--- ray/src/rt/ambcomp.c	2014/05/09 22:53:11	2.57
+++ ray/src/rt/ambcomp.c	2014/05/17 00:49:17	2.60
@@ -1,5 +1,5 @@
 #ifndef lint
-static const char	RCSid[] = "$Id: ambcomp.c,v 2.57 2014/05/09 22:53:11 greg Exp $";
+static const char	RCSid[] = "$Id: ambcomp.c,v 2.60 2014/05/17 00:49:17 greg Exp $";
 #endif
 /*
  * Routines to compute "ambient" values using Monte Carlo
@@ -600,6 +600,9 @@ ambcorral(AMBHEMI *hp, FVECT uv[2], const double r0, c
 	const double	ang_step = ang_res/((int)(16/PI*ang_res) + (1+FTINY));
 	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 < 12)
@@ -617,10 +620,6 @@ ambcorral(AMBHEMI *hp, FVECT uv[2], const double r0, c
 	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);
-		FVECT	vec;
-		double	u, v;
-		double	ang, a1;
-		int	abp;
 		if ((ap->d <= FTINY) | (ap->d >= max_d))
 			continue;	/* too far or too near */
 		VSUB(vec, ap->p, hp->rp->rop);
@@ -632,6 +631,20 @@ ambcorral(AMBHEMI *hp, FVECT uv[2], const double r0, c
 		for (a1 = ang-.5*ang_res; a1 <= ang+.5*ang_res; a1 += ang_step)
 			flgs |= 1L<<(int)(16/PI*(a1 + 2.*PI*(a1 < 0)));
 	    }
+					/* add low-angle incident (< 20deg) */
+	if (fabs(hp->rp->rod) <= 0.342) {
+		u = -DOT(hp->rp->rdir, uv[0]);
+		v = -DOT(hp->rp->rdir, uv[1]);
+		if ((r0*r0*u*u + r1*r1*v*v) > hp->rp->rot*hp->rp->rot) {
+			ang = atan2a(v, u);
+			ang += 2.*PI*(ang < 0);
+			ang *= 16/PI;
+			if ((ang < .5) | (ang >= 31.5))
+				flgs |= 0x80000001;
+			else
+				flgs |= 3L<<(int)(ang-.5);
+		}
+	}
 	return(flgs);
 }
 
@@ -676,15 +689,10 @@ doambient(				/* compute ambient component */
 				addcolor(acol, ap->v);
 				++cnt;
 			}
-	if (!cnt) {
-		setcolor(rcol, 0.0, 0.0, 0.0);
-		free(hp);
-		return(0);		/* no valid samples */
-	}
-	if (cnt < hp->ns*hp->ns) {	/* incomplete sampling? */
+	if ((hp->ns < 4) | (cnt < hp->ns*hp->ns)) {
+		free(hp);		/* inadequate sampling */
 		copycolor(rcol, acol);
-		free(hp);
-		return(-1);		/* return value w/o Hessian */
+		return(-cnt);		/* value-only result */
 	}
 	cnt = ambssamp*wt + 0.5;	/* perform super-sampling? */
 	if (cnt > 8)
@@ -692,7 +700,7 @@ doambient(				/* compute ambient component */
 	copycolor(rcol, acol);		/* final indirect irradiance/PI */
 	if ((ra == NULL) & (pg == NULL) & (dg == NULL)) {
 		free(hp);
-		return(-1);		/* no radius or gradient calc. */
+		return(-1);		/* no Hessian or gradients requested */
 	}
 	if ((d = bright(acol)) > FTINY) {	/* normalize Y values */
 		d = 0.99*(hp->ns*hp->ns)/d;
@@ -729,7 +737,7 @@ doambient(				/* compute ambient component */
 			if (ra[1] < minarad)
 				ra[1] = minarad;
 		}
-		ra[0] *= d = 1.0/sqrt(sqrt(wt));
+		ra[0] *= d = 1.0/sqrt(wt);
 		if ((ra[1] *= d) > 2.0*ra[0])
 			ra[1] = 2.0*ra[0];
 		if (ra[1] > maxarad) {