#include <gtk/gtk.h>

static gboolean

da_expose (GtkWidget *widget,

           GdkEventExpose *event,

           gpointer user_data)

{

  GtkOffscreenWindow *offscreen = (GtkOffscreenWindow *)user_data;

  GdkPixmap *pixmap;

  cairo_t *cr;

  if (gtk_widget_is_drawable (widget))

    {

      pixmap = gtk_offscreen_window_get_pixmap (offscreen);

      cr = gdk_cairo_create (widget->window);

      gdk_cairo_set_source_pixmap (cr, pixmap, 50, 50);

      cairo_paint (cr);

      cairo_destroy (cr);

    }

  return FALSE;

}

static gboolean

offscreen_damage (GtkWidget      *widget,

                  GdkEventExpose *event,

                  GtkWidget      *da)

{

  gtk_widget_queue_draw (da);

  return TRUE;

}

static gboolean

da_button_press (GtkWidget *area, GdkEventButton *event, GtkWidget *button)

{

  gtk_widget_set_size_request (button, 150, 60);

  return TRUE;

}

int

main (int argc, char **argv)

{

  GtkWidget *window;

  GtkWidget *button;

  GtkWidget *offscreen;

  GtkWidget *da;

  gtk_init (&argc, &argv);

  offscreen = gtk_offscreen_window_new ();

  button = gtk_button_new_with_label ("Test");

  gtk_widget_set_size_request (button, 50, 50);

  gtk_container_add (GTK_CONTAINER (offscreen), button);

  gtk_widget_show (button);

  gtk_widget_show (offscreen);

  /* Queue exposures and ensure they are handled so

   * that the result is uptodate for the first

   * expose of the window. If you want to get further

   * changes, also track damage on the offscreen

   * as done above.

   */

  gtk_widget_queue_draw (offscreen);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

  g_signal_connect (window, "delete-event",

                    G_CALLBACK (gtk_main_quit), window);

  da = gtk_drawing_area_new ();

  gtk_container_add (GTK_CONTAINER (window), da);

  g_signal_connect (da,

                    "expose-event",

                    G_CALLBACK (da_expose),

                    offscreen);

  g_signal_connect (offscreen,

                    "damage-event",

                    G_CALLBACK (offscreen_damage),

                    da);

  gtk_widget_add_events (da, GDK_BUTTON_PRESS_MASK);

  g_signal_connect (da, "button_press_event", G_CALLBACK (da_button_press),

                    button);

  gtk_widget_show_all (window);

  gtk_main();

  return 0;

}