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I'm not really aware of the legal issues surrounding game clones.

I'm around halfway done of making a clone, but it's not just the same gaming concepts, I'm literally using the original game's files (which I do not intend to distribute in any way) in my clone. My original intention was to add features to the game (Firefly studios's first Stronghold) while still using the same art.

Is it ok to distribute the source of my clone?

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What is the original license of the game you are "copying" from? – Dan Oct 23 '11 at 17:24
Go the route of OpenTTD. Distribute your code/source/exe/whatever, but not the files of the game you're cloning. OpenTTD did this without any actual problems, and various other open source ports have done the same thing without any major problems. – thedaian Oct 23 '11 at 19:36
Just because other people done it before without problems does not necessarily mean it is legally right. Just because you are legally in the right, does not prevent companies from attempting to sue you. When you tread in legal gray areas (clones etc..), such risk must be assumed and seeking legal advice is the only way to minimize the risks. – 5ound Oct 24 '11 at 11:34
If you have to ask, there's probably something fishy about it. 90% of English common law (and therefore USA) comes from some guy with a big, curly white wig sitting down and thinking "Yeah there's something fishy about that so look out, new law against that incoming." – Patrick Hughes Mar 25 '12 at 19:49
up vote 9 down vote accepted

Short Answer:

Yes, as long as the codebase differs from the cloned project in its implementations. (i.e. You don't directly use code from the original game)

Long(er) Answer:

This entirely depends upon the legal copyrights set forth by the original creator.

By default, U.S. copyright law automatically grants copyright ownership to the original creator of the content.

The artwork, sounds (music and effects), narratives, and other such assets can not typically be re-used unless explicitly specified in a license chosen by the original author. An example of non-restrictive licenses for creative assets would be the Creative Commons licenses.

Code for the original game is often licensed separately from the art assets, but has the same set of rules. However, as long as your code base differs significantly in its implementation, it is not generally considered a "copy", and therefore is not in violation of copyright. Much software out there provides similar features of other software, but they differ in specific implementation.

As far as gameplay goes, there are plenty of clones around already, so it's not quite as restricted. Although you may make some people pretty furious if they're protective of their ideas. :-)

Extra reading on copyright laws:


Answered quite a while ago, but some additions are necessary.

I'm not a lawyer


@Josh1Billion is correct regarding patents. They're an entirely different beast. Unlike copyright, which pertains to your specific implementation of code, these will get you for using the general architecture of a concept (and not necessarily with code). @Josh1Billion's comment provides a good example.

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Ozanma's answer sounds right, but to add to that: Be sure to check and see if the company has any patents on any of the game's gameplay elements as well. For example, Squaresoft has patented the Active Time Battle system. You can see the actual patent documents here (they're surprisingly short and readable):… – Josh1billion Oct 23 '11 at 20:20

Disclaimer: I'm not a lawyer.

Game play can't be copyrighted so you're definitely safe on that aspect.

Is it ok to distribute the source of my clone?

You certainly are. You are the owner of the code.

However, you cannot distribute the game's graphics. Using them in the game is allowable because they are separate works, so long as the user provides the graphics from the original game. Also be careful not to modify the graphics as that may be violating their copyright.

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I highly disagree. Unless the graphics were explicitly licensed for re-use, you cannot use them. They are the intellectual property rights of someone else and this is pretty much standard throughout international law. I'm a game developer and if I caught you using my works in your game I'd bury you in a lawsuit for every penny you might have made off of it. – Technik Empire Oct 23 '11 at 17:13
@AscensionSystems, OpenTTD did something like this for a very long time. They did not distribute the content, they required that you owned the original game and copied the content directory yourself. The game would not run unless you did this. I agree that it's sketchy, but is it violating a copyright if they don't distribute it? – John McDonald Oct 23 '11 at 17:21
@AscensionSystem Would you sue a googly-eye company because someone is putting them on a copyrighted image? No. They are two separate things, even if the googly-eyes were designed for such purpose. Also, why would you sue a company that is giving you sales? After all, you have to purchase the copyrighted game to be able to use the graphics in a clone. – Pubby Oct 23 '11 at 17:22
I misunderstood the original Q/A then and I apologize. If you're building onto another game then I would call this a mod, not a clone. – Technik Empire Oct 23 '11 at 17:34
@Ascension Systems, no its a game that uses another games content only, but requires the user to have purchased that content. – dcousens Oct 23 '11 at 21:38

Plenty of answers on copyright law already (summary: if you're not distributing the game resources, you're probably OK with respect to actual copyright law), but nobody has brought up EULAs yet. Regardless of whether copyright law would allow this or not, you also need to examine the EULA of the original game to determine whether it allows the game's assets to be reused by other games. I strongly suspect that it does not, unless you're dealing with an indie game whose developer(s) either deliberately chose to allow reuse or lack the legal experience to realize that they need to restrict it. Any mass-market game most likely prohibits it.

Standard disclaimer: I am not a lawyer and, even if I were, I'm not your lawyer. Consult an appropriate legal professional licensed to practice in your jurisdiction before distributing anything that you think could potentially get you sued. Your laws may vary. Do not taunt Happy Fun Ball.

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Quick question: Aren't EULA's worthless when it comes to a lawsuit? Like you can't sue someone for using a fake name even if the EULA explicitly forbids it – TheLQ Oct 30 '11 at 14:42

I'm aware of a situation where Valve C&D'ed a Counterstrike clone some 10 years ago. The scenario was almost identical - the engine code and game code were either original or based on existing open source material, but it used the actual Counterstrike content. I believe that the basis for the C&D was that it removed the requirement to own a copy of Half Life.

Unfortunately links and sources for this are long lost, but the lesson remains. Step carefully, and make sure that you're on watertight grounds before doing anything.

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Serously can't you come up with something more creative and original? But of course, FreeCiv and OpenTTD are very popular open source games based on originals.

You better not use any trademarks, graphics, sounds or other assets from the original game, even if you only publish it as open source.

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