Licencing Issue: Linking

[Aterion]

Hello! First of all, thanks for all the effort on the libraries. It looks very interesting and promising!

This is one of the libraries I’ve been considering for our Unity project, due to its functionality and lightweight dependencies. Some other libraries have caused issues due to incompatible dependencies, while this one seems like it would integrate well.

I have one concern regarding the LGPLv3 license, if I understand it correctly. For some engines like Unity and Godot, the linking requirement in the license can be a significant issue. When building for certain target platforms with Unity, C# code and .dlls are translated through the IL2CPP system and compiled ahead-of-time into native C++ code. This process makes dynamic linking currently impossible for platforms like Web (WebAssembly), Android, and iOS.

This makes the LGPLv3 requirement from section 4. Combined Works technically infeasible to fulfill on some of the platforms:

d) Do one of the following:
0) Convey the Minimal Corresponding Source under the terms of this License, and the Corresponding Application Code in a form suitable for, and under terms that permit, the user to recombine or relink the Application with a modified version of the Linked Version to produce a modified Combined Work, in the manner specified by section 6 of the GNU GPL for conveying Corresponding Source.
1) Use a suitable shared library mechanism for linking with the Library. A suitable mechanism is one that (a) uses at run time a copy of the Library already present on the user's computer system, and (b) will operate properly with a modified version of the Library that is interface-compatible with the Linked Version.

If it is the case; would you consider to make the license more permissive in the terms of linking? It would make it possible to use the libraries in more modern platforms and perhaps more easily on existing ones. Thank you for considering my request! :)

[arklumpus]

Hi, thank you for your interest! To clarify, my main intent would be for people to be able to freely use the library, provided that any modifications they make to the library (e.g., bugfixes) be distributed in source code form along with any compiled artifacts. So, I would be OK with you (or anyone else) statically linking the unmodified library in your project.

However, as you note, static linking with the LGPL is complicated... I have done some reading, and an option would be to move to the Mozilla Public License (MPL) 2.0, which allows this (Q8 in the FAQ); however, I'm not comfortable with point 10.2 of this license, which allows redistribution under the terms of any subsequent version of the license. The (L)GPL has a similar point, but it also has explicit language that allows opting out of this provision (which I do), unlike the MPL.

So, I think the best solution would be to keep the LGPLv3, with the addition of a "linking exception":

As a special exception to the GNU Lesser General Public License version 3 ("LGPL3"), the copyright holders
of this Library give you permission to convey to a third party a Combined Work that links statically or
dynamically to this Library without providing any Minimal Corresponding Source or Minimal Application
Code as set out in 4d or providing the installation information set out in section 4e, provided that you
comply with the other provisions of LGPL3 and provided that you meet, for the Application the terms and
conditions of the license(s) which apply to the Application.

Except as stated in this special exception, the provisions of LGPL3 will continue to comply in full to this
Library. If you modify this Library, you may apply this exception to your version of this Library, but you
are not obliged to do so. If you do not wish to do so, delete this exception statement from your version.
This exception does not (and cannot) modify any license terms which apply to the Application, with which
you must still comply.

Would this work for your use case?

P.S. Note that VectSharp.Raster and VectSharp.MuPDFUtils will have to remain under AGPLv3 (because they depend on MuPDF).

[Aterion]

I thought it might be the case! It seems that such licenses were not originally designed considering pipelines building for browsers, mobile devices or even consoles where environments operate with different constraints. Either way it is good to clarify.

Both options make sense depending what you consider as most important. I completely agree that you should protect your work in a way that is the most comfortable to you. Adding given exception to LGPLv3 should make the libraries safe to use in such situations, which I believe solves the issue in my case. It is also more convenient and safer to eventually release any modifications (like bugfixes) either here or as a linked fork.

I'm not a licensing expert, though I know it is best to keep the license as simple and clear as possible... but in this case like this it might be hard to find an alternative that combines best of both worlds without additions.

I'm aware that VectSharp.Raster sadly needs to remain under AGPLv3. It is limiting but something outside of your control.