<div dir="ltr"><div>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. <a href="https://drive.google.com/file/d/0BxB9fW-JZz-ST3dfeFNxakRhMnRzcGtPQUtuaWJxMVRQTEFz/view">https://drive.google.com/file/d/0BxB9fW-JZz-ST3dfeFNxakRhMnRzcGtPQUtuaWJxMVRQTEFz/view</a> </div>Pause it around the 1 sec mark. </div><div class="gmail_extra"> <div class="gmail_quote">On Mon, Oct 6, 2014 at 7:10 AM, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu" target="_blank">matthias@ccs.neu.edu</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> 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: <a href="http://www.ccs.neu.edu/home/matthias/Tmp/UFO/i-animated.gif" target="_blank">http://www.ccs.neu.edu/home/matthias/Tmp/UFO/i-animated.gif</a> -- Matthias <div class="HOEnZb"><div class="h5"> On Oct 5, 2014, at 11:52 PM, Brian Craft <<a href="mailto:bcboy@thecraftstudio.com">bcboy@thecraftstudio.com</a>> 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 <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> 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: > > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> > > </div></div></blockquote></div> </div>