Choosing a GUI Library for Your Embedded Device

Evaluating two very different GUI libraries, Qtopia and Nano-X.

The documentation for Nano-X is a bit lacking. There are some great documents out there; however, the links from the Web page are not updated, and many of them are dead. I used Google to find the most useful documentation. One also can use the Nano-X source and the mailing lists. The mailing list is very active, and Greg Haerr is right there, giving quick responses to questions.

A make doc in the sources will make some doc on the API using Doxygen, but not all functions are documented. I had to look directly in the source a few times.

Figure 2. The Application Built with Nano-X


Nano-X does win by miles when it comes to size. However, Qtopia is far ahead when it comes to polished graphics and nice, well-structured programming. Don't get me wrong, this is not entirely a C vs. C++ issue. You can do nice programming using C and Nano-X, but it does require more skill and discipline from the programmer. Hard-core C programmers will often crank out muddy C++ code with Qtopia, so C++ doesn't always translate into good practices—it all depends on your existing skills, time and willingness to learn.

Regarding speed, I did not see much difference, except in my scrolling graph. Using Qtopia, the graph was jittery, because I did not find a way actually to scroll the bitmap, so I had to redraw the complete graph for each step. The graph turned out nicely in Nano-X, using a bitmap copy to make the scrolling, and then just drawing the new part of the graph. Given more time and trial and error, it is likely that you could scroll more efficiently in Qtopia too—probably by sub-classing the right object. But given the current documentation, I did not find a way to do it.

Table 1 is a summary table for the two versions of the PMMD that I made, PMMD-QT and PMMD-NX. Installation includes compiling of the libraries. Code size is taken from the documentation.

Table 1. Summary Table

GUIQtopia from Trolltech (GPL version)Nano-X
Programming LanguageC++C
Time spent learning to use the libraryApprox. one week (three days for the installation and two days to learn the API)Approx. one week (three days for the installation and two days to learn the API)
Development time for GUI and heartbeat monitor graphApprox. two to four daysApprox. five to seven days
Code size of libraryCompressed: 1.1 - 3.2MB<100K
DocumentationAPI: really good; installation: needs workAPI: usable; installation: needs work
LicenseGPL license and commercial license. The GPL version is free to download; the commercial version must be purchased.MPL license with possibility for closed source drivers and applications. Nano-X is free to download.

Resources for this article: /article/9460.

Martin Hansen works at the Danish company Center for Software Innovation (CSI, CSI provides knowledge in embedded development to companies, both through advisory and by giving “Technology Injections”. Martin is the company expert on embedded Linux. He has been using Linux for more than ten years and has worked with embedded Linux for the last two years. He has a practical education in electronics and a Bachelor's degree in computer science.



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Library for heartbeat graphic

Claudia Rodriguez's picture

Nice article! I'm working right now in some projects with Qt Embedded and it's been good so far, but I'm curious about what specific library did you use to graph the heartbeat with Qtopia.

The only thing I've found that can make anything like this is a library called QWT which is not included in the Qt package.


Has anyone an example code

Ben's picture

Has anyone an example code for a graph that is updated continiously?

using Nano-X

Vladimir's picture

Using Nano-X is a real headache. Documentation is not good. Though we have no better solution for uClinux we are using in our project (another option is Framebuffer, he-he).
E.g. it's quite unobvious how to setup a regional-specific font.

You have to look into the sources all the time.

Linux, frame buffer, embedded

Venkat's picture

This is a nice start article for business and technical people also. This provides the first feel of the technology and the information.


Sören Wellhöfer's picture

Nano-X is indeed very small and basic but this is exactly why I think it's so worthwhile using it.

Many things can be implemented using simpler means and one has no difficulty looking directly at the Nano-X source code to get a grasp on how things are done there; an insight can be easily gained. I think this gives a developer more freedom of choice how to get things implemented in his own way - at least to some extend.

Also, another advantage arises in my opinion from the conceptual closeness of Nano-X to X. Nano-X might have nothing to do with X11 in any way, however, porting applications that use Xlib by design is very much feasible.

Although it is true that Nano-X lacks widgets to be natively used, there is an extension called TinyWidgets that builds on top of the Nano-X library. In addition to providing most of the elements of a modern graphical user interface it does also come with a graphical designer which I have found helpful so far for my work with Nano-X.



samsung's picture

A good effort indeed !
May i note that Qtopia is NOT the embedded version of QT.
Qt library comes in many flavors, mainly for Desktop(development purpose) called Qt/X11 and Embedded(OSrc version for embedded systems) called Qt/Emb. Qt library makes use of the Frame buffer and Input devices.
Now comes Qtopia. It is more of a server (Palmtop-Environment UI for embedded systems) than a library, which runs _above_ the Qt/Emb(or Qt/X11 with Virtual Framebuffer on a development PC). In a way, Qtopia is itself an application making use of the underslying Qt library.
When you write applications for the final GUI, you usually use Qtopia headers and libraries(which in turn makes use of functions in Qt library).

By the way, i wonder why was OPIE(Open Palmtop Integrated Environment) not worth comparing in this study?

With Best Regards

Shashwat Rishi
Engineer Server development group
Samsung India Electronics Pvt. Ltd. (SRI Delhi)
Plot No. 2A, Optimus IT Park, Near Lotus Valley School

Sector - 126, Noida - 201303, U.P., India - 91

which Nano-X?

Marc Lindahl's picture

I found two on a web search:

you're clearly writing about the first one, but what's up with the second one??

RE: which Nano-X?

Martin Hansen's picture

It's the same. centurysoftware is run by Greg Haerr, who is also the main force behind Nano-x, the Nano-X SDK mentioned in your second link is pretty much outdated and abandoned.

Qtopia more then a GUI

Anonymous's picture

Very good article, but I think you should mention that Qtopia Core is more then a GUI, it is an application framework. with a complete set of classes for things such as:

Session Management
Does your application need to save and restore settings, Qtopia hs this built in

Does your app need to talk to a server. or maybe be a server. QSockets(UDP & TCP) and QTcpServer are nifty classes for doing this.

Do you need to do a heavy process outside the GUI thread, QThreads will aid here, and most classes in Qtopia are now thread safe

Qt comes with SQLite built in, and of course can talk to almost all major databases

Data Serialization
If you send data to and from other devices QT will take care of little endian/ big endian. All objects are easy to serialize with QDataStream

Do you need to support more then one language. Qtopia comes with a tool called Linguist which allows you to add multi language support without additional programing. It also supports Asian charactor sets as well as manages right to left languages in every GUI widget

Pixmap Management
Need to use something like a cancel pixmap in more then one location. Qtopia apps will cache pixmaps so they get stored once no matter how many places you use them. QImage and QPixmaps work hand in hand so images can be scaled on depending how they are to be used.

Interprocess Communication
QDbus makes it very easy for apps to talk to other Qtopia apps.

Want to have multiple looks for your display, perhaps a daytime display and a night time display. QTheme makes this very easy to do

Focus on the GUI

Martin Hansen's picture

I could have mentioned a lot of things, but as i was writing an article and not a book I had a limit on space, and then some things is left out.

nice sales pitch

Marc Lindahl's picture

nice to see trolltech salesmen trolling :)

don't forget to mention - the commercial embedded license for QT is ridiculously expensive.

wxWidgets is a viable route for a commercial product - LGPL.

scrolling a widget

Anonymous's picture

"In Qtopia, I simply made a class, connected some signals and slots, and puff, the magic happened."

:) As for the scolling I check out the scroll function in QWidget. It is probably what you are looking for.

Available browsers on these two GUI systems

Marco Wang's picture

It's nice to compare the these two windowing system on embedded systems. But IMO there are two major parts are missed in this article: software ported on these two systems and what kind of browser these two GUI systems support respectively. For example, besides Mozilla based browsers, is there a browser can run on Nano-X with Javascript capability?

Maybe You think of internet

Martin Hansenn's picture

Maybe You think of internet tablets like the Nokia 770. But most of my customers do not have the need for a browser, they need a GUI specific for their device most often with no desktop.

And yes i would have liked to dive into the software availiable on the two platforms. And I would also have liked to research more on the add on libraries, that You can put on top of Nano-x to give you the buttons, textpads a.s.o. that you have in QTopia, but I had to set the limit somewhere or I would still be writing on the article.

Regards Martin