let x = ref 0 in
            let y = ref 0 in
            let x_coordinates = Array.init !num_points (fun i ->
                let flag = DynArray.get flags i in
                if flag land 0x10 <> 0 then begin
                    if flag land 0x02 <> 0 then begin x:= !x + read_byte ch; !x end
                    else 0
                end else begin
                    if flag land 0x02 <> 0 then begin x:= !x -read_byte ch; !x end
                    else begin x := !x + rd16 ch; !x end
                end
            ) in