--- ray/src/rt/rpict.c	1991/07/18 14:42:54	1.30
+++ ray/src/rt/rpict.c	1991/10/10 12:58:13	1.34
@@ -15,9 +15,9 @@ static char SCCSid[] = "$SunId$ LBL";
 #ifdef BSD
 #include  <sys/time.h>
 #include  <sys/resource.h>
-#else
-#include  <signal.h>
 #endif
+
+#include  <signal.h>
 #include  <fcntl.h>
 
 #include  "view.h"
@@ -122,6 +122,7 @@ char  *zfile, *oldfile;
 	float  *zbar[MAXDIV+1];		/* z values */
 	int  ypos;			/* current scanline */
 	int  ystep;			/* current y step size */
+	int  hstep;			/* h step size */
 	int  zfd;
 	COLOR  *colptr;
 	float  *zptr;
@@ -167,9 +168,14 @@ char  *zfile, *oldfile;
 	pctdone = 100.0*i/vresolu;
 	if (ralrm > 0)			/* report init stats */
 		report();
+#ifndef  BSD
+	else
+#endif
+	signal(SIGALRM, report);
 	ypos = vresolu-1 - i;
-	fillscanline(scanbar[0], zbar[0], hresolu, ypos, psample);
-	ystep = psample;
+	hstep = (psample*140+49)/99;		/* quincunx sampling */
+	ystep = (psample*99+70)/140;
+	fillscanline(scanbar[0], zbar[0], hresolu, ypos, hstep);
 						/* compute scanlines */
 	for (ypos -= ystep; ypos > -ystep; ypos -= ystep) {
 							/* bottom adjust? */
@@ -184,10 +190,13 @@ char  *zfile, *oldfile;
 		zbar[ystep] = zbar[0];
 		zbar[0] = zptr;
 							/* fill base line */
-		fillscanline(scanbar[0], zbar[0], hresolu, ypos, psample);
+		fillscanline(scanbar[0], zbar[0], hresolu, ypos, hstep);
 							/* fill bar */
 		fillscanbar(scanbar, zbar, hresolu, ypos, ystep);
 							/* write it out */
+#ifndef  BSD
+		signal(SIGALRM, SIG_IGN);	/* don't interrupt writes */
+#endif
 		for (i = ystep; i > 0; i--) {
 			if (zfd != -1 && write(zfd, (char *)zbar[i],
 					hresolu*sizeof(float))
@@ -202,6 +211,10 @@ char  *zfile, *oldfile;
 		pctdone = 100.0*(vresolu-1-ypos)/vresolu;
 		if (ralrm > 0 && time((long *)0) >= tlastrept+ralrm)
 			report();
+#ifndef  BSD
+		else
+			signal(SIGALRM, report);
+#endif
 	}
 						/* clean up */
 	if (zfd != -1) {
@@ -232,14 +245,15 @@ register COLOR  *scanline;
 register float  *zline;
 int  xres, y, xstep;
 {
+	static int  nc = 0;		/* number of calls */
 	int  b = xstep;
 	double  z;
 	register int  i;
 	
 	z = pixvalue(scanline[0], 0, y);
 	if (zline) zline[0] = z;
-
-	for (i = xstep; i < xres-1+xstep; i += xstep) {
+				/* zig-zag start for quincunx pattern */
+	for (i = nc++ & 1 ? xstep/2 : xstep; i < xres-1+xstep; i += xstep) {
 		if (i >= xres) {
 			xstep += xres-1-i;
 			i = xres-1;
@@ -354,7 +368,7 @@ int  x, y;			/* pixel position */
 
 	rayorigin(&thisray, NULL, PRIMARY, 1.0);
 
-	samplendx = 3*y + x;			/* set pixel index */
+	samplendx = pixnumber(x,y,hresolu,vresolu);	/* set pixel index */
 
 	rayvalue(&thisray);			/* trace ray */
 
@@ -413,4 +427,16 @@ char  *oldfile;
 	return(y);
 writerr:
 	error(SYSTEM, "write error in salvage");
+}
+
+
+int
+pixnumber(x, y, xres, yres)		/* compute pixel index (brushed) */
+register int  x, y;
+int  xres, yres;
+{
+	x -= y;
+	while (x < 0)
+		x += xres;
+	return((((x>>2)*yres + y) << 2) + (x & 3));
 }