--- ray/src/rt/ambcomp.c	1991/06/07 10:03:52	1.1
+++ ray/src/rt/ambcomp.c	1998/06/24 09:35:00	2.7
@@ -17,18 +17,17 @@ static char SCCSid[] = "$SunId$ LBL";
 typedef struct {
 	short  t, p;		/* theta, phi indices */
 	COLOR  v;		/* value sum */
-	float  k;		/* error contribution for this division */
+	float  r;		/* 1/distance sum */
+	float  k;		/* variance for this division */
 	int  n;			/* number of subsamples */
-}  AMBSAMP;		/* ambient division sample */
+}  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 */
 
-extern double  sin(), cos(), sqrt();
 
-
 static int
 ambcmp(d1, d2)				/* decreasing order */
 AMBSAMP  *d1, *d2;
@@ -53,39 +52,41 @@ AMBSAMP  *d1, *d2;
 }
 
 
-static double
 divsample(dp, h, r)			/* sample a division */
 register AMBSAMP  *dp;
 AMBHEMI  *h;
 RAY  *r;
 {
 	RAY  ar;
-	int  hlist[4];
+	int  hlist[3];
+	double  spt[2];
 	double  xd, yd, zd;
 	double  b2;
 	double  phi;
-	register int  k;
+	register int  i;
 
-	if (rayorigin(&ar, r, AMBIENT, 0.5) < 0)
-		return(0.0);
+	if (rayorigin(&ar, r, AMBIENT, AVGREFL) < 0)
+		return(-1);
 	hlist[0] = r->rno;
 	hlist[1] = dp->t;
 	hlist[2] = dp->p;
-	hlist[3] = 0;
-	zd = sqrt((dp->t+urand(ilhash(hlist,4)+dp->n))/h->nt);
-	hlist[3] = 1;
-	phi = 2.0*PI * (dp->p+urand(ilhash(hlist,4)+dp->n))/h->np;
+	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 (k = 0; k < 3; k++)
-		ar.rdir[k] =	xd*h->ux[k] +
-				yd*h->uy[k] +
-				zd*h->uz[k];
-	dimlist[ndims++] = dp->t*h->np + dp->p + 38813;
+	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);
@@ -93,14 +94,15 @@ RAY  *r;
 		dp->k = b2/(dp->n*dp->n);
 	} else
 		dp->k = 0.0;
-	return(ar.rot);
+	return(0);
 }
 
 
 double
-doambient(acol, r, pg, dg)		/* compute ambient component */
+doambient(acol, r, wt, pg, dg)		/* compute ambient component */
 COLOR  acol;
 RAY  *r;
+double  wt;
 FVECT  pg, dg;
 {
 	double  b, d;
@@ -114,12 +116,12 @@ FVECT  pg, dg;
 					/* initialize color */
 	setcolor(acol, 0.0, 0.0, 0.0);
 					/* initialize hemisphere */
-	inithemi(&hemi, r);
+	inithemi(&hemi, r, wt);
 	ndivs = hemi.nt * hemi.np;
 	if (ndivs == 0)
 		return(0.0);
 					/* set number of super-samples */
-	ns = ambssamp * r->rweight + 0.5;
+	ns = ambssamp * wt + 0.5;
 	if (ns > 0 || pg != NULL || dg != NULL) {
 		div = (AMBSAMP *)malloc(ndivs*sizeof(AMBSAMP));
 		if (div == NULL)
@@ -134,31 +136,26 @@ FVECT  pg, dg;
 		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 ((d = divsample(dp, &hemi, r)) == 0.0)
+			if (divsample(dp, &hemi, r) < 0)
 				goto oopsy;
-			if (d < FHUGE)
-				arad += 1.0 / d;
+			arad += dp->r;
 			if (div != NULL)
 				dp++;
 			else
 				addcolor(acol, dp->v);
 		}
-	if (ns > 0) {			/* perform super-sampling */
-		comperrs(div, hemi);			/* compute errors */
+	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 */
-		dp = div + ndivs;			/* skim excess */
-		for (i = ndivs; i > ns; i--) {
-			dp--;
-			addcolor(acol, dp->v);
-		}
 						/* super-sample */
 		for (i = ns; i > 0; i--) {
 			copystruct(&dnew, div);
-			if ((d = divsample(&dnew, &hemi)) == 0.0)
+			if (divsample(&dnew, &hemi, r) < 0)
 				goto oopsy;
-			if (d < FHUGE)
-				arad += 1.0 / d;
 							/* reinsert */
 			dp = div;
 			j = ndivs < i ? ndivs : i;
@@ -167,38 +164,67 @@ FVECT  pg, dg;
 				dp++;
 			}
 			copystruct(dp, &dnew);
-							/* extract darkest */
-			if (i <= ndivs) {
-				dp = div + i-1;
-				if (dp->n > 1) {
-					b = 1.0/dp->n;
-					scalecolor(dp->v, b);
-					dp->n = 1;
-				}
-				addcolor(acol, dp->v);
-			}
 		}
-		if (pg != NULL || dg != NULL)	/* reorder */
+		if (pg != NULL || dg != NULL)	/* restore order */
 			qsort(div, ndivs, sizeof(AMBSAMP), ambnorm);
 	}
 					/* compute returned values */
-	if (pg != NULL)
-		posgradient(pg, div, &hemi);
-	if (dg != NULL)
-		dirgradient(dg, div, &hemi);
-	if (div != NULL)
+	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 = FHUGE;
+		arad = maxarad;
 	else
 		arad = (ndivs+ns)/arad;
-	if (arad > maxarad)
-		arad = maxarad;
-	else if (arad < minarad)
+	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;
-	arad /= sqrt(r->rweight);
+		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)
@@ -207,31 +233,36 @@ oopsy:
 }
 
 
-inithemi(hp, r)			/* initialize sampling hemisphere */
+inithemi(hp, r, wt)		/* initialize sampling hemisphere */
 register AMBHEMI  *hp;
 RAY  *r;
+double  wt;
 {
-	register int  k;
+	register int  i;
 					/* set number of divisions */
-	hp->nt = sqrt(ambdiv * r->rweight * 0.5) + 0.5;
-	hp->np = 2 * hp->nt;
+	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 (k = 0; k < 3; k++)
-		if (hp->uz[k] < 0.6 && hp->uz[k] > -0.6)
+	for (i = 0; i < 3; i++)
+		if (hp->uz[i] < 0.6 && hp->uz[i] > -0.6)
 			break;
-	if (k >= 3)
+	if (i >= 3)
 		error(CONSISTENCY, "bad ray direction in inithemi");
-	hp->uy[k] = 1.0;
-	fcross(hp->ux, hp->uz, hp->uy);
+	hp->uy[i] = 1.0;
+	fcross(hp->ux, hp->uy, hp->uz);
 	normalize(hp->ux);
-	fcross(hp->uy, hp->ux, hp->uz);
+	fcross(hp->uy, hp->uz, hp->ux);
 }
 
 
 comperrs(da, hp)		/* compute initial error estimates */
-AMBSAMP  *da;
+AMBSAMP  *da;		/* assumes standard ordering */
 register AMBHEMI  *hp;
 {
 	double  b, b2;
@@ -241,6 +272,11 @@ register AMBHEMI  *hp;
 	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;
@@ -253,12 +289,11 @@ register AMBHEMI  *hp;
 				b2 *= b2 * 0.25;
 				dp[0].k += b2;
 				dp[-1].k += b2;
-			}
-			if (j == hp->np-1) {	/* around */
-				b2 = bright(dp[-(hp->np-1)].v) - b;
+			} 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[hp->np-1].k += b2;
 			}
 			dp++;
 		}
@@ -278,17 +313,88 @@ register AMBHEMI  *hp;
 
 posgradient(gv, da, hp)				/* compute position gradient */
 FVECT  gv;
-AMBSAMP  *da;
-AMBHEMI  *hp;
+AMBSAMP  *da;			/* assumes standard ordering */
+register AMBHEMI  *hp;
 {
-	gv[0] = 0.0; gv[1] = 0.0; gv[2] = 0.0;
+	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;
-AMBHEMI  *hp;
+AMBSAMP  *da;			/* assumes standard ordering */
+register AMBHEMI  *hp;
 {
-	gv[0] = 0.0; gv[1] = 0.0; gv[2] = 0.0;
+	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);
 }