Cloning a GPL game, legal issues

[Rubs]

Hi everyone,

Is it possible to clone a game with a GNU GPL (port it to other platform) and make it commercial? And if it is to what bounds?

I know that game mechanics cannot be copyrighted and you can release a commercial title if you change game name/artwork/levels/etc. Now the question is can you release a commercial title based on a freeware GPL product (for other platform)? Also can you use its assets, like name/artwork/levels?

Any info will be highly appreciated!

[KatieL]

The GPL covers the code and assets. Copying the game mechanics and ideas is not covered.

If you use the code or assets your project is "derived" from the original. A derived project MUST supply a buildable source and full assets, thus allowing anyone else to derive projects from it.

There is absolutely nothing to stop you charging for your derived software -- or even just taking the GPL'd game that's out there and selling it. The restriction is that you must supply the source code/assets - and therefore are at risk someone will just undercut you by supplying it for free or will use your assets in their game (which would then also have to be GPL'd).

Many people make an honest living, for example, selling Linux on CD for people who don't want to download it, so it's not inceivable to do the latter. People also make a living installing and configuring tools like Apache, which also has to have the source given away with it.

Red Hat makes their living by providing support to the software. Just because their customers must have the source code, doesn't mean they're necessarily in a position to make any use of that. They COULD go out and hire software engineers, but it's easier to have Red Hat act as their tech support people.

An option which might appeal is talk to the owners of the assets in the original, and see if you can come to an agreement over the use of them; you use their assets in your software without it having to be GPL'd (be re-licencing them) as long as extra assets you use are also placed under (say) a creative commons licence, opening them up to further re-use in other games. Obviously this works better for textures and models than it would levels. But this would be in keeping with the spirit of open-source philosophy and so may be something the original authors could be interested in.

[GBGames]

The GPL covers the code and assets. Copying the game mechanics and ideas is not covered.


Can you explain the assets part? As I understand it, the GPL is only appropriate for code. There are GPL-licensed games that don't provide a separate license for the data (images, sounds, etc), but I believe that is more careless than anything. How do you release the source to a music file or an image file? It isn't well-defined, at least not under the GPL.

I would agree that asking the author for a special license is a good idea. Some people have no problem granting such permission, but others might tell you that it is the GPL or nothing.

I am planning on making games that have proprietary assets with free/open source code. As said above, the GPL does allow you to charge for the software, and if you take care to make sure your assets are not specific to the code, you should be fine. For instance, if you can plug in a different configuration file to get a different set of assets loaded, I think the assets can be considered separate from the code.

[Rubs]

In my case I don't need game's source code, but I would like to use game's name and levels. If I provide access to levels (say, via Level editor), is it ok? What about game's name?

I already wrote to game's author and am waiting for his reply. I told him that I can implement the game using other name and levels, but I told him also that I would like the original classic levels to be included in the package as well so that game fans can enjoy it on other platform. I was wondering about the possibility of using levels in my implementation. Besides, all the levels themselves are free. Everyone will be able to download them and open in a free editor. Users pay only for ability to open other than demo levels.

Yes, and thanks for the detailed reply Katie! Your signature rocks :)

[MibUK]

In my case I don't need game's source code, but I would like to use game's name and levels. If I provide access to levels (say, via Level editor), is it ok? What about game's name?

I already wrote to game's author and am waiting for his reply. I told him that I can implement the game using other name and levels, but I told him also that I would like the original classic levels to be included in the package as well so that game fans can enjoy it on other platform. I was wondering about the possibility of using levels in my implementation. Besides, all the levels themselves are free. Everyone will be able to download them and open in a free editor. Users pay only for ability to open other than demo levels.

The GPL is applicable to all works that are distributed, not just the source code. (The license says source code, but the FSF's FAQ's section says that other thigns can be distributed under GPL.)

This suggests to me that the whole package that was distributed under the GPL is under GPL. Therefor you cannot use any of the assets from the original without applying the GPL to them. As the GPL is viral, this means that you will hae to make your application GPL as well.

The original copyright holder is able to relicence any portion of the package at will, on the provision hey have the agreement of all of the copyright holders. In the case of the levels, The original designers could agree to use LGPL or CreativeCommons based license.

However, allowing uses to download the original levels and use them in your game is allowed under the GPL as the GPL only covers distribution not usage.

Your best bet would be to rewrite it from scratch with all new assets, levels etc, and offer the opportunity to download and install levels from other sources.

You will definately not be able to use icons/graphics/sounds/music etc from the original, they are combined to constitute the distributed package of the game, and will be covered by the GPL.
Again, you could offer the users the facility to download and install those from elsewhere as well if you wanted.

Finally on the name, I think the use of the original name for the game constitutes as a trademark, or at least prior art if it ever came to a legal battle. I would not use the same name If I were you.

Hope that helps,

In essence, I want to ask a couple of questions,
Why do you want to do this?
The GPL allows you to provide the product for a price.
You could support the GPL game, providing any code enhancements to the project, and sell the result from your website, on the provision you will also offer the source code to every purchaser of the game if requested.
You can provide a seperate, non-GPL music/graphics/level pack for sale as well if you want to.

Therefore, you would gain from the benefits of the other devleopers looking at the source code of the game, and the improved karma in the Open source community. You can sell level / map packs for anybody who wants to experience more than the free version provides.
You get better coding, free hosting of your "demo" version, and much better marketing. Sounds like a win/win to me.

[GBGames]

The GPL is applicable to all works that are distributed, not just the source code. (The license says source code, but the FSF's FAQ's section says that other thigns can be distributed under GPL.)


They have clarified their FAQ sometime in the past couple of months, apparently: http://www.gnu.org/licenses/gpl-faq.html


Can I use the GPL for something other than software?
You can apply the GPL to any kind of work, as long as it is clear what constitutes the "source code" for the work. The GPL defines this as the preferred form of the work for making changes in it.


So if they provide the assets without providing the "source" to such assets, they are violating their own license. Of course, they won't likely sue themselves, so what can be done?

In any case, I think that when you provide art and sound for a game, and the source for the game is under the GPL, the art and sound SHOULD be licensed under a different, more appropriate license. Since you can swap out different images or sounds using the same names, I think you should be able to distribute them under a different license from the engine/code without violating the GPL.

Whether people actually do provide a separate license for the data is a different question. I think a lot of people are careless to simply throw the image and sound files under the license since I don't believe they provide or intend to provide the original files to edit them, such as PSDs for the resulting tga files.

In any case, the GPL doesn't prevent commercialization, and in fact by definition free software requires that you allow the right to sell copies. What I plan to do is sell access to the full version of a game and promise equivalent access to the source to those customers who want it. I am under no obligation to provide access to everyone, but I also understand that customers can take the source and redistribute it themselves; however, the data will be proprietary and legally customers cannot redistribute it like they could with the source.

I suppose I could also start selling games like freeciv and frozen bubble, as well, so long as the code and data licenses allow it.

[HairyTroll]

They have clarified their FAQ sometime in the past couple of months, apparently: http://www.gnu.org/licenses/gpl-faq.html

So if they provide the assets without providing the "source" to such assets, they are violating their own license. Of course, they won't likely sue themselves, so what can be done?

I think a lot of people are careless to simply throw the image and sound files under the license since I don't believe they provide or intend to provide the original files to edit them, such as PSDs for the resulting tga files.

I disagree. If I understand what you are saying then....

- If someone includes an mp3 soundtrack for a level, then the GPL forces them to include the uncompressed PCM version of the track as the 'source' file?

What of the sound-effects that went into creating that track, must each of these effects be included in the distribution as well?
And if the programmer used a commercial music program to sequence the music/effects, must this application also be included in order to allow everyone to build/edit the assets?

[GBGames]

I disagree. If I understand what you are saying then....

- If someone includes an mp3 soundtrack for a level, then the GPL forces them to include the uncompressed PCM version of the track as the 'source' file?

What of the sound-effects that went into creating that track, must each of these effects be included in the distribution as well?


And that's exactly why the GPL is not appropriate for stuff that is not code. How would you break it down? If you still insist on using the GPL for non-code, you will need to specify what exactly is covered and what the nature of the "source" will be. I think a lot of games under the GPL are careless about this aspect. The entire game could be under the GPL, but other than the code, how does the GPL apply unless the author explains how he/she wants it to apply to the assets?

EDIT: "The GPL defines this as the preferred form of the work for making changes in it." So if you think that you would prefer to have those sound effects separate from the track to edit it, then that is the preferred form.


And if the programmer used a commercial music program to sequence the music/effects, must this application also be included in order to allow everyone to build/edit the assets?

Actually, in this hypothetical example, I think the answer would be no since the data created and the program that created it are not usually bound together. On the other hand, if the commercial program is proprietary and is the only one that could read the sound files, you have effectively required its use in order to build/edit the sound files. Even then, however, the application itself is not required to be distributed.

[Pyabo]

Ah yes... this old discussion. You guys might want to refer to a long-dead thread where we discusses whether or not it's legal to use the art assets from a time-limited DEMO game in your own work, since they are provided "free!" (answer: no)

Funny stuff.

[GBGames]

Ah yes... this old discussion. You guys might want to refer to a long-dead thread where we discusses whether or not it's legal to use the art assets from a time-limited DEMO game in your own work, since they are provided "free!" (answer: no)

Funny stuff.

But this isn't just a time-limited demo. This discussion is about using assets from a game with a license that says that the source must be made available, and that you can do whatever you want so long as you comply with that aspect. With a time-limited demo, presumably the license does not allow you to separate the assets from the code and distribute it separately.

[ErikH2000]

Don't rely on a FAQ that explains what the GPL is supposed to cover. Any attempts to explain what the GPL does or doesn't do are always superceded by the text of the GPL itself. Be wary of hidden agendas and mistakes in the GPL camp, too--they are a bit zealous over there, and I wouldn't put it past them to say that you could copyleft a bottle of beer. (So "free beer" would finally be "Free Beer"!) The GPL is not a hard thing to read and understand. Put aside an hour and just read the thing. (Pet peeve of mine: everyone acting like legal agreements are magic spells inscrutable to all but the annointed.)

My interpretation--the GPL is meant for source code and the binaries produced by them. You can come to the same conclusion be reading the GPL and taking it literally, which is what courts do. Many people sloppily apply it to other media in projects, including, regretably, the people who maintain the projects. If someone has not specified a separate license to cover their non-source/binary content, then you should assume (even if they haven't assumed it) that the creators of the content reserve all rights. That means you'd want written permission from the creators before using the content. And I wouldn't be satisfied with an informal "sure, buddy, do what you want with it" in an e-mail. Because later after you've released your commercial title somebody can come along and say you don't have IP rights. And they'll be right.

My project's source code and binaries are licensed under Mozilla Public License so anybody can grab them up and exploit within the boundaries of that license. The other media is "all rights reserved" to my company, and I get signed releases from all contributors. There has been much confusion from well-intentioned people who assume the music, graphics, levels, etc. are free for the taking, and it requires extra vigilance to prevent problems.

-Erik

[Rubs]

Thanks for attention to this topic everyone, I learned a lot here!

I contacted game authors and even they didn't know for sure if the levels were under GPL or not, but they said that if I provide access to levels via editor and a link to the project page everything is ok.

As for name, it can be also used, since the game is free and there are no claims on the name.

So I think about making a decent implementation of that game for windows and linking to the free version page and original authors. That should be ok for a small puzzle game :)

[soniCron]

Check out the following regarding a similar discussion of GPL'd assets:

http://forums.indiegamer.com/showthread.php?t=4095