Folks,

please find attached the promised implementation of Conway's "Game of Life" 
in the StarSqueak framework (as mentioned on the "Lots of concurrency" thread).

I have also just published it as a project on Bob's SuperSwiki.  Since this 
is the first time I've gone through the chore, I'm not sure whether it has 
worked out OK or not.  I'd be grateful for reports to that end.  (It was 
published from a 3.1a4332 image.)

As for what is different about this implementation, feel free to skip forward.

---

In case you want to load it manually:  You'll need two of the changesets I 
posted a couple of minutes ago, before filing in this one.  They are:

* StarSqueakFixes.3.cs -- "[FIX] Assorted StarSqueak Fixes"
* StarSqueakEnh.1.cs -- "[ENH] Faster StarSqueak patch variables"

With these under your image's belt, file in this one (StarSqueakLife.12.cs) 
and open a StarSqueakLife with

	StarSqueakLife new openInWorld

Next, get a menu on that Morph (from the red halo), and keep it up.  Maybe 
set the scale to 4 (from the menu).  Now you can start, stop and step the 
Life from the menu.

Note how cells change colour with age, i.e. the number of generations they 
survived.  They are, as specified in LifeTurtle>>ageColor and LifeTurtle 
class>>ageColors, going through

	Color showColors: (Color hotColdShades: 100).

You can change this to e.g. the gradient

	Color showColors: (Color smoothShades: 50)

but don't forget to zap LifeTurtle's class variable AgeColors (easiest from 
a Browser, select LifeTurtle's class declaration and evaluate "AgeColors _ 
nil").

---

Further fun:  Get an Explorer on Life (don't you wish) from the gray halo 
("explore morph"), and from its lower pane, send it the messages

	self deleteTurtles.
	self putForm: Form fromUser at: 5 at 20

Or.  Define custom Forms like

     form _ Form extent: 37 at 10.
     y _ 0.
     '
     .........................*..........
     ......................****....*.....
     .............*.......****.....*.....
     ............*.*......*..*.........**
     ...........*...**....****.........**
     **.........*...**.....****..........
     **.........*...**........*..........
     ............*.*.....................
     .............*......................'
         linesDo: [:line |
             line withIndexDo: [:c :x |
                 c = $.
                     ifFalse: [form colorAt: x at y put: Color black]].
             y _ y+1].
     GliderGun _ form

and in the Explorer do

	self deleteTurtles.
	self putForm: GliderGun at: 20 at 20.

and start.

---

Implementation Notes

LifeTurtles play the role of cells, while patches keep track of neighbor 
counts. LifeTurtles keep track of their age, and change color accordingly. 
If StarSqueak places more than one LifeTurtle in a patch, the LifeTurtles 
will wander to find an empty patch.

There are a lot of Life implementations out there (including Dan's bitblt 
wizardry) that are a lot faster.  Don't expect 100s of generations per 
second, expect more like 5-7 per second.  Why?  Each "cell" is actually an 
object with more state than 1 bit, and birth is handled by a global demon 
that examines each cell for birth conditions.

See LifeTurtle>>live for the algorithm that cells follow.  This method runs 
for each cell during each turn.  See StarSqueakLife>>giveBirth for the 
demon that creates new cells.  That method runs once for each turn.

Questions?  Post away.

Enjoy,
Helge
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