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/* 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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* sphere.c - compute ray intersection with spheres.
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*
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* 8/19/85
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*/
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#include "ray.h"
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#include "otypes.h"
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o_sphere(so, r) /* compute intersection with sphere */
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OBJREC *so;
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register RAY *r;
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{
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double a, b, c; /* coefficients for quadratic equation */
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double root[2]; /* quadratic roots */
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int nroots;
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double t;
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register double *ap;
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register int i;
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if (so->oargs.nfargs != 4 || so->oargs.farg[3] <= FTINY)
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objerror(so, USER, "bad arguments");
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ap = so->oargs.farg;
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/*
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* We compute the intersection by substituting into
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* the surface equation for the sphere. The resulting
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* quadratic equation in t is then solved for the
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* smallest positive root, which is our point of
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* intersection.
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* Because the ray direction is normalized, a is always 1.
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*/
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a = 1.0; /* compute quadratic coefficients */
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b = c = 0.0;
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for (i = 0; i < 3; i++) {
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t = r->rorg[i] - ap[i];
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b += 2.0*r->rdir[i]*t;
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c += t*t;
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}
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c -= ap[3] * ap[3];
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nroots = quadratic(root, a, b, c); /* solve quadratic */
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for (i = 0; i < nroots; i++) /* get smallest positive */
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if ((t = root[i]) > FTINY)
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break;
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if (i >= nroots)
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return(0); /* no positive root */
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if (t < r->rot) { /* found closer intersection */
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r->ro = so;
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r->rot = t;
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/* compute normal */
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a = ap[3];
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if (so->otype == OBJ_BUBBLE)
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a = -a; /* reverse */
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for (i = 0; i < 3; i++) {
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r->rop[i] = r->rorg[i] + r->rdir[i]*t;
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r->ron[i] = (r->rop[i] - ap[i]) / a;
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}
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r->rod = -DOT(r->rdir, r->ron);
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}
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return(1);
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}
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