src/rt/ambcomp.c

#ifndef lint
static const char       RCSid[] = "$Id: ambcomp.c,v 2.91 2023/11/17 20:02:07 greg Exp $";
#endif
/*
 * Routines to compute "ambient" values using Monte Carlo
 *
 *  Hessian calculations based on "Practical Hessian-Based Error Control
 *      for Irradiance Caching" by Schwarzhaupt, Wann Jensen, & Jarosz
 *      from ACM SIGGRAPH Asia 2012 conference proceedings.
 *
 *  Added book-keeping optimization to avoid calculations that would
 *      cancel due to traversal both directions on edges that are adjacent
 *      to same-valued triangles.  This cuts about half of Hessian math.
 *
 *  Declarations of external symbols in ambient.h
 */

#include "copyright.h"

#include  "ray.h"
#include  "ambient.h"
#include  "random.h"

#ifndef MINADIV
#define MINADIV         7       /* minimum # divisions in each dimension */
#endif

typedef struct {
        FVECT   p;              /* intersection point */
        float   d;              /* reciprocal distance */
        SCOLOR  v;              /* hemisphere sample value */
} AMBSAMP;              /* sample value */

typedef struct {
        RAY     *rp;            /* originating ray sample */
        int     ns;             /* number of samples per axis */
        int     sampOK;         /* acquired full sample set? */
        int     atyp;           /* RAMBIENT or TAMBIENT */
        SCOLOR  acoef;          /* division contribution coefficient */
        SCOLOR  acol;           /* accumulated color */
        FVECT   onrm;           /* oriented unperturbed surface normal */
        FVECT   ux, uy;         /* tangent axis unit vectors */
        AMBSAMP sa[1];          /* sample array (extends struct) */
}  AMBHEMI;             /* ambient sample hemisphere */

#define AI(h,i,j)       ((i)*(h)->ns + (j))
#define ambsam(h,i,j)   (h)->sa[AI(h,i,j)]

typedef struct {
        FVECT   r_i, r_i1, e_i, rcp, rI2_eJ2;
        double  I1, I2;
} FFTRI;                /* vectors and coefficients for Hessian calculation */


static int
ambcollision(                           /* proposed direciton collides? */
        AMBHEMI *hp,
        int     i,
        int     j,
        FVECT   dv
)
{
        double  cos_thresh;
        int     ii, jj;
                                        /* min. spacing = 1/4th division */
        cos_thresh = (PI/4.)/(double)hp->ns;
        cos_thresh = 1. - .5*cos_thresh*cos_thresh;
                                        /* check existing neighbors */
        for (ii = i-1; ii <= i+1; ii++) {
                if (ii < 0) continue;
                if (ii >= hp->ns) break;
                for (jj = j-1; jj <= j+1; jj++) {
                        AMBSAMP *ap;
                        FVECT   avec;
                        double  dprod;
                        if (jj < 0) continue;
                        if (jj >= hp->ns) break;
                        if ((ii==i) & (jj==j)) continue;
                        ap = &ambsam(hp,ii,jj);
                        if (ap->d <= .5/FHUGE)
                                continue;       /* no one home */
                        VSUB(avec, ap->p, hp->rp->rop);
                        dprod = DOT(avec, dv);
                        if (dprod >= cos_thresh*VLEN(avec))
                                return(1);      /* collision */
                }
        }
        return(0);                      /* nothing to worry about */
}


static int
ambsample(                              /* initial ambient division sample */
        AMBHEMI *hp,
        int     i,
        int     j,
        int     n
)
{
        AMBSAMP *ap = &ambsam(hp,i,j);
        RAY     ar;
        int     hlist[3], ii;
        RREAL   spt[2];
        double  zd;
                                        /* generate hemispherical sample */
                                        /* ambient coefficient for weight */
        if (ambacc > FTINY)
                setscolor(ar.rcoef, AVGREFL, AVGREFL, AVGREFL);
        else
                copyscolor(ar.rcoef, hp->acoef);
        if (rayorigin(&ar, hp->atyp, hp->rp, ar.rcoef) < 0)
                return(0);
        if (ambacc > FTINY) {
                smultscolor(ar.rcoef, hp->acoef);
                scalescolor(ar.rcoef, 1./AVGREFL);
        }
        hlist[0] = hp->rp->rno;
        hlist[1] = j;
        hlist[2] = i;
        multisamp(spt, 2, urand(ilhash(hlist,3)+n));
resample:
        square2disk(spt, (j+spt[1])/hp->ns, (i+spt[0])/hp->ns);
        zd = sqrt(1. - spt[0]*spt[0] - spt[1]*spt[1]);
        for (ii = 3; ii--; )
                ar.rdir[ii] =   spt[0]*hp->ux[ii] +
                                spt[1]*hp->uy[ii] +
                                zd*hp->onrm[ii];
        checknorm(ar.rdir);
                                        /* avoid coincident samples */
        if (!n && ambcollision(hp, i, j, ar.rdir)) {
                spt[0] = frandom(); spt[1] = frandom();
                goto resample;          /* reject this sample */
        }
        dimlist[ndims++] = AI(hp,i,j) + 90171;
        rayvalue(&ar);                  /* evaluate ray */
        ndims--;
        zd = raydistance(&ar);
        if (zd <= FTINY)
                return(0);              /* should never happen */
        smultscolor(ar.rcol, ar.rcoef); /* apply coefficient */
        if (zd*ap->d < 1.0)             /* new/closer distance? */
                ap->d = 1.0/zd;
        if (!n) {                       /* record first vertex & value */
                if (zd > 10.0*thescene.cusize + 1000.)
                        zd = 10.0*thescene.cusize + 1000.;
                VSUM(ap->p, ar.rorg, ar.rdir, zd);
                copyscolor(ap->v, ar.rcol);
        } else {                        /* else update recorded value */
                sopscolor(hp->acol, -=, ap->v);
                zd = 1.0/(double)(n+1);
                scalescolor(ar.rcol, zd);
                zd *= (double)n;
                scalescolor(ap->v, zd);
                saddscolor(ap->v, ar.rcol);
        }
        saddscolor(hp->acol, ap->v);    /* add to our sum */
        return(1);
}


/* Estimate variance based on ambient division differences */
static float *
getambdiffs(AMBHEMI *hp)
{
        const double    normf = 1./bright(hp->acoef);
        float   *earr = (float *)calloc(hp->ns*hp->ns, sizeof(float));
        float   *ep;
        AMBSAMP *ap;
        double  b, b1, d2;
        int     i, j;

        if (earr == NULL)               /* out of memory? */
                return(NULL);
                                        /* sum squared neighbor diffs */
        for (ap = hp->sa, ep = earr, i = 0; i < hp->ns; i++)
            for (j = 0; j < hp->ns; j++, ap++, ep++) {
                b = pbright(ap[0].v);
                if (i) {                /* from above */
                        b1 = pbright(ap[-hp->ns].v);
                        d2 = b - b1;
                        d2 *= d2*normf/(b + b1 + FTINY);
                        ep[0] += d2;
                        ep[-hp->ns] += d2;
                }
                if (!j) continue;
                                        /* from behind */
                b1 = pbright(ap[-1].v);
                d2 = b - b1;
                d2 *= d2*normf/(b + b1 + FTINY);
                ep[0] += d2;
                ep[-1] += d2;
                if (!i) continue;
                                        /* diagonal */
                b1 = pbright(ap[-hp->ns-1].v);
                d2 = b - b1;
                d2 *= d2*normf/(b + b1 + FTINY);
                ep[0] += d2;
                ep[-hp->ns-1] += d2;
            }
                                        /* correct for number of neighbors */
        earr[0] *= 8./3.;
        earr[hp->ns-1] *= 8./3.;
        earr[(hp->ns-1)*hp->ns] *= 8./3.;
        earr[(hp->ns-1)*hp->ns + hp->ns-1] *= 8./3.;
        for (i = 1; i < hp->ns-1; i++) {
                earr[i*hp->ns] *= 8./5.;
                earr[i*hp->ns + hp->ns-1] *= 8./5.;
        }
        for (j = 1; j < hp->ns-1; j++) {
                earr[j] *= 8./5.;
                earr[(hp->ns-1)*hp->ns + j] *= 8./5.;
        }
        return(earr);
}


/* Perform super-sampling on hemisphere (introduces bias) */
static void
ambsupersamp(AMBHEMI *hp, int cnt)
{
        float   *earr = getambdiffs(hp);
        double  e2rem = 0;
        float   *ep;
        int     i, j, n, nss;

        if (earr == NULL)               /* just skip calc. if no memory */
                return;
                                        /* accumulate estimated variances */
        for (ep = earr + hp->ns*hp->ns; ep > earr; )
                e2rem += *--ep;
        ep = earr;                      /* perform super-sampling */
        for (i = 0; i < hp->ns; i++)
            for (j = 0; j < hp->ns; j++) {
                if (e2rem <= FTINY)
                        goto done;      /* nothing left to do */
                nss = *ep/e2rem*cnt + frandom();
                for (n = 1; n <= nss && ambsample(hp,i,j,n); n++)
                        if (!--cnt) goto done;
                e2rem -= *ep++;         /* update remainder */
        }
done:
        free(earr);
}


static AMBHEMI *
samp_hemi(                              /* sample indirect hemisphere */
        SCOLOR  rcol,
        RAY     *r,
        double  wt
)
{
        int     backside = (wt < 0);
        AMBHEMI *hp;
        double  d;
        int     n, i, j;
                                        /* insignificance check */
        d = sintens(rcol);
        if (d <= FTINY)
                return(NULL);
                                        /* set number of divisions */
        if (backside) wt = -wt;
        if (ambacc <= FTINY &&
                        wt > (d *= 0.8*r->rweight/(ambdiv*minweight)))
                wt = d;                 /* avoid ray termination */
        n = sqrt(ambdiv * wt) + 0.5;
        i = 1 + (MINADIV-1)*(ambacc > FTINY);
        if (n < i)                      /* use minimum number of samples? */
                n = i;
                                        /* allocate sampling array */
        hp = (AMBHEMI *)malloc(sizeof(AMBHEMI) + sizeof(AMBSAMP)*(n*n - 1));
        if (hp == NULL)
                error(SYSTEM, "out of memory in samp_hemi");

        if (backside) {
                hp->atyp = TAMBIENT;
                hp->onrm[0] = -r->ron[0];
                hp->onrm[1] = -r->ron[1];
                hp->onrm[2] = -r->ron[2];
        } else {
                hp->atyp = RAMBIENT;
                VCOPY(hp->onrm, r->ron);
        }
        hp->rp = r;
        hp->ns = n;
        scolorblack(hp->acol);
        memset(hp->sa, 0, sizeof(AMBSAMP)*n*n);
        hp->sampOK = 0;
                                        /* assign coefficient */
        copyscolor(hp->acoef, rcol);
        d = 1.0/(n*n);
        scalescolor(hp->acoef, d);
                                        /* make tangent plane axes */
        if (!getperpendicular(hp->ux, hp->onrm, 1))
                error(CONSISTENCY, "bad ray direction in samp_hemi");
        VCROSS(hp->uy, hp->onrm, hp->ux);
                                        /* sample divisions */
        for (i = hp->ns; i--; )
            for (j = hp->ns; j--; )
                hp->sampOK += ambsample(hp, i, j, 0);
        copyscolor(rcol, hp->acol);
        if (!hp->sampOK) {              /* utter failure? */
                free(hp);
                return(NULL);
        }
        if (hp->sampOK < hp->ns*hp->ns) {
                hp->sampOK *= -1;       /* soft failure */
                return(hp);
        }
        if (hp->sampOK <= MINADIV*MINADIV)
                return(hp);             /* don't bother super-sampling */
        n = ambssamp*wt + 0.5;
        if (n > 8) {                    /* perform super-sampling? */
                ambsupersamp(hp, n);
                copyscolor(rcol, hp->acol);
        }
        return(hp);                     /* all is well */
}


/* Return brightness of farthest ambient sample */
static double
back_ambval(AMBHEMI *hp, const int n1, const int n2, const int n3)
{
        if (hp->sa[n1].d <= hp->sa[n2].d) {
                if (hp->sa[n1].d <= hp->sa[n3].d)
                        return(hp->sa[n1].v[0]);
                return(hp->sa[n3].v[0]);
        }
        if (hp->sa[n2].d <= hp->sa[n3].d)
                return(hp->sa[n2].v[0]);
        return(hp->sa[n3].v[0]);
}


/* Compute vectors and coefficients for Hessian/gradient calcs */
static void
comp_fftri(FFTRI *ftp, AMBHEMI *hp, const int n0, const int n1)
{
        double  rdot_cp, dot_e, dot_er, rdot_r, rdot_r1, J2;
        int     ii;

        VSUB(ftp->r_i, hp->sa[n0].p, hp->rp->rop);
        VSUB(ftp->r_i1, hp->sa[n1].p, hp->rp->rop);
        VSUB(ftp->e_i, hp->sa[n1].p, hp->sa[n0].p);
        VCROSS(ftp->rcp, ftp->r_i, ftp->r_i1);
        rdot_cp = 1.0/DOT(ftp->rcp,ftp->rcp);
        dot_e = DOT(ftp->e_i,ftp->e_i);
        dot_er = DOT(ftp->e_i, ftp->r_i);
        rdot_r = 1.0/DOT(ftp->r_i,ftp->r_i);
        rdot_r1 = 1.0/DOT(ftp->r_i1,ftp->r_i1);
        ftp->I1 = acos( DOT(ftp->r_i, ftp->r_i1) * sqrt(rdot_r*rdot_r1) ) *
                        sqrt( rdot_cp );
        ftp->I2 = ( DOT(ftp->e_i, ftp->r_i1)*rdot_r1 - dot_er*rdot_r +
                        dot_e*ftp->I1 )*0.5*rdot_cp;
        J2 =  ( 0.5*(rdot_r - rdot_r1) - dot_er*ftp->I2 ) / dot_e;
        for (ii = 3; ii--; )
                ftp->rI2_eJ2[ii] = ftp->I2*ftp->r_i[ii] + J2*ftp->e_i[ii];
}


/* Compose 3x3 matrix from two vectors */
static void
compose_matrix(FVECT mat[3], FVECT va, FVECT vb)
{
        mat[0][0] = 2.0*va[0]*vb[0];
        mat[1][1] = 2.0*va[1]*vb[1];
        mat[2][2] = 2.0*va[2]*vb[2];
        mat[0][1] = mat[1][0] = va[0]*vb[1] + va[1]*vb[0];
        mat[0][2] = mat[2][0] = va[0]*vb[2] + va[2]*vb[0];
        mat[1][2] = mat[2][1] = va[1]*vb[2] + va[2]*vb[1];
}


/* Compute partial 3x3 Hessian matrix for edge */
static void
comp_hessian(FVECT hess[3], FFTRI *ftp, FVECT nrm)
{
        FVECT   ncp;
        FVECT   m1[3], m2[3], m3[3], m4[3];
        double  d1, d2, d3, d4;
        double  I3, J3, K3;
        int     i, j;
                                        /* compute intermediate coefficients */
        d1 = 1.0/DOT(ftp->r_i,ftp->r_i);
        d2 = 1.0/DOT(ftp->r_i1,ftp->r_i1);
        d3 = 1.0/DOT(ftp->e_i,ftp->e_i);
        d4 = DOT(ftp->e_i, ftp->r_i);
        I3 = ( DOT(ftp->e_i, ftp->r_i1)*d2*d2 - d4*d1*d1 + 3.0/d3*ftp->I2 )
                        / ( 4.0*DOT(ftp->rcp,ftp->rcp) );
        J3 = 0.25*d3*(d1*d1 - d2*d2) - d4*d3*I3;
        K3 = d3*(ftp->I2 - I3/d1 - 2.0*d4*J3);
                                        /* intermediate matrices */
        VCROSS(ncp, nrm, ftp->e_i);
        compose_matrix(m1, ncp, ftp->rI2_eJ2);
        compose_matrix(m2, ftp->r_i, ftp->r_i);
        compose_matrix(m3, ftp->e_i, ftp->e_i);
        compose_matrix(m4, ftp->r_i, ftp->e_i);
        d1 = DOT(nrm, ftp->rcp);
        d2 = -d1*ftp->I2;
        d1 *= 2.0;
        for (i = 3; i--; )              /* final matrix sum */
            for (j = 3; j--; ) {
                hess[i][j] = m1[i][j] + d1*( I3*m2[i][j] + K3*m3[i][j] +
                                                2.0*J3*m4[i][j] );
                hess[i][j] += d2*(i==j);
                hess[i][j] *= -1.0/PI;
            }
}


/* Reverse hessian calculation result for edge in other direction */
static void
rev_hessian(FVECT hess[3])
{
        int     i;

        for (i = 3; i--; ) {
                hess[i][0] = -hess[i][0];
                hess[i][1] = -hess[i][1];
                hess[i][2] = -hess[i][2];
        }
}


/* Add to radiometric Hessian from the given triangle */
static void
add2hessian(FVECT hess[3], FVECT ehess1[3],
                FVECT ehess2[3], FVECT ehess3[3], double v)
{
        int     i, j;

        for (i = 3; i--; )
            for (j = 3; j--; )
                hess[i][j] += v*( ehess1[i][j] + ehess2[i][j] + ehess3[i][j] );
}


/* Compute partial displacement form factor gradient for edge */
static void
comp_gradient(FVECT grad, FFTRI *ftp, FVECT nrm)
{
        FVECT   ncp;
        double  f1;
        int     i;

        f1 = 2.0*DOT(nrm, ftp->rcp);
        VCROSS(ncp, nrm, ftp->e_i);
        for (i = 3; i--; )
                grad[i] = (0.5/PI)*( ftp->I1*ncp[i] + f1*ftp->rI2_eJ2[i] );
}


/* Reverse gradient calculation result for edge in other direction */
static void
rev_gradient(FVECT grad)
{
        grad[0] = -grad[0];
        grad[1] = -grad[1];
        grad[2] = -grad[2];
}


/* Add to displacement gradient from the given triangle */
static void
add2gradient(FVECT grad, FVECT egrad1, FVECT egrad2, FVECT egrad3, double v)
{
        int     i;

        for (i = 3; i--; )
                grad[i] += v*( egrad1[i] + egrad2[i] + egrad3[i] );
}


/* Compute anisotropic radii and eigenvector directions */
static void
eigenvectors(FVECT uv[2], float ra[2], FVECT hessian[3])
{
        double  hess2[2][2];
        FVECT   a, b;
        double  evalue[2], slope1, xmag1;
        int     i;
                                        /* project Hessian to sample plane */
        for (i = 3; i--; ) {
                a[i] = DOT(hessian[i], uv[0]);
                b[i] = DOT(hessian[i], uv[1]);
        }
        hess2[0][0] = DOT(uv[0], a);
        hess2[0][1] = DOT(uv[0], b);
        hess2[1][0] = DOT(uv[1], a);
        hess2[1][1] = DOT(uv[1], b);
                                        /* compute eigenvalue(s) */
        i = quadratic(evalue, 1.0, -hess2[0][0]-hess2[1][1],
                        hess2[0][0]*hess2[1][1]-hess2[0][1]*hess2[1][0]);
        if (i == 1)                     /* double-root (circle) */
                evalue[1] = evalue[0];
        if (!i || ((evalue[0] = fabs(evalue[0])) <= FTINY*FTINY) |
                        ((evalue[1] = fabs(evalue[1])) <= FTINY*FTINY) ) {
                ra[0] = ra[1] = maxarad;
                return;
        }
        if (evalue[0] > evalue[1]) {
                ra[0] = sqrt(sqrt(4.0/evalue[0]));
                ra[1] = sqrt(sqrt(4.0/evalue[1]));
                slope1 = evalue[1];
        } else {
                ra[0] = sqrt(sqrt(4.0/evalue[1]));
                ra[1] = sqrt(sqrt(4.0/evalue[0]));
                slope1 = evalue[0];
        }
                                        /* compute unit eigenvectors */
        if (fabs(hess2[0][1]) <= FTINY)
                return;                 /* uv OK as is */
        slope1 = (slope1 - hess2[0][0]) / hess2[0][1];
        xmag1 = sqrt(1.0/(1.0 + slope1*slope1));
        for (i = 3; i--; ) {
                b[i] = xmag1*uv[0][i] + slope1*xmag1*uv[1][i];
                a[i] = slope1*xmag1*uv[0][i] - xmag1*uv[1][i];
        }
        VCOPY(uv[0], a);
        VCOPY(uv[1], b);
}


static void
ambHessian(                             /* anisotropic radii & pos. gradient */
        AMBHEMI *hp,
        FVECT   uv[2],                  /* returned */
        float   ra[2],                  /* returned (optional) */
        float   pg[2]                   /* returned (optional) */
)
{
        static char     memerrmsg[] = "out of memory in ambHessian()";
        FVECT           (*hessrow)[3] = NULL;
        FVECT           *gradrow = NULL;
        FVECT           hessian[3];
        FVECT           gradient;
        FFTRI           fftr;
        int             i, j;
                                        /* be sure to assign unit vectors */
        VCOPY(uv[0], hp->ux);
        VCOPY(uv[1], hp->uy);
                        /* clock-wise vertex traversal from sample POV */
        if (ra != NULL) {               /* initialize Hessian row buffer */
                hessrow = (FVECT (*)[3])malloc(sizeof(FVECT)*3*(hp->ns-1));
                if (hessrow == NULL)
                        error(SYSTEM, memerrmsg);
                memset(hessian, 0, sizeof(hessian));
        } else if (pg == NULL)          /* bogus call? */
                return;
        if (pg != NULL) {               /* initialize form factor row buffer */
                gradrow = (FVECT *)malloc(sizeof(FVECT)*(hp->ns-1));
                if (gradrow == NULL)
                        error(SYSTEM, memerrmsg);
                memset(gradient, 0, sizeof(gradient));
        }
                                        /* compute first row of edges */
        for (j = 0; j < hp->ns-1; j++) {
                comp_fftri(&fftr, hp, AI(hp,0,j), AI(hp,0,j+1));
                if (hessrow != NULL)
                        comp_hessian(hessrow[j], &fftr, hp->onrm);
                if (gradrow != NULL)
                        comp_gradient(gradrow[j], &fftr, hp->onrm);
        }
                                        /* sum each row of triangles */
        for (i = 0; i < hp->ns-1; i++) {
            FVECT       hesscol[3];     /* compute first vertical edge */
            FVECT       gradcol;
            comp_fftri(&fftr, hp, AI(hp,i,0), AI(hp,i+1,0));
            if (hessrow != NULL)
                comp_hessian(hesscol, &fftr, hp->onrm);
            if (gradrow != NULL)
                comp_gradient(gradcol, &fftr, hp->onrm);
            for (j = 0; j < hp->ns-1; j++) {
                FVECT   hessdia[3];     /* compute triangle contributions */
                FVECT   graddia;
                double  backg;
                backg = back_ambval(hp, AI(hp,i,j),
                                        AI(hp,i,j+1), AI(hp,i+1,j));
                                        /* diagonal (inner) edge */
                comp_fftri(&fftr, hp, AI(hp,i,j+1), AI(hp,i+1,j));
                if (hessrow != NULL) {
                    comp_hessian(hessdia, &fftr, hp->onrm);
                    rev_hessian(hesscol);
                    add2hessian(hessian, hessrow[j], hessdia, hesscol, backg);
                }
                if (gradrow != NULL) {
                    comp_gradient(graddia, &fftr, hp->onrm);
                    rev_gradient(gradcol);
                    add2gradient(gradient, gradrow[j], graddia, gradcol, backg);
                }
                                        /* initialize edge in next row */
                comp_fftri(&fftr, hp, AI(hp,i+1,j+1), AI(hp,i+1,j));
                if (hessrow != NULL)
                    comp_hessian(hessrow[j], &fftr, hp->onrm);
                if (gradrow != NULL)
                    comp_gradient(gradrow[j], &fftr, hp->onrm);
                                        /* new column edge & paired triangle */
                backg = back_ambval(hp, AI(hp,i+1,j+1),
                                        AI(hp,i+1,j), AI(hp,i,j+1));
                comp_fftri(&fftr, hp, AI(hp,i,j+1), AI(hp,i+1,j+1));
                if (hessrow != NULL) {
                    comp_hessian(hesscol, &fftr, hp->onrm);
                    rev_hessian(hessdia);
                    add2hessian(hessian, hessrow[j], hessdia, hesscol, backg);
                    if (i < hp->ns-2)
                        rev_hessian(hessrow[j]);
                }
                if (gradrow != NULL) {
                    comp_gradient(gradcol, &fftr, hp->onrm);
                    rev_gradient(graddia);
                    add2gradient(gradient, gradrow[j], graddia, gradcol, backg);
                    if (i < hp->ns-2)
                        rev_gradient(gradrow[j]);
                }
            }
        }
                                        /* release row buffers */
        if (hessrow != NULL) free(hessrow);
        if (gradrow != NULL) free(gradrow);
        
        if (ra != NULL)                 /* extract eigenvectors & radii */
                eigenvectors(uv, ra, hessian);
        if (pg != NULL) {               /* tangential position gradient */
                pg[0] = DOT(gradient, uv[0]);
                pg[1] = DOT(gradient, uv[1]);
        }
}


/* Compute direction gradient from a hemispherical sampling */
static void
ambdirgrad(AMBHEMI *hp, FVECT uv[2], float dg[2])
{
        AMBSAMP *ap;
        double  dgsum[2];
        int     n;
        FVECT   vd;
        double  gfact;

        dgsum[0] = dgsum[1] = 0.0;      /* sum values times -tan(theta) */
        for (ap = hp->sa, n = hp->ns*hp->ns; n--; ap++) {
                                        /* use vector for azimuth + 90deg */
                VSUB(vd, ap->p, hp->rp->rop);
                                        /* brightness over cosine factor */
                gfact = ap->v[0] / DOT(hp->onrm, vd);
                                        /* sine = proj_radius/vd_length */
                dgsum[0] -= DOT(uv[1], vd) * gfact;
                dgsum[1] += DOT(uv[0], vd) * gfact;
        }
        dg[0] = dgsum[0] / (hp->ns*hp->ns);
        dg[1] = dgsum[1] / (hp->ns*hp->ns);
}


/* Compute potential light leak direction flags for cache value */
static uint32
ambcorral(AMBHEMI *hp, FVECT uv[2], const double r0, const double r1)
{
        const double    max_d = 1.0/(minarad*ambacc + 0.001);
        const double    ang_res = 0.5*PI/hp->ns;
        const double    ang_step = ang_res/((int)(16/PI*ang_res) + 1.01);
        double          avg_d = 0;
        uint32          flgs = 0;
        FVECT           vec;
        double          u, v;
        double          ang, a1;
        int             i, j;
                                        /* don't bother for a few samples */
        if (hp->ns < 8)
                return(0);
                                        /* check distances overhead */
        for (i = hp->ns*3/4; i-- > hp->ns>>2; )
            for (j = hp->ns*3/4; j-- > hp->ns>>2; )
                avg_d += ambsam(hp,i,j).d;
        avg_d *= 4.0/(hp->ns*hp->ns);
        if (avg_d*r0 >= 1.0)            /* ceiling too low for corral? */
                return(0);
        if (avg_d >= max_d)             /* insurance */
                return(0);
                                        /* else circle around perimeter */
        for (i = 0; i < hp->ns; i++)
            for (j = 0; j < hp->ns; j += !i|(i==hp->ns-1) ? 1 : hp->ns-1) {
                AMBSAMP *ap = &ambsam(hp,i,j);
                if ((ap->d <= FTINY) | (ap->d >= max_d))
                        continue;       /* too far or too near */
                VSUB(vec, ap->p, hp->rp->rop);
                u = DOT(vec, uv[0]);
                v = DOT(vec, uv[1]);
                if ((r0*r0*u*u + r1*r1*v*v) * ap->d*ap->d <= u*u + v*v)
                        continue;       /* occluder outside ellipse */
                ang = atan2a(v, u);     /* else set direction flags */
                for (a1 = ang-ang_res; a1 <= ang+ang_res; a1 += ang_step)
                        flgs |= 1L<<(int)(16/PI*(a1 + 2.*PI*(a1 < 0)));
            }
        return(flgs);
}


int
doambient(                              /* compute ambient component */
        SCOLOR  rcol,                   /* input/output color */
        RAY     *r,
        double  wt,                     /* negative for back side */
        FVECT   uv[2],                  /* returned (optional) */
        float   ra[2],                  /* returned (optional) */
        float   pg[2],                  /* returned (optional) */
        float   dg[2],                  /* returned (optional) */
        uint32  *crlp                   /* returned (optional) */
)
{
        AMBHEMI *hp = samp_hemi(rcol, r, wt);
        FVECT   my_uv[2];
        double  d, K;
        AMBSAMP *ap;
        int     i;
                                        /* clear return values */
        if (uv != NULL)
                memset(uv, 0, sizeof(FVECT)*2);
        if (ra != NULL)
                ra[0] = ra[1] = 0.0;
        if (pg != NULL)
                pg[0] = pg[1] = 0.0;
        if (dg != NULL)
                dg[0] = dg[1] = 0.0;
        if (crlp != NULL)
                *crlp = 0;
        if (hp == NULL)                 /* sampling falure? */
                return(0);

        if ((ra == NULL) & (pg == NULL) & (dg == NULL) ||
                        (hp->sampOK < 0) | (hp->ns < MINADIV)) {
                free(hp);               /* Hessian not requested/possible */
                return(-1);             /* value-only return value */
        }
        if ((d = scolor_mean(rcol)) > FTINY) {
                d = 0.99*(hp->ns*hp->ns)/d;     /* normalize avg. values */
                K = 0.01;
        } else {                        /* or fall back on geometric Hessian */
                K = 1.0;
                pg = NULL;
                dg = NULL;
                crlp = NULL;
        }
        ap = hp->sa;                    /* single channel from here on... */
        for (i = hp->ns*hp->ns; i--; ap++)
                ap->v[0] = scolor_mean(ap->v)*d + K;

        if (uv == NULL)                 /* make sure we have axis pointers */
                uv = my_uv;
                                        /* compute radii & pos. gradient */
        ambHessian(hp, uv, ra, pg);

        if (dg != NULL)                 /* compute direction gradient */
                ambdirgrad(hp, uv, dg);

        if (ra != NULL) {               /* scale/clamp radii */
                if (pg != NULL) {
                        if (ra[0]*(d = fabs(pg[0])) > 1.0)
                                ra[0] = 1.0/d;
                        if (ra[1]*(d = fabs(pg[1])) > 1.0)
                                ra[1] = 1.0/d;
                        if (ra[0] > ra[1])
                                ra[0] = ra[1];
                }
                if (ra[0] < minarad) {
                        ra[0] = minarad;
                        if (ra[1] < minarad)
                                ra[1] = minarad;
                }
                ra[0] *= d = 1.0/sqrt(fabs(wt));
                if ((ra[1] *= d) > 2.0*ra[0])
                        ra[1] = 2.0*ra[0];
                if (ra[1] > maxarad) {
                        ra[1] = maxarad;
                        if (ra[0] > maxarad)
                                ra[0] = maxarad;
                }
                                        /* flag encroached directions */
                if (crlp != NULL)       /* XXX doesn't update with changes to ambacc */
                        *crlp = ambcorral(hp, uv, ra[0]*ambacc, ra[1]*ambacc);
                if (pg != NULL) {       /* cap gradient if necessary */
                        d = pg[0]*pg[0]*ra[0]*ra[0] + pg[1]*pg[1]*ra[1]*ra[1];
                        if (d > 1.0) {
                                d = 1.0/sqrt(d);
                                pg[0] *= d;
                                pg[1] *= d;
                        }
                }
        }
        free(hp);                       /* clean up and return */
        return(1);
}
Revision:	2.92
Committed:	Fri Apr 5 01:10:26 2024 UTC (2 months, 1 week ago) by greg
Content type:	text/plain
Branch:	MAIN
Changes since 2.91:	+32 -18 lines
Log Message:	fix: Improved tracking of reflected vs. transmitted rays for antimatter