(defconstant MAX_ITERATIONS 27)

(defconstant OUTPUT_RES_X 3.5)

(defconstant OUTPUT_RES_Y 2)

(defconstant OUTPUT_OFFSET_X -2.5)

(defconstant OUTPUT_OFFSET_Y -1)

(defconstant RESOLUTION_X 150)

(defconstant RESOLUTION_Y 60)

; turn # interations into a char for display

(defun show (val) 

    (if (<= val 26)

        (code-char (+ val 

                          -1

                          (char-code #\A)))

        " "))

; Calculate how many steps are required.

(defun calc (x y)

    (let (

      (xi (+ OUTPUT_OFFSET_X (* OUTPUT_RES_X (/ x RESOLUTION_X))))

      (yi (+ OUTPUT_OFFSET_Y (* OUTPUT_RES_Y (/ y RESOLUTION_Y)))))

      (loop for iters below MAX_ITERATIONS

	    for x = 0 then (+ (+ xi (* x x) (* -1 y y)))

	    and y = 0 then (+ yi (* x y 2))

	    when (< 4 (+ (* x x) (* y y)))

	    	do (return iters)

	    finally (return iters))))

(defun draw_window (width height) 

  (dotimes (y height)

    (dotimes (x width)

        (princ (show (calc x y))))

    (terpri)))

(defun main ()

    (draw_window RESOLUTION_X RESOLUTION_Y))