--- ray/src/rt/normal.c	1992/05/16 08:37:06	2.19
+++ ray/src/rt/normal.c	1993/02/12 10:41:02	2.23
@@ -24,10 +24,8 @@ extern double  specthresh;		/* specular sampling thres
 extern double  specjitter;		/* specular sampling jitter */
 
 /*
- *	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 +102,13 @@ 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 +136,7 @@ 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);
@@ -369,7 +368,7 @@ 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)