Almost Burning Ship

Have an almost Burning Ship fractal.

open Prelude

let niter = 32
let limit = 4.0

let burning_ship z x y =
  let cr = 2.0 *. float x /. z -. 2.1 in
  let ci = 2.0 *. float y /. z -. 1.8 in
  let rec aux i zr zi = if i >= niter then 0 else
    let nzr = absf (zr *. zr -. zi *. zi +. cr)
    and nzi = 2.0 *. absf (zr *. zi +. ci) in
    if nzr *. nzr +. nzi *. nzi > limit then niter-i
    else aux (i+1) nzr nzi in
  aux 0 0.0 0.0

let pbinit2D f w h = pbinit (fun i -> let y,x = quot_rem i w in f x y) (w*h)
let draw_fractal z w h = pbinit2D (burning_ship (float z *. 0.8)) w h
let pgm_fractal w h = sprintf "P5 %i %i %i\n" w h niter ^ draw_fractal (min w h) w h

let () = print_string @@ pgm_fractal (parseInt Sys.argv.(1)) (parseInt Sys.argv.(2))