OpenSCAD hole array

use <tyler.scad>;

inch=25.4;
dx=80;//2*inch;
dy=80;//2*inch;
dia = 9;

sx=500;
sy=500;

nx=ceil(sx/dx);
ny=ceil(sy/dy);

occ_x = dx*(nx-1);
occ_y = dy*(ny-1);

off_x = (sx-occ_x)/2;
off_y = (sy-occ_y)/2;

echo("x in ",off_x,occ_x+off_x, "span:", occ_x,"nx=",nx);
echo("y in ",off_y,occ_y+off_y, "span:", occ_y,"ny=",ny);
echo("#holes:",nx*ny);

$fn=32;

module T(c) { if (len(c)==undef) translate([0,0,c]) children(); else translate(c) children(); }

for (i=[0:nx-1]) for (j=[0:ny-1]) {
    x = off_x+dx*i;
    y = off_y+dy*j;
    T([x,y]) {
        circle(d=dia);
        //arc(dia/2, a1=-45,a2=-45+90);
        //arc(dia/2, a1=-45+180,a2=-45+90+180);
    }
    #T([x,y]) square([0,5]);

}