What's wrong with my button callback

[kadil <ksadil bigpond net au>]

I used glade to "build" some a simple app. Why does my
on_button1_clicked callback segfault. The very same function call works
in the expose event.

Thanks,
Kim


#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <gtk/gtk.h>

#include "callbacks.h"
#include "interface.h"
#include "support.h"
static GdkPixmap *pixmap = NULL;
GtkWidget *drawingarea1;

void
on_button1_clicked                     (GtkButton       *button,
                                        gpointer         user_data)
{ 
 
        gdk_draw_rectangle(pixmap, drawingarea1->style->black_gc,TRUE,50,
50,99, 88);
 
}

gboolean
on_drawingarea1_expose_event           (GtkWidget       *widget,
                                        GdkEventExpose  *event,
                                        gpointer         user_data)
{
gdk_draw_drawable(widget->window, widget->style->fg_gc[GTK_WIDGET_STATE
(widget)], pixmap,  event->area.x, event->area.y,  event->area.x,
event->area.y, event->area.width, event->area.height);
  return FALSE;
}

gboolean
on_drawingarea1_configure_event        (GtkWidget       *widget,
                                        GdkEventConfigure *event,
                                        gpointer         user_data)
{
if (pixmap)
    g_object_unref (pixmap);

  pixmap = gdk_pixmap_new (widget->window,  widget->allocation.width,
widget->allocation.height,-1);
  gdk_draw_rectangle (pixmap, widget->style->white_gc, TRUE, 0, 0,
widget->allocation.width, widget->allocation.height);
  gdk_draw_rectangle(pixmap, widget->style->black_gc,TRUE,0, 0,99, 88);
  return TRUE;

}