I would like to know what license these source codes have.

Is it possible to revise or redistribute add-on written by someone?

To begin with, an add-on you find aren't different from any other code snippet you find online. So these general Q&A's apply:

When its not explicitly stated, you can't assume anything regarding the license of code you find. (Blender related or not).

Contact the author and ask them to either...

(convention for all Blender's code).
• include LICENSE file in the source code repository.
(also valid but can make tracking down the license harder if files are re-arranged or re-used between projects).

Doing so will save others this hassle in the future.

Note that even in the case where the license is open-source and compatible with Blender, you may want to know the copyright holder(s) later on, especially if this ends up being used in larger projects.

• Really? I've heard that all addon code must be GNU GPL. Bundled content like textures or models can be under a separate license, but the code itself must be GNU GPL. Its the reason that paid tools like Retopoflow from CGCookie can be legally downloaded without purchase. Happy to be proved wrong though! Feb 25 '16 at 5:49
• @AndrewPrice, this is probably too big a topic to cover in comments. if you want to go into more details it would be better to ask a separate question. Feb 25 '16 at 6:21
• Thanks for your answer. I get it about add-ons' license. By the way, is the source code license free pasted on pasteall.org? There is a description Anyone can see/copy/use it. on pasteall.org/about. Feb 25 '16 at 12:24
• @nutti - again. I don't think you can make any assumptions here. This question isn't really specific to Blender or Blender's code. Suggest asking at programmers.stackexchange.com Feb 25 '16 at 19:07
• @AndrewPrice, in response to your comment, see: blender.stackexchange.com/q/47810/55 Feb 27 '16 at 5:05

According to the Blender FAQ at the Blender Foundation Website:

Python scripts – if they use the Blender API calls – have to be compliant to the GNU GPL as well. We are currently reviewing this with Free Software Foundation though.

This practically means that if you're using the Blender API in your script or addon (whether original or borrowed from another person's code), it needs to comply to the GPL license. I.e. (as I understand the license) if you want to distribute it (whether for profit or not), you need to publish the full source code.

• This is only if you distribute them with Blender, for scripts you find online without any licensing information, there is no guarantee they are GPL compatible (though in practice most are). Feb 24 '16 at 22:53
• @ideasman42, That makes sense but is not quite how the FAQ is phrased. I assumed that if you distribute code that uses the Blender API, than at least according to the license, you're supposed to comply with GPL (even if many probably do not). Feb 24 '16 at 22:58
• The FAQ doesn't go over possible exceptions to the rule, TBH not sure it should. If you mix licensing in a way that's incompatible with Blender, it seriously limits what you can do... going over these in detail would have to cover a lot of technical language. Though it could be prefaced with "Assuming you want to distribute this with Blender..." Feb 24 '16 at 23:05
• I'd like to add that being GPL complaint doesn't mean it's GPL. It could be a more liberal license or even a public domain license. Feb 25 '16 at 23:18
• A python script calling a function that was compiled from GPL code is the same thing as linking a binary program to a library that is GPL'ed. The viral nature of GPL means that the program/script that links to the GPL'ed library is also covered by the GPL as a derivative work. As @someonewithpc says, a less restrictive license can be used, but it cannot prevent you from complying with the GPL terms. That is why they also have the LGPL to allow libraries to be released that don't infect programs that link to them. Feb 26 '16 at 14:06