--- ray/src/util/glarendx.c	1991/04/18 15:18:20	1.4
+++ ray/src/util/glarendx.c	1991/04/29 08:31:23	1.7
@@ -134,7 +134,7 @@ char	*s;
 		sscanview(&midview, s+VIEWSTRL);
 	else if (isformat(s)) {
 		formatval(fmt, s);
-		wrongformat = strcmp(fmt, "ASCII");
+		wrongformat = strcmp(fmt, "ascii");
 	}
 }
 
@@ -239,6 +239,7 @@ struct glare_dir	*gd;
  * All vectors are assumed to be normalized.
  * This function is an implementation of the method proposed by
  * Robert Levin in his 1975 JIES article.
+ * This calculation presumes the view direction and up vectors perpendicular.
  * We return a value less than zero for improper positions.
  */
 
@@ -252,8 +253,14 @@ FVECT	sd, vd, vu;
 	d = DOT(sd,vd);
 	if (d <= 0.0)
 		return(-1.0);
+	if (d >= 1.0)
+		return(1.0);
 	sigma = acos(d) * (180./PI);
-	tau = acos(DOT(sd,vu)/sqrt(1.0-d*d)) * (180./PI);
+	d = DOT(sd,vu)/sqrt(1.0-d*d);
+	if (d >= 1.0)
+		tau = 0.0;
+	else
+		tau = acos(d) * (180./PI);
 	return( exp( sigma*( (35.2 - tau*.31889 - 1.22*exp(-.22222*tau))*1e-3
 			+ sigma*(21. + tau*(.26667 + tau*-.002963))*1e-5 )
 		) );
@@ -266,14 +273,16 @@ struct glare_dir	*gd;
 {
 #define q(w)	(20.4*w+1.52*pow(w,.2)-.075)
 	register struct glare_src	*gs;
+	FVECT	mydir;
 	double	p;
 	double	sum;
 	double	wtot, brsum;
 	int	n;
 
+	spinvector(mydir, midview.vdir, midview.vup, gd->ang);
 	sum = wtot = brsum = 0.0; n = 0;
 	for (gs = all_srcs; gs != NULL; gs = gs->next) {
-		p = posindex(gs->dir, midview.vdir, midview.vup);
+		p = posindex(gs->dir, mydir, midview.vup);
 		if (p <= FTINY)
 			continue;
 		sum += gs->lum * q(gs->dom) / p;
@@ -304,5 +313,10 @@ double
 guth_vcp(gd)		/* compute Guth visual comfort probability */
 struct glare_dir	*gd;
 {
-	return(100.*norm_integral(6.374-1.3227*log(guth_dgr(gd))));
+	double	dgr;
+
+	dgr = guth_dgr(gd);
+	if (dgr <= FTINY)
+		return(100.0);
+	return(100.*norm_integral(6.374-1.3227*log(dgr)));
 }