src/rt/ambcomp.c

/* Copyright (c) 1991 Regents of the University of California */

#ifndef lint
static char SCCSid[] = "$SunId$ LBL";
#endif

/*
 * Routines to compute "ambient" values using Monte Carlo
 */

#include  "ray.h"

#include  "ambient.h"

#include  "random.h"

typedef struct {
        short  t, p;            /* theta, phi indices */
        COLOR  v;               /* value sum */
        float  r;               /* 1/distance sum */
        float  k;               /* variance for this division */
        int  n;                 /* number of subsamples */
}  AMBSAMP;             /* ambient sample division */

typedef struct {
        FVECT  ux, uy, uz;      /* x, y and z axis directions */
        short  nt, np;          /* number of theta and phi directions */
}  AMBHEMI;             /* ambient sample hemisphere */


static int
ambcmp(d1, d2)                          /* decreasing order */
AMBSAMP  *d1, *d2;
{
        if (d1->k < d2->k)
                return(1);
        if (d1->k > d2->k)
                return(-1);
        return(0);
}


static int
ambnorm(d1, d2)                         /* standard order */
AMBSAMP  *d1, *d2;
{
        register int  c;

        if (c = d1->t - d2->t)
                return(c);
        return(d1->p - d2->p);
}


divsample(dp, h, r)                     /* sample a division */
register AMBSAMP  *dp;
AMBHEMI  *h;
RAY  *r;
{
        RAY  ar;
        int  hlist[3];
        double  spt[2];
        double  xd, yd, zd;
        double  b2;
        double  phi;
        register int  i;

        if (rayorigin(&ar, r, AMBIENT, AVGREFL) < 0)
                return(-1);
        hlist[0] = r->rno;
        hlist[1] = dp->t;
        hlist[2] = dp->p;
        multisamp(spt, 2, urand(ilhash(hlist,3)+dp->n));
        zd = sqrt((dp->t + spt[0])/h->nt);
        phi = 2.0*PI * (dp->p + spt[1])/h->np;
        xd = cos(phi) * zd;
        yd = sin(phi) * zd;
        zd = sqrt(1.0 - zd*zd);
        for (i = 0; i < 3; i++)
                ar.rdir[i] =    xd*h->ux[i] +
                                yd*h->uy[i] +
                                zd*h->uz[i];
        dimlist[ndims++] = dp->t*h->np + dp->p + 90171;
        rayvalue(&ar);
        ndims--;
        addcolor(dp->v, ar.rcol);
                                        /* be conservative and use rot */
        if (ar.rot > FTINY && ar.rot < FHUGE)
                dp->r += 1.0/ar.rot;
                                        /* (re)initialize error */
        if (dp->n++) {
                b2 = bright(dp->v)/dp->n - bright(ar.rcol);
                b2 = b2*b2 + dp->k*((dp->n-1)*(dp->n-1));
                dp->k = b2/(dp->n*dp->n);
        } else
                dp->k = 0.0;
        return(0);
}


double
doambient(acol, r, wt, pg, dg)          /* compute ambient component */
COLOR  acol;
RAY  *r;
double  wt;
FVECT  pg, dg;
{
        double  b, d;
        AMBHEMI  hemi;
        AMBSAMP  *div;
        AMBSAMP  dnew;
        register AMBSAMP  *dp;
        double  arad;
        int  ndivs, ns;
        register int  i, j;
                                        /* initialize color */
        setcolor(acol, 0.0, 0.0, 0.0);
                                        /* initialize hemisphere */
        inithemi(&hemi, r, wt);
        ndivs = hemi.nt * hemi.np;
        if (ndivs == 0)
                return(0.0);
                                        /* set number of super-samples */
        ns = ambssamp * wt + 0.5;
        if (ns > 0 || pg != NULL || dg != NULL) {
                div = (AMBSAMP *)malloc(ndivs*sizeof(AMBSAMP));
                if (div == NULL)
                        error(SYSTEM, "out of memory in doambient");
        } else
                div = NULL;
                                        /* sample the divisions */
        arad = 0.0;
        if ((dp = div) == NULL)
                dp = &dnew;
        for (i = 0; i < hemi.nt; i++)
                for (j = 0; j < hemi.np; j++) {
                        dp->t = i; dp->p = j;
                        setcolor(dp->v, 0.0, 0.0, 0.0);
                        dp->r = 0.0;
                        dp->n = 0;
                        if (divsample(dp, &hemi, r) < 0)
                                goto oopsy;
                        arad += dp->r;
                        if (div != NULL)
                                dp++;
                        else
                                addcolor(acol, dp->v);
                }
        if (ns > 0 && arad > FTINY && ndivs/arad < minarad)
                ns = 0;                 /* close enough */
        else if (ns > 0) {              /* else perform super-sampling */
                comperrs(div, &hemi);                   /* compute errors */
                qsort(div, ndivs, sizeof(AMBSAMP), ambcmp);     /* sort divs */
                                                /* super-sample */
                for (i = ns; i > 0; i--) {
                        copystruct(&dnew, div);
                        if (divsample(&dnew, &hemi, r) < 0)
                                goto oopsy;
                                                        /* reinsert */
                        dp = div;
                        j = ndivs < i ? ndivs : i;
                        while (--j > 0 && dnew.k < dp[1].k) {
                                copystruct(dp, dp+1);
                                dp++;
                        }
                        copystruct(dp, &dnew);
                }
                if (pg != NULL || dg != NULL)   /* restore order */
                        qsort(div, ndivs, sizeof(AMBSAMP), ambnorm);
        }
                                        /* compute returned values */
        if (div != NULL) {
                arad = 0.0;
                for (i = ndivs, dp = div; i-- > 0; dp++) {
                        arad += dp->r;
                        if (dp->n > 1) {
                                b = 1.0/dp->n;
                                scalecolor(dp->v, b);
                                dp->r *= b;
                                dp->n = 1;
                        }
                        addcolor(acol, dp->v);
                }
                b = bright(acol);
                if (b > FTINY) {
                        b = ndivs/b;
                        if (pg != NULL) {
                                posgradient(pg, div, &hemi);
                                for (i = 0; i < 3; i++)
                                        pg[i] *= b;
                        }
                        if (dg != NULL) {
                                dirgradient(dg, div, &hemi);
                                for (i = 0; i < 3; i++)
                                        dg[i] *= b;
                        }
                } else {
                        if (pg != NULL)
                                for (i = 0; i < 3; i++)
                                        pg[i] = 0.0;
                        if (dg != NULL)
                                for (i = 0; i < 3; i++)
                                        dg[i] = 0.0;
                }
                free((char *)div);
        }
        b = 1.0/ndivs;
        scalecolor(acol, b);
        if (arad <= FTINY)
                arad = maxarad;
        else
                arad = (ndivs+ns)/arad;
        if (pg != NULL) {               /* reduce radius if gradient large */
                d = DOT(pg,pg);
                if (d*arad*arad > 1.0)
                        arad = 1.0/sqrt(d);
        }
        if (arad < minarad) {
                arad = minarad;
                if (pg != NULL && d*arad*arad > 1.0) {  /* cap gradient */
                        d = 1.0/arad/sqrt(d);
                        for (i = 0; i < 3; i++)
                                pg[i] *= d;
                }
        }
        if ((arad /= sqrt(wt)) > maxarad)
                arad = maxarad;
        return(arad);
oopsy:
        if (div != NULL)
                free((char *)div);
        return(0.0);
}


inithemi(hp, r, wt)             /* initialize sampling hemisphere */
register AMBHEMI  *hp;
RAY  *r;
double  wt;
{
        register int  i;
                                        /* set number of divisions */
        if (wt < (.25*PI)/ambdiv+FTINY) {
                hp->nt = hp->np = 0;
                return;                 /* zero samples */
        }
        hp->nt = sqrt(ambdiv * wt / PI) + 0.5;
        hp->np = PI * hp->nt + 0.5;
                                        /* make axes */
        VCOPY(hp->uz, r->ron);
        hp->uy[0] = hp->uy[1] = hp->uy[2] = 0.0;
        for (i = 0; i < 3; i++)
                if (hp->uz[i] < 0.6 && hp->uz[i] > -0.6)
                        break;
        if (i >= 3)
                error(CONSISTENCY, "bad ray direction in inithemi");
        hp->uy[i] = 1.0;
        fcross(hp->ux, hp->uy, hp->uz);
        normalize(hp->ux);
        fcross(hp->uy, hp->uz, hp->ux);
}


comperrs(da, hp)                /* compute initial error estimates */
AMBSAMP  *da;           /* assumes standard ordering */
register AMBHEMI  *hp;
{
        double  b, b2;
        int  i, j;
        register AMBSAMP  *dp;
                                /* sum differences from neighbors */
        dp = da;
        for (i = 0; i < hp->nt; i++)
                for (j = 0; j < hp->np; j++) {
#ifdef  DEBUG
                        if (dp->t != i || dp->p != j)
                                error(CONSISTENCY,
                                        "division order in comperrs");
#endif
                        b = bright(dp[0].v);
                        if (i > 0) {            /* from above */
                                b2 = bright(dp[-hp->np].v) - b;
                                b2 *= b2 * 0.25;
                                dp[0].k += b2;
                                dp[-hp->np].k += b2;
                        }
                        if (j > 0) {            /* from behind */
                                b2 = bright(dp[-1].v) - b;
                                b2 *= b2 * 0.25;
                                dp[0].k += b2;
                                dp[-1].k += b2;
                        } else {                /* around */
                                b2 = bright(dp[hp->np-1].v) - b;
                                b2 *= b2 * 0.25;
                                dp[0].k += b2;
                                dp[hp->np-1].k += b2;
                        }
                        dp++;
                }
                                /* divide by number of neighbors */
        dp = da;
        for (j = 0; j < hp->np; j++)            /* top row */
                (dp++)->k *= 1.0/3.0;
        if (hp->nt < 2)
                return;
        for (i = 1; i < hp->nt-1; i++)          /* central region */
                for (j = 0; j < hp->np; j++)
                        (dp++)->k *= 0.25;
        for (j = 0; j < hp->np; j++)            /* bottom row */
                (dp++)->k *= 1.0/3.0;
}


posgradient(gv, da, hp)                         /* compute position gradient */
FVECT  gv;
AMBSAMP  *da;                   /* assumes standard ordering */
register AMBHEMI  *hp;
{
        register int  i, j;
        double  nextsine, lastsine, b, d;
        double  mag0, mag1;
        double  phi, cosp, sinp, xd, yd;
        register AMBSAMP  *dp;

        xd = yd = 0.0;
        for (j = 0; j < hp->np; j++) {
                dp = da + j;
                mag0 = mag1 = 0.0;
                lastsine = 0.0;
                for (i = 0; i < hp->nt; i++) {
#ifdef  DEBUG
                        if (dp->t != i || dp->p != j)
                                error(CONSISTENCY,
                                        "division order in posgradient");
#endif
                        b = bright(dp->v);
                        if (i > 0) {
                                d = dp[-hp->np].r;
                                if (dp[0].r > d) d = dp[0].r;
                                                        /* sin(t)*cos(t)^2 */
                                d *= lastsine * (1.0 - (double)i/hp->nt);
                                mag0 += d*(b - bright(dp[-hp->np].v));
                        }
                        nextsine = sqrt((double)(i+1)/hp->nt);
                        if (j > 0) {
                                d = dp[-1].r;
                                if (dp[0].r > d) d = dp[0].r;
                                mag1 += d * (nextsine - lastsine) *
                                                (b - bright(dp[-1].v));
                        } else {
                                d = dp[hp->np-1].r;
                                if (dp[0].r > d) d = dp[0].r;
                                mag1 += d * (nextsine - lastsine) *
                                                (b - bright(dp[hp->np-1].v));
                        }
                        dp += hp->np;
                        lastsine = nextsine;
                }
                mag0 *= 2.0*PI / hp->np;
                phi = 2.0*PI * (double)j/hp->np;
                cosp = cos(phi); sinp = sin(phi);
                xd += mag0*cosp - mag1*sinp;
                yd += mag0*sinp + mag1*cosp;
        }
        for (i = 0; i < 3; i++)
                gv[i] = (xd*hp->ux[i] + yd*hp->uy[i])/PI;
}


dirgradient(gv, da, hp)                         /* compute direction gradient */
FVECT  gv;
AMBSAMP  *da;                   /* assumes standard ordering */
register AMBHEMI  *hp;
{
        register int  i, j;
        double  mag;
        double  phi, xd, yd;
        register AMBSAMP  *dp;

        xd = yd = 0.0;
        for (j = 0; j < hp->np; j++) {
                dp = da + j;
                mag = 0.0;
                for (i = 0; i < hp->nt; i++) {
#ifdef  DEBUG
                        if (dp->t != i || dp->p != j)
                                error(CONSISTENCY,
                                        "division order in dirgradient");
#endif
                                                        /* tan(t) */
                        mag += bright(dp->v)/sqrt(hp->nt/(i+.5) - 1.0);
                        dp += hp->np;
                }
                phi = 2.0*PI * (j+.5)/hp->np + PI/2.0;
                xd += mag * cos(phi);
                yd += mag * sin(phi);
        }
        for (i = 0; i < 3; i++)
                gv[i] = (xd*hp->ux[i] + yd*hp->uy[i])/(hp->nt*hp->np);
}
Revision:	2.7
Committed:	Wed Jun 24 09:35:00 1998 UTC (25 years, 10 months ago) by gwlarson
Content type:	text/plain
Branch:	MAIN
Changes since 2.6:	+3 -2 lines
Log Message:	changed from using effective ray distance to object distance in divsample()
#	User	Rev	Content
1	greg	1.1	/* Copyright (c) 1991 Regents of the University of California */
2
3			#ifndef lint
4			static char SCCSid[] = "$SunId$ LBL";
5			#endif
6
7			/*
8			* Routines to compute "ambient" values using Monte Carlo
9			*/
10
11			#include "ray.h"
12
13			#include "ambient.h"
14
15			#include "random.h"
16
17			typedef struct {
18			short t, p; /* theta, phi indices */
19			COLOR v; /* value sum */
20	greg	1.2	float r; /* 1/distance sum */
21			float k; /* variance for this division */
22	greg	1.1	int n; /* number of subsamples */
23	greg	1.2	} AMBSAMP; /* ambient sample division */
24	greg	1.1
25			typedef struct {
26			FVECT ux, uy, uz; /* x, y and z axis directions */
27			short nt, np; /* number of theta and phi directions */
28			} AMBHEMI; /* ambient sample hemisphere */
29
30
31			static int
32			ambcmp(d1, d2) /* decreasing order */
33			AMBSAMP d1, d2;
34			{
35			if (d1->k < d2->k)
36			return(1);
37			if (d1->k > d2->k)
38			return(-1);
39			return(0);
40			}
41
42
43			static int
44			ambnorm(d1, d2) /* standard order */
45			AMBSAMP d1, d2;
46			{
47			register int c;
48
49			if (c = d1->t - d2->t)
50			return(c);
51			return(d1->p - d2->p);
52			}
53
54
55			divsample(dp, h, r) /* sample a division */
56			register AMBSAMP *dp;
57			AMBHEMI *h;
58			RAY *r;
59			{
60			RAY ar;
61	greg	1.11	int hlist[3];
62			double spt[2];
63	greg	1.1	double xd, yd, zd;
64			double b2;
65			double phi;
66	greg	1.2	register int i;
67	greg	1.1
68	greg	1.12	if (rayorigin(&ar, r, AMBIENT, AVGREFL) < 0)
69	greg	1.4	return(-1);
70	greg	1.1	hlist[0] = r->rno;
71			hlist[1] = dp->t;
72			hlist[2] = dp->p;
73	greg	1.13	multisamp(spt, 2, urand(ilhash(hlist,3)+dp->n));
74	greg	1.11	zd = sqrt((dp->t + spt[0])/h->nt);
75			phi = 2.0PI (dp->p + spt[1])/h->np;
76	greg	1.1	xd = cos(phi) * zd;
77			yd = sin(phi) * zd;
78			zd = sqrt(1.0 - zd*zd);
79	greg	1.2	for (i = 0; i < 3; i++)
80			ar.rdir[i] = xd*h->ux[i] +
81			yd*h->uy[i] +
82			zd*h->uz[i];
83			dimlist[ndims++] = dp->t*h->np + dp->p + 90171;
84	greg	1.1	rayvalue(&ar);
85			ndims--;
86			addcolor(dp->v, ar.rcol);
87	gwlarson	2.7	/* be conservative and use rot */
88			if (ar.rot > FTINY && ar.rot < FHUGE)
89			dp->r += 1.0/ar.rot;
90	greg	1.1	/* (re)initialize error */
91			if (dp->n++) {
92			b2 = bright(dp->v)/dp->n - bright(ar.rcol);
93			b2 = b2b2 + dp->k((dp->n-1)*(dp->n-1));
94			dp->k = b2/(dp->n*dp->n);
95			} else
96			dp->k = 0.0;
97	greg	1.4	return(0);
98	greg	1.1	}
99
100
101			double
102	greg	1.12	doambient(acol, r, wt, pg, dg) /* compute ambient component */
103	greg	1.1	COLOR acol;
104			RAY *r;
105	greg	1.12	double wt;
106	greg	1.1	FVECT pg, dg;
107			{
108			double b, d;
109			AMBHEMI hemi;
110			AMBSAMP *div;
111			AMBSAMP dnew;
112			register AMBSAMP *dp;
113			double arad;
114			int ndivs, ns;
115			register int i, j;
116			/* initialize color */
117			setcolor(acol, 0.0, 0.0, 0.0);
118			/* initialize hemisphere */
119	greg	1.12	inithemi(&hemi, r, wt);
120	greg	1.1	ndivs = hemi.nt * hemi.np;
121			if (ndivs == 0)
122			return(0.0);
123			/* set number of super-samples */
124	greg	1.12	ns = ambssamp * wt + 0.5;
125	greg	1.1	if (ns > 0 \|\| pg != NULL \|\| dg != NULL) {
126			div = (AMBSAMP )malloc(ndivssizeof(AMBSAMP));
127			if (div == NULL)
128			error(SYSTEM, "out of memory in doambient");
129			} else
130			div = NULL;
131			/* sample the divisions */
132			arad = 0.0;
133			if ((dp = div) == NULL)
134			dp = &dnew;
135			for (i = 0; i < hemi.nt; i++)
136			for (j = 0; j < hemi.np; j++) {
137			dp->t = i; dp->p = j;
138			setcolor(dp->v, 0.0, 0.0, 0.0);
139	greg	1.2	dp->r = 0.0;
140	greg	1.1	dp->n = 0;
141	greg	1.4	if (divsample(dp, &hemi, r) < 0)
142	greg	1.1	goto oopsy;
143	greg	2.6	arad += dp->r;
144	greg	1.1	if (div != NULL)
145			dp++;
146	greg	2.6	else
147	greg	1.1	addcolor(acol, dp->v);
148			}
149	greg	2.5	if (ns > 0 && arad > FTINY && ndivs/arad < minarad)
150			ns = 0; /* close enough */
151			else if (ns > 0) { /* else perform super-sampling */
152	greg	1.4	comperrs(div, &hemi); /* compute errors */
153	greg	1.1	qsort(div, ndivs, sizeof(AMBSAMP), ambcmp); /* sort divs */
154			/* super-sample */
155			for (i = ns; i > 0; i--) {
156			copystruct(&dnew, div);
157	greg	1.4	if (divsample(&dnew, &hemi, r) < 0)
158	greg	1.1	goto oopsy;
159			/* reinsert */
160			dp = div;
161			j = ndivs < i ? ndivs : i;
162			while (--j > 0 && dnew.k < dp[1].k) {
163			copystruct(dp, dp+1);
164			dp++;
165			}
166			copystruct(dp, &dnew);
167			}
168	greg	1.2	if (pg != NULL \|\| dg != NULL) /* restore order */
169	greg	1.1	qsort(div, ndivs, sizeof(AMBSAMP), ambnorm);
170			}
171			/* compute returned values */
172	greg	1.3	if (div != NULL) {
173	greg	2.6	arad = 0.0;
174	greg	1.3	for (i = ndivs, dp = div; i-- > 0; dp++) {
175			arad += dp->r;
176			if (dp->n > 1) {
177			b = 1.0/dp->n;
178			scalecolor(dp->v, b);
179			dp->r *= b;
180			dp->n = 1;
181			}
182			addcolor(acol, dp->v);
183			}
184	greg	1.5	b = bright(acol);
185	greg	1.6	if (b > FTINY) {
186	greg	1.5	b = ndivs/b;
187	greg	1.6	if (pg != NULL) {
188			posgradient(pg, div, &hemi);
189			for (i = 0; i < 3; i++)
190			pg[i] *= b;
191			}
192			if (dg != NULL) {
193			dirgradient(dg, div, &hemi);
194			for (i = 0; i < 3; i++)
195			dg[i] *= b;
196			}
197			} else {
198			if (pg != NULL)
199			for (i = 0; i < 3; i++)
200			pg[i] = 0.0;
201			if (dg != NULL)
202			for (i = 0; i < 3; i++)
203			dg[i] = 0.0;
204	greg	1.5	}
205	greg	1.1	free((char *)div);
206	greg	1.3	}
207	greg	1.1	b = 1.0/ndivs;
208			scalecolor(acol, b);
209			if (arad <= FTINY)
210	greg	1.16	arad = maxarad;
211	greg	2.3	else
212	greg	1.1	arad = (ndivs+ns)/arad;
213	greg	1.15	if (pg != NULL) { /* reduce radius if gradient large */
214			d = DOT(pg,pg);
215			if (daradarad > 1.0)
216			arad = 1.0/sqrt(d);
217			}
218	greg	1.16	if (arad < minarad) {
219	greg	1.1	arad = minarad;
220	greg	1.16	if (pg != NULL && daradarad > 1.0) { /* cap gradient */
221			d = 1.0/arad/sqrt(d);
222			for (i = 0; i < 3; i++)
223			pg[i] *= d;
224			}
225			}
226	greg	2.3	if ((arad /= sqrt(wt)) > maxarad)
227			arad = maxarad;
228			return(arad);
229	greg	1.1	oopsy:
230			if (div != NULL)
231			free((char *)div);
232			return(0.0);
233			}
234
235
236	greg	1.12	inithemi(hp, r, wt) /* initialize sampling hemisphere */
237	greg	1.1	register AMBHEMI *hp;
238			RAY *r;
239	greg	1.12	double wt;
240	greg	1.1	{
241	greg	1.2	register int i;
242	greg	1.1	/* set number of divisions */
243	greg	1.14	if (wt < (.25*PI)/ambdiv+FTINY) {
244			hp->nt = hp->np = 0;
245			return; /* zero samples */
246			}
247	greg	1.12	hp->nt = sqrt(ambdiv * wt / PI) + 0.5;
248	greg	1.14	hp->np = PI * hp->nt + 0.5;
249	greg	1.1	/* make axes */
250			VCOPY(hp->uz, r->ron);
251			hp->uy[0] = hp->uy[1] = hp->uy[2] = 0.0;
252	greg	1.2	for (i = 0; i < 3; i++)
253			if (hp->uz[i] < 0.6 && hp->uz[i] > -0.6)
254	greg	1.1	break;
255	greg	1.2	if (i >= 3)
256	greg	1.1	error(CONSISTENCY, "bad ray direction in inithemi");
257	greg	1.2	hp->uy[i] = 1.0;
258	greg	1.3	fcross(hp->ux, hp->uy, hp->uz);
259			normalize(hp->ux);
260			fcross(hp->uy, hp->uz, hp->ux);
261	greg	1.1	}
262
263
264			comperrs(da, hp) /* compute initial error estimates */
265	greg	1.2	AMBSAMP da; / assumes standard ordering */
266	greg	1.1	register AMBHEMI *hp;
267			{
268			double b, b2;
269			int i, j;
270			register AMBSAMP *dp;
271			/* sum differences from neighbors */
272			dp = da;
273			for (i = 0; i < hp->nt; i++)
274			for (j = 0; j < hp->np; j++) {
275	greg	1.6	#ifdef DEBUG
276			if (dp->t != i \|\| dp->p != j)
277			error(CONSISTENCY,
278			"division order in comperrs");
279			#endif
280	greg	1.1	b = bright(dp[0].v);
281			if (i > 0) { /* from above */
282			b2 = bright(dp[-hp->np].v) - b;
283			b2 = b2 0.25;
284			dp[0].k += b2;
285			dp[-hp->np].k += b2;
286			}
287			if (j > 0) { /* from behind */
288			b2 = bright(dp[-1].v) - b;
289			b2 = b2 0.25;
290			dp[0].k += b2;
291			dp[-1].k += b2;
292	greg	1.4	} else { /* around */
293			b2 = bright(dp[hp->np-1].v) - b;
294	greg	1.1	b2 = b2 0.25;
295			dp[0].k += b2;
296	greg	1.4	dp[hp->np-1].k += b2;
297	greg	1.1	}
298			dp++;
299			}
300			/* divide by number of neighbors */
301			dp = da;
302			for (j = 0; j < hp->np; j++) /* top row */
303			(dp++)->k *= 1.0/3.0;
304			if (hp->nt < 2)
305			return;
306			for (i = 1; i < hp->nt-1; i++) /* central region */
307			for (j = 0; j < hp->np; j++)
308			(dp++)->k *= 0.25;
309			for (j = 0; j < hp->np; j++) /* bottom row */
310			(dp++)->k *= 1.0/3.0;
311			}
312
313
314			posgradient(gv, da, hp) /* compute position gradient */
315			FVECT gv;
316	greg	1.2	AMBSAMP da; / assumes standard ordering */
317	greg	2.2	register AMBHEMI *hp;
318	greg	1.1	{
319	greg	1.2	register int i, j;
320	greg	2.2	double nextsine, lastsine, b, d;
321	greg	1.2	double mag0, mag1;
322			double phi, cosp, sinp, xd, yd;
323			register AMBSAMP *dp;
324
325			xd = yd = 0.0;
326			for (j = 0; j < hp->np; j++) {
327			dp = da + j;
328			mag0 = mag1 = 0.0;
329	greg	2.2	lastsine = 0.0;
330	greg	1.2	for (i = 0; i < hp->nt; i++) {
331			#ifdef DEBUG
332			if (dp->t != i \|\| dp->p != j)
333			error(CONSISTENCY,
334			"division order in posgradient");
335			#endif
336			b = bright(dp->v);
337			if (i > 0) {
338			d = dp[-hp->np].r;
339			if (dp[0].r > d) d = dp[0].r;
340	greg	2.2	/* sin(t)cos(t)^2 /
341			d = lastsine (1.0 - (double)i/hp->nt);
342	greg	1.2	mag0 += d*(b - bright(dp[-hp->np].v));
343			}
344	greg	2.2	nextsine = sqrt((double)(i+1)/hp->nt);
345	greg	1.2	if (j > 0) {
346			d = dp[-1].r;
347			if (dp[0].r > d) d = dp[0].r;
348	greg	2.2	mag1 += d * (nextsine - lastsine) *
349			(b - bright(dp[-1].v));
350	greg	1.2	} else {
351			d = dp[hp->np-1].r;
352			if (dp[0].r > d) d = dp[0].r;
353	greg	2.2	mag1 += d * (nextsine - lastsine) *
354			(b - bright(dp[hp->np-1].v));
355	greg	1.2	}
356			dp += hp->np;
357	greg	2.2	lastsine = nextsine;
358	greg	1.2	}
359	greg	2.2	mag0 = 2.0PI / hp->np;
360	greg	1.2	phi = 2.0PI (double)j/hp->np;
361			cosp = cos(phi); sinp = sin(phi);
362			xd += mag0cosp - mag1sinp;
363			yd += mag0sinp + mag1cosp;
364			}
365			for (i = 0; i < 3; i++)
366	greg	1.5	gv[i] = (xdhp->ux[i] + ydhp->uy[i])/PI;
367	greg	1.1	}
368
369
370			dirgradient(gv, da, hp) /* compute direction gradient */
371			FVECT gv;
372	greg	1.2	AMBSAMP da; / assumes standard ordering */
373	greg	2.2	register AMBHEMI *hp;
374	greg	1.1	{
375	greg	1.2	register int i, j;
376			double mag;
377			double phi, xd, yd;
378			register AMBSAMP *dp;
379
380			xd = yd = 0.0;
381			for (j = 0; j < hp->np; j++) {
382			dp = da + j;
383			mag = 0.0;
384			for (i = 0; i < hp->nt; i++) {
385			#ifdef DEBUG
386			if (dp->t != i \|\| dp->p != j)
387			error(CONSISTENCY,
388			"division order in dirgradient");
389			#endif
390	greg	2.2	/* tan(t) */
391			mag += bright(dp->v)/sqrt(hp->nt/(i+.5) - 1.0);
392	greg	1.2	dp += hp->np;
393			}
394			phi = 2.0PI (j+.5)/hp->np + PI/2.0;
395			xd += mag * cos(phi);
396			yd += mag * sin(phi);
397			}
398			for (i = 0; i < 3; i++)
399	greg	2.2	gv[i] = (xdhp->ux[i] + ydhp->uy[i])/(hp->nt*hp->np);
400	greg	1.1	}