heading = forwardDirection + rotationDegrees (was Re: How can we deal with Message rot?)

Bert Freudenberg bert at freudenbergs.de
Wed Dec 27 14:14:12 UTC 2006

On Dec 27, 2006, at 6:36 , Jerome Peace wrote:
>  more details of the heading etc. confusion
> can be found mantis
> http://bugs.impara.de/view.php?id=5674
> 0005674: Why doesn't heading = forwardDirection +
> rotationDegrees for all morphs all the time?

As far as I know, rotation and animation (that is, LOGO-style turtle  
semantics) is only seriously used in Etoys. For most other UI users  
it's merely a gimmick, so you would not need to worry about backwards  
compatibility too much. Etoys uses a very small set of messages  
(manifest in the Player class). As long as you ensure this small  
protocol does not break, Etoys should be fine.

Now, Player is very careful to always figure out the "right" morph to  
apply rotations to, depending on whether it wants to be "flexed" (in  
a TransformMorph) or if it handles rotation itself etc. This is why  
you see inconsistent behavior in the individual morph classes - in  
Etoys they are not used directly, but through the Player, and this is  
why your equation does not hold for each individual morph. I think  
you would have to eliminate TransformMorph completely, which might  
complicate other Morphs - until now, that "ugly" transformation stuff  
was factored out.

- Bert -

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