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A very simple way of integrating Vg support that could be used as a starting point. Credit goes to Etienne Marais.

Try it for example with the following snippet (taken from the Vg demos):

open Gg
open Vg

let arrowhead n =
  let arrowhead_path i len =
    let angle = Float.pi /. 3. in
    let rec loop i len sign turn p =
      if i = 0 then p |> P.line ~rel:true V2.(polar len turn) else
        p |>
        loop (i - 1) (len /. 2.) (-. sign) (turn +. sign *. angle) |>
        loop (i - 1) (len /. 2.) sign turn |>
        loop (i - 1) (len /. 2.) (-. sign) (turn -. sign *. angle)
    in
    P.empty |> loop i len 1. 0.
  in
  let area = `O { P.o with P.width = 0.005 } in
  I.const Color.black
  |> I.cut ~area (arrowhead_path n 0.8)
  |> I.move (V2.v 0. 0.1)
;;
arrowhead 7