Re: [racket-users] Re: Trying to understand racket/gui and racket/draw

2016-09-16 Thread Robby Findler 
You could draw into a bitmap and then have on-paint draw that bitmap, too.

Robby

On Fri, Sep 16, 2016 at 2:53 AM, Jens Axel Søgaard
 wrote:
> As Alex writes the operating system (the system GUI) might erase parts of a
> window at
> any time. Therefore you need to do all your drawing from within on-paint.
>
> http://stackoverflow.com/q/16084690/23567
>
> /Jens Axel
>
>
> 2016-09-16 7:09 GMT+02:00 Alex Harsanyi :
>>
>> According to the documentation for the canvas<%> interface you cannot rely
>> on the canvas not being cleared
>> (http://docs.racket-lang.org/gui/canvas___.html?q=canvas%3C%25%3E):
>>
>> Even when the canvas’s style suppresses explicit clearing of the canvas, a
>> canvas may be erased by the windowing system due to window-moving and
>> -resizing operations. For a transparent canvas, “erased” means that the
>> canvas’s parent window shows through.
>>
>> I suspect the window system clears the canvas when the frame is resized.
>>
>> Alex.
>>
>>
>> On Friday, September 16, 2016 at 9:06:01 AM UTC+8, David K. Storrs wrote:
>> > How do I draw into a canvas and have the results persist past the next
>> > call to paint-callback?
>> >
>> >
>> > Given the code below I was expecting to see:
>> >
>> > 1) A window opens with a diagonal green line on it
>> >
>> > 2) A vertical blue line appears, crossing with the green line
>> >
>> > 3) The window goes fullscreen, still showing the green and blue lines
>> >
>> >
>> >
>> > Instead what I get is:
>> >
>> > 1) A window appears with vertical blue line
>> >
>> > 2) The blue line disappears and is replaced by a diagonal green line
>> >
>> > 3) The window goes fullscreen.  Only the green line is shown.
>> >
>> >
>> > I'm guessing that what's happening is that the window opens, completes
>> > going through the script (and therefore calling the section of code that
>> > displays the blue line), then the on-paint event is triggered and erases 
>> > the
>> > canvas's dc before calling the paint callback.
>> >
>> >
>> > I tried removing the paint-callback on the theory that the default one
>> > probably just told the dc to render its content.  That made no change 
>> > except
>> > that (unsurprisingly) the green line is not painted -- the blue line is, 
>> > but
>> > promptly disappears.
>> >
>> >
>> > Assuming I'm right about what's going on, how do I draw into a dc and
>> > have the changes persist?
>> >
>> >
>> >
>> > #lang racket
>> > (require racket/gui)
>> >
>> >
>> > (define-values (w h) (get-display-size))
>> > (displayln (format "Display size (pixels): ~a x ~a" w h))  ;; 1440 x 877
>> > (define frame (new frame%
>> >(label "Example")
>> >(width w)
>> >(height h)
>> >))
>> > (define canvas
>> >   (new canvas%
>> >(parent frame)
>> >(style '(border hscroll vscroll resize-corner))
>> >(paint-callback (lambda (canvas dc)
>> >  (send dc set-pen (send the-pen-list
>> > find-or-create-pen "green" 1 'solid))
>> >  (send dc draw-line 0 0 1430 867)
>> >
>> >
>> > (define dc (send canvas get-dc))
>> >
>> > (send frame show #t)
>> > (send dc set-pen (send the-pen-list find-or-create-pen "blue" 1 'solid))
>> > (send dc draw-line 700 0 700 877)
>> > (send frame fullscreen #t)
>>
>> --
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>
>
>
>
> --
> --
> Jens Axel Søgaard
>
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Re: [racket-users] Re: Trying to understand racket/gui and racket/draw

2016-09-16 Thread Jens Axel Søgaard 
As Alex writes the operating system (the system GUI) might erase parts of a
window at
any time. Therefore you need to do all your drawing from within on-paint.

http://stackoverflow.com/q/16084690/23567

/Jens Axel


2016-09-16 7:09 GMT+02:00 Alex Harsanyi :

> According to the documentation for the canvas<%> interface you cannot rely
> on the canvas not being cleared (http://docs.racket-lang.org/
> gui/canvas___.html?q=canvas%3C%25%3E):
>
> Even when the canvas’s style suppresses explicit clearing of the canvas, a
> canvas may be erased by the windowing system due to window-moving and
> -resizing operations. For a transparent canvas, “erased” means that the
> canvas’s parent window shows through.
>
> I suspect the window system clears the canvas when the frame is resized.
>
> Alex.
>
>
> On Friday, September 16, 2016 at 9:06:01 AM UTC+8, David K. Storrs wrote:
> > How do I draw into a canvas and have the results persist past the next
> call to paint-callback?
> >
> >
> > Given the code below I was expecting to see:
> >
> > 1) A window opens with a diagonal green line on it
> >
> > 2) A vertical blue line appears, crossing with the green line
> >
> > 3) The window goes fullscreen, still showing the green and blue lines
> >
> >
> >
> > Instead what I get is:
> >
> > 1) A window appears with vertical blue line
> >
> > 2) The blue line disappears and is replaced by a diagonal green line
> >
> > 3) The window goes fullscreen.  Only the green line is shown.
> >
> >
> > I'm guessing that what's happening is that the window opens, completes
> going through the script (and therefore calling the section of code that
> displays the blue line), then the on-paint event is triggered and erases
> the canvas's dc before calling the paint callback.
> >
> >
> > I tried removing the paint-callback on the theory that the default one
> probably just told the dc to render its content.  That made no change
> except that (unsurprisingly) the green line is not painted -- the blue line
> is, but promptly disappears.
> >
> >
> > Assuming I'm right about what's going on, how do I draw into a dc and
> have the changes persist?
> >
> >
> >
> > #lang racket
> > (require racket/gui)
> >
> >
> > (define-values (w h) (get-display-size))
> > (displayln (format "Display size (pixels): ~a x ~a" w h))  ;; 1440 x 877
> > (define frame (new frame%
> >(label "Example")
> >(width w)
> >(height h)
> >))
> > (define canvas
> >   (new canvas%
> >(parent frame)
> >(style '(border hscroll vscroll resize-corner))
> >(paint-callback (lambda (canvas dc)
> >  (send dc set-pen (send the-pen-list
> find-or-create-pen "green" 1 'solid))
> >  (send dc draw-line 0 0 1430 867)
> >
> >
> > (define dc (send canvas get-dc))
> >
> > (send frame show #t)
> > (send dc set-pen (send the-pen-list find-or-create-pen "blue" 1 'solid))
> > (send dc draw-line 700 0 700 877)
> > (send frame fullscreen #t)
>
> --
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>



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-- 
Jens Axel Søgaard

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