--- ray/src/rt/normal.c	1992/05/15 13:07:55	2.18
+++ ray/src/rt/normal.c	1993/03/08 12:37:27	2.24
@@ -23,11 +23,11 @@ static char SCCSid[] = "$SunId$ LBL";
 extern double  specthresh;		/* specular sampling threshold */
 extern double  specjitter;		/* specular sampling jitter */
 
+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.
  *
@@ -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? */
@@ -135,9 +136,9 @@ double  omega;			/* light source size */
 		 *  is always modified by material color.
 		 */
 						/* roughness + source */
-		dtmp = np->alpha2/4.0 + omega/PI;
+		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);
@@ -240,8 +241,7 @@ register RAY  *r;
 				transtest = 2;
 			} else {
 				for (i = 0; i < 3; i++)		/* perturb */
-					nd.prdir[i] = r->rdir[i] -
-							0.5*r->pert[i];
+					nd.prdir[i] = r->rdir[i] - r->pert[i];
 				if (DOT(nd.prdir, r->ron) < -FTINY)
 					normalize(nd.prdir);	/* OK */
 				else
@@ -370,7 +370,7 @@ register NORMDAT  *np;
 		if (rv[1] <= FTINY)
 			d = 1.0;
 		else
-			d = sqrt( np->alpha2/4.0 * -log(rv[1]) );
+			d = sqrt( -log(rv[1]) * np->alpha2 );
 		for (i = 0; i < 3; i++)
 			sr.rdir[i] = np->prdir[i] + d*(cosp*u[i] + sinp*v[i]);
 		if (DOT(sr.rdir, r->ron) < -FTINY)