SCREEN 12
w = 640: h = 480

h = h \ 4
y2 = h - 1

FOR i = 1 TO 4
    col = 0
    y = (i - 1) * h
    FOR x = 1 TO w STEP i
        IF col MOD 15 = 0 THEN col = 0
        LINE (x, y)-(x + i, y + h), col, BF
        col = col + 1
    NEXT x
NEXT i