[camgunz]

To be specific, if you modify actual Qt code--which you shouldn't be doing generally--then you have to release those modifications.

But if you dynamically link your app with Qt you're fine; you don't have to open source anything.

[Buttons840]

You also must provide the Qt source code yourself, giving instructions on how to get Qt from the official website is not sufficient.

You also must allow relinking of your proprietary binary with different versions of Qt. This is easy on desktops but not on embedded or mobile devices.

You also may not begin using a commercial license for your proprietary code which you developed using the LGPL licensed Qt, unless you have written permission. Part of this also means you cannot use, let's say, a MIT licensed wrapper or utility for Qt, because that was probably developed against the LGPL licensed Qt, and thus cannot be used with a commercially licensed Qt.

There's certainly a reason people worry about Qt licensing.

Source: https://www.qt.io/faq/

(And despite all this, let's remember how great it is that one of the best widget toolkits in the world is open source.)

[camgunz]

I don't mean to be harsh, but everything you wrote here is either wrong or misleading.

> You also must provide the Qt source code yourself, giving instructions on how to get Qt from the official website is not sufficient.

This isn't true [1].

> You also must allow relinking of your proprietary binary with different versions of Qt. This is easy on desktops but not on embedded or mobile devices.

If I'm distributing a game written with SDLv1 on mobile, I don't have to do anything at all differently than if I distribute the exact same game on desktop. Many, many games did this.

> You also may not begin using a commercial license for your proprietary code which you developed using the LGPL licensed Qt, unless you have written permission. Part of this also means you cannot use, let's say, a MIT licensed wrapper or utility for Qt, because that was probably developed against the LGPL licensed Qt, and thus cannot be used with a commercially licensed Qt.

This is also not at all true [2], in fact they couldn't release Qt under the LGPL if it were. That would be LGPL with a non-commercial-use clause, which would be incompatible.

> There's certainly a reason people worry about Qt licensing.

Yeah and honestly, it's because there's a lot of bad information out there. GPL and LGPL are subject to so much FUD. We as developers have a responsibility to know the facts.

[1] https://copyleft.org/guide/comprehensive-gpl-guidech10.html#...

[2] https://www.qt.io/faq/ (section 3.7)