--- ray/src/rt/t_data.c	1989/03/14 11:31:17	1.1
+++ ray/src/rt/t_data.c	1989/10/05 07:23:19	1.5
@@ -48,6 +48,7 @@ RAY  *r;
 	int  nv;
 	FVECT  dval, disp;
 	double  pt[MAXDIM];
+	double  d;
 	DATARRAY  *dp;
 	register XFORM  *mxf;
 	register char  **sa;
@@ -57,22 +58,18 @@ RAY  *r;
 		objerror(m, USER, "bad # arguments");
 	sa = m->oargs.sarg;
 
+	for (i = 7; i < m->oargs.nsargs && sa[i][0] != '-'; i++)
+		;
+	nv = i-7;
 	if ((mxf = (XFORM *)m->os) == NULL) {
-		for (i = 7; i < m->oargs.nsargs && sa[i][0] != '-'; i++)
-			;
-		nv = i-7;
 		mxf = (XFORM *)malloc(sizeof(XFORM));
 		if (mxf == NULL)
 			goto memerr;
-		mxf->fore.sca = 1.0;
-		setident4(mxf->fore.xfm);
 		if (xf(mxf->fore.xfm, &mxf->fore.sca,
 			m->oargs.nsargs-i, sa+i) != m->oargs.nsargs-i)
 			objerror(m, USER, "bad transform");
 		if (mxf->fore.sca < 0.0)
 			mxf->fore.sca = -mxf->fore.sca;
-		mxf->back.sca = 1.0;
-		setident4(mxf->back.xfm);
 		invxf(mxf->back.xfm, &mxf->back.sca,
 				m->oargs.nsargs-i, sa+i);
 		if (mxf->back.sca < 0.0)
@@ -103,11 +100,11 @@ RAY  *r;
 	if (errno)
 		goto computerr;
 
+	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;
 dimerr:
 	objerror(m, USER, "dimension error");