Is it legal?



  • I build a GUI application with the free Qt creator version, but this application will be used on machines world wide. Is this legal?


  • Lifetime Qt Champion

    Hi,

    The licensing of the libraries your used for your application has nothing to do with Qt Creator itself.

    The real points of interest here are:

    • What license of Qt did you use to build your application
    • Are you compliant with all the requirements of that license
    • What are the license(s) of the other libraries you are using
    • Are you compliant with all the requirements of these licenses.


  • Well from what I read about Qt licences, we would need to purchase a license for 'Qt for device creating'.

    But I do not understand how the prices work, it is unclear what 'Qt for device creating' costs per year. A monthly breakdown of $295 per month, does that mean we would need to pay 12 x $295 = $3540 per year?



  • @bask185

    For Desktop and Mobile devices, yes

    If I understood correctly, for Device Creation you need to contact Qt about the price



  • I have send an e-mail to Qt company and I am waiting for a respons, but does it make any difference that we are interested in open-source? We do not care about proprietary about our software.


  • Lifetime Qt Champion

    Open Source doesn't mean you can do whatever you want with a library/piece of code etc.

    Both LGPL and GPL have their constraints both software and hardware wise. As long as you follow the constraints of the license(s) of the libraries you use in your application you are fine.



  • @bask185 If you are asking about using Qt Creator (not Qt) for your applications, you can develop whatever you want with it without any restrictions, just like with any other text editor.



  • @Konstantin-Tokarev said in Is it legal?:

    @bask185 If you are asking about using Qt Creator (not Qt) for your applications, you can develop whatever you want with it without any restrictions, just like with any other text editor.

    So we can sell 200 Raspberry based HMIs which run my Qt application per year across the globe without any riscs?


  • Lifetime Qt Champion

    Again: look at the licenses of the libraries you use for your application.

    As stated before, Qt Creator itself has nothing to do with your application distribution.



  • @bask185
    To add to @SGaist's statement

    If you are not sure which license model to choose in your case, feel free to contact the Qt Company and/or the author of the external modules you need for your project.



  • "Is it legal?" is a tricky question to answer: It depends on exactly what you do and your local legislation.

    My interpretation (and I am not a lawyer) is that you can use whatever license you want for code written inside Qt Creator. If you write code that uses code taken from Qt Creator, then Qt Creator's license applies. If you do not do that, then you are not bound by Qt Creator's license.

    If you use Qt (or any other library) in your product, then you need to adhere to the license of Qt (or other libraries). If that is an open source license than you may need to ship all or some of your code to your customers (and only your customers, which may pass it on of course). In my understanding it does not matter whether you mail a zip file with the binaries to one customer or sell 200 million devices with the code baked in.

    When you feel uncertain about a license, then please get in contact with a lawyer specializing in intellectual property laws for your legislation.



  • This is a really nice post. I have a similar doubt regarding the license.
    I felt the responses from @SGaist and @hunger are interesting. But, am not still clear about the things running in my mind about the licensing. I will write it down here:

    I am developing a Qt application on Raspberry Pi which runs Yocto Krogoth version 2.2.1 and Qt version 5.6.2. I am using the below Qt Modules:
    Qt GUI
    Qt SQL

    And now, I am planning to use the Qt Add-On: Qt Charts and I see that the Qt Charts Add-on is under the section (mentioned below) from this link I read:

    Add-ons available under Commercial Licenses, or GNU General Public License v3
    

    I am not planning to change / alter the Qt Code in any manner, What I am planning to do was just to take the Qt 5.6.2 source code for the Krogoth Yocto Line and cross compile for the Raspberry Pi to get the SDK and extract the tool chain that's going to be in my Raspberry board which will be referenced by my Qt Application to run as intended.

    So Do I need worry anything about the licensing here, since am not going to modify any Qt Source Code ? Like @bask185 asked will I be charged any money if my Qt application is going to run on the boards that am planning to use myself or sell to end user. ?

    I dont completely understand the LGPL and GPL licenses. After I saw this post I felt it is right area to just speak out and get the experts opinions. Sorry for posting a question back in this thread, thought it is worth to discuss and update my understanding about the Qt licensing.

    Thanks for any feedback.


  • Lifetime Qt Champion

    Using a GPL component in your software means that all your software becomes GPL so you have to abide to that license constraints.

    If you want to keep your application closed source and use the QtCharts module then you have to get a commercial license.



  • @SGaist said in Is it legal?:

    Using a GPL component in your software means that all your software becomes GPL so you have to abide to that license constraints.

    Only if you link your code with GPLed code. For example, it's absolutely fine to have GPL software in the same firmware image with proprietary, if executables are separate. However, one should be aware of anti-tivoization clauses of (L)GPL v3


  • Lifetime Qt Champion

    @Konstantin-Tokarev that's exactly what I meant, thanks for the clarification.


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