> (you can also use perfplot, but note it’s GPL-licensed)
Surly using a GPL-licensed development tool cannot affect the licensing of the project it's being used to develop?
Surly using a GPL-licensed development tool cannot affect the licensing of the project it's being used to develop?
Is there some way that I can GPL the output people get from use of my program? For example, if my program is used to develop hardware designs, can I require that these designs must be free?
In general this is legally impossible; copyright law does not give you any say in the use of the output people make from their data using your program. If the user uses your program to enter or convert her own data, the copyright on the output belongs to her, not you. More generally, when a program translates its input into some other form, the copyright status of the output inherits that of the input it was generated from.
So the only way you have a say in the use of the output is if substantial parts of the output are copied (more or less) from text in your program. For instance, part of the output of Bison (see above) would be covered by the GNU GPL, if we had not made an exception in this specific case.
You could artificially make a program copy certain text into its output even if there is no technical reason to do so. But if that copied text serves no practical purpose, the user could simply delete that text from the output and use only the rest. Then he would not have to obey the conditions on redistribution of the copied text.
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https://www.gnu.org/licenses/gpl-faq.html#WhatCaseIsOutputGP...
In what cases is the output of a GPL program covered by the GPL too?
The output of a program is not, in general, covered by the copyright on the code of the program. So the license of the code of the program does not apply to the output, whether you pipe it into a file, make a screenshot, screencast, or video.
The exception would be when the program displays a full screen of text and/or art that comes from the program. Then the copyright on that text and/or art covers the output. Programs that output audio, such as video games, would also fit into this exception.
If the art/music is under the GPL, then the GPL applies when you copy it no matter how you copy it. However, fair use may still apply.
Keep in mind that some programs, particularly video games, can have artwork/audio that is licensed separately from the underlying GPLed game. In such cases, the license on the artwork/audio would dictate the terms under which video/streaming may occur.
The tricky part here is that it's a library that produces graphs which themselves aren't covered by the terms of the GPL. The intent of the tool seems to be that you use it to produce graphs during development for benchmarking or during research or whatever where the tool is internal but the graphs aren't necessarily internal, in which case the licence of the library is mostly irrelevant as the GPL is mostly concerned with distributing software to other users of said software, not the output of the software, but if you later choose to want to release that tool it really aught to follow the terms of the GPL and be under a licence compatible with the GPL, so the note about it being a GPL licenced library is completely valid. You should use a more permissive LGPL/MIT/BSD/whatever licenced library like benchit if you don't want to have to think about this sort of stuff.
This may be in the spirit of Free-as-in-freedom software, but I don't think it's grounded in the reality of copyright and the GPL. With the usual disclaimer that IANAL: copyright attaches to the work (the code), and is retained by the author. The author grants you certain rights to use, modify, and redistribute the code subject to conditions (the GPL). Those constraints only encumber your works that are derivative of the GPL-licensed code i.e. either direct modifications of original source or linking original/derived object code.
A product that directly and necessarily imported perfplot would probably itself need to be GPL licensed to be distributed. A product developed with merely the assistance of something like perfplot would not need to be licensed in any particular way, any more than software written in Emacs needs to be GPL licensed.
There's a lot of GPL FUD though from commercial interests though.
Those boundaries are nowhere close to the situation in the OP though. I guess the FUD is working...