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Saturday, November 27, 2010

Box of Marbles meets Device Orientation

Remember my Box of Marble demo?. It was a native Qt/C++ application running on Maemo-powered Nokia N900.

With the wave of DeviceOrientation Event Specification implementation, now it's possible to have the demo as a web app, running just inside the web browser. In fact, this is what you can see from this demo:

Right now, it works with iPhone or iPad or iPod Touch running the new iOS 4.2, due to the brand new DeviceMotionEvent support. If you own a MacBook with accelerometer and you use Google Chrome, that works as well (tilt your laptop to see the gravity effect). But fear not, with the recent support to hook the acceleration data from Qt Mobilty to QtWebKit, don't be shocked if the next Nokia phone with built-in QtWebKit sports this feature as well.

While my previous demo uses Chipmunk physics engine, this web version relies on box2d-js instead, mostly because I am too lazy to port Chipmunk to JavaScript and also I want to try something else. If you are curious about the code, check the usual X2 repository under javascript/marblebox directory. Enjoy!

Wednesday, November 10, 2010

V8 + jslint + vim

Usually, you would want to use scripting solution, e.g. Perl/Python/whatever, to manipulate file contents. Somehow, it's also fun to use JavaScript instead. After I did the V8-based jsbeautify, I was doing V8-based jslint as well. Then I realized, let's just extend it to be generic. With API loosely modelled after CommonJS, filejs was born. Find it in the usual X2 repository under the javascript/filejs. There are two examples so far, ROT-13 and line counter. If you write more examples, feel free to pass them to me!

Of course, the twist is: use filejs to drive a command-line jslint. This is one way to do it. First build filejs (follow the instructions in the included README), then place the executable in your PATH. Create a simple shell script, which contains one line filejs /path/to/filejs/jslint.js $1 and make it executable. That's it! If you also store this shell script in your PATH, then you just need to run:

jslint source-code.js

If you use vim, jslint can be combined with Quickfix. First of all, associate *.js with the tool by putting this line in your personal .vimrc:

au FileType javascript set makeprg=jslint\ %

Now open a JavaScript file and run :make (or whatever shortcut you map this into), which will launch jslint with the current file. After a while, use :cope to open the quickfix little window, move up and down, and press Enter to bring you back to the main editor and set the cursor at the specified problem. Use standard window navigation, e.g. Ctrl+W W to switch to quickfix pane again. Check the quickfix documentation for details. All in all, you may want to map mostly used commands to some shortcuts for faster access.

Note that since this is dynamic JavaScript, rather than matching errorformat, technically I just tweaked the tool to spit something similar to what a C/C++ compiler would do. Also, if you need different jslint options, simply edit the invocation to suit your needs.

It's been a while since I blogged about vim. The last one was about the project plugin, which is surprisingly still quite popular. Hopefully this one also teaches you a trick or two, especially if you work a lot with JavaScript code.

Note 1: It does not work on Windows yet. No idea if I would have the time to do it, patch is welcomed.

Note 2: This is not a replacement for NodeJS, nor would it grow to include more functions.

Note 3: For the sake of completeness, let me mention that there are already other countless solutions for command-line jslint (using Rhino, SpiderMonkey, JSC, etc), even with vim integration.

Tuesday, November 09, 2010

chunks inside PNG

Here is a few minutes of hack which would hopefully help someone else:

pngchunks logo.png
File size: 5967 byte(s)

Offset    Chunk    Size
      8    IHDR      13
     33    iCCP    2627
   2672    IDAT    3271
   5955    IEND       0

Useful to quickly find out if we can further strip unnecessary chunks from the PNG image. Or even as a warming up before you fire your favorite hex viewer/editor.

It's pure, stand-alone, self-contained C code (i.e. compile using gcc -o pngchunks pngchunks.c), available at the usual X2 repository, find it under graphics/pngchunks.

Friday, November 05, 2010

the fun of remote JavaScript debugging

Remote feature of Web Inspector, whereby you use an instance of WebKit and debug another one in different machine, is one important feature (that is being worked on) of WebKit I can't wait to start using. Till that day, remote debugging is always a challenge. There are of course assorted workarounds out there. At Sencha we decide to have and share with you a little tool that helps JavaScript remote debugging. It is available in two flavors: GUI-based (using Qt obviously) and Python-based for scripts and automation. Right now, the target is Android WebKit but there is no reason why we should not march to other platforms as well (e.g. QtWebKit on Symbian and MeeGo). Get it while it's hot!