Pendulum

[Bert Freudenberg]

Am Freitag, 18.04.03 um 22:51 Uhr schrieb Alan Kay:

> Hi Phil --
>
> At 5:38 PM -0400 4/17/03, Phil Firsenbaum wrote:
>> Interesting...I actually saw this message on the Squeak archive. i 
>> didn't receive it on the mailing list, though.
>>
>> Anyhow, even if the pen were down and the pendulum simulated reality 
>> i think it would draw lines on top of lines  unless the area under 
>> the pen was scrolling. Do you see what I mean?
>
> Well, here's a little exercise in relativized thinking ...
>
> Embed a round little object like an ellipse to be the bob of the 
> pendulum, call it "bob". Make another little object called "plotter", 
> put its pen down. See what happens when you do:
>
>                 plotter's y increase by 1
>                 plotter's x <- bob's x

"Relativized thinking" is fine, but the implementation is itself 
relative, so this does not work.

After embedding, the bob lives in the coordinate system of its parent, 
the pendulum. Rotating the pendulum does nothing to the bob - just look 
at its geometry category, it's static. I then tried using a 
PolygonMorph as pendulum because it does not use a TransformMorph, but 
then, the transform of the embedded bob goes wild (try it).

The latter behavior looks like a bug, while the former is probably 
supposed to behave like this. We would have to introduce a "global" or 
"absolute" position to make this work.

-- Bert