--- ray/src/rt/glass.c	2010/09/26 15:51:15	2.18
+++ ray/src/rt/glass.c	2014/01/25 18:27:39	2.21
@@ -1,5 +1,5 @@
 #ifndef lint
-static const char RCSid[] = "$Id: glass.c,v 2.18 2010/09/26 15:51:15 greg Exp $";
+static const char RCSid[] = "$Id: glass.c,v 2.21 2014/01/25 18:27:39 greg Exp $";
 #endif
 /*
  *  glass.c - simpler shading function for thin glass surfaces.
@@ -50,7 +50,7 @@ m_glass(		/* color a ray which hit a thin glass surfac
 	COLOR  mcolor;
 	double  pdot;
 	FVECT  pnorm;
-	double  rindex, cos2;
+	double  rindex=0, cos2;
 	COLOR  trans, refl;
 	int  hastexture, hastrans;
 	double  d, r1e, r1m;
@@ -65,6 +65,11 @@ m_glass(		/* color a ray which hit a thin glass surfac
 		rindex = m->oargs.farg[3];	/* use their value */
 	else
 		objerror(m, USER, "bad arguments");
+						/* check back face visibility */
+	if (!backvis && r->rod <= 0.0) {
+		raytrans(r);
+		return(1);
+	}
 						/* check transmission */
 	setcolor(mcolor, m->oargs.farg[0], m->oargs.farg[1], m->oargs.farg[2]);
 	if ((hastrans = (intens(mcolor) > 1e-15))) {
@@ -112,9 +117,7 @@ m_glass(		/* color a ray which hit a thin glass surfac
 						/* transmitted ray */
 		if (rayorigin(&p, TRANS, r, trans) == 0) {
 			if (!(r->crtype & SHADOW) && hastexture) {
-				for (i = 0; i < 3; i++)	/* perturb direction */
-					p.rdir[i] = r->rdir[i] +
-						2.*(1.-rindex)*r->pert[i];
+				VSUM(p.rdir, r->rdir, r->pert, 2.*(1.-rindex));
 				if (normalize(p.rdir) == 0.0) {
 					objerror(m, WARNING, "bad perturbation");
 					VCOPY(p.rdir, r->rdir);
@@ -143,8 +146,7 @@ m_glass(		/* color a ray which hit a thin glass surfac
 	}
 						/* reflected ray */
 	if (rayorigin(&p, REFLECTED, r, refl) == 0) {
-		for (i = 0; i < 3; i++)
-			p.rdir[i] = r->rdir[i] + 2.0*pdot*pnorm[i];
+		VSUM(p.rdir, r->rdir, pnorm, 2.*pdot);
 		checknorm(p.rdir);
 		rayvalue(&p);
 		multcolor(p.rcol, p.rcoef);