--- ray/src/rt/aniso.c	1992/05/19 17:09:06	2.18
+++ ray/src/rt/aniso.c	1992/10/16 10:20:27	2.22
@@ -20,8 +20,8 @@ extern double  specthresh;		/* specular sampling thres
 extern double  specjitter;		/* specular sampling jitter */
 
 /*
- *	This anisotropic reflection model uses a variant on the
- *  exponential Gaussian used in normal.c.
+ *	This routine implements the anisotropic 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.
  *
@@ -117,7 +117,7 @@ double  omega;			/* light source size */
 		dtmp2 *= dtmp2 / av2;
 						/* gaussian */
 		dtmp = (dtmp1 + dtmp2) / (1.0 + DOT(np->pnorm, h));
-		dtmp = exp(-2.0*dtmp) * 1.0/(4.0*PI)
+		dtmp = exp(-2.0*dtmp) * (1.0/4.0/PI)
 				* sqrt(ldot/(np->pdot*au2*av2));
 						/* worth using? */
 		if (dtmp > FTINY) {
@@ -149,19 +149,21 @@ double  omega;			/* light source size */
 		h[0] = ldir[0] - np->prdir[0];
 		h[1] = ldir[1] - np->prdir[1];
 		h[2] = ldir[2] - np->prdir[2];
-		dtmp = DOT(h,np->pnorm);
-		dtmp = DOT(h,h) - dtmp*dtmp;
+		dtmp = DOT(h,h);
 		if (dtmp > FTINY*FTINY) {
-			dtmp1 = DOT(h,np->u);
-			dtmp1 = dtmp1*dtmp1 / (au2*dtmp);
-			dtmp2 = DOT(h,np->v);
-			dtmp2 = dtmp2*dtmp2 / (av2*dtmp);
-			dtmp = 2. - 2.*DOT(ldir,np->prdir);
-			dtmp *= dtmp1 + dtmp2;
+			dtmp1 = DOT(h,np->pnorm);
+			dtmp = 1.0 - dtmp1*dtmp1/dtmp;
+			if (dtmp > FTINY*FTINY) {
+				dtmp1 = DOT(h,np->u);
+				dtmp1 = dtmp1*dtmp1 / au2;
+				dtmp2 = DOT(h,np->v);
+				dtmp2 = dtmp2*dtmp2 / av2;
+				dtmp = (dtmp1 + dtmp2) / dtmp;
+			}
 		} else
 			dtmp = 0.0;
 						/* gaussian */
-		dtmp = exp(-dtmp) * 1.0/(4.0*PI)
+		dtmp = exp(-dtmp) * (1.0/PI)
 				* sqrt(-ldot/(np->pdot*au2*av2));
 						/* worth using? */
 		if (dtmp > FTINY) {