--- ray/src/rt/normal.c	1992/05/19 17:09:03	2.20
+++ ray/src/rt/normal.c	1994/12/21 09:51:49	2.28
@@ -23,11 +23,13 @@ static char SCCSid[] = "$SunId$ LBL";
 extern double  specthresh;		/* specular sampling threshold */
 extern double  specjitter;		/* specular sampling jitter */
 
+extern int  backvis;			/* back faces visible? */
+
+static  gaussamp();
+
 /*
- *	This routine uses portions of the reflection
- *  model described by Cook and Torrance.
- *	The computation of specular components has been simplified by
- *  numerous approximations and ommisions to improve speed.
+ *	This routine implements the isotropic Gaussian
+ *  model described by Ward in Siggraph `92 article.
  *	We orient the surface towards the incoming ray, so a single
  *  surface can be used to represent an infinitely thin object.
  *
@@ -38,8 +40,6 @@ extern double  specjitter;		/* specular sampling jitte
  *	red 	grn	blu	rspec	rough	trans	tspec
  */
 
-#define  BSPEC(m)	(6.0)		/* specularity parameter b */
-
 				/* specularity flags */
 #define  SP_REFL	01		/* has reflected specular component */
 #define  SP_TRAN	02		/* has transmitted specular */
@@ -104,12 +104,13 @@ double  omega;			/* light source size */
 						/* + source if flat */
 		if (np->specfl & SP_FLAT)
 			dtmp += omega/(4.0*PI);
-						/* delta */
+						/* half vector */
 		vtmp[0] = ldir[0] - np->rp->rdir[0];
 		vtmp[1] = ldir[1] - np->rp->rdir[1];
 		vtmp[2] = ldir[2] - np->rp->rdir[2];
 		d2 = DOT(vtmp, np->pnorm);
-		d2 = 2.0 - 2.0*d2/sqrt(DOT(vtmp,vtmp));
+		d2 *= d2;
+		d2 = (DOT(vtmp,vtmp) - d2) / d2;
 						/* gaussian */
 		dtmp = exp(-d2/dtmp)/(4.*PI*dtmp);
 						/* worth using? */
@@ -137,7 +138,7 @@ double  omega;			/* light source size */
 						/* roughness + source */
 		dtmp = np->alpha2 + omega/PI;
 						/* gaussian */
-		dtmp = exp((2.*DOT(np->prdir,ldir)-2.)/dtmp)/(4.*PI*dtmp);
+		dtmp = exp((2.*DOT(np->prdir,ldir)-2.)/dtmp)/(PI*dtmp);
 						/* worth using? */
 		if (dtmp > FTINY) {
 			copycolor(ctmp, np->mcolor);
@@ -155,12 +156,11 @@ register RAY  *r;
 {
 	NORMDAT  nd;
 	double  transtest, transdist;
-	double  dtmp;
 	COLOR  ctmp;
 	register int  i;
 						/* easy shadow test */
 	if (r->crtype & SHADOW && m->otype != MAT_TRANS)
-		return;
+		return(1);
 
 	if (m->oargs.nfargs != (m->otype == MAT_TRANS ? 7 : 5))
 		objerror(m, USER, "bad number of arguments");
@@ -175,9 +175,14 @@ register RAY  *r;
 	nd.alpha2 = m->oargs.farg[4];
 	if ((nd.alpha2 *= nd.alpha2) <= FTINY)
 		nd.specfl |= SP_PURE;
-						/* reorient if necessary */
-	if (r->rod < 0.0)
-		flipsurface(r);
+						/* check for back side */
+	if (r->rod < 0.0) {
+		if (!backvis && m->otype != MAT_TRANS) {
+			raytrans(r);
+			return(1);
+		}
+		flipsurface(r);			/* reorient if backvis */
+	}
 						/* get modifiers */
 	raytexture(r, m->omod);
 	nd.pdot = raynormal(nd.pnorm, r);	/* perturb normal */
@@ -185,6 +190,7 @@ register RAY  *r;
 		nd.pdot = .001;			/* non-zero for dirnorm() */
 	multcolor(nd.mcolor, r->pcol);		/* modify material color */
 	transtest = 0;
+	transdist = r->rot;
 						/* get specular component */
 	if ((nd.rspec = m->oargs.farg[3]) > FTINY) {
 		nd.specfl |= SP_REFL;
@@ -194,16 +200,8 @@ register RAY  *r;
 		else
 			setcolor(nd.scolor, 1.0, 1.0, 1.0);
 		scalecolor(nd.scolor, nd.rspec);
-						/* improved model */
-		dtmp = exp(-BSPEC(m)*nd.pdot);
-		for (i = 0; i < 3; i++)
-			colval(nd.scolor,i) += (1.0-colval(nd.scolor,i))*dtmp;
-		nd.rspec += (1.0-nd.rspec)*dtmp;
 						/* check threshold */
-		if (!(nd.specfl & SP_PURE) &&
-				specthresh > FTINY &&
-				(specthresh >= 1.-FTINY ||
-				specthresh + .05 - .1*frandom() > nd.rspec))
+		if (!(nd.specfl & SP_PURE) && specthresh >= nd.rspec-FTINY)
 			nd.specfl |= SP_RBLT;
 						/* compute reflected ray */
 		for (i = 0; i < 3; i++)
@@ -230,9 +228,8 @@ register RAY  *r;
 		if (nd.tspec > FTINY) {
 			nd.specfl |= SP_TRAN;
 							/* check threshold */
-			if (!(nd.specfl & SP_PURE) && specthresh > FTINY &&
-					(specthresh >= 1.-FTINY ||
-				specthresh + .05 - .1*frandom() > nd.tspec))
+			if (!(nd.specfl & SP_PURE) &&
+					specthresh >= nd.tspec-FTINY)
 				nd.specfl |= SP_TBLT;
 			if (r->crtype & SHADOW ||
 					DOT(r->pert,r->pert) <= FTINY*FTINY) {
@@ -265,12 +262,12 @@ register RAY  *r;
 		transtest = 0;
 
 	if (r->crtype & SHADOW)			/* the rest is shadow */
-		return;
+		return(1);
 						/* diffuse reflection */
 	nd.rdiff = 1.0 - nd.trans - nd.rspec;
 
 	if (nd.specfl & SP_PURE && nd.rdiff <= FTINY && nd.tdiff <= FTINY)
-		return;				/* 100% pure specular */
+		return(1);			/* 100% pure specular */
 
 	if (r->ro != NULL && (r->ro->otype == OBJ_FACE ||
 			r->ro->otype == OBJ_RING))
@@ -304,6 +301,8 @@ register RAY  *r;
 					/* check distance */
 	if (transtest > bright(r->rcol))
 		r->rt = transdist;
+
+	return(1);
 }