gtkexample.c

#include <math.h>
#include <gtk/gtk.h>
#include <epoxy/gl.h>

static GLuint vao = 0;

/* We need to set up our state when we realize the GtkGLArea widget */
static void
realize (GtkWidget *widget)
{
  gtk_gl_area_make_current (GTK_GL_AREA (widget));
  glGenVertexArrays (1, &vao);
}

/* We should tear down the state when unrealizing */
static void
unrealize (GtkWidget *widget)
{
  gtk_gl_area_make_current (GTK_GL_AREA (widget));

  if (gtk_gl_area_get_error (GTK_GL_AREA (widget)) != NULL)
    return;

  glDeleteVertexArrays (1, &vao);
}

static gboolean
render (GtkGLArea    *area,
        GdkGLContext *context)
{
  if (gtk_gl_area_get_error (area) != NULL)
    return FALSE;

  /* Clear the viewport */
  glClearColor (0.5, 0.5, 0.5, 1.0);
  glClear (GL_COLOR_BUFFER_BIT);

  /* Flush the contents of the pipeline */
  glFlush ();

  return TRUE;
}

static void
activate (GtkApplication* app,
          gpointer        user_data)
{
    GtkWidget *window, *box, *gl_area;

    window = gtk_application_window_new (app);
    gtk_window_set_title (GTK_WINDOW (window), "OpenGL Area");
    gtk_window_set_default_size (GTK_WINDOW (window), 400, 600);
    gtk_container_set_border_width (GTK_CONTAINER (window), 12);

    box = gtk_box_new (GTK_ORIENTATION_VERTICAL, FALSE);
    gtk_box_set_spacing (GTK_BOX (box), 6);
    gtk_container_add (GTK_CONTAINER (window), box);

    gl_area = gtk_gl_area_new ();
    gtk_widget_set_hexpand (gl_area, TRUE);
    gtk_widget_set_vexpand (gl_area, TRUE);
    gtk_container_add (GTK_CONTAINER (box), gl_area);

    /* We need to initialize and free GL resources, so we use
     * the realize and unrealize signals on the widget
     */
    g_signal_connect (gl_area, "realize", G_CALLBACK (realize), NULL);
    g_signal_connect (gl_area, "unrealize", G_CALLBACK (unrealize), NULL);

    /* The main "draw" call for GtkGLArea */
    g_signal_connect (gl_area, "render", G_CALLBACK (render), NULL);

    gtk_widget_show_all (window);
}

int
main (int    argc,
      char **argv)
{
  GtkApplication *app;
  int status;

  app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

  return status;
}

Build with: gcc $(pkg-config --cflags --libs gtk+-3.0 epoxy) gtkexample.c