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Qt license policy and paid for apps

asked 2014-04-23 12:17:32 +0300

2Ti gravatar image

updated 2019-02-11 15:09:16 +0300

jiit gravatar image

It may be somewhat premature to ask this as there is currently no support (related) for paid for apps in Harbour.

I was however wondering how the licensing for paid apps would work. Specifically the licensing of Qt from Digia. Digia is licensing Qt under GPLv3 and LPGLv2 and a commercial license. LGPLv2 section 2.c says:

  • You must cause the whole of the work to be licensed at no charge to all third parties under the terms of this License.

and GPLv3 section 5.c says:

  • You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy. This License will therefore apply, along with any applicable section 7 additional terms, to the whole of the work, and all its parts, regardless of how they are packaged. This License gives no permission to license the work in any other way, but it does not invalidate such permission if you have separately received it.

Neither LPGLv2 or GPLv3 prohibit anyone from charging for the application (sources or object code), they do in fact explicitly allow it, but they also require the sources to be released under GPLv3 and LPGLv2.

So should someone wish to create a proprietary Sailfish app it would seem to me that it requires licensing either Qt Mobile from Digia at €109/month or the enterprise version at some undefined price that needs to be agreed with Digia separately. http://qt.digia.com/Try-Buy/

Was there some special clause in the Sailfish SDK that I missed, that allows developing non-free Sailfish apps without separately licensing Qt from Digia with a commercial license? GPLv3 to my knowledge requires all of the program that uses a GPLv3 library also to be GPLv3. LPGL doesn't, but I don't understand their interaction with each other.

I am not an expert on copyright law, so could someone clarify if I've understood this correctly. Also could someone from Jolla shed some light on this.

Given that the Android dev license is free (as in beer), and Apple charges (or at least used to) some €70/year for AppStore(tm) access, €109/month seems quite pricey. You really need to believe in your app to take that on, all upfront.



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IANAL, but Section 6 of LGPLv2 provides an exception for distributing executables, and the conditions under which this can be done. (In particular, it does not require that you license your work under LGPL).

vvvv ( 2014-04-23 17:59:35 +0300 )edit

That seems clear enough, however I'm not entirely sure what the GPLv3 is doing there. Qt is licensed under both not one or the other, and the Sailfish SDK installer requires you to accept both.

2Ti ( 2014-04-23 18:56:15 +0300 )edit

The debugger (GDB) that gets installed with the SDK is licensed GPLv3, which is why the license is shown in the installer.

kaltsi ( 2014-04-23 23:27:25 +0300 )edit

Qt is not licensed under both GPL and LGPL, but eitherGPL or LGPL. http://qt-project.org/doc/qt-5/licensing.html

vvvv ( 2014-04-24 10:47:23 +0300 )edit

@vvvv Ah, I see. So the GPLv3 is there so that people can use Qt in projects that already have other GPLv3 stuff in them. Thanks for the clarification. You want to put that down as an answer so I can accept it.

2Ti ( 2014-04-24 11:05:08 +0300 )edit

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answered 2014-04-24 11:55:13 +0300

incognito gravatar image

Qt is licensed under LGPL or GPL (or commercial) and LGPL doesn't require you to license your app under it if you're using a LGPL licensed library. Qt, however, requires you to link dynamically to it if you want to use it under LGPL, but that shouldn't be of concern to you as you would dynamically link to the existing Qt libs that come with Sailfish. You can even ship your app bundled with modified Qt libs (thus not relying on what comes with Sailfish) and you would only need to LGPL those changes as long as your app links to those libs dynamically.

Thus, unless you want to statically link to Qt libs you don't need to pay for a Qt license or apply the Qt's license to the rest of your work.

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answered 2014-04-23 12:36:37 +0300

tokaru gravatar image

I am not a lawyer, but as far as I know, the citations refer to "derivative works", which is not the case when using a framework to build an application. (Otherwise, a whole lot of frameworks could not be used legally for closed source aplications).

If you were to build (and distribute) your own app framework based on Qt source code, things would look different.

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Asked: 2014-04-23 12:17:32 +0300

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Last updated: Apr 24 '14