[plt-scheme] Calling Superclass Methods

I think you probably want to leave the get-dc method alone and have
instead a get-current-bitmap-dc or similar that you call from your
drawing routines and whose result differs. Then, the on-paint method
can use get-dc to get the actual dc for the screen, and then draw the
appropriate bitmap into it.

Would that work?

Robby

On Dec 9, 2007 8:48 PM, Doug Williams <m.douglas.williams at gmail.com> wrote:
> I am trying to create an animated-canvas% class that has two bitmaps that I
> swap for some simple animation.  I have the code working with a straight
> canvas% instance (with the bitmaps, and dcs in variables), but wanted to
> abstract it into a subclass.  The problem is that I haven't figured out how
> to override the get-dc (to return a dc for one of the bitmaps) and still
> call the superclass's get-dc to draw the bit map on the canvas.  Any other
> suggestions on the approach would also be welcome.
>
> (module animated-canvas mzscheme
>
>   (require (lib "class.ss"))
>   (require (lib "mred.ss" "mred"))
>   (require (lib "etc.ss"))
>
>   (provide (all-defined))
>
>   (define animated-canvas%
>     (class canvas%
>       (inherit refresh)
>       (inherit get-client-size)
>       (inherit min-client-height)
>       (inherit min-client-width)
>       (super-instantiate ())
>       (define bitmap-vector
>         (let ((w (min-client-width))
>               (h (min-client-height)))
>           ;(printf "width = ~a, height = ~a~n" w h)
>           (build-vector
>            2
>            (lambda (i)
>              (make-object bitmap% w h)))))
>       (define from-bitmap 0)
>       (define to-bitmap 1)
>       (define from-bitmap-dc (make-object bitmap-dc%))
>       (define to-bitmap-dc (make-object bitmap-dc%))
>       (define/public (swap-bitmaps)
>         ;; Reset bitmap-dc instances.
>         (send from-bitmap-dc set-bitmap #f)
>         (send to-bitmap-dc set-bitmap #f)
>         ;; Swap bitmaps.
>         (set! from-bitmap (modulo (+ from-bitmap 1) 2))
>         (set! to-bitmap (modulo (+ to-bitmap 1) 2))
>         ;; Set bitmap-dc instances.
>         (send from-bitmap-dc set-bitmap (vector-ref bitmap-vector
> from-bitmap))
>         (send to-bitmap-dc set-bitmap (vector-ref bitmap-vector to-bitmap))
>         ;;
>         (refresh))
>       (rename (super-get-dc get-dc)) ; this doesn't work, for example
>       (define/override (get-dc)
>         (printf "animated-canvas% get-dc~n")
>         to-bitmap-dc)
>       (define/override (on-paint)
>         (let ((canvas-dc (super-get-dc))) ; here is where I want to call the
> get-dc method for the superclass
>           (send canvas-dc draw-bitmap (vector-ref bitmap-vector from-bitmap)
> 0 0)))
>         ))
>
>   )
>
> Doug
>
>
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