let draw_line (x1 : float) (y1 : float) (x2 : float) (y2 : float) (col : Tk.color) (tag_number : int) : unit =
let xc1 = xconv x1 in
let yc1 = yconv y1 in
let xc2 = xconv x2 in
let yc2 = yconv y2 in
ignore(Canvas.create_line ~xys:[xc1, yc1 ; xc2, yc2] ~width:4 ~tags:[("tag"^(string_of_int tag_number))] ~fill:col canvas)