#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 <a href="http://groups.google.com/group/plt-scheme/browse_thread/thread/28af25a01200bc3c/7937bb0314cc231e?lnk=raot">http://groups.google.com/group/plt-scheme/browse_thread/thread/28af25a01200bc3c/7937bb0314cc231e?lnk=raot</a> 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. |#