Quake3World

I just realised - with the Quake 1 source code now being GPL'd, and Half-Life and many other non-GPL games using that source code (definitely 'derivative works'), does this invalidate id's GPL-release of the Q1 source code, or does it mean the code to HL must legally be made available?

Minefield.

id retain the copyright on their own code, so they are free to license it how they like. For example, there is nothing to stop them GPLing it and simultaneously having a commercial license that doesn't require source code disclosure -- in fact this is exactly what they do.

Valve bought a Q1/Q2 source license from id for HL, and as such they're are legally 100% fine. It doesn't matter what happened to the licensing options of the code thereafter, since their license was a commercial one agreed prior to the GPLing.

What Valve or any other commerical licensee cannot do is use any code that was derived from the GPL release, for example the Nexuiz or Tenebrae projects.

So blah, the underlying point is that having one code base but multiple licenses is legally fine.

Am I right in thinking that if they had released the code under GPL <i>then</i> released under a commercial license, that would be a violation of the GPL?

No, because (as I said before) id hold the copyright, so they can do what the hell they like. The GPL doesn't restrict the licensers rights at all. Any license that did would be a legal minefield.

As an example, I own one or two GPLed projects. There is nothing to stop me deciding one day that I want to sell or license said projects without providing source.

Thanks for clearing that up