how to shrink a drawing area as its toplevel window is shrunk

[Chisheng Huang <cph chi-square-works com>]

*** C source code attached at the end ***

I have a toplevel window that contains a scrolled window, which contains
a drawing area.  The height of the drawing area is initially set to 256.
The scrolled window is told never to enable vertical scrolling.  A
configure event handler is connected to the toplevel window to print out
the height of the toplevel window and the height of the drawing area.

The height of the drawing area increases as the height of the toplevel
window increases without any problem.  For example, the printout would
look like the following:
  Toplevel h: 277   Drawing area h: 256
  Toplevel h: 281   Drawing area h: 258
  Toplevel h: 287   Drawing area h: 264
  Toplevel h: 291   Drawing area h: 268
  Toplevel h: 295   Drawing area h: 272

If I decrease the height of the toplevel window, the height of the drawing
area will only decrease to 256 and stay there no matter how short the
toplevel window is resized.  For example:
  Toplevel h: 311   Drawing area h: 288
  Toplevel h: 308   Drawing area h: 285
  Toplevel h: 297   Drawing area h: 274
  Toplevel h: 281   Drawing area h: 258
  Toplevel h: 270   Drawing area h: 256
  Toplevel h: 259   Drawing area h: 256
  Toplevel h: 241   Drawing area h: 256
  Toplevel h: 217   Drawing area h: 256
  Toplevel h: 199   Drawing area h: 256
  Toplevel h: 188   Drawing area h: 256
  Toplevel h: 172   Drawing area h: 256
  Toplevel h: 156   Drawing area h: 256
  Toplevel h: 153   Drawing area h: 256

Does anybody know how to make the drawing area keep reducing its
height below 256 as the toplevel window is getting shorter and
shorter?  (Note: In my real program code, there is a minimum height
for the toplevel window so that the drawing area will always have
meaningful height.)  Any suggestions will be appreciated.

Best wishes,

Chisheng Huang


#include <gtk/gtk.h>

void destroy( GtkWidget *widget,
              gpointer   data )
{
    gtk_main_quit();
}

static GtkWidget *area;

static gint configure_event( GtkWidget         *widget,
                             GdkEventConfigure *event )
{
  g_print ("Toplevel h: %d   Drawing area h: %d\n", 
           widget->allocation.height, 
           area->allocation.height);
  return TRUE;
}

int main( int   argc,
          char *argv[] )
{
    static GtkWidget *window;
    GtkWidget *scrolled_window;
    
    gtk_init (&argc, &argv);
    
    /* toplevel window */
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_signal_connect (GTK_OBJECT (window), "destroy",
                        (GtkSignalFunc) destroy, NULL);
    gtk_signal_connect (GTK_OBJECT(window),"configure_event",
                        (GtkSignalFunc) configure_event, NULL);
    gtk_widget_set_usize(window, 256, 256);
    gtk_window_set_policy(GTK_WINDOW(window), TRUE, TRUE, FALSE);
    
    /* scrolled window */
    scrolled_window = gtk_scrolled_window_new (NULL, NULL);
    gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW (scrolled_window),
                                    GTK_POLICY_AUTOMATIC, GTK_POLICY_NEVER);
    gtk_container_add(GTK_CONTAINER (window), scrolled_window);
    gtk_widget_show (scrolled_window);

    /* drawing area */
    area = gtk_drawing_area_new();
    gtk_widget_set_usize(area, 256, 256);
    gtk_scrolled_window_add_with_viewport (
                      GTK_SCROLLED_WINDOW (scrolled_window), area);
    gtk_widget_show (area);
    
    gtk_widget_show (window);
    gtk_main();
    return(0);
}
/* example-end */