--- ray/src/rt/m_brdf.c	1993/08/24 12:59:25	2.8
+++ ray/src/rt/m_brdf.c	1995/11/22 09:27:53	2.14
@@ -16,6 +16,8 @@ static char SCCSid[] = "$SunId$ LBL";
 
 #include  "func.h"
 
+extern int  backvis;			/* back faces visible? */
+
 /*
  *	Arguments to this material include the color and specularity.
  *  String arguments include the reflection function and files.
@@ -88,10 +90,10 @@ double  omega;			/* light source size */
 	double  dtmp;
 	COLOR  ctmp;
 	FVECT  ldx;
-	double  lddx[3], pt[MAXDIM];
-	double  vldx[4];
+	static double  vldx[5], pt[MAXDIM];
 	register char	**sa;
 	register int	i;
+#define lddx (vldx+1)
 
 	setcolor(cval, 0.0, 0.0, 0.0);
 	
@@ -132,32 +134,32 @@ double  omega;			/* light source size */
 	multv3(ldx, ldir, funcxf.xfm);
 	for (i = 0; i < 3; i++)
 		lddx[i] = ldx[i]/funcxf.sca;
+	lddx[3] = omega;
 					/* compute BRTDF */
 	if (np->mp->otype == MAT_BRTDF) {
 		if (sa[6][0] == '0')		/* special case */
 			colval(ctmp,RED) = 0.0;
 		else
-			colval(ctmp,RED) = funvalue(sa[6], 3, lddx);
+			colval(ctmp,RED) = funvalue(sa[6], 4, lddx);
 		if (!strcmp(sa[7],sa[6]))
 			colval(ctmp,GRN) = colval(ctmp,RED);
 		else
-			colval(ctmp,GRN) = funvalue(sa[7], 3, lddx);
+			colval(ctmp,GRN) = funvalue(sa[7], 4, lddx);
 		if (!strcmp(sa[8],sa[6]))
 			colval(ctmp,BLU) = colval(ctmp,RED);
 		else if (!strcmp(sa[8],sa[7]))
 			colval(ctmp,BLU) = colval(ctmp,GRN);
 		else
-			colval(ctmp,BLU) = funvalue(sa[8], 3, lddx);
+			colval(ctmp,BLU) = funvalue(sa[8], 4, lddx);
 		dtmp = bright(ctmp);
 	} else if (np->dp == NULL) {
-		dtmp = funvalue(sa[0], 3, lddx);
+		dtmp = funvalue(sa[0], 4, lddx);
 		setcolor(ctmp, dtmp, dtmp, dtmp);
 	} else {
 		for (i = 0; i < np->dp->nd; i++)
-			pt[i] = funvalue(sa[3+i], 3, lddx);
+			pt[i] = funvalue(sa[3+i], 4, lddx);
 		vldx[0] = datavalue(np->dp, pt);
-		vldx[1] = lddx[0]; vldx[2] = lddx[1]; vldx[3] = lddx[2];
-		dtmp = funvalue(sa[0], 4, vldx);
+		dtmp = funvalue(sa[0], 5, vldx);
 		setcolor(ctmp, dtmp, dtmp, dtmp);
 	}
 	if (errno) {
@@ -185,10 +187,11 @@ double  omega;			/* light source size */
 		scalecolor(ctmp, dtmp);
 		addcolor(cval, ctmp);
 	}
+#undef lddx
 }
 
 
-m_brdf(m, r)			/* color a ray which hit a BRDTF material */
+m_brdf(m, r)			/* color a ray which hit a BRDTfunc material */
 register OBJREC  *m;
 register RAY  *r;
 {
@@ -197,7 +200,7 @@ register RAY  *r;
 	double  transtest, transdist;
 	int  hasrefl, hastrans;
 	COLOR  ctmp;
-	double  dtmp;
+	FVECT  vtmp;
 	register MFUNC  *mf;
 	register int  i;
 						/* check arguments */
@@ -269,7 +272,7 @@ register RAY  *r;
 		transdist = r->rot + sr.rt;
 	}
 	if (r->crtype & SHADOW)			/* the rest is shadow */
-		return;
+		return(1);
 						/* compute reflected ray */
 	setbrdfunc(&nd);
 	errno = 0;
@@ -287,18 +290,28 @@ register RAY  *r;
 	}
 						/* compute ambient */
 	if (hasrefl) {
-		if (nd.pdot < 0.0)
+		if (nd.pdot < 0.0) {
 			flipsurface(r);
-		ambient(ctmp, r);
+			vtmp[0] = -nd.pnorm[0];
+			vtmp[1] = -nd.pnorm[1];
+			vtmp[2] = -nd.pnorm[2];
+		} else
+			VCOPY(vtmp, nd.pnorm);
+		ambient(ctmp, r, vtmp);
 		multcolor(ctmp, nd.rdiff);
 		addcolor(r->rcol, ctmp);	/* add to returned color */
 		if (nd.pdot < 0.0)
 			flipsurface(r);
 	}
 	if (hastrans) {				/* from other side */
-		if (nd.pdot > 0.0)
+		if (nd.pdot > 0.0) {
 			flipsurface(r);
-		ambient(ctmp, r);
+			vtmp[0] = -nd.pnorm[0];
+			vtmp[1] = -nd.pnorm[1];
+			vtmp[2] = -nd.pnorm[2];
+		} else
+			VCOPY(vtmp, nd.pnorm);
+		ambient(ctmp, r, vtmp);
 		multcolor(ctmp, nd.tdiff);
 		addcolor(r->rcol, ctmp);
 		if (nd.pdot > 0.0)
@@ -309,6 +322,8 @@ register RAY  *r;
 						/* check distance */
 	if (transtest > bright(r->rcol))
 		r->rt = transdist;
+
+	return(1);
 }
 
 
@@ -319,10 +334,11 @@ register RAY  *r;
 {
 	BRDFDAT  nd;
 	COLOR  ctmp;
+	FVECT  vtmp;
 	double  dtmp;
 						/* always a shadow */
 	if (r->crtype & SHADOW)
-		return;
+		return(1);
 						/* check arguments */
 	if (m->oargs.nsargs < (hasdata(m->otype)?4:2) | m->oargs.nfargs <
 			(m->otype==MAT_TFUNC|m->otype==MAT_TDATA?6:4))
@@ -348,9 +364,15 @@ register RAY  *r;
 						/* compute reflectance */
 	dtmp = 1.0 - nd.trans - nd.rspec;
 	setcolor(nd.rdiff, dtmp, dtmp, dtmp);
-						/* fix orientation */
-	if (r->rod < 0.0)
-		flipsurface(r);
+						/* check for back side */
+	if (r->rod < 0.0) {
+		if (!backvis && m->otype != MAT_TFUNC
+				&& m->otype != MAT_TDATA) {
+			raytrans(r);
+			return(1);
+		}
+		flipsurface(r);			/* reorient if backvis */
+	}
 						/* get modifiers */
 	raytexture(r, m->omod);
 	nd.pdot = raynormal(nd.pnorm, r);	/* perturb normal */
@@ -367,14 +389,17 @@ register RAY  *r;
 	}
 						/* compute ambient */
 	if (nd.trans < 1.0-FTINY) {
-		ambient(ctmp, r);
+		ambient(ctmp, r, nd.pnorm);
 		scalecolor(ctmp, 1.0-nd.trans);
 		multcolor(ctmp, nd.mcolor);	/* modified by material color */
 		addcolor(r->rcol, ctmp);	/* add to returned color */
 	}
 	if (nd.trans > FTINY) {		/* from other side */
 		flipsurface(r);
-		ambient(ctmp, r);
+		vtmp[0] = -nd.pnorm[0];
+		vtmp[1] = -nd.pnorm[1];
+		vtmp[2] = -nd.pnorm[2];
+		ambient(ctmp, r, vtmp);
 		scalecolor(ctmp, nd.trans);
 		multcolor(ctmp, nd.mcolor);
 		addcolor(r->rcol, ctmp);
@@ -382,6 +407,8 @@ register RAY  *r;
 	}
 						/* add direct component */
 	direct(r, dirbrdf, &nd);
+
+	return(1);
 }