Developing Games based on Evidyon

Over the last few weeks, I have received many questions about what a developer creating their own game based on Evidyon can do. Instead of copy/pasting my answers, I hope to address many of the things that have come up here in this one post simply and directly.

First, I would like to say that I am very interested in encouraging developers to make new versions of Evidyon and, yes, even profit from hosting the game and creating a great experience for players.  It is not my intention to limit you in this way; however, consider the amount of work that went into producing Evidyon and you’ll understand why there are conditions on what you can do.

As stated in various locations (including everywhere in the source code) Evidyon is licensed to you under the GPL.  Jointly, Joe Muller, my brother Erich, and I assert copyright over all of the source code and content.  This means the following:

From http://www.novell.com/coolsolutions/feature/1532.html

In US copyright law, a copyright owner of an original work is the only one with the right to make or license derivative works based upon a previously copyrighted work. A derivative work is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. US copyright law stipulates that a work will only be considered an infringing derivative work if it is substantially similar to the copyrighted work, and if the copyright holder did not authorize the derivative.

By releasing this content under the GPL, we have exerted our rights to “license derivative works,” given some set of conditions.  In order to use the source code or models, you have to agree to be bound by the terms of the license.  So what are those terms?

  1. Nothing you anything you add or modify can be proprietary (you must make open-source all changes to the game)
  2. Source code and source media must be provided alongside the compiled game
  3. Include along with your distribution the terms of the GPLv3
  4. There is no warranty of any kind

There are a number of things you must and must not do in order to comply with these terms and the fact that Evidyon is copyrighted.  While the following is not exhaustive list, I’ll try to spell out some examples.

You cannot claim to have made Evidyon, claim to have ‘ownership’ of Evidyon, copyright the name Evidyon or any part of the game, or file for a patent or trademark based on Evidyon.

The following example is absolutely false, is forbidden by the terms of the GPL and is just plain offensive.

I am going to publish this game. and copyright any products and icons ideas I make.
this game is now MINE

Changing the name “Hogwarts” to “Graycastle” and introducing a few new characters doesn’t mean that you own the Harry Potter series.  I don’t think I need to say any more about this.

You can charge players to play on a game server you host

Yep!  You could download a copy of Evidyon, host an unmodified server and charge people a monthly fee to play on it.  No problems there, as long as you let them know that they can get the complete source code to the game.

You must provide all changes to the game’s source code or content for free

If you read the statement of US copyright law on derivative works, it is apparent that anything you do with the game can be considered a “derivative work” and, as a broad umbrella statement, if you’re in doubt about whether you have to release something you’ve made to be incorporated in the game, the default answer is “yes, you must release it under the GPL”.

At first glance, this seems to mean that it would be difficult to make money hosting a server, since this term means that anyone could download your copy of the game, start up their own server and compete with you.  By some interpretations of the GPL, this is true.  However, as I explain next, I don’t intend this to be the case with Evidyon.

You don’t have to release game-files, media, server databases, log files, or anything that is 100% new but works with Evidyon’s engine

This is parallel to a topic in the open-source vs. free software debate.  Linux, like Evidyon, is licensed under the GPL.  By many interpretations, including my own, software the runs on Linux does not need to be open source or use the GPL  in order to comply with Linux’s license.

Similarly, new content you create to use with the Evidyon engine in your own version of the game (maps, character models, textures, sounds) does not need to be released under the GPL or made public.

Look at tools like Open Office (GPL document editor) and GIMP (GPL image editor).  These do not assert ownership of the content created with those tools–if you write something in Open Office or draw something in GIMP, that content is your own.  With Evidyon, the database the server makes to store character & game data falls in that “100% new” category so you can keep that secret.

This means that almost everything that makes your edition of this game unique–the content–is your own.  Just to be clear, though, the same interpretation does not apply the the code.  The code that runs the game is a single entity.  Even 100% new features you add to the software itself are still bound by the GPL and must be publicly re-released for everyone to enjoy.

If you want to be sure you won’t accidentally violate the GPL, there’s a really easy way to do it

Get a DropBox account, make a publicly-accessible DropBox folder, and only work on your game inside of that DropBox folder.  Then, with each release, all you need to do is provide a link to the public web-interface of this DropBox folder to stay legit with the terms of the GPL.  Since DropBox synchronizes automatically, you will never have to worry about it being out of date!

In fact, when you recompile the game players will be able to get the latest copy from that folder so you can even use it as a distribution channel.

“I gave the Volucris model some new clothes.  Do I have to release my model?”

Yes

“I changed the GUI to look more futuristic, do I have to release the image?”

Yep

“I took the map, modified the drop rate, gave it some new ground textures, changed the names of stuff etc. etc.  Do I have to release my changes?”

Affirmative.  If your game file has any relationship whatsoever to the original game file, it’s a derivative work.

“I purchased some items from 3drt to add to my game… do I have to release those?”

Nope! In fact, it would be in violation of your agreement with them to do so.  That’s new content that doesn’t derive from Evidyon.

Be aware that this does introduce some caveats.  Should you buy armor models (for example) you can’t put them on our original Evidyon avatar meshes, since that would require you to release those meshes for free under terms of the GPL (thanks Qubodup).  As long as you keep custom and original content separate, there should be no problems.

“I modified the code to add an item merchant and a new player class….”

Those are modifications to Evidyon’s source code, and you need to make those changes available for others.

But wait, the GPL doesn’t say anything about charging to distribute derivative works–how come I have to give my stuff away for free?

This addition is thanks to the anonymous comment below.  I’ll just quote the post since he/she explained it well:

Note that GPL does not say anything about price. If you make a derivative work you may well charge a fee for it if you want to. If you distribute the work to someone (for free or for a price), you are obliged to give them the source for free (or for a reasonable price covering only the medium/postage). However, the person you charge is free to make further copies, either for free or for a price, so in practice it’s not feasible to charge for GPL-licensed works.

There you have it folks!  Hopefully this guide is complete enough to answer all the questions I’ve been receiving.  Feel free to post if anything isn’t clear, and I’ll update with more information as necessary.

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4 Responses to “Developing Games based on Evidyon”

  1. Memnon Says:
    April 9th, 2010 at 10:03 am

    i wouldnt dream of breaking those rules. when i said that i meant my content ideas and icons that i add to it. thanks again man you should try playing the game sometime :)

  2. anon Says:
    April 9th, 2010 at 2:18 pm

    Note that GPL does not say anything about price. If you make a derivative work you may well charge a fee for it if you want to. If you distribute the work to someone (for free or for a price), you are obliged to give them the source for free (or for a reasonable price covering only the medium/postage). However, the person you charge is free to make further copies, either for free or for a price, so in practice it’s not feasible to charge for GPL-licensed works.

  3. qubodup Says:
    April 9th, 2010 at 7:19 pm

    Wow! I have only taken a quick look but this looks like a solid licensing guide for GPL games. Gotta finish reading it later, for now the only ‘problem’ might be that “free” is not clear sometimes. For example you say “Should you buy armor models (for example) you can’t put them on our original Evidyon avatar meshes, since that would require you to release those meshes for free.” and I think you mean gratis, but it in fact should be “under terms of the GPL” or “free as in freedom” or something.

    I might be wrong of course and you mean the FSF-’free’ :) In that case the wording might be confusing as well though. I often use “open source” simply to avoid this :|

  4. Karl Gluck Says:
    April 10th, 2010 at 12:35 am

    Qubodup: Exactly right, thanks for catching that–by “free” I do mean open-source by the GPL free.

    anon: Thank you for the note. I overlooked that in the GPL, and you are completely correct. I’ll add another note at the end of the post about it.

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