QT Commercial vs Open Source

Stevendragoes · wrote on 6 Feb 2020, 07:57

Hello Moderators or whoever used the Commercial Liscenses in QT,

I understand that this is a repeated question in this forum. I read through the post and unable to come to a firm understanding. Hence, this post is created

I want to know the Main Differences between the OpenSourced and Commercial License. Maybe links to the comparison tables between the licenses? Or a detailed explanation of what are the essential differences between the opensourced license and Commercial LIcense.

sierdzio · wrote on 6 Feb 2020, 08:36

@Stevendragoes said in QT Commercial vs Open Source:

Alright. So, It is possible for me to get a confirmation from the QT sales team that they will not come after me if I released a proprietary software that I developed on my own?

Ask Qt Company then :-) I'm not their employee. But I can say that if you make sure you don't break LGPL, Qt Company won't have any basis to "chase" you.

What do I have to worry here? I heard that the Open Source license can be copied by anyone?

Yes, but LGPL applies only to Qt not to your code. That's why you have to inform your users that you are using Qt and that they can replace Qt with their own version if they want to.

How can i check my QT license? from the Update Manger?

If you have installed Qt without paying the commercial license, it is safe to assume you are using the open source version ;-)

The choice between LGPL and GPL is arbitrary - you choose which license you want Qt to be under (unless you chose some module which is not available under LGPL, like QtCharts, Lottie etc.).

Please pardon me for being a total ignorant newbie here

No problem, that's what this forum is for :-)

EDIT: I think I have to make my software with the source code public for 3 years. Am I right?

No, this is only about Qt. Your code is not bound by LGPL license (unless you decide to ship your code under LGPL as well).

So you have to provide Qt source code to your clients if they ask for it. In practice it means you should have a copy of Qt source code somewhere on your PC/ server for 3 years (just in case that official Qt archive goes offline or something). And if you patch Qt (for example, change something in QString code), these patches need to be under LGPL and you have to make them available to your clients.

That's one more point - to your clients. LGPL does not apply to every human being in existence :-) You don't have to publish Qt and your patches online for everybody. LGPL requires you to do it only for your clients (people using your app).

sierdzio · wrote on 6 Feb 2020, 08:09

Qt Company's page has a summary of the differences here: https://www.qt.io/download-open-source

In terms of features - FOSS and Commercial are the same on desktop and mobile platforms. On embedded devices, Qt comes with some extra stuff (base Qt code is the same but there are extra tools provided which make deployment and development easier).

The main difference - of course - is the license. Most of Qt is available under LGPL, but some modules are GPL only. If you are making an application under a different license (for example, a commercial application), you have to be careful to meet the requirements of LGPL and/or GPL. On some platforms (Android, iOS) this is very hard or even impossible. On others (Windows, Linux) it is quite easy.

Stevendragoes · wrote on 6 Feb 2020, 08:15

@sierdzio
I am developing on desktop platform. Hence, a Free Open Sourced License will do? What if I want to sell my invention/personal project? will QT charge? Because I believe that there exists a commercial license for a reason. Hence, I don't want to make any mistakes.

sierdzio · 2 Jun 2020, 17:32

As long as you use LGPL Qt (no GPL modules like QtCharts) and meet LGPL requirements you do not need the commercial license. You can sell your app, no problem there. Even the GPL does not forbid selling of stuff.

Stevendragoes · 2 Jun 2020, 08:25

Alright. So, It is possible for me to get a confirmation from the QT sales team that they will not come after me if I released a proprietary software that I developed on my own?

What do I have to worry here? I heard that the Open Source license can be copied by anyone?

How can i check my QT license? from the Update Manger?

Please pardon me for being a total ignorant newbie here

EDIT: I think I have to make my software with the source code public for 3 years. Am I right?

JonB · 6 Feb 2020, 08:32

@Stevendragoes said in QT Commercial vs Open Source:

Alright. So, It is possible for me to get a confirmation from the QT sales team that they will not come after me if I released a proprietary software that I developed on my own?

You would have to contact The Qt Company if you really want to ask a question like that. This is a user forum.

EDIT: I think I have to make my software with the source code public for 3 years. Am I right?

Where does that come from?

ODБOï · 6 Feb 2020, 08:37

@JonB said in QT Commercial vs Open Source:

Where does that come from?

column 3 row 3

sierdzio · wrote on 6 Feb 2020, 08:36

@Stevendragoes said in QT Commercial vs Open Source:

Alright. So, It is possible for me to get a confirmation from the QT sales team that they will not come after me if I released a proprietary software that I developed on my own?

Ask Qt Company then :-) I'm not their employee. But I can say that if you make sure you don't break LGPL, Qt Company won't have any basis to "chase" you.

What do I have to worry here? I heard that the Open Source license can be copied by anyone?

Yes, but LGPL applies only to Qt not to your code. That's why you have to inform your users that you are using Qt and that they can replace Qt with their own version if they want to.

How can i check my QT license? from the Update Manger?

If you have installed Qt without paying the commercial license, it is safe to assume you are using the open source version ;-)

The choice between LGPL and GPL is arbitrary - you choose which license you want Qt to be under (unless you chose some module which is not available under LGPL, like QtCharts, Lottie etc.).

Please pardon me for being a total ignorant newbie here

No problem, that's what this forum is for :-)

EDIT: I think I have to make my software with the source code public for 3 years. Am I right?

No, this is only about Qt. Your code is not bound by LGPL license (unless you decide to ship your code under LGPL as well).

So you have to provide Qt source code to your clients if they ask for it. In practice it means you should have a copy of Qt source code somewhere on your PC/ server for 3 years (just in case that official Qt archive goes offline or something). And if you patch Qt (for example, change something in QString code), these patches need to be under LGPL and you have to make them available to your clients.

That's one more point - to your clients. LGPL does not apply to every human being in existence :-) You don't have to publish Qt and your patches online for everybody. LGPL requires you to do it only for your clients (people using your app).

jsulm · wrote on 6 Feb 2020, 08:37

@LeLev I think it is about Qt source code, not the code of an application. There is no requirement in LGPL2/3 to make your own source code public when linking against LGPL libs dynamically!

J.Hilk · wrote on 6 Feb 2020, 08:39

@Stevendragoes said in QT Commercial vs Open Source:

Alright. So, It is possible for me to get a confirmation from the QT sales team that they will not come after me if I released a proprietary software that I developed on my own?

No, there is no guarantee
I had been developing with the normal Qt License for about 3 years, and then in a real d*move the Qt Company contacted me and said I had the wrong license and I would own them money.

IIRC they did not retroactively apply it(at least)

JonB · 2 Jun 2020, 08:40

@LeLev said in QT Commercial vs Open Source:

@JonB said in QT Commercial vs Open Source:

Where does that come from?

column 3 row 3

From an unlinked/unreferenced pasted screenshot? That is not what I meant....

sierdzio · 6 Feb 2020, 08:42

@JonB said in QT Commercial vs Open Source:

@LeLev said in QT Commercial vs Open Source:

@JonB said in QT Commercial vs Open Source:

Where does that come from?

column 3 row 3

From an unlinked/unreferenced pasted screenshot? That is not what I meant....

It's linked to in my post... https://tldrlegal.com/license/gnu-lesser-general-public-license-v3-(lgpl-3)

JonB · 2 Jun 2020, 08:48

@sierdzio
Yep, I now see that. I can only say that picture/table does not come out like that in my (~~Chrome~~ Firefox) browser!

J.Hilk · 6 Feb 2020, 08:44

@JonB probably simply "dark mode"

JonB · J J.Hilk 6 Feb 2020, 08:42

@J-Hilk
Yep, plus the user must have manually expanded every item :) I didn't recognise it! Anyway I now see the 3 year reference, I was not aware of that, thanks.

ODБOï · 6 Feb 2020, 08:47

@JonB +expand tabs

JonB · 6 Feb 2020, 08:51

@LeLev said in QT Commercial vs Open Source:

@JonB +expand tabs

This is about as OT as it gets (sorry!), but what does that mean? :confused:

ODБOï · 6 Feb 2020, 09:00

@JonB H.Hilk said, "dark mode" and i added "+ expanded tabs"

JonB · 2 Jun 2020, 09:01

@LeLev
Got it, sorry, I thought you were trying to tell me something to press in browser to auto-expand all those folded points! :)

I will be quiet now, and allow OP's discussion to continue if needed. Sorry for interruption.

Stevendragoes · wrote on 7 Feb 2020, 02:16

@All thanks for the clarifications. especially @sierdzio I will contact the QT company as well to see which license is right for me