--- ray/src/rt/glass.c	1989/02/02 10:41:24	1.1
+++ ray/src/rt/glass.c	1991/10/29 16:30:46	1.11
@@ -1,4 +1,4 @@
-/* Copyright (c) 1986 Regents of the University of California */
+/* Copyright (c) 1991 Regents of the University of California */
 
 #ifndef lint
 static char SCCSid[] = "$SunId$ LBL";
@@ -49,7 +49,8 @@ register RAY  *r;
 	FVECT  pnorm;
 	double  cos2;
 	COLOR  trans, refl;
-	double  d, r1;
+	double  d, r1e, r1m;
+	double  transtest, transdist;
 	RAY  p;
 	register int  i;
 
@@ -60,6 +61,7 @@ register RAY  *r;
 
 	if (r->rod < 0.0)			/* reorient if necessary */
 		flipsurface(r);
+	transtest = 0;
 						/* get modifiers */
 	raytexture(r, m->omod);
 	pdot = raynormal(pnorm, r);
@@ -71,36 +73,52 @@ register RAY  *r;
 			 pow(colval(mcolor,BLU), 1.0/cos2));
 
 						/* compute reflection */
-	r1 = (pdot - RINDEX*cos2) / (pdot + RINDEX*cos2);
-	d = (1.0/pdot - RINDEX/cos2) / (1.0/pdot + RINDEX/cos2);
-	r1 = (r1*r1 + d*d) / 2.0;
+	r1e = (pdot - RINDEX*cos2) / (pdot + RINDEX*cos2);
+	r1e *= r1e;
+	r1m = (1.0/pdot - RINDEX/cos2) / (1.0/pdot + RINDEX/cos2);
+	r1m *= r1m;
 						/* compute transmittance */
 	for (i = 0; i < 3; i++) {
 		d = colval(mcolor, i);
-		colval(trans,i) = (1.0-r1)*(1.0-r1)*d / (1.0 - r1*r1*d*d);
+		colval(trans,i) = .5*(1.0-r1e)*(1.0-r1e)*d/(1.0-r1e*r1e*d*d);
+		colval(trans,i) += .5*(1.0-r1m)*(1.0-r1m)*d/(1.0-r1m*r1m*d*d);
 	}
 						/* transmitted ray */
-	if (rayorigin(&p, r, TRANS, intens(trans)) == 0) {
-		VCOPY(p.rdir, r->rdir);
+	if (rayorigin(&p, r, TRANS, bright(trans)) == 0) {
+		if (!(r->crtype & SHADOW) &&
+				DOT(r->pert,r->pert) > FTINY*FTINY) {
+			for (i = 0; i < 3; i++)		/* perturb direction */
+				p.rdir[i] = r->rdir[i] - r->pert[i]/RINDEX;
+			normalize(p.rdir);
+		} else {
+			VCOPY(p.rdir, r->rdir);
+			transtest = 2;
+		}
 		rayvalue(&p);
 		multcolor(p.rcol, r->pcol);	/* modify */
 		multcolor(p.rcol, trans);
 		addcolor(r->rcol, p.rcol);
+		transtest *= bright(p.rcol);
+		transdist = r->rot + p.rt;
 	}
+
 	if (r->crtype & SHADOW)			/* skip reflected ray */
 		return;
 						/* compute reflectance */
 	for (i = 0; i < 3; i++) {
 		d = colval(mcolor, i);
 		d *= d;
-		colval(refl,i) = r1 * (1.0 + (1.0-2.0*r1)*d) / (1.0 - r1*r1*d);
+		colval(refl,i) = .5*r1e*(1.0+(1.0-2.0*r1e)*d)/(1.0-r1e*r1e*d);
+		colval(refl,i) += .5*r1m*(1.0+(1.0-2.0*r1m)*d)/(1.0-r1m*r1m*d);
 	}
 						/* reflected ray */
-	if (rayorigin(&p, r, REFLECTED, intens(refl)) == 0) {
+	if (rayorigin(&p, r, REFLECTED, bright(refl)) == 0) {
 		for (i = 0; i < 3; i++)
 			p.rdir[i] = r->rdir[i] + 2.0*pdot*pnorm[i];
 		rayvalue(&p);
 		multcolor(p.rcol, refl);
 		addcolor(r->rcol, p.rcol);
 	}
+	if (transtest > bright(r->rcol))
+		r->rt = transdist;
 }