Binary Elysium

I’m exactly three months into my Arabic studies in Cairo, where I’ve been taking time off university studies and Amarok development. I’ve realized that acquiring a large vocabulary as fast as you can manage is a crucial part of studying a language intensively, and thanks to the awesome KDE-Edu folks I’ve been successfully barely keeping up with the hundreds of new words I’m assigned per week with Parley.

The major problem I have with Parley is that I have to be in front of my computer to use it!

I know you’re laughing. That’s like saying a major fault of beer is that you have to drink it to get drunk, after all Parley is a computer program.
You’re right, just because I hardly find the time to actually use the computer doesn’t mean I should lay the blame on Parley. Technically, I should blame the denizens of Cairo and their insane traffic. Seriously, too many of my life’s hours are wasted in the smelly, stuffy, taxis of Cairo (today was particularly bad, pardon the rant).

This past weekend I ignored the towering pile of homework and whipped up a little application for Android devices that groks Parley’s kvtml2 file format, displays lessons, and provides flashcard exercises. My app is really an Android Port of the J2ME mobile application MobVoc. Michael, the MobVoc developer, did most of the hard work for me: parsing kvtml2 files into java data structures. Mad props to Michael; I definitely plan to pass along any contribute any bug fixes/optimizations I make to his code (such as sub-lessons support).

The application – unimaginatively dubbed ParleyDroid for now – is extremely bare-bones. Here is the current feature set

• Pick a kvtml2 file from the SD card
• Choose 1 or more lessons to practice
• View flashcards of the words in the selected lessons.
• Gesture support in the flashcards: Long Press marks card as known, Fling Left/Right changes to Next/Prev card.
• Each practice session has a short-term memory: i.e., if you mark a card as known you won’t see it again that session but if you restart the session you will.
• Arabic Support – if the 2nd language is Arabic, it will be rendered correctly on screen

The last feature is probably the most noteworthy. Android, by default does not support RTL or non-Latin scripts, but with a little Android-trickery-that-deserves-another-blog-post I’m finally able to practice my vocabulary in the back of the taxi or while walking along the Nile.

Binary and Source:
ParleyDroid Source
ParleyDroid Android Binary

Obligatory Screenshots (click for full view):

Short version: @Ramblurr is my new public Tech/FOSS twitter account, please follow it.

I have been on twitter for quite awhile, for several years at least. My original use case for twitter was something like a web/sms based IRC channel for my good friends from my hometown. Twitter is responsible for keeping us close in the years after we parted ways for different colleges. This use case worked great until my online communities (KDE, tech industry, etc) started jumping aboard the twitter boat.

At first I tried to handle both social spheres—online professional, and raucous college student—with the same account. Needless to say one group did not appreciate the drunken tweets or lengthy star wars quotation contests, and the other group did not appreciate my Java vs C++ discussions. Eventually, I made my account private and left the online technology twitter sphere, but now things are changing.

Twitter has risen to prominence in the online community, and I am missing out on this form of social communication with my fellow technology and open source enthusiasts. So, I’ve renamed my private account, and opened my original for public use.

Please feel free to follow @Ramblurr, my public account, without need to fear a flood of inane, hyper-context-sensitive, ramblings between friends.

Several of us at Camp KDE—myself included—owe a great debt to Till Adam. When he came to the sunny, beautiful beaches of Jamaica, instead of spending his days lounging on the shore or swimming in the warm Caribbean, he chose to pen himself in a stuffy room with a dozen geeks and teach them Qt.

Till works for Klarälvdalens Datakonsult AB (KDAB), the Qt consultancy firm. Besides working on large-scale, enterprise Qt applications, KDAB provides professional Qt training to such companies as IBM, Boeing, Ericsson, and J.D. Edwards. These training sessions usually run a few thousand Euros per person. With the OK from Nokia and Qt Software, Till provided us with a mini two day training course for free!

While the content and materials Till used during the sessions is copyrighted, the information I learned is not. With his permission I’m going to discuss a few pointers in this post. The topics covered somewhat basic/intermediate Qt skills, so those of you who have been programming with Qt for any length of time might not find anything new or interesting. However, for those, like me, who haven’t quite developed our Qt Fu to the Master level, take away tips from here knowing it was passed from a master.

#1 Most Common Performance Issue in Qt
Converting from a QPixmap to QImage too often.

This tip is actually fairly well known, but apparently KDAB consultants run across this mistake very often while in the field. There is a great discussion of this topic over at KDE’s techbase. In summary:

• A QImage is stored in main memory
• A QPixmap is stored in video memory
• Converting from a QPixmap to a QImage is a very expensive operation (see the above article for the explanation)

#1 Most Common Cause of Crashes in Qt
Deleting this from slots

This tip needs some more explanation. Essentially, a mistake many Qt programmers do is include executable code after emitting a signal. Consider this flow of execution:

• The function Produce::blend() emits signal pineapple()
• The slot slotBlender() deletes the instance of Produce
• The signal/slot connection returns to the function Produce::blend(), which has some other executable code such as variable assignments after the emit.
• Crash. Since the slot deleted Produce, any code following the emit statement that modifies memory is now attempting to write to invalid memory.

One good practice to follow is: don’t have any executable code following the last emit statement in your objects’ methods.
However, the real solution is: Use deleteLater() on your QObjects.

This post is getting somewhat lengthy and I potentially still have two topics to cover (Threading and Model/View). Most likely I’ll dedicate a post regarding threading in Qt (I took better notes during that talk) in the next couple days. Many thanks to Till for the sessions, as well as KDAB and Qt Software for allowing them to happen.

The “conference” ended yesterday as the final presentations were given, however we still have 4 days left here among the sunny beaches. Today Till Adam gave a fantastic lecture-slash-hands-on-workshop of Qt’s Model/View and plugin architecture. Just a couple weeks ago I was slamming my head against the desk trying to wrap my head around Qt’s M/V concepts, the results of which can be seen in Amarok’s new last.fm service browser. Through the creative use of roleplaying (thanks Ade, Jeff, Sebas, and Leo!) and two helpful hands-on exercises I’ve finally gotten a decent grasp of the system. Tomorrow morning we hope to sip QtConcurrent knowledge from the cup that is Till.

I’d write more, but the ocean is calling and I still need to get a Pina Colada. But before I go, check out some photos from the past couple days.

The internet is on the fritz here in Negril, Jamaica at Camp KDE, but while it is working I’ll post this photo taken from the balcony during lunch.

This is also a field test of the WordPress Android application.

We have had 3 presentations so far. Right now Sebastian Kügler is giving a great talk concerning optimizing your applications for mobile devices.

More quality updates soon.