I'm not an law expert and I want to create a python C4 level editor addon for gimp. C4 engine is commercial engine with access to sources for relatively small payment.
The problem is:
|Not OK is:
Author publishes a Blender script, calling a compiled C library with own code, both under own license.
I would like to create GPL script for Blender, but calling closed C code. Anyone who will use that code, should buy C4 license to make use of it.
By the level/model editor, I mean add changes in blender, and see them in C4 Game engine instantly. (inter process communication, like in Oxygen2 and RealVirtuality engine).
This will call extern C code.
Another approach would be to export level/model to file, and check file modification timestamp. After every output file update, just read whole file by C4 plugin. This is much weaker solution.
I see, that Blender community is not against closed python addons:
Author publishes a Blender script mixed with own code, under own license.
So why not to publish Python API with LGPL that allows linking?
Little offtop too, but Linus is not against GPL linux kernel and closed drivers. Some people say, that calling an API functions is not a violation.
Well, I don't see your problem. Anyway the deal with GPL is this: if you charge money for your work and used GLPed code then you must provide the source code. If you don't charge then noone cares.
LGPL means you can dynamically link against the library and you can keep your source closed.
With that said I maintain a complex exporter plugin for Blender for a proprietary engine.
GPL makes no distinction whether you redistribute for money or not; if you redistribute, you must offer the source.
By the way, as per recent court cases in both the US and Europe, APIs are not copyrightable.