133x126. The PNG itself is 3K. Running racket 5.0.2.<div> </div><div>As an irrelevant side-note, I noticed that I had a broken trig function in there. I fixed it, but that actually had nothing to do with the performance. I also went ahead and implemented caching of the rotated images, and the performance still isn't that great, although it's far better, at least when I don't move the mouse.</div> <div> </div><div>y <div class="gmail_quote">On Tue, Feb 1, 2011 at 9:35 PM, Robby Findler <<a href="mailto:robby@eecs.northwestern.edu">robby@eecs.northwestern.edu</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"> I'll leave the pedagogy questions to others, but for the performance questions, can you tell me what version you were using and the size of the png images (wxh)? Robby <div><div></div><div class="h5"> On Tue, Feb 1, 2011 at 8:27 PM, Yaron Minsky <<a href="mailto:yminsky@gmail.com">yminsky@gmail.com</a>> wrote: > I am trying to teach my scratch-addicted son a bit about racket, and I'm > finding it to be rather tough going, mostly because a lot of things that are > really easy in scratch seem surprisingly hard in racket. Also, even when I > can get things done, the performance of the graphics leaves something to be > desired. I'm wondering if this is just the way the world is right now, or > if somehow I'm approaching this the wrong way. > I was trying to put together a simple animation using the universe and image > teachpacks where: > - there is a "sprite" which switches between two images periodically > - the sprite is always pointing at the mouse > I wrote some code for doing this. One problem is that getting this to work > required some actual trigonometry, which my 9 year old isn't quite ready > for. But that I could fix by writing a simple helper function. But the > other problem is that the resulting code is horribly slow. As soon as you > rotate the image, the rendering performance falls through the floor, and you > see a ton of flickering. > I've attached the code below. I can imagine some ways of optimizing this > (for example, doing the rotations only on mouse moves, and storing the > resulting rotated images in the world-struct), but I want to keep the coding > style pretty simple, and I think these kinds of optimizations get in the way > of comprehensibility. > Another thing I'd be interested in suggestions with is how to deal with > updating a struct in a clean way. Right now, you need to explicitly wrote > set-world-X functions for each field in your struct, which is pretty ugly. > Also, the fact that structs don't have field names makes them more error > prone. None of this is well suited towards building complex worlds with > lots of components. I'm wondering if there is a better way of approaching > this that doesn't require quadratic boilerplate, and that is suitable for > teaching to a kid. > Anyway, here's the code. Thanks in advance! > ;; the images here are actual PNG images, which don't show up nicely in > ascii... > (define pic1 .) > (define pic2 .) > (define (posn-diff a b) > (make-posn > (- (posn-x a) (posn-x b)) > (- (posn-y a) (posn-y b)))) > (define (posn-mag p) > (sqrt (+ (sqr (posn-x p)) (sqr (posn-y p))))) > (define (angle-between pos1 pos2) > (let* > ((delta (posn-diff pos2 pos1)) > (hyp (posn-mag delta)) > (angle-in-radians (if (= hyp 0) 0 (asin (/ (posn-y delta) hyp)))) > ) > (-(* angle-in-radians (/ 180 pi))))) > > (define-struct world (pos mouse-pos time)) > (define initial-world (make-world (make-posn 200 200) (make-posn 200 200) > 0)) > (define (draw w) > (place-image > (rotate (angle-between (world-pos w) (world-mouse-pos w)) > (if (is-even (round (world-time w))) pic1 pic2)) > (posn-x (world-pos w)) > (posn-y (world-pos w)) > (empty-scene 400 400))) > (define (tick w) > (make-world > (world-pos w) > (world-mouse-pos w) > (+ 0.1 (world-time w)))) > (define (mouse w x y event) > (make-world > (world-pos w) > (make-posn x y) > (world-time w) > )) > (big-bang > initial-world > (on-draw draw) > (on-tick tick) > (on-mouse mouse) > ) </div></div>> _________________________________________________ > For list-related administrative tasks: > <a href="http://lists.racket-lang.org/listinfo/users" target="_blank">http://lists.racket-lang.org/listinfo/users</a> > </blockquote></div> </div>