--- ray/src/hd/rhdisp3.c	1997/11/25 16:52:51	3.6
+++ ray/src/hd/rhdisp3.c	1997/12/19 11:54:16	3.8
@@ -84,19 +84,20 @@ getback:
  * The ray directions that define the pyramid in visit_cells() needn't
  * be normalized, but they must be given in clockwise order as seen
  * from the pyramid's apex (origin).
+ * If no cell centers fall within the domain, the closest cell is visited.
  */
 int
 visit_cells(orig, pyrd, hp, vf, dp)	/* visit cells within a pyramid */
 FVECT	orig, pyrd[4];		/* pyramid ray directions in clockwise order */
-HOLO	*hp;
+register HOLO	*hp;
 int	(*vf)();
 char	*dp;
 {
-	int	n = 0;
+	int	ncalls = 0, n = 0;
 	int	inflags = 0;
 	FVECT	gp, pn[4], lo, ld;
 	double	po[4], lbeg, lend, d, t;
-	GCOORD	gc;
+	GCOORD	gc, gc2[2];
 	register int	i;
 					/* figure out whose side we're on */
 	hdgrid(gp, hp, orig);
@@ -142,11 +143,26 @@ char	*dp;
 			if (lbeg >= lend)
 				continue;
 			i = lend + .5;		/* visit cells on this scan */
-			for (gc.i[0] = lbeg + .5; gc.i[0] < i; gc.i[0]++)
+			for (gc.i[0] = lbeg + .5; gc.i[0] < i; gc.i[0]++) {
 				n += (*vf)(&gc, dp);
+				ncalls++;
+			}
 		}
 	}
-	return(n);
+	if (ncalls)			/* got one at least */
+		return(n);
+					/* else find closest cell */
+	VSUM(ld, pyrd[0], pyrd[1], 1.);
+	VSUM(ld, ld, pyrd[2], 1.);
+	VSUM(ld, ld, pyrd[3], 1.);
+#if 0
+	if (normalize(ld) == 0.0)	/* technically not necessary */
+		return(0);
+#endif
+	d = hdinter(gc2, NULL, &t, hp, orig, ld);
+	if (d >= FHUGE || t <= 0.)
+		return(0);
+	return((*vf)(gc2+1, dp));	/* visit it */
 }
 
 
@@ -278,32 +294,47 @@ int	(*f)();
 {
 	register int	hd, w, i;
 	int	g0, g1;
-	FVECT	wp[2];
+	FVECT	wp[2], mov;
 	double	d;
 					/* do each wall on each section */
 	for (hd = 0; hdlist[hd] != NULL; hd++)
 		for (w = 0; w < 6; w++) {
 			g0 = ((w>>1)+1)%3;
 			g1 = ((w>>1)+2)%3;
-			for (i = hdlist[hd]->grid[g0]; i--; ) {	/* g0 lines */
-				d = (double)i/hdlist[hd]->grid[g0];
+			d = 1.0/hdlist[hd]->grid[g0];
+			mov[0] = d * hdlist[hd]->xv[g0][0];
+			mov[1] = d * hdlist[hd]->xv[g0][1];
+			mov[2] = d * hdlist[hd]->xv[g0][2];
+			if (w & 1) {
 				VSUM(wp[0], hdlist[hd]->orig,
-						hdlist[hd]->xv[g0], d);
-				if (w & 1)
-				    VSUM(wp[0], wp[0],
 						hdlist[hd]->xv[w>>1], 1.);
-				VSUM(wp[1], wp[0], hdlist[hd]->xv[g1], 1.);
+				VSUM(wp[0], wp[0], mov, 1.);
+			} else
+				VCOPY(wp[0], hdlist[hd]->orig);
+			VSUM(wp[1], wp[0], hdlist[hd]->xv[g1], 1.);
+			for (i = hdlist[hd]->grid[g0]; ; ) {	/* g0 lines */
 				(*f)(wp);
+				if (!--i) break;
+				wp[0][0] += mov[0]; wp[0][1] += mov[1];
+				wp[0][2] += mov[2]; wp[1][0] += mov[0];
+				wp[1][1] += mov[1]; wp[1][2] += mov[2];
 			}
-			for (i = hdlist[hd]->grid[g1]; i--; ) {	/* g1 lines */
-				d = (double)i/hdlist[hd]->grid[g1];
+			d = 1.0/hdlist[hd]->grid[g1];
+			mov[0] = d * hdlist[hd]->xv[g1][0];
+			mov[1] = d * hdlist[hd]->xv[g1][1];
+			mov[2] = d * hdlist[hd]->xv[g1][2];
+			if (w & 1)
 				VSUM(wp[0], hdlist[hd]->orig,
-						hdlist[hd]->xv[g1], d);
-				if (w & 1)
-				    VSUM(wp[0], wp[0],
 						hdlist[hd]->xv[w>>1], 1.);
-				VSUM(wp[1], wp[0], hdlist[hd]->xv[g0], 1.);
+			else
+				VSUM(wp[0], hdlist[hd]->orig, mov, 1.);
+			VSUM(wp[1], wp[0], hdlist[hd]->xv[g0], 1.);
+			for (i = hdlist[hd]->grid[g1]; ; ) {	/* g1 lines */
 				(*f)(wp);
+				if (!--i) break;
+				wp[0][0] += mov[0]; wp[0][1] += mov[1];
+				wp[0][2] += mov[2]; wp[1][0] += mov[0];
+				wp[1][1] += mov[1]; wp[1][2] += mov[2];
 			}
 		}
 }