133x126. The PNG itself is 3K. Running racket 5.0.2. 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.
y On Tue, Feb 1, 2011 at 9:35 PM, Robby Findler <[email protected]>wrote: > 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 > > On Tue, Feb 1, 2011 at 8:27 PM, Yaron Minsky <[email protected]> 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) > > ) > > _________________________________________________ > > For list-related administrative tasks: > > http://lists.racket-lang.org/listinfo/users > > >
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