Sorry if this is in the wrong forum. Ive been searching for technology to build a game from a concept I've been overhearing that Tech 4(technology behind quake 4 and doom 3) will be available sometime next year under the GPL. Does this mean that the entire engine and its editors will be freely available to use for commercial works? If so then I'm tempted to start using it. On the wiki John Carmack mentions this stuff but Ive heard that wiki's arent always 100% accurate. Heres the site: http://en.wikipedia.org/wiki/Id_Tech_4 and heres what it mentions about it... "At the QuakeCon 2007, John Carmack, the lead graphics engine developer at id, said to LinuxGames: "I mean, I won't commit to a date, but the Doom 3 stuff will be open source." And like its predecessors, John Carmack has said that id Tech 4 will be released as open source. [3] At the QuakeCon 2009, Carmack said that he planned to petition Zenimax to release the id Tech 4 source upon the release of Rage (expected in 2010)." So Im curious if it will be safe to start working on a project now and wait until its released under the general public license to market my project. Or would that not be a safe wager? I really would like to because the SDK is perfect. It has the editors as well as a user made mod that enhances the graphics pretty nice. I appreciate any comments and suggestions on this. thanks a lot.

I don't know if it will be available or not, but GPL usually means you need to publish your source code. Maybe not so good idea for game, usually.

Well I have the Quake 4 SDK lying on my HD, but I forget exactly where I got it from so let me google that for you. :)

The GPL is incompatible with commercial use in the traditional sense. It doesn't care if you make money, but the terms of the license will put you in a position where making money directly through the software just isn't going to happen. There are companies who release GPL "commercial" software and then charge for support, but that's not really going to work in a game.

Correct me if I'm wrong, but isn't only the source code covered by the GPL? If the other creative assets (levels, models, textures, audio and so on) are still under your copyright, then you can still sell that commercially while releasing your engine under the GPL.

That said, I'm not 100% sure if that's the case or whether there are some additional requirements for using the Quake engine, although that's mostly because I just don't know of any commercial games freely using a GPL'd Quake engine. The only projects I know of are free ports of the existing Quake-engined games where you need to supply your own (paid) version of the original WADs.

The two big problems I can see with using the GPL Quake engine is that, firstly, there's a marketing danger people might see your game as just a glorified Quake mod ("after all, the engine's free, right? Why do I need to pay for a mod?"). Secondly, if you're going multiplayer, your game is open to all sorts of cheats and exploits due to free access to the source code.

As for whether it's safe to bet on Carmack releasing Tech 4 to the GPL, it depends a bit on your definition of "safe". I don't know a lot about the internal politics at id now that ZeniMax is in the picture.

Yeah it would be possible to do a commercial game with it (as long as you also go open source) -- after all, Quake1/2/3 still cost money to buy a copy even though their code is now GPL (you're basically paying for the level data, not the code, which is free).

Quote: Original post by Trapper Zoid
Correct me if I'm wrong, but isn't only the source code covered by the GPL?

Mostly correct.

The GNU GPL is written around the concept of textual source code. It refers specifically to "source code" and notices placed within the source code.

Version 3 of the GNU GPL is the most friendly to non-text source, but it is still based around the concepts of human-readable source code.

What is the source code of an image? What is the source code of a sound file? How do you place a copyright notice at the beginning of such a file?

They can still meet the fundamental license requirements, and obviously their intention is to release it under those terms.





This will probably never be challenged in courts. Since the GNU GPL is permissive rather than restrictive, if you challenge it then you are effectively denying yourself access.


You can't sue if it won't affect you, so the only way to sue is to be using the material or the person who distributed it. If the plaintiff is the one who distributed, the courts will (likely) interpret that your intentions were to release it under those terms and require a waiver. If the plaintiff were the user then denying GPL coverage would put them in blatant breach of copyright.


When content is mistakenly offered under the GPL you simply accept that their intentions are to follow the GPL. You can accept it under those terms, or try to get your own special licensing.

Quote: Original post by Hodgman
after all, Quake1/2/3 still cost money to buy a copy even though their code is now GPL (you're basically paying for the level data, not the code, which is free).

No, their source code is not GPL.

They still own the copyright to the source, they offered some of it as a non-exclusive license to the public. It does not release their ownership, nor their ability to license it under other terms.

They released a snapshot of a portion of their source under the GPL so that others can learn from it. Their stated intention was never to put it out to produce competing programs. The fact that a few people did is an interesting and expected side effect, but that was not their goal.

I'm sure they found many benefits to releasing it the way they did. The released source was not a complete game, and the license terms meant they would see very little backlash. It has been heavily studied and globally discussed. Errors were found. There was a lot of discussion about what was good and what was bad.


Sometimes I wish I could have global code reviews the same way they accomplished the first time. I'm guessing this one will be much less effective.