MODULE gl ;

(*
   m2-GTK4 example - OpenGL in a GtkGLArea.

   A GtkGLArea with auto-render; the "render" callback clears the
   framebuffer to a colour.

   Build:  make examples
   Run:    ./build/examples/gl
*)

FROM Gio IMPORT g_application_run;
FROM GtkApplication IMPORT gtk_application_new;
FROM GtkWindow IMPORT gtk_application_window_new, gtk_window_set_title,
   gtk_window_set_default_size, gtk_window_set_child, gtk_window_present;
FROM GtkGLArea IMPORT gtk_gl_area_new, gtk_gl_area_set_auto_render,
   gtk_gl_area_set_has_depth_buffer;
FROM GL IMPORT glClear, glClearColor, GLColorBufferBit;
FROM GObject IMPORT g_signal_connect_data, GConnectDefault;
FROM GtkClosures IMPORT Connect2;
FROM SYSTEM IMPORT ADDRESS, ADR;
FROM libc IMPORT printf;

CONST
   AppId = "org.example.m2gtk4.Gl";

(* gboolean render(GtkGLArea *area, GdkGLContext *context, gpointer user) *)
PROCEDURE OnRender (area: ADDRESS; context: ADDRESS; user: ADDRESS) : INTEGER;
BEGIN
   glClearColor(0.16, 0.50, 0.72, 1.0);
   glClear(GLColorBufferBit);
   RETURN 1
END OnRender;

PROCEDURE OnActivate (application: ADDRESS; data: ADDRESS);
VAR
   window, area: ADDRESS;
BEGIN
   area := gtk_gl_area_new();
   gtk_gl_area_set_auto_render(area, 1);
   gtk_gl_area_set_has_depth_buffer(area, 1);
   g_signal_connect_data(area, "render", ADR(OnRender), NIL, NIL,
                         GConnectDefault);

   window := gtk_application_window_new(application);
   gtk_window_set_title(window, "m2-GTK4 GL");
   gtk_window_set_default_size(window, 400, 300);
   gtk_window_set_child(window, area);
   gtk_window_present(window)
END OnActivate;

VAR
   app: ADDRESS;
BEGIN
   app := gtk_application_new(AppId, 0);
   IF app = NIL THEN
      printf("gtk_application_new failed\n");
      HALT(1)
   END;
   Connect2(app, "activate", OnActivate, NIL);
   g_application_run(app, 0, NIL)
END gl.