simple (?!) redisplay question

[maglio%cogsci@ucsd.edu (Paul Maglio)]

Suppose I have a program framework with several configurations.
Suppose each configuration has a bunch of display panes, each of
which do incremental redisplay.  Suppose each pane's displayer
carefully creates redisplay cache's using
dw:with-redisplayable-output.  

The question is, why---when I switch configurations---do all my
presentations blink?  I understand that it does redisplay in
several passes, but why does it erase and then redisplay each
object?  Perhaps I'm doing something wrong.  If I had sources I
could tell better.  (I am running Genera 7.4 on a MacIvory).   

Below is a simple example adapted from the documentation on
redisplay.  If you wanna take a few seconds to see what I'm
talking about, wipe it into a buffer, compile it, and
select-<circle>.  Click in the main window a few times to draw
some circles, then click on `other configuration.'  Now click on
`other configuration' again.  All the circles appear, then they
disappear, then they're back.  For complex configurations with
lotsa panes, this blinking is quite a loss.  What am I missing?  

Thanks.

-Paul

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;;; -*- Mode: LISP; Syntax: Common-lisp; Package: USER; Base: 10 -*-

1(dw:define-program-framework circles
0  1:command-definer t
0  :select-key #\circle
  1:command-table (:inherit-from nil
0		  1:kbd-accelerator-p t)
0  1:top-level 0(circle-top-level)
  1:panes ((display :display 
0		   1:redisplay-function 'draw-circles0-main1 
0		   1:incremental-redisplay t)
0	  (listener :interactor)
	  1(menu :command-menu)
	  0(other 1:display
0		 1:redisplay-function0 1'draw-circles0-other
		 1:incremental-redisplay0 1t)0)
  1:state-variables ((circles 0(list (list 'main) (list 'random))))
1  0:configurations
1  0'((main (:layout (main :column 1display0 1menu0 listener))
1	  0(:sizes (main (menu :ask-window scl::self :size-for-pane menu)
			(listener 1 :lines)
			:then (display :even))))
    (random (:layout (random :column other 1menu0 listener))
	    (:sizes (random (menu :ask-window scl::self :size-for-pane menu)
			    (listener 1 :lines)
			    :then (other :even)))))
  :configuration 'main)

(defun circle-top-level (instance)
  (sys:standard-value-let ((lisp:*package* (find-package 'user)))
    1(dw:default-command-top-level 0instance1)0))
 
1(defstruct circle
0  1center-x
0  1center-y
0  1radius)

0(defmacro circles-of (config)
  `(second (find ,config 1circles0 :key #'first1)0))

(defmacro circle-alist (config)
  `(find ,config 1circles0 :key #'first))

1(defmethod (draw-circles0-main1 circles) (stream)
0  1(dolist (circle 0(circles-of 'main))
    1(dw:with-redisplayable-output 
0	1(:unique-id circle :stream stream0 1:cache-value t)
0      1(dw:with-output-as-presentation 
0	  1(:object circle :type 'circle :stream stream)
0	1(graphics:draw-circle 
0	  1(circle-center-x circle) (circle-center-y circle)
0	  1(circle-radius circle)
	  :stream stream)))))

(defmethod (draw-circles0-other1 circles) (stream)
0  1(dolist (circle 0(circles-of 'random))
    1(dw:with-redisplayable-output 
0	1(:unique-id circle :stream stream :cache-value t)
0      1(dw:with-output-as-presentation 
0	  1(:object circle :type 'circle :stream stream)
0	1(graphics:draw-circle 
0	  1(circle-center-x circle) (circle-center-y circle)
0	  1(circle-radius circle)
	  :stream stream)))))
0            
1(define-circles-command (com-delete-circle )
0			1((circle 'circle))
0   (let ((config (send (dw:program-frame dw:*program*) :configuration)))
     1(set0f1 circles 0(list (circle-alist (other-config config))
			 (list config 1(delete circle 0(circles-of config1)0)1))0)))

(1define-circles-command0 (com-other-configuration 1:menu-accelerator0 t)
    ()
   (let ((config (send (dw:program-frame dw:*program*) :configuration)))
     (dw:set-program-frame-configuration (other-config config))))

(defun other-config (config)
  (if (eq config 'main) 'random 'main))

1(define-presentation-to-command-translator0 1delete-this-circle
   (circle)
   (circle)
0  1`(com-delete-circle ,circle))

(define-circles-command (com-add-circle)
0    1((x 'number :default 100)
0     1(y 'number :default 100)
0     1(radius 'number :default 50))
0   (let ((config (send (dw:program-frame dw:*program*) :configuration)))
     1(set0f1 circles 0(list (circle-alist (other-config config))
			 (list config (nconc (list 1(make-circle :center-x x 
0								1:center-y y 
0								1:radius radius)0)
					     (circles-of config1))0)))))

1(define-presentation-to-command-translator add-circle-here
0   1(dw:no-type0 1:documentation "Add a circle here.")
0   1(ignore &key x y)
0  1`(com-add-circle ,x ,y))

(define-circles-command (com-delete-all-circles :menu-accelerator t)
0    1()
0  1(set0f1 circles 0(list (list 'main) (list 'random)1))0)

1(compile-flavor-methods circles)

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