If I record to a gif the effect isn't in the gif, though it does happen on-screen while it is recording the gif. Here's a video, using a camera phone. Sorry for the poor quality.
https://drive.google.com/file/d/0BxB9fW-JZz-ST3dfeFNxakRhMnRzcGtPQUtuaWJxMVRQTEFz/view Pause it around the 1 sec mark. On Mon, Oct 6, 2014 at 7:10 AM, Matthias Felleisen <matth...@ccs.neu.edu> wrote: > > Sorry, I don't understand what you mean. I have modified the main function > so that (1) the whole thing is slower and (2) it records the whole thing as > an animated gif: > > (define (main) > (big-bang 0 ;; initial state > (record? #t) ;; <--------------- > (on-tick add-3-to-state 1/10) ;; when the clock > ticks, add ... <------------- > (to-draw draw-a-ufo-onto-an-empty-scene) ;; when the state > changes, draw ... > (stop-when state-is-300))) ;; when the UFO's y > coordinate is 300, stop. > > > > The animated gif is here: > > http://www.ccs.neu.edu/home/matthias/Tmp/UFO/i-animated.gif > > -- Matthias > > > > On Oct 5, 2014, at 11:52 PM, Brian Craft <bc...@thecraftstudio.com> wrote: > > > The same effect occurs in > racket/share/pkgs/realm/chapter5/ufo-source.rkt. When the state is > increasing from 0, the image is not moving down the screen. It stays in one > place, but is initially clipped to 0 horizontal lines. Then 1 line, then 2, > and only when the state is 1/2 the image height does it start moving down > the screen. > > > > Also, if I call (draw-a-ufo-onto-an-empty-scene 0) in the interactions > window, I once again get a different result: it renders the lower half of > the image. This is the same behavior I see with my code. > > > > Maybe a platform issue? (version) reports 6.0. I'm running it on ubuntu. > > > > > > > > On Sun, Oct 5, 2014 at 6:13 PM, Matthias Felleisen <matth...@ccs.neu.edu> > wrote: > > > > Can you send the full program please? Thanks -- Matthias > > > > > > > > On Oct 5, 2014, at 8:52 PM, Brian Craft wrote: > > > > > Hello -- Newbie here. I'm going through "Realm of Racket". I'm seeing > an odd effect when using this to-draw handler in big-bang: > > > > > > (define (draw-a-ufo-onto-an-empty-scene game) > > > (let ([pos (game-pos game)]) > > > (place-image IMAGE-of-UFO (round (vec-x pos)) (round (vec-y pos)) > > > (empty-scene WIDTH HEIGHT)))) > > > > > > vec is (struct vec (x y)) > > > > > > As the y coordinate approaches zero, IMAGE-of-UFO gets clipped on the > top and bottom, looking a bit like it's winking out of existence, rather > than sliding off the canvas. This doesn't happen on any other edge. It's > only as y approaches zero. It starts when the edge of the image meets the > edge of the scene. That is, if the image is 20px high, and y starts at 30, > and decreases by 1 on each tick, it will move up the canvas for 30..10, but > from 10 on the image will not change position, but will instead be clipped > on the top & bottom, until it disappears. > > > > > > This does not happen in the interactions window. If I call the above > function in the interactions window, it renders as expected, with the image > moving smoothly off the edge. > > > > > > > > > ____________________ > > > Racket Users list: > > > http://lists.racket-lang.org/users > > > > > >
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