--- ray/src/rt/aniso.c	1994/01/12 16:46:32	2.27
+++ ray/src/rt/aniso.c	1995/11/22 09:27:51	2.31
@@ -19,6 +19,8 @@ static char SCCSid[] = "$SunId$ LBL";
 extern double  specthresh;		/* specular sampling threshold */
 extern double  specjitter;		/* specular sampling jitter */
 
+extern int  backvis;			/* back faces visible? */
+
 static  agaussamp(), getacoords();
 
 /*
@@ -201,9 +203,14 @@ register RAY  *r;
 	nd.v_alpha = m->oargs.farg[5];
 	if (nd.u_alpha < FTINY || nd.v_alpha <= FTINY)
 		objerror(m, USER, "roughness too small");
-						/* reorient if necessary */
-	if (r->rod < 0.0)
-		flipsurface(r);
+						/* check for back side */
+	if (r->rod < 0.0) {
+		if (!backvis && m->otype != MAT_TRANS2) {
+			raytrans(r);
+			return(1);
+		}
+		flipsurface(r);			/* reorient if backvis */
+	}
 						/* get modifiers */
 	raytexture(r, m->omod);
 	nd.pdot = raynormal(nd.pnorm, r);	/* perturb normal */
@@ -256,8 +263,7 @@ register RAY  *r;
 						/* diffuse reflection */
 	nd.rdiff = 1.0 - nd.trans - nd.rspec;
 
-	if (r->ro != NULL && (r->ro->otype == OBJ_FACE ||
-			r->ro->otype == OBJ_RING))
+	if (r->ro != NULL && isflat(r->ro->otype))
 		nd.specfl |= SP_FLAT;
 
 	getacoords(r, &nd);			/* set up coordinates */
@@ -266,7 +272,7 @@ register RAY  *r;
 		agaussamp(r, &nd);
 
 	if (nd.rdiff > FTINY) {		/* ambient from this side */
-		ambient(ctmp, r);
+		ambient(ctmp, r, nd.pnorm);
 		if (nd.specfl & SP_RBLT)
 			scalecolor(ctmp, 1.0-nd.trans);
 		else
@@ -275,8 +281,13 @@ register RAY  *r;
 		addcolor(r->rcol, ctmp);	/* add to returned color */
 	}
 	if (nd.tdiff > FTINY) {		/* ambient from other side */
+		FVECT  bnorm;
+
 		flipsurface(r);
-		ambient(ctmp, r);
+		bnorm[0] = -nd.pnorm[0];
+		bnorm[1] = -nd.pnorm[1];
+		bnorm[2] = -nd.pnorm[2];
+		ambient(ctmp, r, bnorm);
 		if (nd.specfl & SP_TBLT)
 			scalecolor(ctmp, nd.trans);
 		else