[racket] Using 2htdp/image with racket-gui

Oh, I see. In that case, they should use the render-image function
directly. Override the on-paint method, call the get-dc method and
pass that and some suitable coordinates to do the drawing. I recommend
using this only for drawing the final image, don't use other dc
methods (I mean, you can, but you don't want to).

But a much better approach overall is to use the universe library:

  http://docs.racket-lang.org/teachpack/2htdpuniverse.html

Robby


On Thu, Mar 19, 2015 at 9:53 PM, Andrew Mauer-Oats <maueroats at gmail.com> wrote:
> Thanks. Yes, they want to (say) draw a solid green circle next to the name
> of someone who has been active in the last five minutes. As I understand it,
> they followed the GUI Toolkit intro and arrived at the point where they have
> a canvas% with the on-paint method specified in its constructor. The
> on-paint method then needs to draw the green circle. They are familiar with
> (circle 20 "solid" "green"), so they just want to do the equivalent of
> (place-image green-circle x y ?dc?).
>
> I think the image->bitmap function Alexander provided looks like what they
> need, and then they can use the draw-bitmap message.
>
> I didn't know how to pull the functions from different packages to make them
> usable one file.
>
> Thanks for the help.
>
> Andrew
>
>
> Andrew Mauer-Oats
> Mathematics Ph.D.
> Chicago Public Schools: Whitney Young
>
> On Thu, Mar 19, 2015 at 8:15 PM, Alexander D. Knauth <alexander at knauth.org>
> wrote:
>>
>> Here’s one way, if you mean a bitmap% object:
>>
>> #lang racket/base
>>
>> (provide image->bitmap)
>>
>> (require racket/class
>>          (only-in racket/draw make-bitmap bitmap-dc%)
>>          (only-in 2htdp/image image-width image-height)
>>          (only-in mrlib/image-core render-image))
>>
>> (define (image->bitmap image)
>>   (let* ([width (image-width image)]
>>          [height (image-height image)]
>>          [bm (make-bitmap width height)]
>>          [dc (make-object bitmap-dc% bm)])
>>     (send dc clear)
>>     (render-image image dc 0 0)
>>     bm))
>>
>>
>> On Mar 19, 2015, at 7:05 PM, Robby Findler <robby at eecs.northwestern.edu>
>> wrote:
>>
>> > When you say "bitmap" do you mean "bitmap% object"? And if so, why do
>> > they want to do that? If not, do you mean something else?
>> >
>> > Robby
>> >
>> >
>> > On Thu, Mar 19, 2015 at 5:24 PM, Andrew Mauer-Oats <maueroats at gmail.com>
>> > wrote:
>> >> Is there a public way to change an image created using the 2htdp/image
>> >> library into a bitmap?
>> >>
>> >> My students are used to those functions and it would be easier for some
>> >> of
>> >> them to go and build the GUI they want if they didn't have to change
>> >> over to
>> >> explicitly using drawing contexts.
>> >>
>> >> I have looked at the source for mrlib/image-core,
>> >> 2htdp/private/image-more,
>> >> and 2htdp/image. It looks like no exported functions can change an
>> >> image to
>> >> a bitmap.
>> >>
>> >> The only thing they want to do is be able to render an image onto a dc.
>> >> Presumably the render-image function would do that, were it exported.
>> >>
>> >> What should I do?
>> >>
>> >> Thanks for your help,
>> >>
>> >> Andrew Mauer-Oats
>> >> Mathematics Ph.D.
>> >> Chicago Public Schools: Whitney Young
>> >>
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