License compatibility?

[gitbugr]

I understand that OpenToonz uses the modified 3-Clause BSD License, though for sake of clarity, I thought I'd ask about compatibility with other licenses.

I think GPL specifically is of concern. I know that GPLv3 is in some way compatible with BSD-3, however there are requirements that OpenToonz wants to avoid? What are these requirements and does this apply to other GPL licenses, such as GPLv2, GPLv2-or-later or LGPL?

For instance this Tahoma feature request hinges on pulling in a library using a GPLv2-or-later license.

I understand many of us may not be entirely in-the-know on licensing, but I think this is important as depending on the status of what libraries are acceptable to use or not, it could open up more possibilities for future development.

[shun-iwasawa]

IANAL but here's why, as far as I understand:

"Compatible" means that you can combine code released under NewBSD with code released under the GPL in one larger program. But what happens when they are actually used together?

Regardless of the version, for OSS licensed under the GPL, the obligation to disclose source code applies not only to the GPL part itself but also to ANY programs dynamically or statically linked with the program.
(Please refer to the section 5 in GPL v3)

The obligation to disclose source code is not in the original NewBSD license. However, when they are combined with GPL programs, they become obligated to disclose.
This is so-called GPL contamination, and is the reason we are hesitant to incorporate GPL programs.

The LZO library for compressing Toonz Raster Level (TLV) is released under the GPL. We have separated the LZO-based components into independent programs (lzocompress.exe) to limit the scope of the obligation to disclose source code under the GPL license.

OTOH for OSS licensed under the LGPL, the obligation to disclose source code does not apply to programs that are dynamically linked with it. Actually, OpenToonz dynamically links and uses the Qt library which is released under LGPL.

[RodneyBaker]

Transferring this report over to Opentoonz-docs where it can help fill in the gaps with reqard to questions related to licensing.