(
    (sc-init 800 600)

    (sym x r6)
    (sym y r7)

    (def BOXSIZE 7)

    (:loop)
        (sc-poll)
        (sc-blit 0)
        (sc-mouse x y (ov? (j :next)))
        (sc-mbtn _ 1 (nz? (sc-erase) (sc-blit 1)))
        (sc-mbtn _ 0 (z? (j :next)))

        (call draw_box x y)

        (:next)
        (uslp 500)
    (j :loop)

    (proc draw_box x y
        (sym vx r0)
        (sym vy r1)
        (sym endx r2)
        (sym endy r3)

        (add endx x BOXSIZE)
        (add endy y BOXSIZE)
        (sub vy y BOXSIZE)

        (:nextline)
            (cmp vy endy (eq? (ret)))
            (sub vx x BOXSIZE)
            (:nextpx)
                (sc-px vx vy 0xffffff)
                (inc vx)
                (cmp vx endx
                    (eq? (inc vy)(j :nextline)))
                (j :nextpx)
    )
)