how to synchronize height reduction

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

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 drawing area 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, drawing area h) = (284, 261)
  (toplevel h, drawing area h) = (285, 262)
  (toplevel h, drawing area h) = (286, 263)
  (toplevel h, drawing area h) = (288, 265)
  (toplevel h, drawing area h) = (290, 267)
  (toplevel h, drawing area h) = (292, 269)
  (toplevel h, drawing area h) = (294, 271)
  (toplevel h, drawing area h) = (297, 274)

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, drawing area h) = (314, 291)
  (toplevel h, drawing area h) = (311, 288)
  (toplevel h, drawing area h) = (293, 270)
  (toplevel h, drawing area h) = (245, 256)
  (toplevel h, drawing area h) = (197, 256)
  (toplevel h, drawing area h) = (145, 256)
  (toplevel h, drawing area h) = (101, 256)
  (toplevel h, drawing area h) = (55, 256)
  (toplevel h, drawing area h) = (15, 256)
  (toplevel h, drawing area h) = (1, 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.)

Following is some Common Lisp code to demonstrate the problem.
Sorry about not using C to write the sample code.  Any suggestions
will be appreciated.

Best wishes,

Chisheng Huang

ps.  I do use GTK+ Reference Manual and occasionally poke into GTK+
     source code.  So replies contain C code is perfect, too.

pps. I'm using GTK+-1.2.10.


;; NOTE: comments start with semicolons.
;;
;; Create a top level window that contains a scrolled window, which
;; contains a drawing area.  The width of the top level window is
;; 256.  The drawing area is 512 wide and 256 high.  The scrolled
;; window is told never to enable vertical scrolling.
;; 
(setf toplevel (gtk:window-new :toplevel))
(setf (gtk:widget-width toplevel) 256)
(setf (gtk:window-allow-grow-p toplevel) t)
(setf (gtk:window-allow-shrink-p toplevel) t)

;; create a scrolled window and stuff it into the top level window.
(setf scrolled (gtk:scrolled-window-new))
(gtk:container-add toplevel scrolled)
;; never show vertical scroll bar
(setf (gtk:scrolled-window-vscrollbar-policy scrolled) :never)
;; automatically show horizontal scroll bar
(setf (gtk:scrolled-window-hscrollbar-policy scrolled) :automatic)

;; create a 512x256 drawing area and stuff it into the scrolled window.
(setf drawing-area (gtk:drawing-area-new))
(gtk:scrolled-window-add-with-viewport scrolled drawing-area)
(setf (gtk:widget-width drawing-area) 512)
(setf (gtk:widget-height drawing-area) 256)

;; returns the height allocation.
(defun widget-height-allocation (widget)
  (multiple-value-bind (w h)
      (gtk:widget-allocation widget)
    (declare (ignore w))
    h))

;; connect a configure event handler to drawing-area to print out
;; the height of toplevel and the height of drawing-area.
(gtk:signal-connect drawing-area
                    :configure-event
                    #'(lambda (event)
                        (declare (ignore event))
                        (format t
                                "~&(toplevel h, drawing area h) = (~A, ~A)~%"
                                (widget-height-allocation toplevel)
                                (widget-height-allocation drawing-area))
                        (finish-output)))

;; now we show the top level window and all of its kids.
(gtk:widget-show-all toplevel)