Fun and games with the GPL
Nokia announced last week that as of version 4.5, the Qt GUI toolkit, most famously used as the basis of the KDE desktop, would change licences from the GPL to the LGPL.
Believe it or not, that one little letter could boost Qt's popularity significantly, potentially at the expense of the GNOME desktop and its GTK toolkit.
Licencing fine print
The GPL has been described as a "viral" licence because while GPL code is free for all to use, if you use it as part of your own project, it must too fall under the GPL's terms. This restriction ensures that GPL code can't be ripped off wholesale by commercial closed-source apps, and creates an environment that encourages people to re-use existing open-source code in new open-source projects.
Where the GPL falls down is at the boundary between open-source and closed-source software. Even the simplest programs rely on system libraries to run, and if those libraries were under the GPL, any software using them would have to be as well. Put simply, if the core Linux libraries were under the GPL, it would be illegal to run any closed-source software on a Linux system.
This problem lead to the LGPL (originally the "Library" GPL, but now called the "Lesser" GPL), which removes the "viral" clauses. If you make changes to LGPL code, then you have to release those changes, just like with the GPL, but if you just use the code with your project as-is, then your project remains free of any licencing issues. The LGPL is used on most Linux libraries, including the Linux core libraries and the GTK GUI toolkit.
Quirky Qt
Why, then, did Qt use the standard GPL? The answer lies in the fact that Qt is, somewhat paradoxically, a very commercial project. Qt was originally aimed at developers working on expensive niche apps for proprietary UNIX systems, and it came with a hefty price tag to match. There was also a free version, which KDE 1 used, but its use was heavily restricted.
As KDE rose in prominence, Qt and its developers, Trolltech, became more open-source friendly, releasing new Linux versions first under a custom open-source licence called the Q Public Licence (QPL), and later under the GPL. Far from giving the code away, though, Trolltech continued to sell Qt under its own proprietary licence. Using the GPL for the free version ensured that commercial customer working on closed-source apps had to pay for the commercial licence.
While KDE has been a great success in its own right, Trolltech's commercial licencing arrangements drove many Linux system vendors to back GTK and GNOME, to ensure that commercial developers can target Linux without cost.
Nokia changes the balance
Times have changed for Qt, though, since Trolltech was bought out by Nokia. The Finnish giant has been selling its Linux-based Internet Tablet devices for some time now, and while those currently use a GTK-based interface called Maemo, Qt has excellent embedded device support and may be a better option for future device.
Under Nokia, moving Qt to the LGPL makes perfect sense. Nokia makes its money selling devices, not software licences, and if it releases a Qt-based device, it would want to make as cheap and easy to develop for as possible, to encourage the kind of third-part innovation that can drive device sales.
Where to now?
It's hard to say exactly what effect an LGPL Qt will have, but two things seem inevitable: more closed-source apps choosing Qt instead of GTK, and more Linux-based devices opting for Qt-based user interfaces.
In fact, there's already talk of Ubuntu Mobile, a distribution designed for low-end netbooks and MIDs (like the Nokia Internet Tablets) looking at Qt.
I don't see KDE seeing any immediate benefit, though. The big Linux players, like Red Hat, Novell, and Ubuntu have invested too much time and money in GTK and the GNOME desktop to do a backflip now.
There's really no call for one anyway -- GNOME is an excellent desktop that's constantly improving, while KDE 4 is still undergoing rapid development to smooth out its many rough edges.
If future KDE releases can combine improved developer friendliness with something a bit special on the desktop, though, a lot of users may start to rethink their choice of desktop.
Other Blog Entries written by Leigh Dyer:
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