Something I have seen done for other projects in the past is to distribute a separate tarball with large assets used to generate graphics, textures, sounds, etc. in the same distribution locations. This has the advantage of making it easily available to those who want it, but not forcing everyone to use it.

The occasional practice in Debian of ensuring all sources are present as part of the distributed tarball comes from being extra careful about the "preferred form for modification" clause in the GPL. Only by building the distributed binaries from the modification sources can one be certain that the distributed object code can be reliably reproduced from the modification sources (and consequently that any recipient can easily/safely modify the result to match their tastes) using the Debian system (this also acts as a test of any dependent tools: for example, if blender were an essential part of the workflow, it would be extra annoying for Debian users if the blender included in a given release of Debian couldn't reprocess the graphics for some other package in that release). This definition of "source" is not hardened in Debian policy, so that if freeciv declares that although these materials may have been used as part of a generation process, that generation process was in part manual, and the (smaller) graphics actually used by the game are the preferred targets for modification, that would likely be honoured. That said, the same logic that drives this practice may apply in other environments.

Anyway, looking at data/graphics, we don't seem to have any build system instructions that can produce the png files from the blend files, making me think that the blend files aren't actually "source code", but rather "materials" used by the artists in the construction of the "source code" png files. Mind you, that's only my opinion, but were I handling the release, I'd probably only reference source control or maybe provide a tarball, but avoid calling the blend files "source code" as much as possible. Alternately, if they are already considered "source code", there should be automake hints that allow one to regenerate the graphics files from the blend files, and then they should definitely be in the tarball.

> There is precedent

That doesn't mean it has been handled perfectly, though.

My interpretation is that at least documentation in tarball should tell where the sources are easily available, and that is entirely sufficient (GPL doesn't require one to automatically push out sources at all - promise to provide them for someone asking for them is enough) I'm not entirely sure about Debian policy, but at least with some packages they have wanted to put everything like this to their source packages, so README.packaging would be one place to mention these.

Currently cimpletoon unit .blend files are not put to tarball.

I'm not really into adding them there, either. Most people wanting just to compile freeciv wouldn't want size of the tarball to grow with these files. Of course putting them to tarball would be most idiot-proof way to distribute them in a GPL compliant way.

Should we package them separately? Could we go by only pointing to our version control in documentation?