gistfile1.c

#include <gtk/gtk.h>

void on_realize(GtkWidget* widget, gpointer user_data);

int main(int argc, char* argv[]) {
  GtkWidget* widget;

  gtk_init(&argc, &argv);

  widget = gtk_window_new(GTK_WINDOW_TOPLEVEL);
  g_signal_connect(widget, "realize", G_CALLBACK(on_realize), NULL);

  gtk_widget_show_all(widget);

  gtk_main();

  return 0;
}

void on_realize(GtkWidget* widget, gpointer user_data) {
  cairo_region_t *input_region;
  input_region = cairo_region_create ();
  gdk_window_input_shape_combine_region (gtk_widget_get_window (widget),
                                         input_region, 0, 0);
  /* gdk_window_shape_combine_region (gtk_widget_get_window (widget),
                                      input_region, 0, 0); */
  cairo_region_destroy (input_region);
}