How to draw a triangle with OCaml and GLFW? - opengl

Question

I tried to draw a triangle with OCaml using glfw-ocaml and lablgl libraries. The program only shows a black window and I didn't manage to draw something in.
I've tried to use shader and the result is the same. I succeed to draw a simple triangle with GLUT. But how to do it with GLFW?
Here's my code (without shader):
let of_float_array_static arr ~kind =
let raw = Raw.create_static kind ~len:(Array.length arr) in
Raw.sets_float raw ~pos:0 arr;
raw
let () =
(* Initialize the library *)
GLFW.init ();
GLFW.windowHint ~hint:Samples ~value:(Some 4);
GLFW.windowHint ~hint:ContextVersionMajor ~value:3;
GLFW.windowHint ~hint:ContextVersionMinor ~value:3;
GLFW.windowHint ~hint:OpenGLForwardCompat ~value:true;
GLFW.windowHint ~hint:OpenGLProfile ~value:CoreProfile;
(* Create a windowed mode window and its OpenGL context *)
let window = GLFW.createWindow ~width:1024 ~height:768 ~title:"Triangle" () in
(* Make the window's context current *)
GLFW.makeContextCurrent ~window:(Some window);
(* Ensure we can capture the escape key being pressed below *)
GLFW.setInputMode ~window:window ~mode:StickyKeys ~value:true;
(* Dark blue background *)
GlClear.color (0., 0., 0.4);
let raw = of_float_array_static [|-1.; -1.; 0.; 1.; -1.; 0.; 0.; 1.; 0.|] ~kind:`float in
GlArray.vertex `three raw;
while (not ((GLFW.getKey ~window:window ~key:Escape) || (GLFW.windowShouldClose ~window:window))) do
(* Render here *)
(* Clear the screen *)
GlClear.clear [`color; `depth];
(* Draw triangle... *)
GlArray.enable `vertex;
GlArray.draw_arrays `triangles ~first:0 ~count:3;
GlArray.disable `vertex;
(* Swap front and back buffers *)
GLFW.swapBuffers ~window:window;
(* Poll for and process events *)
GLFW.pollEvents ()
done;
GLFW.terminate ()
I suppose I didn't succeed to draw in the right buffer, but I didn't find any function allowing to draw in a specific buffer. Moreover, the program (except the shaders) works when I use glut.