--- ray/src/rt/ambient.c	2014/04/19 02:39:44	2.74
+++ ray/src/rt/ambient.c	2014/04/24 19:16:52	2.78
@@ -1,5 +1,5 @@
 #ifndef lint
-static const char	RCSid[] = "$Id: ambient.c,v 2.74 2014/04/19 02:39:44 greg Exp $";
+static const char	RCSid[] = "$Id: ambient.c,v 2.78 2014/04/24 19:16:52 greg Exp $";
 #endif
 /*
  *  ambient.c - routines dealing with ambient (inter-reflected) component.
@@ -152,7 +152,7 @@ setambient(void)				/* initialize calculation */
 	ambdone();
 						/* init ambient limits */
 	setambres(ambres);
-	setambacc(ambacc);
+	qambacc = sqrt(sqrt(ambacc *= (ambacc > FTINY)));
 	if (ambfile == NULL || !ambfile[0])
 		return;
 	if (ambacc <= FTINY) {
@@ -398,7 +398,7 @@ sumambient(		/* get interpolated ambient value */
 		delta_t2 = d*d;
 		d = DOT(ck0, uvw[1]) / av->rad[1];
 		delta_t2 += d*d;
-		if (delta_t2 >= ambacc*ambacc)
+		if (delta_t2 >= qambacc*qambacc)
 			continue;
 		/*
 		 *  Intersection behind test
@@ -406,14 +406,14 @@ sumambient(		/* get interpolated ambient value */
 		d = 0.0;
 		for (j = 0; j < 3; j++)
 			d += (r->rop[j] - av->pos[j])*(uvw[2][j] + r->ron[j]);
-		if (d*0.5 < -minarad*ambacc-.001)
+		if (d*0.5 < -minarad*qambacc-.001)
 			continue;
 		/*
 		 *  Extrapolate value and compute final weight (hat function)
 		 */
 		extambient(ct, av, r->rop, rn, uvw);
 		d = tfunc(maxangle, sqrt(delta_r2), 0.0) *
-			tfunc(ambacc, sqrt(delta_t2), 0.0);
+			tfunc(qambacc, sqrt(delta_t2), 0.0);
 		scalecolor(ct, d);
 		addcolor(acol, ct);
 		wsum += d;
@@ -461,7 +461,7 @@ makeambient(		/* make a new ambient value for storage 
 						/* compute ambient */
 	i = doambient(acol, r, amb.weight, uvw, amb.rad, amb.gpos, amb.gdir);
 	scalecolor(acol, 1./AVGREFL);		/* undo assumed reflectance */
-	if (i <= 0)				/* no Hessian => no storage */
+	if (i <= 0 || amb.rad[0] <= FTINY)	/* no Hessian or zero radius */
 		return(i);
 						/* store value */
 	VCOPY(amb.pos, r->rop);