Fast UI with Qt 4 on mobile

For device manufacturers, and those targeting device manufacturers like us in the Mer¹ and Nemo Mobile².communities, we need a performant base, and Qt's default configuration on Linux is ..not really that performant. It uses what is known as the 'native' graphics system, which uses X (and XRender) to do a lot of the grunt work. Unfortunately, XRender isn't exactly what you'd call speedy in many cases, and making loads of round trips to ask X to draw things probably doesn't help either.

There's another option in the 'raster' graphics system, which does all rendering client-side in your application using (as you'd expect) Qt's software rasterizer, which is adequate enough for performance on most desktops, but still not quite optimal on desktops: hardware acceleration is the missing goodie.

Qt as of 4.8 also includes what's known as the MeeGo graphics system - as the name implies, it's used on the Nokia N9. It uses hardware acceleration (plus some additional EGL extensions) to perform absolute magic and make your pixels (especially QML :)) fly, so if you're working on getting a device together using Qt 4, I'd highly recommend you look at it.

Because no blog post is complete without a video, here's one:

(comparing the performance of raster and MeeGo graphics systems on a Lenovo S10-3t)

This sounds great, but there's one caveat. If you're on certain types of graphics hardware (SGX in particular), then you'll probably not to just want to enable the MeeGo graphics system for everything, because you'll end up with a lot of GL contexts allocated, which is not good for two reasons; they're scarce resources, and they take up a large chunk of RAM (something in the order of 5-10mb, depending on your PVR configuration file. I never actually looked).

There is good news at hand, though! Qt has *another* graphics system, specifically designed to proxy everything through another system, and allow for runtime switching back to raster. In our case, obviously, we want it to use MeeGo's graphics system by default, but fall back to raster to avoid taking extra resources when not needed.

There's also some bad news: it didn't work out of the box with Qt 4.8 RC1.

But some more good news: I fixed it (and yes, I upstreamed the patches)!
http://qt.gitorious.org/qt/qt/commit/a7c77bd46ef85bae624e829cb2a02110ec60b318
and
http://qt.gitorious.org/qt/qt/commit/0ceab866c76e0d9eb17bc1f3d42af06c0033560b
are the two commits you'll want.

After that, configure Qt with -graphicssystem runtime, and -runtimegraphicssystem meego (or set QT_DEFAULT_RUNTIME_SYSTEM=meego), and it'll work beautifully, provided your system has the required GL extensions.

Alternatively, you can use Mer, which already includes these patches right now, and, as of this week, has this beautiful magic enabled by default on the Nokia N900/N950/N9 hardware ports, where this is really needed (and works well). I'm working on getting it enabled by default on other systems that can support it, too, like the Lenovo S10-3t, as time permits.

MeeGo Reconstructed - a plan of action and direction for MeeGo

A few days ago, I posted MeeGo not being dead until the fat lady sings. Now, the reason why I was being so cagey is out in the open: Mer is alive again, and aiming for MeeGo 2.0.

This isn't just a continuation of MeeGo, of course - nobody in the MeeGo community proper would argue that there is a need for change, and we've got a few lined up, such as an easier porting story to other devices and architectures (and a much friendlier community atmosphere to such projects), complete meritocracy, and many more.

To get one thing out in the open: this is just the core OS, a Linux distribution. There is no UI, and hardware adaptations are seperate from that core OS. It's an extremely slim Linux vehicle for making products out of. What you put on top is entirely your business - it's just a tool.

The idea being that you can then take it, drop a hardware reference for a device you love quite a bit, drop a UX in on top (either one you write yourself, or one from the greater community, like the MeeGo handset UX), and you have a product. Plasma Active is another example of what could be dropped in as a UX. The MeeGo handset community edition will most likely be looking to rebase on top of Mer in the near future.

In terms of the app stories available: Qt is available on Mer, so for developers seeking to target Qt, look to install Mer derivatives on your devices. This doesn't stop other toolkits or technologies, of course - all are welcome to come and base around Mer. We also have high hopes that we can achieve some base sharing with Tizen, and ideally, easily atain Tizen compliance. It is HTML5, after all.

I look forward to running a MeeGo handset UX on top of a Mer core on my n900 soon, and what can be accomplished in the future.

If you'd like to talk with us, pop onto #mer on freenode or use the webchat. We also have threads on both the MeeGo and maemo.org forums, should you be a fan of those.