[Newbies] Creating a coverflow effect in Squeak

Karl Ramberg karlramberg at gmail.com
Sat Jun 14 12:04:17 UTC 2008

Bert Freudenberg wrote:
> On 14.06.2008, at 09:19, Herbert König wrote:
>> Andy,
>> AB> (not a very good description, but if you have seen iTunes, you
>> AB> know what I mean).
>> never seen but:
>> AB> I had a look in Squeaksource but found nothing similar.
>> AB> Could anyone give me some pointers on how to start this project.
>> AB> For example, is there a 'film strip' morph that already handles
>> AB> lists of images or something similar?
>> this looks like classic animation (search the swiki for animation)
>> which is one of the built in features of every morph.
>> In general you would need a path which the Morph will follow and you
>> would have to modify the step method of a Morph to follow that path.
>> And your Morph would have to return something smaller than the default
>> 1000ms when sent stepTime.
>> Something to play (I just did it the first time myself :-)) using
>> 3.8.2
>> Something to play:
>> World menu, objects, drag out an Ellipse into the centre of your
>> screen.
>> Open the halo, open an Inspector on the ellipse.
>> In the Inspector type "self definePath" (without "") and doIt.
>> With a pressed mouse button (left on Windows) move around the screen
>> until Squeak croaks and the cursor changes back.
>> Then bring up the Halo again, the red one has "Extras" there "follow
>> existing path". I just noticed that in Extras you also find "draw new
>> path"
>> If you have a Menu open (Extras for example), middle click twice on
>> the the interesting entry, bring up an Inspector and look into the
>> target (self) and the selector (#definePath) and the arguments (if
>> any).
>> Oh and not to forget, there are tutorials on how to provide different
>> pictures while a Morph follows an animation. I remember seeing an
>> Etoys project where a worm creeps using this technique.
>> After you know all this I guess you will just provide your own
>> animation methods and paths.
> Sorry to jump in again, nothing personal, really ;)
> The path methods are a beautifully simple and useful, but they are 
> also a particularly bad example of Morphic programming.
> You may notice how the entire World stops while you define a path 
> (have a clock morph running to see this). Also it uses Sensor 
> directly, and calls displayWorld. Both big no-nos in proper Morphic 
> programs. The followPath method even does the actual animation in a 
> background thread. Really Bad Things can happen if you do that.
> Tweak did set out to allow this kind of programming (because it is so 
> convenient), and it succeeded in that.
> For the original question - if you want the actual cover flow effect 
> you need a 3D renderer. You could use Croquet and OpenGL for that, but 
> it might be overkill. The Balloon3D render should be enough for this 
> simple type of animating.
> If you can live with a pseudo-3D effect (like the carousel seen on the 
> amazon.com frontpage) you can use simple 2D morphic animation of 
> course. In that effect, the covers always remain parallel to the 
> screen but only move position in a 3D circle so that they become 
> smaller in the back and larger in the front, and of course are sorted 
> back-to-front ...
> In fact, that is so simple I couldn't resist to make an etoy version, 
> 4 lines of code :)
> Uploaded as
>     http://wiki.squeak.org/squeak/uploads/Carousel.pr
> - Bert - 
Cool, you can even edit the text in the morphs as they move :-)


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