GTK method patching

gtk-method-patching.c

// gtk-method-patching.c: an example of patching GTK methods. 
// gcc `pkg-config --libs --cflags gtk+-3.0` gtk-method-patching.c 

#include <gtk/gtk.h>

typedef void (* get_preferred_width) (GtkWidget *, gint *, gint *);

get_preferred_width original; // A place to store real function

void patched_gpw (GtkWidget *w, gint *min_w, gint *nat_w)
{
  original (w, min_w, nat_w);
  g_message ("Patched: %p %i %i", w, min_w ? *min_w : 0, nat_w ? *nat_w : 0);
}

int
main (int argc, char **argv)
{
  GtkWidget *window;
  GtkWidget *box, *box2;

  gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

  box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 0);
  box2 = gtk_box_new (GTK_ORIENTATION_VERTICAL, 0);

  // Patching
  {
    GtkWidgetClass *widget_class = GTK_WIDGET_GET_CLASS (box);
    original = widget_class->get_preferred_width;
    widget_class->get_preferred_width = patched_gpw;
  }

  gtk_container_add (GTK_CONTAINER (box), gtk_button_new_with_label ("hello"));
  gtk_container_add (GTK_CONTAINER (box2), gtk_button_new_with_label ("world"));
  gtk_container_add (GTK_CONTAINER (box), box2);
  gtk_container_add (GTK_CONTAINER (window), box);
  gtk_widget_show_all (window);

  gtk_main ();

  return 0;
}