OCaml, C, SDL2 and cairo fused together

ocaml-c/Makefile

@@ -1,11 +1,10 @@
-hello: hello.cmo dllhello_stubs.so
-	ocamlc -o hello hello.cmo -dllib dllhello_stubs.so
+all: hello.opt
 
-hello.cmo: hello.ml
-	ocamlc -c  hello.ml
+hello.opt: hello.cmx hello_stubs.o
+	ocamlopt -o hello.opt hello_stubs.o hello.cmx -ccopt "$(shell pkg-config --cflags --libs sdl2 cairo)" 
 
-dllhello_stubs.so: hello_stubs.o
-	ocamlmklib -o hello_stubs hello_stubs.o
+hello.cmx: hello.ml
+	ocamlopt -c hello.ml -ccopt "$(shell pkg-config --cflags --libs sdl2 cairo)"
 
 hello_stubs.o: hello_stubs.c
-	ocamlc -c hello_stubs.c
+	ocamlopt -c hello_stubs.c -ccopt "$(shell pkg-config --cflags --libs sdl2 cairo)"

ocaml-c/hello.ml

@@ -1,4 +1,5 @@
 external print_hello: unit -> unit = "caml_print_hello"
 
 let () =
-  print_hello ()
+  print_hello ();
+  print_endline "Ran from OCaml"

ocaml-c/hello_stubs.c

@@ -1,9 +1,100 @@
 #include <stdio.h>
+#include <stdbool.h>
 #include <caml/mlvalues.h>
+#include <cairo.h>
+#include <SDL2/SDL.h>
+
+#define SCREEN_WIDTH 800
+#define SCREEN_HEIGHT 600
 
 CAMLprim value
 caml_print_hello(value unit)
 {
-    printf("Hello\n");
+    SDL_Rect screen_rect = {
+        .x = 0, .y = 0,
+        .w = SCREEN_WIDTH,
+        .h = SCREEN_HEIGHT
+    };
+
+    SDL_Init(SDL_INIT_EVERYTHING);
+    SDL_Window *const window = SDL_CreateWindow(
+        "Multik",
+        100, 100,
+        SCREEN_WIDTH, SCREEN_HEIGHT,
+        SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE);
+    SDL_Renderer *const renderer = SDL_CreateRenderer(
+        window, -1,
+        SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
+    SDL_Texture *texture = SDL_CreateTexture(
+        renderer,
+        SDL_PIXELFORMAT_ARGB8888,
+        SDL_TEXTUREACCESS_STREAMING,
+        SCREEN_WIDTH, SCREEN_HEIGHT);
+
+    float a = 0.0f;
+    bool stop = false;
+    SDL_Event event;
+    /* TODO: FPS is not shown */
+    while (!stop) {
+        while (!stop && SDL_PollEvent(&event)) {
+            switch (event.type) {
+            case SDL_QUIT:
+                stop = true;
+                break;
+            }
+        }
+
+        SDL_RenderClear(renderer);
+
+        void *pixels;
+        int pitch;
+
+        SDL_LockTexture(texture, NULL, &pixels, &pitch);
+
+        cairo_surface_t *surface =
+            cairo_image_surface_create_for_data(
+                pixels,
+                CAIRO_FORMAT_ARGB32,
+                SCREEN_WIDTH, SCREEN_HEIGHT, pitch);
+        cairo_t *cr = cairo_create(surface);
+
+        cairo_set_source_rgb (cr, 0, 0, 0);
+        cairo_paint (cr);
+
+        cairo_select_font_face(
+            cr, "serif",
+            CAIRO_FONT_SLANT_NORMAL,
+            CAIRO_FONT_WEIGHT_BOLD);
+        cairo_set_font_size(cr, 32.0);
+        cairo_set_source_rgb(cr, 0.0, 1.0, 1.0);
+        cairo_move_to(cr, 10.0, 50.0);
+        cairo_show_text(cr, "4HEad");
+
+        cairo_set_source_rgb(cr, 1.0, 0.0, 0.0);
+        cairo_move_to(cr, 0.0, 0.0);
+        cairo_curve_to(cr, 0.0 + a, SCREEN_HEIGHT + a,
+                       SCREEN_WIDTH - a, SCREEN_HEIGHT - a,
+                       SCREEN_WIDTH, 0.0);
+        cairo_set_line_width(cr, 5);
+        cairo_stroke(cr);
+
+        cairo_destroy(cr);
+        cairo_surface_destroy(surface);
+
+        SDL_UnlockTexture(texture);
+
+        SDL_RenderCopy(renderer, texture,
+                       &screen_rect,
+                       &screen_rect);
+
+        SDL_RenderPresent(renderer);
+        a += 1.0f;
+    }
+
+    SDL_DestroyTexture(texture);
+    SDL_DestroyRenderer(renderer);
+    SDL_DestroyWindow(window);
+    SDL_Quit();
+
     return Val_unit;
 }