--- ray/src/rt/ambient.c	2014/04/11 22:54:34	2.72
+++ ray/src/rt/ambient.c	2014/04/25 23:04:16	2.81
@@ -1,5 +1,5 @@
 #ifndef lint
-static const char	RCSid[] = "$Id: ambient.c,v 2.72 2014/04/11 22:54:34 greg Exp $";
+static const char	RCSid[] = "$Id: ambient.c,v 2.81 2014/04/25 23:04:16 greg Exp $";
 #endif
 /*
  *  ambient.c - routines dealing with ambient (inter-reflected) component.
@@ -51,6 +51,8 @@ static int  nunflshed = 0;	/* number of unflushed ambi
 #define MAX_SORT_INTVL	(SORT_INTVL<<6)
 #endif
 
+
+static double  qambacc = 0.;		/* ambient accuracy to the 1/4 power */
 static double  avsum = 0.;		/* computed ambient value sum (log) */
 static unsigned int  navsum = 0;	/* number of values in avsum */
 static unsigned int  nambvals = 0;	/* total number of indirect values */
@@ -132,8 +134,11 @@ setambacc(				/* set ambient accuracy */
 	if (newa < 0.0)
 		newa = 0.0;
 	ambdiff = fabs(newa - ambacc);
-	if (ambdiff >= .01 && (ambacc = newa) > FTINY && nambvals > 0)
-		sortambvals(1);			/* rebuild tree */
+	if (ambdiff >= .01 && (ambacc = newa) > FTINY) {
+		qambacc = sqrt(sqrt(ambacc));
+		if (nambvals > 0)
+			sortambvals(1);		/* rebuild tree */
+	}
 }
 
 
@@ -147,7 +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) {
@@ -320,7 +325,7 @@ multambient(		/* compute ambient component & multiply 
 	ok = makeambient(acol, r, nrm, rdepth-1);
 	rdepth--;
 	if (ok) {
-		multcolor(aval, acol);		/* got new value */
+		multcolor(aval, acol);		/* computed new value */
 		return;
 	}
 dumbamb:					/* return global value */
@@ -352,8 +357,10 @@ sumambient(		/* get interpolated ambient value */
 	FVECT  c0,
 	double	s
 )
-{					/* initial limit is ambacc radians */
-	const double	maxangle = (ambacc-PI/2.)*pow(r->rweight,0.13) + PI/2.;
+{			/* initial limit is 10 degrees plus ambacc radians */
+	const double	minangle = 10.0 * PI/180.;
+	const double	maxangle = (minangle+ambacc-PI/2.)*pow(r->rweight,0.13)
+					+ PI/2.;
 	double		wsum = 0.0;
 	FVECT		ck0;
 	int		i, j;
@@ -384,31 +391,33 @@ sumambient(		/* get interpolated ambient value */
 		if (delta_r2 >= maxangle*maxangle)
 			continue;
 		/*
+		 *  Modified ray behind test
+		 */
+		VSUB(ck0, av->pos, r->rop);
+		d = DOT(ck0, uvw[2]);
+		if (d < -minarad*qambacc-.001)
+			continue;
+		d /= av->rad[0];
+		delta_t2 = d*d;
+		if (delta_t2 >= qambacc*qambacc)
+			continue;
+		/*
 		 *  Elliptical radii test based on Hessian
 		 */
 		decodedir(uvw[0], av->udir);
 		VCROSS(uvw[1], uvw[2], uvw[0]);
-		VSUB(ck0, av->pos, r->rop);
 		d = DOT(ck0, uvw[0]) / av->rad[0];
-		delta_t2 = d*d;
+		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
-		 */
-		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)
-			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;
@@ -454,11 +463,10 @@ makeambient(		/* make a new ambient value for storage 
 		amb.weight = 1.25*r->rweight;
 	setcolor(acol, AVGREFL, AVGREFL, AVGREFL);
 						/* compute ambient */
-	if (!doambient(acol, r, amb.weight, uvw, amb.rad, amb.gpos, amb.gdir)) {
-		setcolor(acol, 0.0, 0.0, 0.0);
-		return(0);
-	}
+	i = doambient(acol, r, amb.weight, uvw, amb.rad, amb.gpos, amb.gdir);
 	scalecolor(acol, 1./AVGREFL);		/* undo assumed reflectance */
+	if (i <= 0 || amb.rad[0] <= FTINY)	/* no Hessian or zero radius */
+		return(i);
 						/* store value */
 	VCOPY(amb.pos, r->rop);
 	amb.ndir = encodedir(r->ron);
@@ -530,7 +538,7 @@ avinsert(				/* insert ambient value in our tree */
 	at = &atrunk;
 	VCOPY(ck0, thescene.cuorg);
 	s = thescene.cusize;
-	while (s*(OCTSCALE/2) > av->rad[1]*ambacc) {
+	while (s*(OCTSCALE/2) > av->rad[1]*qambacc) {
 		if (at->kid == NULL)
 			if ((at->kid = newambtree()) == NULL)
 				error(SYSTEM, "out of memory in avinsert");