Sensor vs. Hand (was: Re: Squeak-3.7: Title-Bar Buttons)

Bert Freudenberg bert at
Fri Mar 5 10:35:44 UTC 2004

Am 05.03.2004 um 09:59 schrieb ducasse:

> hi andreas
> I need your help :) about ActiveHand use instead of Sensor

Andreas is not yet in, so I'll answer that ;-)

> Turtle>>anyButtonPressed
> 	(Delay forMilliseconds: 2) wait.
> 	^ ActiveHand anyButtonPressed

> Turtle>>wand
> 	[self anyButtonPressed]
> 		whileFalse: [self go: 30 atRandom.
> 			self turnLeft: 30 atRandom]

This will not work (as you have discovered) since this piece of code 
runs on its own and does not give Morphic the chance to check for 
events, hence the button state will never change. You may have noticed 
that the rest of Squeak (or, more specifically, Morphic) is blocked 
while you execute this code.

Andreas did not say to *never* use Sensor. But certainly you should 
never refer to Sensor in well-behaved *Morphic* code. Your Turtle code 
is an example of simple "I-have-the-whole-machine-for-me" code, but it 
does not cooperate well with the event-driven logic of Morphic.

There are several options for you:

a) Continue to use Sensor and accept that Morphic will block while your 
code is running.

b) Rewrite your example to follow the Morphic philosophy. This is 
certainly possible, but I doubt it will exhibit the same simplicity 
that the "old"code has.

c) Apply a little hacker-fu to make Morphic run under your control:
		World doOneCycle.		"Bert's magic hacker-fu"
		^ ActiveHand anyButtonPressed
	This one works, since essentially Morphic runs the #doOneCycle method 
in a loop all day anyway. You have to be careful though to when you can 
call this, because I doubt Morphic is fully reentrant.

d) Write a system that allows and encourages the coding style you used 
(because it is so beautifully simple and almost obvious), but is 
actually event-driven under the hood. Your code would run 
quasi-parallel with all the other UI code. Tough stuff, though.

e) Do not write system d) yourself, but wait for Andreas to release it 

- Bert -

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