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#ifndef lint
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static const char RCSid[] = "$Id: ashikhmin.c,v 2.11 2025/06/20 16:48:39 greg Exp $";
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#endif
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/*
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* Shading functions for Ashikhmin-Shirley anisotropic materials.
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*/
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#include "copyright.h"
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#include "ray.h"
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#include "ambient.h"
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#include "otypes.h"
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#include "rtotypes.h"
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#include "source.h"
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#include "func.h"
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#include "random.h"
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#include "pmapmat.h"
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#ifndef MAXITER
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#define MAXITER 10 /* maximum # specular ray attempts */
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#endif
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/*
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* Ashikhmin-Shirley model
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*
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* Arguments for MAT_ASHIKHMIN are:
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* 4+ ux uy uz funcfile [transform...]
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* 0
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* 8 dred dgrn dblu sred sgrn sblu u-power v-power
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*/
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/* specularity flags */
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#define SPA_REFL 01 /* has reflected specular component */
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#define SPA_FLAT 02 /* reflecting surface is flat */
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#define SPA_RBLT 010 /* reflection below sample threshold */
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typedef struct {
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OBJREC *mp; /* material pointer */
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RAY *rp; /* ray pointer */
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short specfl; /* specularity flags, defined above */
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SCOLOR mcolor; /* color of this material */
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SCOLOR scolor; /* color of specular component */
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FVECT u, v; /* u and v vectors orienting anisotropy */
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double u_power; /* u power */
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double v_power; /* v power */
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FVECT pnorm; /* perturbed surface normal */
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double pdot; /* perturbed dot product */
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} ASHIKDAT; /* anisotropic material data */
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static void getacoords_as(ASHIKDAT *np);
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static void ashiksamp(ASHIKDAT *np);
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#undef MAX
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#define MAX(a,b) ((a)>(b) ? (a) : (b))
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static double
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schlick_fres(double dprod)
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{
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double pf = 1. - dprod;
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return(pf*pf*pf*pf*pf);
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}
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static void
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dirashik( /* compute source contribution */
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SCOLOR scval, /* returned coefficient */
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void *nnp, /* material data */
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FVECT ldir, /* light source direction */
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double omega /* light source size */
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)
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{
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ASHIKDAT *np = nnp;
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double ldot;
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double dtmp, dtmp1, dtmp2;
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FVECT h;
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SCOLOR sctmp;
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scolorblack(scval);
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ldot = DOT(np->pnorm, ldir);
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if (ldot <= FTINY)
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return; /* wrong side */
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/*
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* Compute and add diffuse reflected component to returned
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* color.
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*/
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copyscolor(sctmp, np->mcolor);
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dtmp = ldot * omega * (1.0/PI) * (1. - schlick_fres(ldot));
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scalescolor(sctmp, dtmp);
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saddscolor(scval, sctmp);
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if (!(np->specfl & SPA_REFL) || ambRayInPmap(np->rp))
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return;
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/*
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* Compute specular reflection coefficient
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*/
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/* half vector */
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VSUB(h, ldir, np->rp->rdir);
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normalize(h);
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/* ellipse */
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dtmp1 = DOT(np->u, h);
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dtmp1 *= dtmp1 * np->u_power;
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dtmp2 = DOT(np->v, h);
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dtmp2 *= dtmp2 * np->v_power;
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/* Ashikhmin-Shirley model*/
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dtmp = DOT(np->pnorm, h);
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dtmp = pow(dtmp, (dtmp1+dtmp2)/(1.-dtmp*dtmp));
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dtmp *= sqrt((np->u_power+1.)*(np->v_power+1.));
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dtmp /= 8.*PI * DOT(ldir,h) * MAX(ldot,np->pdot);
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/* worth using? */
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if (dtmp > FTINY) {
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copyscolor(sctmp, np->scolor);
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dtmp *= ldot * omega;
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scalescolor(sctmp, dtmp);
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saddscolor(scval, sctmp);
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}
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}
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int
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m_ashikhmin( /* shade ray that hit something anisotropic */
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OBJREC *m,
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RAY *r
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)
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{
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ASHIKDAT nd;
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SCOLOR sctmp;
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double fres;
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int i;
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/* easy shadow test */
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if (r->crtype & SHADOW)
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return(1);
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if (m->oargs.nfargs != 8)
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objerror(m, USER, "bad number of real arguments");
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/* check for back side */
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if (r->rod < 0.0) {
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if (!backvis) {
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raytrans(r);
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return(1);
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}
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raytexture(r, m->omod);
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flipsurface(r); /* reorient if backvis */
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} else
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raytexture(r, m->omod);
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/* get material color */
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nd.mp = m;
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nd.rp = r;
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setscolor(nd.mcolor, m->oargs.farg[0],
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m->oargs.farg[1],
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m->oargs.farg[2]);
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setscolor(nd.scolor, m->oargs.farg[3],
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m->oargs.farg[4],
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m->oargs.farg[5]);
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/* get specular power */
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nd.specfl = 0;
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nd.u_power = m->oargs.farg[6];
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nd.v_power = m->oargs.farg[7];
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nd.pdot = raynormal(nd.pnorm, r); /* perturb normal */
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if (nd.pdot < .001)
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nd.pdot = .001; /* non-zero for dirashik() */
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smultscolor(nd.mcolor, r->pcol); /* modify diffuse color */
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if (sintens(nd.scolor) > FTINY) { /* adjust specular color */
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nd.specfl |= SPA_REFL;
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/* check threshold */
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if (specthresh >= pbright(nd.scolor)-FTINY)
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nd.specfl |= SPA_RBLT;
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fres = schlick_fres(nd.pdot); /* Schick's Fresnel approx */
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for (i = NCSAMP; i--; )
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nd.scolor[i] += (1.-nd.scolor[i])*fres;
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}
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if (r->ro != NULL && isflat(r->ro->otype))
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nd.specfl |= SPA_FLAT;
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/* set up coordinates */
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getacoords_as(&nd);
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/* specular sampling? */
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if ((nd.specfl & (SPA_REFL|SPA_RBLT)) == SPA_REFL)
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ashiksamp(&nd);
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/* diffuse interreflection */
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if (sintens(nd.mcolor) > FTINY) {
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copyscolor(sctmp, nd.mcolor); /* modified by material color */
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if (nd.specfl & SPA_RBLT) /* add in specular as well? */
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saddscolor(sctmp, nd.scolor);
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multambient(sctmp, r, nd.pnorm);
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saddscolor(r->rcol, sctmp); /* add to returned color */
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}
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direct(r, dirashik, &nd); /* add direct component */
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return(1);
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}
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static void
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getacoords_as( /* set up coordinate system */
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ASHIKDAT *np
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)
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{
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MFUNC *mf;
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int i;
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mf = getfunc(np->mp, 3, 0x7, 1);
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setfunc(np->mp, np->rp);
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errno = 0;
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for (i = 0; i < 3; i++)
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np->u[i] = evalue(mf->ep[i]);
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if ((errno == EDOM) | (errno == ERANGE))
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np->u[0] = np->u[1] = np->u[2] = 0.0;
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if (mf->fxp != &unitxf)
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multv3(np->u, np->u, mf->fxp->xfm);
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fcross(np->v, np->pnorm, np->u);
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if (normalize(np->v) == 0.0) {
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if (fabs(np->u_power - np->v_power) > 0.1)
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objerror(np->mp, WARNING, "bad orientation vector");
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getperpendicular(np->u, np->pnorm, 0); /* punting */
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fcross(np->v, np->pnorm, np->u);
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np->u_power = np->v_power =
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2./(1./(np->u_power+1e-5) + 1./(np->v_power+1e-5));
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} else
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fcross(np->u, np->v, np->pnorm);
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}
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static void
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ashiksamp( /* sample anisotropic Ashikhmin-Shirley specular */
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ASHIKDAT *np
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)
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{
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RAY sr;
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FVECT h;
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double rv[2], dtmp;
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double cosph, sinph, costh, sinth;
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int maxiter, ntrials, nstarget, nstaken;
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int i;
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if (rayorigin(&sr, RSPECULAR, np->rp, np->scolor) < 0)
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return;
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nstarget = 1;
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if (specjitter > 1.5) { /* multiple samples? */
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nstarget = specjitter*np->rp->rweight + .5;
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if (sr.rweight <= minweight*nstarget)
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nstarget = sr.rweight/minweight;
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if (nstarget > 1) {
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dtmp = 1./nstarget;
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scalescolor(sr.rcoef, dtmp);
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sr.rweight *= dtmp;
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} else
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nstarget = 1;
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}
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dimlist[ndims_inc()] = (int)(size_t)np->mp;
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maxiter = MAXITER*nstarget;
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for (nstaken = ntrials = 0; nstaken < nstarget &&
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ntrials < maxiter; ntrials++) {
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if (ntrials)
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dtmp = frandom();
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else
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dtmp = urand(ilhash(dimlist,ndims)+647+samplendx);
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multisamp(rv, 2, dtmp);
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dtmp = 2.*PI * rv[0];
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cosph = sqrt(np->v_power + 1.) * tcos(dtmp);
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sinph = sqrt(np->u_power + 1.) * tsin(dtmp);
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dtmp = 1./sqrt(cosph*cosph + sinph*sinph);
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cosph *= dtmp;
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sinph *= dtmp;
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costh = pow(rv[1], 1./(np->u_power*cosph*cosph+np->v_power*sinph*sinph+1.));
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if (costh <= FTINY)
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continue;
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sinth = sqrt(1. - costh*costh);
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for (i = 0; i < 3; i++)
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h[i] = cosph*sinth*np->u[i] + sinph*sinth*np->v[i] + costh*np->pnorm[i];
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if (nstaken)
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rayclear(&sr);
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dtmp = -2.*DOT(h, np->rp->rdir);
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VSUM(sr.rdir, np->rp->rdir, h, dtmp);
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/* sample rejection test */
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if (DOT(sr.rdir, np->rp->ron) <= FTINY)
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continue;
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checknorm(sr.rdir);
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rayvalue(&sr);
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smultscolor(sr.rcol, sr.rcoef);
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saddscolor(np->rp->rcol, sr.rcol);
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++nstaken;
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}
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dec_ndims();
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}
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