[Caml-list] Problem with Graph module

[Nicolas FRANCOIS (AKA El Bofo) <nicolas.francois@free.fr>]

A strange thing, under Linux : this piece of code :

open Graphics;;
open Random;;

type t_fourmi = {mutable dir : int;
		 mutable x : int;
		 mutable y : int};;

let trace_fourmi_deux_etats n =
  let mouvement = [|(0, 5); (-5, 0); (0, -5); (5, 0)|] in
  let init = open_graph " 800x800+50-50" in
  let ma_fourmi = {dir = 0; x = 349; y = 349} in
  let onestep () =
    if (point_color ma_fourmi.x ma_fourmi.y) = white
    then
      begin
	set_color black;
	ma_fourmi.dir <-
	if ma_fourmi.dir + 1 > 3 then 0 else ma_fourmi.dir + 1
      end
    else
      begin
	set_color white;
	ma_fourmi.dir <-
	if ma_fourmi.dir - 1 < 0 then 3 else ma_fourmi.dir - 1
      end;
    fill_rect ma_fourmi.x ma_fourmi.y 5 5;    
    let (dx, dy) = mouvement.(ma_fourmi.dir) in
      ma_fourmi.x <- ma_fourmi.x + dx;
      ma_fourmi.y <- ma_fourmi.y + dy;
  in
    init;
    for i = 0 to n do
      onestep ();
      for j = 1 to 10000 do begin end done
    done;;

trace_fourmi_deux_etats 10000;;


works perfectly in camllight (with a few modifications to adapt the code),
but not in Ocaml. The graphic window opens well, but the test 

if (point_color ma_fourmi.x ma_fourmi.y) = white

is allways false under Ocaml.

Can you see the problem ?????

Thanks.

-- 

                   Nicolas FRANCOIS
            http://nicolas.francois.free.fr
 A TRUE Klingon programmer does NOT comment his code
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