Qt Attracting Interest Among Application Developers
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More Qt highlights

Qt is also a leader in "internationalization," that is, the ability to create displays appropriate to different countries and human cultures. Qt fully supports, for example, Unicode, which gives it the ability to show not just the alphabet used for English and all the other Western European languages, but also Russian, Arabic, Hebrew, other oriental languages, and essentially all written human tongues.

I've heard that many programmers also like Qt for its outstanding documentation. Trolltech has been quite successful at providing tutorials and references that make developers feel "at home" with the toolkit.

Trolltech has also been aggressive in striking business deals that support development goals. Qt OpenGL is an extension to Qt which makes the OpenGL library fully available to Qt programmers. Trolltech has been innovative in setting up licenses which simultaneously protect both its revenue and developers' need for transparency and accountability.

All these strengths, along with more technical ones beyond the scope of this introduction, simplify development and maintenance of sophisticated GUI applications with Qt. Qt is particularly capable on the "high end" of high-speed or high-complexity GUI programs. The result is that some of the most important GUI projects that have appeared in the last few years have been based on Qt:

  • SuSE's YaST2 installation and configuration tool
  • Maptek Three-dimensional mining geology visualizations
  • A European Space Agency satellite simulation
  • Several computer-assisted engineering applications that combine real-time control and simulation of physical devices such as analogue circuitry and machine tools.

The most famous of all the Qt-based projects is the KDE desktop environment which ships with several Linux distributions. KDE is a showcase for Qt flexibility and performance.

The end-user experience

Is there a payoff in all this cool developer-functionality for end-users? How do users react to the visual displays made by Qt-based applications?

Most developers understand that the shape of widget corners and calculation of border widths is essentially a fashion industry. However, Qt has a couple of characteristics that make it look like a winner in this arena.

The first design strength is that it has reasonable, and even exciting, defaults. Suppose a system administrator writes a minimal Qt-based control panel to mediate his customers' use and configuration of a command-line program. The smallest Qt application has a distinctive appearance and behavior that's widely seen as "professional" and occasionally "pretty." Even in these very simple cases, Qt brings end-users a level of comfort.

At the same time, one of Qt's customizability dimensions is support for "themes." What this means to end-users is that a Qt application can look entirely like a Windows application, for example, whether it's hosted on a Windows or Unix machine. It could also look like a Motif application. In fact, the same application can have either appearance, or one of several other selections, independently of the underlying OS. What's more, the selection between the appearances is open not just to the programmer, but to the end-user as well. Users can configure a properly written "themed" application to fit their personal preferences or organizational standards.

Trading skins

These possibilities hint at the excitement currently stirring the world of GUI toolkits. In the past, many programmers and independent software vendors (ISVs) specialized as "Windows programmers" or "Unix shops." Now, a sufficiently compelling application has the potential to be far more universal. Qt-based applications are in step with this trend because they run correctly on Windows and Unix, and they look good on each. In principle, Qt and other toolkits with comparable strengths have the potential to grow beyond the confines of any single OS or CPU.

Who's using Qt?

So is everyone using Qt? No, at least not yet. Many development organizations have a substantial investment in older toolkits, including third-party packages that enhance their value. Tk and Visual Basic are easier for beginners, at least in several common situations. More crucially, organizations with an interest in MacOS generally use Tk or one of the specialty toolkits, because Qt is not yet available for MacOS. "Development [of Qt for MacOS] has started, but it's too early to estimate a release date," according to Trolltech Product Manager Eirik Aavitsland. Trolltech programmers are currently targeting "both MacOS 8/9 and MacOS X support," according to Aavitsland.

Qt's approach to licensing

Most objections to Qt appear to involve its license. GUI toolkits span a wide range in the liberality of their licenses. Qt occupies a position somewhere in the middle. Aavitsland summarizes, "For commercial developers, Qt has a normal commercial library license, and there aren't even any run-time fees or royalties."

Trolltech's Free Edition is less conventional. The company deliberately chose a nearly unique business model in simultaneously "offering the full freedom of the open-source world while at the same time ensuring active development and support by a professional company. This makes Qt an attractive choice for both commercial and open source development," in Aavitsland's words. Unlike other companies -- JavaSoft, Digital Creations, Metro Link, Caldera, and many others -- searching for a similar balance, Trolltech has explicitly created distinct but linked licenses targeted for both worlds.

Trolltech provides a Free Edition for Unix-based development and deployment of open-sourced and noncommercial applications. Noncommercial applications can also be delivered to Windows end-users without licensing fees. However, the only development package available for Windows has a purchase price -- over $1500 US, as of June 2000 -- high enough to discourage casual hobbyists.

Price isn't the only complaint raised about the license. For a variety of ideological and strategic reasons, certain organizations turn away from Qt, often to the GNU Programmers Licensed (GPLed) Gnome toolkit (GTK). Trolltech is well aware of the controversy.

Among its responses to Qt's user community was the March 1999 introduction of "QPL," the Qt Programming License, which refined the terms of the Free Edition. QPL differs from GPL principally in its treatment of in-house commercial work -- the applications a business writes to manage its own operation, for example. QPL encourages such businesses to pay Trolltech for a commercial license. Aavitsland concludes, "We are working on straightening out the few remaining Free Edition license issues."

Cameron Laird is the vice president of Phaseit, Inc. and frequently writes for the O'Reilly Network and other publications.

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