nomainwin

    w =512
    '   allow for title bar and window border
    WindowWidth  =w +2
    WindowHeight =w +34

    open "XOR Pattern" for graphics_nsb_nf as #w

    #w "trapclose quit"

    #w "down"

    for x =0 to w -1
        for y =0 to w -1
            b =( x xor y) and 255
            print b
            #w "color "; 255 -b; " "; b /2; " "; b
            #w "set "; x; " "; w -y -1
            scan
        next y
    next x

    #w "flush"

    wait

    sub quit j$
    close #w
    end
    end sub