[racket] Making animations in racket (or, why racket is hard to transition to from scratch)

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
<robby at eecs.northwestern.edu>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 <yminsky at gmail.com> 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
> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20110201/a2799072/attachment.html>