[racket] place-image winking effect with low y coord

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 <bcboy at 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 <matthias at 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 <bcboy at 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 <matthias at 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
>> >
>> >
>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20141006/794a57af/attachment-0001.html>