((code
  (label main
    ; Open screen
    (load-immediate $0 &screen-namespace)
    (load-immediate $1 0)
    (syscall DEVICE-OPEN $0 $1)

    ; Draw red box at (10, 20)
    (load-immediate $1 0xE0)   ; color
    (push $1)
    (load-immediate $1 10)     ; x
    (push $1)
    (load-immediate $1 20)     ; y
    (push $1)
    (call &draw-box)

    ; Draw green box at (10, 40)
    (load-immediate $1 0x1C)   ; RGB332 green (00011100)
    (push $1)
    (load-immediate $1 10)
    (push $1)
    (load-immediate $1 40)
    (push $1)
    (call &draw-box)

    ; Flush and halt
    (syscall DEVICE-WRITE $0 $0 $0)
    (halt))

  ; draw-box(color, x, y)
  ; Pops: y, x, color
  (label draw-box
    ; Pop arguments (reverse order)
    (pop $13)        ; y_start
    (pop $11)        ; x_start
    (pop $3)         ; color

    ; Constants
    (load-immediate $1 1)        ; increment
    (load-immediate $2 640)      ; row stride
    (load-immediate $10 36)      ; framebuffer base
    (load-immediate $12 20)      ; width
    (load-immediate $14 20)      ; height

    ; Compute start address: base + y*640 + x
    (mul-int $15 $13 $2)         ; $15 = y * 640
    (add-int $15 $15 $11)        ; $15 += x
    (add-int $4 $10 $15)         ; $4 = base + offset

    ; Outer loop: height times
    (register-move $5 $14)       ; $5 = row counter

    (label draw-box-outer
      (add-int $6 $4 $12)        ; $6 = row end = current + width
      (register-move $7 $4)      ; $7 = pixel pointer

      (label draw-box-inner
        (store-8 $7 $3)          ; write color
        (add-int $7 $7 $1)       ; next pixel
        (jump-lt-int &draw-box-inner $7 $6))

      (add-int $4 $4 $2)         ; next row (+= 640)
      (sub-int $5 $5 $1)         ; decrement row count
      (jump-gt-int &draw-box-outer $5 0))
    (return)))
(data
  (label screen-namespace "/dev/screen/0")))