[racket] question/problem on racket/gui and "on-paint" flooding

Thank you, I filed a bug report.

Prerendering to a bitmap is what I do for now.


Nik


Am Mittwoch, 12. Juni 2013 schrieb Neil Toronto:
> Yes, that's bad.
>
> I don't have a fix (ain't my bailiwick), but a possible workaround.
> Drawing a bitmap should be much less expensive than drawing a plot, and
> IIRC bitmaps don't draw themselves on un-invalidated parts of a GUI
> device context. (Plots shouldn't, either, but they send a lot of drawing
> commands to the dc, which all have to be clipped, and there's a lot of
> processing behind those commands.) For now, you could try using
> `plot-bitmap' to plot once and then draw them using the `draw-bitmap'
> method.
>
> In the meantime, I think you should submit a bug report.
>
> If you're feeling frisky, you could check out the `unstable/gui/snip'
> module. It defines a `snip-canvas%' class, whose instances allow you to
> put arbitrary "snips" in a GUI. Plot snips - the things you get in
> DrRacket's REPL when you use the `plot' function - cache their
> appearance in a bitmap and draw that bitmap when painted. They only
> recompute the bitmap when the plot is manipulated (i.e. zoomed or
> rotated). If you put plot snips on your GUI, you would get manipulatable
> plots, and the snips' internal caching might keep your app responsive
> when being flooded by paint messages.
>
> Neil ⊥
>
> On 06/11/2013 02:19 PM, Mag. Dr. Nikolaus Klepp wrote:
> > As I'm writing a real-world application in racket (and it's a great tool
> > to do so!) I just ran into another problem:
> >
> > When a a panel% has a visible scrollbar and there are enough children to
> > actually use that scrollbar, then all children get flooded with on-paint
> > calls when the scrollbar is used.
> >
> > To be precise, the problem is not that the children get lots of on-paint,
> > but that invisible children get that calls, too, which results in a
> > pileup of on-paint calls that block the application when the drawing
> > operation is expensive.
> >
> > In my case I have several dozen graphs to present and even touching the
> > scrollbar results in a desaster.
> >
> > Is there a workaround, say, can I find out if a child is visible at all?
> >
> >
> >
> > Example code - just scroll around and watch how often the first child is
> > redrawn, even when invisible:
> >
> > #lang racket
> >
> > (require racket/gui)
> > (require plot)
> >
> > (define counter 0)
> >
> > (define frame (new frame% [label "on-paint flooding"] [min-height 800]
> > [min-width 800]))
> > (define panel (new vertical-panel%  [parent frame] [style '(auto-hscroll
> > auto-vscroll)]))
> >
> > (for-each
> >   (λ (a)
> >     (new canvas%
> >          [parent panel] [min-height 150] [min-width 150]
> >          [paint-callback (λ (c dc)
> >                            (when (= a 0) (set! counter (add1 counter)))
> >                            (define-values (w h) (send dc get-size))
> >                            ; uncomment the following line to see the
> > effect on expensive rendering:
> >                            ; (plot/dc (function (λ (x) (sin (* 4 x))) -1
> > 1) dc 0 0 w h )
> >                            (send dc draw-text (format "~a" counter) 0
> > 0))])) '(0 1 2 3 4 5 6 7 8 9 10))
> >
> > (send frame show #t)
> >
> >
> >
> > Nik
>
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Mag. Dr. Nikolaus Klepp
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