Sohrab Ismail-Beigi Personal interests, side projects, and odds and ends.

Gravity Wars

Two spaceships, a handful of planets, and Newtonian gravity: players take turns firing photon torpedoes at each other’s ship, and the planets bend every shot.

▶ Play it in your browser: the 2002 PERL version, ported to JavaScript. This is mainly for demonstration purposes; see below for much more sophisticated implementations by others.

Brief history

Back in the late 1980s when I was in high school, I wrote a game for IBM DOS machines, using Turbo Pascal, called “gravwars,” which was based on an Amiga game that someone else had written and that I liked a lot. That version was distributed, much more widely than I thought or knew about, through BBSs (bulletin board systems) and then through Internet FTP servers and whatnot. A certain number of people liked the game and would email me about the latest version in the intervening years.

Alas, with the demise of DOS and my graduation from high school, I did not have the time to rewrite the game for a more modern system. In 2002, I had a bit of time free so I did a rewrite, but in the most rapid and least difficult manner: thus some of the features went missing and it used PERL, which made my life as a programmer much easier, but required the user to have PERL and some libraries. I took the old Turbo Pascal code and converted the essential parts into PERL. The graphics engine was now the PERL Tk library. Thus, in some sense, the new version was much more universal since PERL exists on many different kinds of systems and is a universal language (unlike Turbo Pascal and graphics commands unique to the DOS system with VGA/EGA of the 1980s).

Furthermore, the code was no longer freeware but is under the GNU General Public License (copyleft). See the file “COPYING” below for what that means in detail. What it means, briefly, is that it is “free” software, by which I mean “free” in the sense of freedom and not money. When you acquire this software, you can read the code, modify it, change it, do whatever you want, and give it to others at no charge. However, you must also propagate it under the GNU copyleft so others can do the same thing. If you make changes, the changes are covered under the copyleft, so you have to include those “free” for the next user. You may charge for the costs of distributing the package if you had to do something to this end (of course, in these days of Internet and web pages, if you charge, most folks will get it elsewhere at no cost since no one can restrict use or distribution of this software). The philosophy is that software should be free so as to allow everyone to have access to the software and its source code to play with it, improve it, or simply learn. And no one can turn it into private software with hidden code (usually to make money).

Files

The program itself is the PERL program “gravity_wars.pl”, and the file “README” explains the game and other useful details. If you have PERL with the Tk library, just download that and run. Otherwise, you have to get PERL yourself (free to download as “free” software at the PERL website www.perl.org). As a convenience, I’ve included the Tk library version 800.021 below (although you can get the latest version of Tk on CPAN too): I’ve checked and it works with this library for sure on a standard Linux box.

Files you can download:

Gravity Wars elsewhere

Get in touch and/or what to do

Feel free to email me at sohrab.ismail-beigi@yale.edu with comments, historical corrections, or stories you have about the game. I would love to hear from you if you have thoughts, testimonials, etc.

Also, if you feel inspired, make your own free version and share it with the world. I’m happy to list your version here with a link. If you found playing the game fun and want to do something, make a new variant or version and give back!