[plt-scheme] creating new widgets for MrEd

Hi,

I just added an entry to the comments in the Scheme cookbook in  the
'GUI: Aggregating
Widgets in a Single Widget' section
 -- http://schemecookbook.org/Cookbook/GUIWidgetAggregation

It is an example of a simple widget created from drawing toolkit elements,
rather than existing widgets.

I'd appreciate any comments/edits to improve it. (technically or
pedagogically)

Cheers, Stephen

;  make new widget'scatter-chart%'
;; do this all in Pretty Big language (DrScheme only)
(define scatter-chart% (class pane% ()
                         (init-field parent)
                         ; Make the drawing area
                         (super-instantiate () (parent parent) ;
instantiate this FIRST
                           [min-width 100] [stretchable-width #f]
                           (min-height 200) [stretchable-height #f])

                         ;; internal data
                         (define list-of-points '()) ;; start with empty list
                         (define canvas (new canvas% [parent this]
                                             (paint-callback (lambda
(canvas dc) (draw-chart)))
                                             [min-width 100]
[stretchable-width #f]
                                             [min-height 200]
[stretchable-height #f]
                                             ))
                         (define dc (send canvas get-dc)) ; Get the
canvas's drawing context
                         ; Make some pens and brushes for use later
                         (define no-pen (make-object pen% "BLACK" 1
'transparent))
                         (define blue-brush (make-object brush% "BLUE" 'solid))
                         (define yellow-brush (make-object brush%
"YELLOW" 'solid))

                         ;; public methods
                         ;; add-point : new-point
                         (define/public (add-point new-point)
                           (set! list-of-points (cons new-point
list-of-points)) ;; add to the list
                           (send dc draw-rectangle 0 new-point 200 1))
;; and draw the line
                         ;; draw-chart : draw a chart based on the
list of integers supplied
                         ;; see
http://download.plt-scheme.org/doc/371/html/mred/mred-Z-H-397.html
                         (define/public (draw-chart)
                           (send dc set-pen no-pen)
                           (send dc set-brush blue-brush)
                           (send dc draw-rectangle 0 0 100 200)  ; big
blue rectangle
                           (send dc set-brush yellow-brush)
                           (map
                            (lambda (y) (send dc draw-rectangle 0 y
200 1)) ; draw a line for each integer.
                            list-of-points ))
                         (draw-chart))) ; draw it for the first time
when this class is instantiated

; Make a  frame
(define frame (new frame% [label "scatter-chart% Example"] [width 100]
[height 200]))

; Show the frame
(send frame show #t)
; Wait a second to let the window get ready
;(sleep/yield 1)
(define new-my-widget (new scatter-chart% (parent frame) ))  ;
instantiate the widget in the frame
(define new-his-widget (new scatter-chart% (parent frame) )) ; make another one

(send new-my-widget draw-chart)
; Draw the face
(define (go)
  (map (lambda (y)

       (send new-my-widget add-point y) ; add a point at a time
         (sleep/yield 0.05)) ; draw it slowly
       '(10 30 22 77 78 79 17 65 97 54 55 56 57 91 33 55 95 99 125 155
157 159 188 187 186 191))) ;; list of datapoints

(go)  ;; !!!


-- 
Cheers,

Stephen



--
Stephen De Gabrielle
s.degabrielle at ucl.ac.uk
Telephone +44 (0)20 7679 5242 (x45242)
Mobile                  079 851 890 45
http://www.uclic.ucl.ac.uk/annb/MaSI.html
University College London Interaction Centre
Remax House - 31/32 Alfred Place
London - WC1E 7DP
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