--- ray/src/rt/t_func.c	1989/03/14 11:02:35	1.4
+++ ray/src/rt/t_func.c	1989/04/19 21:20:29	1.6
@@ -43,6 +43,7 @@ register RAY  *r;
 	extern double  varvalue();
 	extern int  errno;
 	FVECT  disp;
+	double  d;
 	register XFORM  *mxf;
 	register int  i;
 	register char  **sa;
@@ -82,11 +83,11 @@ register RAY  *r;
 		objerror(m, WARNING, "compute error");
 		return;
 	}
+	multv3(disp, disp, mxf->fore.xfm);
+	multv3(disp, disp, r->rofx);
+	d = 1.0 / (mxf->fore.sca * r->rofs);
 	for (i = 0; i < 3; i++)
-		r->pert[i] += (	disp[0]*mxf->fore.xfm[0][i] +
-				disp[1]*mxf->fore.xfm[1][i] +
-				disp[2]*mxf->fore.xfm[2][i] )
-					/ mxf->fore.sca;
+		r->pert[i] += disp[i] * d;
 	return;
 memerr:
 	error(SYSTEM, "out of memory in t_func");