rayvalue(&p); /* reflected ray value */
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scalecolor(p.rcol, refl); /* color contribution */
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addcolor(r->rcol, p.rcol);
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}
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multcolor(r->rcol, mcolor); /* multiply by transmittance */
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}
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#ifdef DISPERSE
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static
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disperse(m, r, vt, tr) /* check light sources for dispersion */
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OBJREC *m;
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RAY *r;
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FVECT vt;
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double tr;
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{
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double sqrt();
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RAY sray, *entray;
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FVECT v1, v2, n1, n2;
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FVECT dv, v2Xdv;
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double v2Xdvv2Xdv;
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greg |
1.7 |
int success = 0;
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SRCINDEX si;
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greg |
1.1 |
FVECT vtmp1, vtmp2;
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double dtmp1, dtmp2;
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int l1, l2;
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COLOR ctmp;
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int i;
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/*
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* This routine computes dispersion to the first order using
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* the following assumptions:
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*
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* 1) The dependency of the index of refraction on wavelength
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* is approximated by Hartmann's equation with lambda0
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* equal to zero.
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* 2) The entry and exit locations are constant with respect
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* to dispersion.
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*
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* The second assumption permits us to model dispersion without
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* having to sample refracted directions. We assume that the
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* geometry inside the material is constant, and concern ourselves
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* only with the relationship between the entering and exiting ray.
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* We compute the first derivatives of the entering and exiting
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* refraction with respect to the index of refraction. This
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* is then used in a first order Taylor series to determine the
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* index of refraction necessary to send the exiting ray to each
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* light source.
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* If an exiting ray hits a light source within the refraction
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* boundaries, we sum all the frequencies over the disc of the
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* light source to determine the resulting color. A smaller light
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* source will therefore exhibit a sharper spectrum.
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*/
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if (!(r->crtype & REFRACTED)) { /* ray started in material */
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VCOPY(v1, r->rdir);
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n1[0] = -r->rdir[0]; n1[1] = -r->rdir[1]; n1[2] = -r->rdir[2];
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} else {
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/* find entry point */
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for (entray = r; entray->rtype != REFRACTED;
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entray = entray->parent)
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;
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entray = entray->parent;
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if (entray->crtype & REFRACTED) /* too difficult */
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return(0);
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VCOPY(v1, entray->rdir);
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VCOPY(n1, entray->ron);
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}
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VCOPY(v2, vt); /* exiting ray */
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VCOPY(n2, r->ron);
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/* first order dispersion approx. */
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dtmp1 = DOT(n1, v1);
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dtmp2 = DOT(n2, v2);
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for (i = 0; i < 3; i++)
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dv[i] = v1[i] + v2[i] - n1[i]/dtmp1 - n2[i]/dtmp2;
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if (DOT(dv, dv) <= FTINY) /* null effect */
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return(0);
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/* compute plane normal */
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fcross(v2Xdv, v2, dv);
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v2Xdvv2Xdv = DOT(v2Xdv, v2Xdv);
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/* check sources */
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greg |
1.7 |
initsrcindex(&si);
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while (srcray(&sray, r, &si)) {
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greg |
1.1 |
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greg |
1.7 |
if (DOT(sray.rdir, v2) < MINCOS)
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greg |
1.1 |
continue; /* bad source */
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/* adjust source ray */
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dtmp1 = DOT(v2Xdv, sray.rdir) / v2Xdvv2Xdv;
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sray.rdir[0] -= dtmp1 * v2Xdv[0];
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sray.rdir[1] -= dtmp1 * v2Xdv[1];
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sray.rdir[2] -= dtmp1 * v2Xdv[2];
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l1 = lambda(m, v2, dv, sray.rdir); /* mean lambda */
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if (l1 > MAXLAMBDA || l1 < MINLAMBDA) /* not visible */
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continue;
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/* trace source ray */
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normalize(sray.rdir);
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rayvalue(&sray);
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greg |
1.2 |
if (bright(sray.rcol) <= FTINY) /* missed it */
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greg |
1.1 |
continue;
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/*
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* Compute spectral sum over diameter of source.
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* First find directions for rays going to opposite
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* sides of source, then compute wavelengths for each.
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*/
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fcross(vtmp1, v2Xdv, sray.rdir);
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greg |
1.7 |
dtmp1 = sqrt(si.dom / v2Xdvv2Xdv / PI);
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greg |
1.1 |
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/* compute first ray */
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for (i = 0; i < 3; i++)
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vtmp2[i] = sray.rdir[i] + dtmp1*vtmp1[i];
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l1 = lambda(m, v2, dv, vtmp2); /* first lambda */
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if (l1 < 0)
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continue;
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/* compute second ray */
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for (i = 0; i < 3; i++)
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vtmp2[i] = sray.rdir[i] - dtmp1*vtmp1[i];
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l2 = lambda(m, v2, dv, vtmp2); /* second lambda */
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if (l2 < 0)
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continue;
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/* compute color from spectrum */
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if (l1 < l2)
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spec_rgb(ctmp, l1, l2);
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else
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spec_rgb(ctmp, l2, l1);
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multcolor(ctmp, sray.rcol);
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scalecolor(ctmp, tr);
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addcolor(r->rcol, ctmp);
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success++;
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}
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return(success);
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}
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static int
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lambda(m, v2, dv, lr) /* compute lambda for material */
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register OBJREC *m;
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FVECT v2, dv, lr;
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{
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FVECT lrXdv, v2Xlr;
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double dtmp, denom;
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int i;
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fcross(lrXdv, lr, dv);
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for (i = 0; i < 3; i++)
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if (lrXdv[i] > FTINY || lrXdv[i] < -FTINY)
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break;
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if (i >= 3)
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return(-1);
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fcross(v2Xlr, v2, lr);
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dtmp = m->oargs.farg[4] / MLAMBDA;
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denom = dtmp + v2Xlr[i]/lrXdv[i] * (m->oargs.farg[3] + dtmp);
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if (denom < FTINY)
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return(-1);
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return(m->oargs.farg[4] / denom);
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}
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#endif /* DISPERSE */
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