--- ray/src/rt/ambcomp.c	1991/06/11 16:37:49	1.4
+++ ray/src/rt/ambcomp.c	1991/10/22 12:15:41	1.15
@@ -60,21 +60,21 @@ 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  i;
 
-	if (rayorigin(&ar, r, AMBIENT, 0.5) < 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);
@@ -86,7 +86,7 @@ RAY  *r;
 	rayvalue(&ar);
 	ndims--;
 	addcolor(dp->v, ar.rcol);
-	if (ar.rt < FHUGE)
+	if (ar.rt > FTINY && ar.rt < FHUGE)
 		dp->r += 1.0/ar.rt;
 					/* (re)initialize error */
 	if (dp->n++) {
@@ -100,9 +100,10 @@ RAY  *r;
 
 
 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;
@@ -116,12 +117,12 @@ 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)
@@ -179,10 +180,27 @@ FVECT  pg, dg;
 			}
 			addcolor(acol, dp->v);
 		}
-		if (pg != NULL)
-			posgradient(pg, div, &hemi);
-		if (dg != NULL)
-			dirgradient(dg, div, &hemi);
+		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;
@@ -191,12 +209,16 @@ FVECT  pg, dg;
 		arad = FHUGE;
 	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 > maxarad)
 		arad = maxarad;
 	else if (arad < minarad)
 		arad = minarad;
-	arad /= sqrt(r->rweight);
-	return(arad);
+	return(arad/sqrt(wt));
 oopsy:
 	if (div != NULL)
 		free((char *)div);
@@ -204,14 +226,19 @@ oopsy:
 }
 
 
-inithemi(hp, r)			/* initialize sampling hemisphere */
+inithemi(hp, r, wt)		/* initialize sampling hemisphere */
 register AMBHEMI  *hp;
 RAY  *r;
+double  wt;
 {
 	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;
@@ -238,6 +265,11 @@ 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;
@@ -297,7 +329,7 @@ AMBHEMI  *hp;
 			if (i > 0) {
 				d = dp[-hp->np].r;
 				if (dp[0].r > d) d = dp[0].r;
-				d *= 1.0 - sqrt((double)i/hp->nt);
+				d *= 1.0 - (double)i/hp->nt;	/* cos(t)^2 */
 				mag0 += d*(b - bright(dp[-hp->np].v));
 			}
 			if (j > 0) {
@@ -321,7 +353,7 @@ AMBHEMI  *hp;
 		yd += mag0*sinp + mag1*cosp;
 	}
 	for (i = 0; i < 3; i++)
-		gv[i] = xd*hp->ux[i] + yd*hp->uy[i];
+		gv[i] = (xd*hp->ux[i] + yd*hp->uy[i])/PI;
 }
 
 
@@ -345,7 +377,7 @@ AMBHEMI  *hp;
 				error(CONSISTENCY,
 					"division order in dirgradient");
 #endif
-			mag += sqrt((i+.5)/hp->nt)*bright(dp->v);
+			mag += sqrt((i+.5)/hp->nt)*bright(dp->v);  /* sin(t) */
 			dp += hp->np;
 		}
 		phi = 2.0*PI * (j+.5)/hp->np + PI/2.0;
@@ -353,5 +385,5 @@ AMBHEMI  *hp;
 		yd += mag * sin(phi);
 	}
 	for (i = 0; i < 3; i++)
-		gv[i] = (xd*hp->ux[i] + yd*hp->uy[i])/(hp->nt*hp->np);
+		gv[i] = (xd*hp->ux[i] + yd*hp->uy[i])*PI/(hp->nt*hp->np);
 }