[Newbies] Creating a coverflow effect in Squeak

[Bert Freudenberg]

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 -