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Comparing ray/src/rt/normal.c (file contents):
Revision 2.20 by greg, Tue May 19 17:09:03 1992 UTC vs.
Revision 2.24 by greg, Mon Mar 8 12:37:27 1993 UTC

# Line 23 | Line 23 | static char SCCSid[] = "$SunId$ LBL";
23   extern double  specthresh;              /* specular sampling threshold */
24   extern double  specjitter;              /* specular sampling jitter */
25  
26 + static  gaussamp();
27 +
28   /*
29 < *      This routine uses portions of the reflection
30 < *  model described by Cook and Torrance.
29 < *      The computation of specular components has been simplified by
30 < *  numerous approximations and ommisions to improve speed.
29 > *      This routine implements the isotropic Gaussian
30 > *  model described by Ward in Siggraph `92 article.
31   *      We orient the surface towards the incoming ray, so a single
32   *  surface can be used to represent an infinitely thin object.
33   *
# Line 104 | Line 104 | double  omega;                 /* light source size */
104                                                  /* + source if flat */
105                  if (np->specfl & SP_FLAT)
106                          dtmp += omega/(4.0*PI);
107 <                                                /* delta */
107 >                                                /* half vector */
108                  vtmp[0] = ldir[0] - np->rp->rdir[0];
109                  vtmp[1] = ldir[1] - np->rp->rdir[1];
110                  vtmp[2] = ldir[2] - np->rp->rdir[2];
111                  d2 = DOT(vtmp, np->pnorm);
112 <                d2 = 2.0 - 2.0*d2/sqrt(DOT(vtmp,vtmp));
112 >                d2 *= d2;
113 >                d2 = (DOT(vtmp,vtmp) - d2) / d2;
114                                                  /* gaussian */
115                  dtmp = exp(-d2/dtmp)/(4.*PI*dtmp);
116                                                  /* worth using? */
# Line 137 | Line 138 | double  omega;                 /* light source size */
138                                                  /* roughness + source */
139                  dtmp = np->alpha2 + omega/PI;
140                                                  /* gaussian */
141 <                dtmp = exp((2.*DOT(np->prdir,ldir)-2.)/dtmp)/(4.*PI*dtmp);
141 >                dtmp = exp((2.*DOT(np->prdir,ldir)-2.)/dtmp)/(PI*dtmp);
142                                                  /* worth using? */
143                  if (dtmp > FTINY) {
144                          copycolor(ctmp, np->mcolor);

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