Here is a solution in the DrRacket beginner language:
(require 2htdp/universe)
(require 2htdp/image)
(define (bundle x) (make-bundle x '() '()))
(launch-many-worlds
(universe 'n/a (on-new (λ (u nw) (bundle u))) (on-msg (λ (u w m) (bundle m)))
(state #t))
(big-bang 'n/a (to-draw (λ (w) (empty-scene 200 200)))
(register LOCALHOST)
(on-mouse (λ (w x y ke) (make-package w x)))))
Here is a solution in Racket derived from yours:
#lang racket
(require racket/gui/base)
(define show-x
(new frame%
[label "frame for displaying the current x coordinate"]
[width 200]
[height 200]
[enabled #t]))
(define x-pos
(new message%
[parent show-x]
[label "No x-pos yet."]))
(define discover-x
(new frame%
[label "frame for noticing mouse evets and their current x coordinates"]
[width 200]
[height 200]
[enabled #t]))
(define y-pos
(new (class canvas%
(inherit get-dc)
(super-new)
(define/override (on-event mouse-event)
(define x-pos (send mouse-event get-x))
(define y-pos (send mouse-event get-y))
(set! *x x-pos)
(refresh)))
[parent discover-x]))
;; for communicating between the two frams
(define *x 'n/a)
(define (refresh)
(send x-pos set-label (format "~a" *x)))
;; run program run
(send show-x show #t)
(send discover-x show #t)
;; you were creating way too many event spaces. No need for that.
On Apr 19, 2012, at 2:32 PM, Patrick Mahoney wrote:
> #lang racket
> #|Hello all, I'm PMah. |#
> (require racket/gui/base)
>
> #|Problem: I have a message% control called x-pos parented by a frame% called
> parent1. I have a canvas% called canvas parented under frame% parent2. I
> would like x-pos to always show the current x coordinate of the mouse
> position over canvas, and for this to be kept up to date as the mouse moves.
> Ultimately I'd love to move to a reactive semantics. |#
>
>
> #|Setting up the first frame and parent. I'm also going to grab the
> eventspace for this frame while I'm at it.|#
> (define parent1 (new frame%
> [label "Parent1"]
> [width 200]
> [height 200]
> [enabled #t]))
>
> (define x-pos (new message%
> [parent parent1]
> [label "No x-pos yet."]))
>
> (send parent1 show #t)
>
> (define eventspace1 (send parent1 get-eventspace))
>
>
> #|The second eventspace*frame*pos combo-|#
> (define parent2 (new frame%
> [label "Parent2"]
> [width 200]
> [height 200]
> [enabled #t]))
>
>
> #|Here comes the canvas subclass-I'm looking to override on-event method to
> grab the x-component of the mouse pos, and I want to have that constantly
> updating the x-pos message%. I really want reactive behavior, but I ran into
> some issues with the frtime-namely, differences in bindings due to the
> mzscheme bindings. the require spec (prefix-in ..) doesn't appear to be in
> the language. I'm probably doing something wrong. |#
> (define y-pos (class canvas%
>
> (inherit get-dc)
> #|My notion of scope in objects is not precise. With those defines within the
> scope of the on-event bindings, do the defines recalculate each time on-event
> receives a message? lo, I wish I had some sort of channel protocol to pass
> messages between threads, along with control.
> The mushrooms kick in now.
> PFFFT MIND
> |#
> (define/override (on-event mouse-event)
> (define min-x (dc:min-x (get-dc)))
> (define max-x (dc:max-x (get-dc)))
> (define min-y (dc:min-y (get-dc)))
> (define max-y (dc:max-y (get-dc)))
> (define x-pos (send mouse-event get-x))
> (define y-pos (send mouse-event get-y))
> (call-in-other-eventspace (make-eventspace) (draw-diagnostics max-x
> max-y x-pos y-pos)))
>
> (super-new)))
>
> (define
> (send parent2 show #t)
>
>
> #|I have tried some of the examples on
> http://groups.google.com/group/plt-scheme/browse_thread/thread/28af25a01200bc3c/7937bb0314cc231e?lnk=raot
>
> Basically, one using a channel, probably incorrectly and the second without.
> Now what I believe I've done is to add the thunk to the queue in the frame%
> parent1's eventspace, but I haven't transferred control. The other
> eventspace's thread still has control. Kind of?
> |#
> (define (call-in-other-eventspace e thunk)
> (let ([ch (make-channel)])
> (parameterize ([current-eventspace e])
> (queue-callback (lambda ()
> (channel-put ch (thunk)))))
> (channel-get ch)))
> #|This blocks both frames updating in some way-im not able to transfer
> control smoothly to the thread in the message% message1 workspace, and so the
> x-pos label updates only sporadically when the other eventspace thread
> yields? |#
> (define (call-in-other-eventspace e thunk)
> (parameterize ([current-eventspace e])
> (queue-callback thunk)))
>
>
> #|How can I get x-pos to update automatically on each on-event send here?
> (draw-diagnostics max-x max-y x-pos y-pos) appears to terminate here in all
> cases. Part 2: how can I apply frtime to make the update relationship I want
> between canvas mouse position and message text (or other racket reactive
> work if it exists.). I really would like to understand this idiom and get it
> in my toolchest for gui programming. Thanks all! Racket is an impressive
> contribution to computer science. |#
>
>
>
> ____________________
> Racket Users list:
> http://lists.racket-lang.org/users
____________________
Racket Users list:
http://lists.racket-lang.org/users
