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open Cairo
let two_pi = 2. *. acos(-1.)
let radius = 150.
(* Based on the example given at
https://developer.gnome.org/pango/stable/pango-Cairo-Rendering.html *)
let draw_text (cr: context) =
let n_words = 10 in
let font = "Sans Bold 26" in
Cairo.translate cr radius radius;
let layout = Cairo_pango.create_layout cr in
Pango.Layout.set_text layout "Text";
let desc = Pango.Font.from_string font in
Pango.Layout.set_font_description layout desc;
(* Draw the layout [n_words] times in a circle. *)
for i = 1 to n_words do
let angle = two_pi *. float i /. float n_words in
Cairo.save cr;
let red = (1. +. cos(angle -. two_pi /. 6.)) /. 2. in
Cairo.set_source_rgb cr red 0. (1. -. red);
Cairo.rotate cr angle;
(* Inform Pango to re-layout the text with the new transformation. *)
Cairo_pango.update_layout cr layout;
let width, _height = Pango.Layout.get_size layout in
Cairo.move_to cr (-. (float width /. float Pango.scale) /. 2.) (-. radius);
Cairo_pango.show_layout cr layout;
Cairo.restore cr;
done
let () =
let diam = truncate(2. *. radius) in
let surface = Cairo.Image.(create ARGB32 ~w:diam ~h:diam) in
let cr = Cairo.create surface in
Cairo.set_source_rgb cr 1. 1. 1.;
Cairo.paint cr;
draw_text cr;
Cairo.PNG.write surface "pango_demo.png"
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