Simple mandelbrot program

[WJ]

WARNING: BE SURE TO REDIRECT THE OUTPUT TO A FILE OR
YOU MAY HAVE TO REBOOT YOUR COMPUTER!


(*
! ! ! Redirect output to file with .ppm extension! ! ! !
*)

module Cm = Complex

let max_iterations = 512
let step_size = 0.0025
let x_min = (-2.0)
let x_max = 1.0000001 -. step_size
let y_min = (-1.2)
let y_max = 1.2000001 -. step_size
let pixels_per_row = (truncate ((x_max -. x_min) /. step_size)) + 1
let pixels_per_column = (truncate ((y_max -. y_min) /. step_size)) + 1;;

Printf.eprintf "pixels per row: %d\n" pixels_per_row;;
Printf.eprintf "pixels per column: %d\n" pixels_per_column;;

(* Printing without added carriage-returns: *)
set_binary_mode_out stdout true ;;


Printf.printf "P5\n%d %d\n255\n" pixels_per_row pixels_per_column;;

let float_lo_hi_by lo hi step func =
let x = ref lo in
while !x <= hi do
func !x ;
x := !x +. step
done

let calc_color count =
let tmp =
if count < 2 then
20
else if count=max_iterations then
0
else
truncate (((log (float count)) /. (log (float max_iterations))) *. 256.)
in 255 - tmp

let mandel () =
float_lo_hi_by y_min y_max step_size
(fun y ->
float_lo_hi_by x_min x_max step_size
(fun x ->
let a = {Complex.re = x; im = y} in
let rec z_loop z count =
if (count = max_iterations) || (Cm.norm2 z) > 4.0 then
let color = calc_color count in
Printf.printf "%c" (char_of_int color)
else
z_loop (Cm.add a (Cm.mul z z)) (count + 1)
in z_loop a 0) ;
Printf.eprintf "." ; flush_all ()) ;;

mandel ()