making dialog items invisible

["Mark A. Tapia" <markt@dgp.toronto.edu>]

Mea culpa, in my response to marsella@athos.rutgers.edu, I should
have mentioned that oodles-of-utils contains the following code
in the low-class-extensions folder in the simple-view-ce.lisp 
(this is a stripped version of the actual file):

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; simple-view-ce.Lisp
;;
;; Copyright  1992 Northwestern University Institute for the Learning Sciences
;; All Rights Reserved
;;
;; author: Michael S. Engber
;;
;; methods for the view class
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(export '(offset-view-position
          view-hide view-show view-shown-p view-shown-position
          ))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(eval-when (:compile-toplevel :load-toplevel :execute)
  
  (defconstant $di-hidden-const  8192)
  (defconstant $di-hide-h-offset 16384)
  
  )

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defmethod offset-view-position ((sv simple-view) dh &optional dv)
  (set-view-position sv (add-points (view-position sv) (make-point dh dv))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; hiding views (as per HideDItem & ShowDItem IM IV p.59)

(defmethod view-hide ((sv simple-view))
  (when (view-shown-p sv)
    (offset-view-position sv #.(make-point $di-hide-h-offset 0))))

(defmethod view-show ((sv simple-view))
  (unless (view-shown-p sv)
    (offset-view-position sv #.(make-point (- $di-hide-h-offset) 0))))

(defmethod view-shown-p ((sv simple-view))
  (< (point-h (view-position sv)) #.$di-hidden-const))

(defmethod view-shown-position ((sv simple-view))
  (if (view-shown-p sv)
    (view-position sv)
    (subtract-points (view-position sv) #.(make-point $di-hide-h-offset 0))))