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.

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.

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!

morphing clock revisited

If you can't see the clock below, visit the stand alone demo.

Technically, I had wanted to wait till it can display the actual time and perhaps ask some designer to polish it. But rather than keeping this lunch-break hack in a safe deposit box forever, let me just release this ugly clock transition (since everyone is on the animation frenzy). So far it works only if you use latest version of Safari, Chrome, Opera, Firefox. Canvas and/or VML fallback (which sadly will require JavaScript) for other browser are in the pipeline.

Basically it is another version of my previous morphing clock attempt (see the video). The principle is the same, except now I modified that C++ program to also output an HTML which renders the clock as above.

Also it morphs only once. Reload the page to enjoy the morphing once more. Maybe I'll find the time (in another lunch break) to toggle the two clock modes. Update: morphing from/to both analog and digital mode is implemented.

Like I said, it's a creepy, machine-generated, ugly looking clock. You've been warned, but feel free to write me anything (should you need to vent your anger).

Look ma, no JavaScript!

Take a look at the following CSS 3 demo. No Flash. No JavaScript. No image.

Hungry for more? Enjoy some other demos created using Sencha Animator.

Qt Developer Days, Bay Area Mobile meetup

We heard that Munich Qt Developer Days was an awesome event, which is why I look forward to the San Francisco Qt Developer Days, which will be held November 1-3.

Now, if you are from outside US, drop me an email in case you fancy some quality tea/coffee time. Even better, on the next day (November 4), Sencha will host the first Meet the Sencha Team, the first Bay Area Mobile meetup. Our team will give an overview of Sencha and the mobile technologies we are developing. RSVP and drop by!

sencha touch hackathon

Are you in the Bay Area? Don't miss our Sencha Touch Hackathon this Saturday (Oct 16) in our Palo Alto Office, 1pm to 5pm. There will be food and drinks as well.

Drop by and upgrade your Sencha Touch kungfu!

yet another command-line JavaScript beautifier (based on V8)

While we're still on the topic of JavaScript, I took the afternoon break to create a command-line runner for jsbeautifier.org . In case you miss it, I did the similar thing using Qt Script module. This time however, the command-line tool uses and exploits Google V8 instead.

If you update your clone of js-beautify repository, check out the fresh v8 subdirectory. I also mirror the code in the usual X2 repository, under the javascript/jsbeautify8 subdirectory. Also, grok the included README.txt first.

Update: I added --overwrite option which (surprise!) will overwrite the original source file (and thus, use it with care). This is useful if you invoke the beautifier tool from your text editor. Nicolas also implemented various settings support so you can specify the indentation level, braces placement, etc.

This is probably the last thing the world needs now, but hey, it was a fun break.

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".

cinquantamila

'nuff said, head to www.sencha.com/contest!

color inversion for web pages

Something I worked on during my last few weeks with Qualcomm was color inversion for the web browser in Android. The patch was then integrated by Enrico (see the diff) because I switched job.

Later on this feature was also pulled into CyanogenMod. Thus, if you are running CyanogenMod 6 on your shiny Android device, you can try this feature already! In the web browser, just pick the Settings menu and then scroll a bit until you see a checkbox for Invert Color. You should get something like the captured screens below:

The idea behind this is to reduce the power consumption of Organic LED display, because on mostly-white web page, it hungrily grabs to 3x more power compared to LCD. This is similar to Jeff's trick of applying color filter in SurfaceFlinger.

Doing it at the user-space level gives one advantage: we can keep the embedded images non-inverted. Blindly inverting the entire screen would result in web pages look rather funky, especially those new sites with photos to accompany the articles. Of course, this hackish approach will not work 100%, (hint: double XOR?) since the web designer likely never intend the page to be color inverted. However it seems to work most of the time, at least with pages which do not have ueberartistic look-and-feel.

Faithful followers of my blog know that I already played with the color inversion ages ago, in the form of giving night mode appearance for QWebView. Thus, it happened that in one afternoon break I played with QtWebKit to do something similar to this selective color inversion.

Now, in the case of Android WebKit, the effect was rather easy to achieve. This is because Skia's SkCanvas is basically an interface which can be subclassed easily, while none of the functions in QPainter is virtual. The trick using Skia was to use a proxy canvas (a slight variation of Skia's built-in SkProxyCanvas) which I invented for this purpose but somehow also useful for another feature.

For QtWebKit however, we need to tweak it with some QPaintEngine voodoo. Check out the code at the usual X2 repository, find it under webkit/nightcapture (it still has some rooms for improvement, left as exercises for the adventurous readers). For simplicity, I made it as capturing tool so you need to pass a URL and the output filename. Unless you do something wrong, expect to get something like this:

The trick is the same as my approach for the Android patch: invert the colors of each image before drawing it, at the end invert the entire viewport. This seems like slow, but it's the best compromise I found out working with most sites. Note how we skip inverting any brush pixmap as usually brush is for the tiled background (and thus we want to keep it that way, i.e. not inverted). You can do some fancy magic with clipping and whatnot, but I doubt the end result is much better. Again, this whole stuff is a hack anyway and there will be always corner cases which will not work, no matter what approach you pick, thus there is no need to make it more complicated that it should be.

Just like they say, we code for life, i.e. the battery life.

quattroporte and hummingbird

Fermi problem of the day, anyone?

Assume there is this large organization, say with over ten thousands employees. For some (legal) reason, each employee needs to write down what she has been doing for the week, usually by Friday afternoon. Some record everything in details (down to the hours), some prefer to just express "8 hours doing FooBar" for every working day.

Since this is 2010, usually the system is web-based. To prevent abuse, some login/credential check and anti-bot system are also in place. It is often unheard that people use their beloved smartphones to do the job.

Let us say it takes one minute to do this. With a really conservative $30/hour rate, this is worth 50 cents. Assume ten thousands do that, so it's worth $5,000. This translates to $260,000 per year.

Of course this is just a gross approximation. It does not even include/exclude the extra time the managers spend to double-check their staff's entries, typically (much) higher hourly rates, non-working (also known as vacation time), wasted effort to setup (and forget) the reminders, occasional weekend shock at times you forgot it, and other similar (intangible) overhead. Or if you just need 5 seconds to accomplish the task. But you get the idea.

Now, $260,000 is a lot of money. You can buy a decent house in San Diego. Or two shiny Maserati Quattroporte. Or several hundreds Hummingbird-powered phones. Or, in some parts of the world, access to fresh water for the entire city all year long.

Surely for a quarter million per year some smart people will figure something out?