Critters (C) 1995 Joe Walsh

Critters - Screenshot 01

Critters – Screenshot 01

  • Artificial Life simulation
  • EXEcutable file


The Critters program is my second foray into the world of Artifical Life (A-Life, or AL). It is also my first assembly language program (other than the piddling programs typed in from the book Atari Roots, and the even more piddling programs I made up to teach myself the language). Finally, Critters is a work-in-progress.

Simply put, the program creates a “world” on your screen, and borders it with walls. Then it randomly places some Critters (some male, some female (males are inverse video, females are normal video)) and some plants around the screen.

Subsequently, the Critters and plants live by the rules I have given for that world. It’s pretty straight-forward. Critters can move, fight, reproduce, eat plants, eat dead critters (yuck!), or stay still. Critters decide what to do based on what they find around them, and their “DNA”.

Plants have a much simpler life. They grow from seedlings to full plants, then wilt and die. When they are at or near their full growth, they can spore another plant (if there is room for them to do so, and if the wind is blowing in that direction).

It’s fun to sit and watch this stuff. I am very interested in perpetually changing display programs, so I enjoy just sitting and watching them go. Others may want to dabble in this little world, so I have provided a couple of meager controls:

OPTION – Press this key to cause plants to sprout in empty spaces. Since the program runs through the screen so fast, you don’t have to hold it down for long. But, since plants die out so quickly (twice as quickly as all but the weakest and least fortunate critters), you may have to do this frequently (or keep pressing it continuously for a while) in order to get the level of plant life you desire.

SELECT – Press this key to cause Critters to be instantly born in empty spaces. Since critters live relatively long lives, just a tap of this key is usually enough to put plenty of Critters on the screen.

Finally, you may press the START button to end the program and return to DOS. A couple of caveats, though:
1) It only checks this key just before it starts checking each square for life from the top of the screen down. In other words, it checks this key only about once every second. So, you may have to hit it twice or so before it realizes you want to quit (or just hold it down for a second). 2) While Atari DOS clears the screen before putting it’s menu up, SpartaDOS does not, so you end up with a screen filled with characters. Just type SHIFT-CLEAR to clear the screen. I don’t have MYDOS, so I don’t know what happens in that system when you exit to DOS.

I hope you enjoy the program!
Let me know what you think. I can be found on the comp.sys.atari.8bit newsgroup, or you can email me at ransom22 AT delphi DOT com.


I couldn’t have made this program without the following:

Atari 8-bit computers – my first computer, and still the best.

Atari Roots, by Mark Andrews – I thought I’d never find a book on Atari Assembler that explained things beyond how to add and subtract. This book is great, and highly recommended if you want to learn ASM.

The people at OSS for putting out the MAC/65 cart.
This includes Mr. Dunion, for his Dunion’s Debugging Tool, which is included in the Mac/65 cart.

Mike at Fine Tooned Engineering, for making the Mac/65 cart available again.

Carole Borowski, for everything.

David Tipton, for making me realize that it was time to get back into the Atari 8-bit world after a six-year hiatus.

All the kind folks at comp.sys.atari. 8bit, Atari Classics (both old and new), and Computer Currents for providing support to our community.

And to you, the user, for sticking with the best computer platform around.

– Joe Walsh

Bootable disk (ATR / 7-Zip): Critters

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