With 'record?' I don't see this in the gif, but do see it on-screen, which is curious. Maybe a hardware acceleration bug? Also don't see it if I render the scene in the interactions window. I only see it when running with big-bang.
If I change the initial state to 100 I don't see this. It only happens on low y value. On Mon, Oct 6, 2014 at 8:52 AM, Spencer florence <spencerflore...@gmail.com> wrote: > huh, I’m unable to reproduce this as well. > > Brian, if you use the `record?` clause in big-bang do you see the same > behavior in the generated gif? [ add (record? "/tmp”) to the big-bang > expression, similar to what Matthias did in his example ] > > Also do you see the same behavior if you change the initial state to be > 100? > > —Spencer > > > > On Mon, Oct 6, 2014 at 10:05 AM, Brian Craft <bc...@thecraftstudio.com> > wrote: > >> 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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