on JavaScript engines

If you are using a modern browser, likely you already have the (arguably) most widely deployed scripting environment: JavaScript engine (or ECMAScript, if you insist). There are many things you can do with it (just look at tons of cool web apps out there). However, since it is contained in the browser, there are also things the embedded JavaScript engine can not do for you.

If you are using KDE, you also have two excellent JavaScript engines: KJS and Qt Script. You can embed either of them (i.e. KJSEmbed) and make your application scriptable. In a not-so-strange twist, they both relate (distantly) to each other via JavaScriptCore, WebKit's default JavaScript engine, because long time ago Apple forked KJS and used it as the base for JavaScriptCore, and Qt Script (for version 4.6 and 4.7) also uses JavaScriptCore as the back-end.

If you are interested in learning, using, and/or dissecting other open-source JavaScript engines, have a look at JavaScript Engines: How to Compile Them I wrote for our Sencha blog, which covers Mozilla's SpiderMonkey, WebKit's JavaScriptCore, and Google V8. The instructions should work on the supported platforms, including ARM, in case (just like me) you want to have and carry around every JavaScript engines in this planet on your Maemo-powered Nokia N900. That is fun.

As the closing, just remember, "Ask not what the JavaScript engine can do for you — ask what you can do for the JavaScript engine".

geocoding based on IP address

Given an IP address, there are different ways to obtain the approximate location: online web service or offline database. It is far from perfect, but it is very useful to give some initial guess before locking into GPS signals or using WiFi-based tracking.

Today's example for X2 is actually an old code lying around which does the former: relying on IpInfoDB web service to guess where your computer is. Combined with the previous example, MapSnap, the guessed position is used to center the shown map (OpenStreetMap, of course).

Of course, as with other examples, it works fine on Maemo-powered Nokia N900 as well. Feel free to give it a try on Symbian or other supported Qt platforms.

The code is found in the usual X2 repository, under the sensor/ipgeocoder subdirectory.

For completeness' sake, let me mention also that Matteo did something similar, using hostip.info and Google Maps via QtWebKit.

Sencha Touch and N900

Being part of the awesome Sencha Team, I did shoot a quick attempt to run Sencha Touch, more precisely its Kitchen Sink demo, on Maemo-powered Nokia N900. Since Sencha Touch targets WebKit but Maemo default browser is Gecko/Firefox-based, I crafted a mini launcher which wraps Sencha Touch in QtWebKit. The screenshots below serve as the proof:

Most of the stuff works just fine. There are some minor issues and performance problems, but I worry not. With the amazing amount of optimizations Qt+Nokia put in place for Qt 4.7 and QtWebKit 2.x, writing applications for Maemo/MeeGo will be fun (again).

box of marbles redux

If you enjoy the box of marbles demo, now we extend it to include some basic network support. The premise is simple, look at this short video first (or watch on YouTube):

The code to handle the physics of the marbles remains the same, i.e. we just use Chipmunk physics engine. However, I added a simple feature to transfer marbles from one place to another. To keep it simple, it is done using UDP. The Qt network module supports UDP quite well, making the datagram code short and readable.

The intended use of this example is easy: run the desktop version and then run the mobile version (tested with Nokia N900). Each instance should find each other and start communicating. Again, we simplify the situation here and handle only 2 (two) peers. To facilitate troubleshooting, the application window title will contain the network address information, if the two peers are fully connected. To avoid complicated setup, discovery is carried out automagically through broadcast. This makes such a demo runs only under the same subnet, which is not a big deal.

It would have been much more fun doing the transfer between two smartphones (instead of a phone and my laptop). However, I own only one Nokia N900. Hint: I will not refuse your donation of Nokia N8 or (preferably) MeeGo-powered Nokia N9 (i.e. the N900's successor, whatever the real name is).

If you want to give it a try, head to the usual X2 repository and look at demo/marblenet subdirectory. Again, have the patient to follow the README file before you start compiling it.

Of course, feel free to extend this example to suit your (more wild) fantasy!

box of marbles

The next logical step after simple bouncing ball example is something which uses a real, full-featured physics engine. Box2D is usually the popular choice. Combining Box2D with Qt has been done by many people, recently demonstrated before by Andreas and Thorbjørn. I decided to pick something else, i.e. Chipmunk physics engine.

Because this is supposed to an example, I tried to make it as simple as possible (you'd be able to extend it, once you grab the basics). Basically we have a box full of colorful marbles (yes, I loved to play marbles when I was a kid, there was not any PlayStation back then). A mouse click, or a screen tap, will generated a new marble with a random color. If you run the example on Nokia N900, you can control how the marbles move and hit each other by tilting and shaking the phone.

Check the code yourself at the usual X2 repository under the demo/marblebox subdirectory. Make sure you open and follow the instructions in the included README file.

For a sneak peek, just watch this video (or enjoy on YouTube).

There is still a sequel to this marble box. And still with Chipmunk.

bouncing ball with accelerometer on N900

First of all, I apologize for my laziness in updating X2 with new code example. I have actually written quite a number of interesting examples, some of which have even been shown back in March, during my talk at Bossa Conference 10, though I did not find the time to clean up and polish them. Although I'd face new challenges in my upcoming adventure, I am quite confident I will reach the designated rate of new X2 example fortnightly.

Now let's focus on the newest example: a minor modification to the previous accelerometer code on Nokia N900 [1]. There has been confusion with my statement there: put this function is a separate thread. This is the alternative to a non-blocking D-Bus code. The main goal of course is not to be able to get faster acceleration values per second, it is only to prevent your code from being blocked by the synchronous D-Bus call.

Rather than just updating the code with the threaded version, I also added some high-school Newtonian physics. Instead of boring sliders, you'll get a ball which moves based on the acceleration [2], i.e. it follows the gravity if you keep your N900 straight.

Here is the obligatory video. Or watch directly on YouTube.

The code can be found in the X2 repository under the sensor/bouncingball subdirectory.

In the next installment, we will integrate a third-party real physics engine and make the example more alive!

[1] Another approach is to use Qt Mobility. However, QTMOBILITY-381 (which was spawn from QTMOBILITY-326) has not been solved yet (as of today).
[2] The overall math is not too scientifically correct, but hey, I always need to leave out something, for your homework :P

n900 and its accelerometer

There is a bunch of code out there (which can be copied and pasted) to grab the acceleration values from Nokia N900. Here I contribute one more, it's Qt-based and using the QtDBus module. The values in x, y, z will have the unit of G.

    QDBusConnection connection(QDBusConnection::systemBus());
    QDBusInterface interface("com.nokia.mce", "/com/nokia/icd", QString(), connection);
    QDBusPendingReply<QString, QString, QString, int, int, int> reply;
    reply = interface.asyncCall("get_device_orientation");
    reply.waitForFinished();
    x = static_cast<qreal>(reply.argumentAt<3>()) / 1000;
    y = static_cast<qreal>(reply.argumentAt<4>()) / 1000;
    z = static_cast<qreal>(reply.argumentAt<5>()) / 1000;

As usual, error checking is omitted (left as an exercise for the reader). Like Star Wars, there is also a reason I skip the first 3 QStrings. Debug it yourself to see what you would get. In addition, I found out that at most it would take 25 ms to grab all three values. It means, if you run your application at > 40 fps, then better put this function is a separate thread. Actually, consider that you don't want QDBusPendingReply::waitForFinished() to block your entire GUI, this is likely a good idea anyway.

For a full-version of an accelerometer tool, check out the X2 repository under the sub-directory sensor/accelview. Note that technically acceleration > 1 G is always possible, I clamp the values in this example to keep the UI simple.

(q)palette viewer

Qt documentation mentions QPalette as the class that contains color groups, Active, Inactive, and Disabled, for each widget state. Knowing the color for many different color roles is important. For example, a style author might want to tweak the colors of each buttons depending on QPalette::Button, QPalette::ButtonText, QPalette::Highlight and likely play with the shades and the saturation. There are probably few different ways to get the RGB values of those colores, here I show one of them: using a small tool that display all the color roles for active, inactive and disabled states:

And here how it looks like on Nokia N900:

The code is in the X2 repository, check the sub-directory widget/palview. A possible exercise for the brave reader: allow the user to choose other color spaces such as HSL or HSV.

Have fun with the colors!

kinetic scrolling: the state machine

Some of the slides from last Maemo Summit in Amsterdam have been made online. Here is the one from the Cross Platform with Qt talk that I held. It does not give much, though, since mostly what counts is the real live demo. Let us hope that at some point in time, the recorded videos will be online as well. Of course, there are also other interesting slides such as Harmattan highlights and its architecture, Web Runtime, Quake3, and many others.

Cross Platform Qt

View more documents from Nokia, Qt Development Frameworks.

While I am there, if you check the slides from my talk above, page 9 shows the secret behind kinetic scrolling code, which I featured before as Flick Charm or Flickable interface. Or, in another version as follows (click to enlarge):

Of course, it is the simplified version and ignore some details, but that should be a good start to really digest the code. Since it was hacked in the old 4.4/4.5 time, I did not have the luxury of using the new state machine framework in Qt 4.6. As an exercise for you, the brave readers, convert the code to use the framework. In addition, it does not support yet bouncing-on-edge feature, something which can serve as another exercise, too.

Have fun with scrolling :)

bye amsterdam. next stop: munich

Today is the last day of Maemo Summit 2009. I am sure the news spreads quickly; everyone and his uncle know already that Nokia lends around 300 shiny N900 (preproduction devices), worth 500 EUR, to the summit participants, excluding Nokia employees and contractors. It's Christmas in Amsterdam!

I had done my Cross Platform with Qt talk, I was quite content with it (that hopelessly small room was jam-packed). There were (and still will be) many other interesting tracks as well. For the detailed coverage, check out All About Maemo site, they are doing great jobs keeping the rest of the world up-to-date with the latest excitements from WesterGasFabriek.

While waiting in Schiphol for my next flight to Munich (for Qt Developer Days 2009), I had a quick glance at some of photos taken in the last few days. Let me just post one:

One evening, we picked Restaurant Sari Citra for our dinner. It serves Indonesian cuisine, the proof is the picture above. You have the choice to mix your own rice dish, such Nasi Kuning (rice with coconut milk and turmeric) with Tempe Kering (slices of fried, crispy tempe mixed with peanuts), Perkedel Kentang (mashed potato fritters) along with a wide selection of vegetables. Authentic experience with a reasonable price. Everyone enjoyed the dinner; happy Trolls :)

And see you in Munich!

Maemo Summit 2009 - Live

Like mentioned before, with other few Trolls, we are now in Amsterdam for the Maemo Summit 2009. If you are there, don't forget to look for us and/or drop us a visit!

Maemo Summit 2009, Amsterdam, 9-11 Oct

Another exciting event coming up soon: Maemo Summit 2009! This time it will be in Amsterdam. My flight ticket is secured already, I look forward to it. And of course, since this will be also my first visit to Amsterdam.

My talk will be on Friday afternoon, see the schedule for details. Although the title "Cross-platform with Qt" is a bit boring, rest assured you will see showcases of many things (which I can pack in 25 minutes) Qt is capable of doing.

A few other Trolls will be there as well so go there and find us. In all cases, if you are around and want to have a chat, drop me an email (ariya.hidayat AT gmail DOT com).