Hello, I have an idea for a game:

It would be just like a traditional Real-Time Strategy game, but with a twist: the user is given the ability to write AI for their units. There would be a a development mode of the game where you could access basic unit functionality (like move here, move there, attack, etc.), and basic information (like type and position of enemy units you have detected), and write your own AI.

I think this would be really cool , both for people who already know how to code, and for people just starting to learn.

It occurs to me that it would be waaaay easier for me to modify an existing open source game to add this functionality than it would be for me to write my own RTS game from stratch. Like probably the difference between me being able to do it and not (I am doing this on the side of my day job). However, I think it would be cool to at least try to make money from this game.

So I was looking into licensing, and it looks like almost all open source games are released under the GNU GPL license, meaning that they are legal to modify and redistribute, even for money, provided that the mod is also released under GNU GPL, and provides the source code. This makes sense, but it of course makes it difficult to make money selling a game, because anyone who buys it can then redistribute it for free if they choose.

I also read about the GNU Limited GPL (LGPL), which looks like closer to what I want--open source stuff that can be included in proprietary works. You don't have to provide the source code for your modification. It looks like you have to clearly separate your work from the LGPL work by using them as dynamically linked libraries, or something like that. I'm not sure how technologically viable that is for my idea yet. I tried to find RTS games made with this license. I might have found one (Evolution RTS: https://github.com/EvolutionRTS/Evolution-RTS/blob/master/license.txt), but it's ambiguous, and I'm unsure. Generally though, it seems like LGPL might be more of a thing for tools like game engines rather than whole games.

One idea I have is to modify a regular GPL game, then host it with servers for competitive play on some site like steam. I of course wouldn't advertise that the code is open source, but people would probably be able to get the game itself for free in this way if they looked into it. However, they wouldn't be able to play it competitively against other people without paying on steam.

Any advice? I'd be happy to hear feedback on the legal issue and/or the idea in general.

Thanks!

Wow, this is cool! I checked it out and it seems to be more of a programmable adventure game than RTS (first person, managing one or a few robots at a time rather than a bird's eye view of a whole civilization). But it looks really fun and educational. I like the animation too. I think that bringing programmability to a competitive RTS would be different enough that it's still worth doing.

Yeah, so maybe the way to do this is to host servers and charge either one-time to unlock access, or a subscription fee to play competitively (and include a free trial in either case). Or I could maybe host it through a platform like steam, which (I think) hosts servers for you, but then takes a significant cut of your profits. Need to look into this more.

I very much like the idea of letting people who haven't paid watch people who have paid program and compete. It would be a good demo of how to do it/what is possible, as well as encouragement to buy it.

Thanks for the feedback!

There is also a (at least one) multiplayer AI-writing RTS: Screeps

Interestingly, they are making money by selling CPU time for your AI.

Huh, that's cool. That is definitely more similar to my idea. The main differences are:

-I want to do it with an existing RTS game so it can have better graphics and more complicated underlying game mechanics (hence the mod)

-I want players to be able to control units concurrently with the AI they write. so you don't have to start out writing code, and you don't ever have to write it if you don't want. the idea is that it might attract people who have less of a coding background, then when they see that coding helps others win, and how they do it, they might give it a try. and it allows human-AI comboing, which I've always thought it is really cool

-I want to include a tutorial series on how to program basic AI within the game so it appeals more to people trying to learn.

Yeah so I just looked at the subscription plan, and it looks like there's a flat fee to buy the game, then a subscription fee for extra AI time. So I guess you can write more memory-intensive programs if you pay for the subscription? Is that the deal?

Back to the business-model thing, I came up with a potential issue with making money hosting servers for competitive play; if it is successful, since the game and the source code would have to be released under GNU GPL, there's nothing to stop another company from taking exactly the same game mod and hosting competitive play on their servers. The only advantage I would have it momentum, because people like to play where others play, etc. But this could be easily beaten by price undercutting, especially by a more established company.

However, if this happened, it would at least validate the popularity of the idea, and maybe justify the much larger investment in making my own RTS from the ground up with this programmability built in, after feedback on the mod version from users.

Thoughts?

Yeah, good point. Even if I was undercut, it would validate interest in the game and i could then maybe go an make my own improved version from the ground up.

Thanks!