Mental Notes » Programming

Yalog (Actionscript 3 log utility with viewer) open source

stephan — Wed, 04 Feb 2009 12:05:27 +0000

A few years ago I developed a logging class plus viewer application for debugging purposes. Main requirement was lightweightedness: the logging code should put as little pressure on the CPU as possible, and so should the viewer. At LBi Lost Boys, the company I’m working for, we’ve been using this utility over the last years, and it’s become an indispensible component of our work flow.
Last week I put out the source, both of the log utility and of the viewer, into open source space. Check the main page on Google Code for source code and downloads.

Yalog consists of the logging utility, comprising one main class (Yalog.as) and a few helper classes, and a viewer. This viewer is basically a swf, so can be used in any context where a swf can be used. Currently it’s available for download as an AIR-application. If you just want to use this and not be bothered with the source of the viewer, download the Yalog source classes, and install the AIR application.

The viewer can be seen in action at http://yala.acidcats.nl/. If you open a Yalog-enabled site (such as www.de.nl), you will see debug messages appear in the viewer. A nifty feature of Yalog is that it buffers the last 200 messages (number can be changed) until the viewer appears, so you can open the viewer after something has gone wrong, and still view the latest messages.

When I have more time, I’ll put up a page here with more info and details.

Spectral analysis with Fast Fourier Transform in Actionscript

stephan — Thu, 04 Dec 2008 13:01:34 +0000

The presentation by Adobe’s Jim Corbett on Alchemy at the Adobe MAX 2008 conference in Milan last Tuesday (2nd of December), got me thinking about something I used to spend quite some time on back in the early 90’s, when I studied Sonology at the Kon. Conservatorium in Den Haag: spectral analysis & (re)synthesis of sound. This is usually done by means of the Fourier Transform, which transforms time-based data such as sound to the frequency domain. The most used algorithm for this is the Fast Fourier Transform, or FFT, which requires the number of samples per transformation to be a power of 2. Usually a block of 1024 samples is used, which equals roughly 50ms of sound at 44.1kHz.

Now the FFT algorithm is quite CPU-intensive, and as Alchemy is put forward as useful for large number-crunching operations, I thought this could be a very interesting case. In order to allow for proper comparison, I decided to first port the FFT code from C to Actionscript, and do some testing. It took some refactoring of the C-code in Actionscript to allow for specific bottlenecks popping up, such as multiple lookup of the same value from a Vector, which turns out to be an expensive operation. Also the calculation of sine & cosine was done beforehand, to allow for a lookup table to be used in the actual FFT algorithm. All in all I managed to gain some 50% speed increase by these optimizations.

To my surprise, a single transformation of one block of 1024 samples takes only 5 ms in Actionscript. Even when performing the necessary after-calculations (normalizing & getting the lenght of vectors, which requires Math.sqrt), a back-and-forth transformation shouldn’t take more than 10 ms, leaving 40ms for doing fun stuff with the data. So even without a C-port it’s possible to do real time audio transformation in the frequency domain.

The first thing to do is plot the data in an image. Right now I’m only posting a screenshot, as I’d like to polish the example a bit more before putting out the actual code, but this is what a frequency plot of a short piece of music looks like:

More about this (including source code) soon!

Flocking

stephan — Wed, 26 Dec 2007 22:28:32 +0000

I’m experimenting a bit with flocking. Haven’t gotten as far a moving stuff in any interesting way yet, but it’s fun enough to fool around with maths I haven’t looked at for decades. In the sample below you can see how the vectors of attraction pull the birds (yeah right!) to the common center, while birdies that are close to each other get nasty long green repulsion vectors.

Click to make them start moving to the center, click again to stop the motion. Makes for a nice hedgehog at some point

The source code is here. No fla file, code only.

And thanks to Arie for his tip about the Kimili Wordpress Flash plugin

ADDED_TO_STAGE

stephan — Mon, 24 Dec 2007 22:42:00 +0000

One of those things… The event ADDED_TO_STAGE, dispatched by any DisplayObject when it gets added to the stage (duh) as opposed to added to a parent, wasn’t available in Flash player 9 before 9.0.28. That basically means we can’t really trust it will be available until statistics prove that any and all minor releases prior to that one have disappeared from the face of the earth. So instead of that, we have to use Moock’s solution (but that’s a hell of a lot of work to be notified of just one little event), or check the event’s phase (also thanks to Moock):

private function handleAdded (e : Event) : void {
if (e.eventPhase != EventPhase.AT_TARGET) return;
// do something useful
}

FDT & automatic class name generation in Flash CS3

stephan — Sun, 25 Nov 2007 20:48:08 +0000

The function flash.utils.getDefinitionByName has been discussed in various other places (amongst others here and of course in the documentation), but it took a bit of a mental jump to use it as the solution for the problem that linked library instances without a class are not known inside FDT.Suppose we have a library item with a linkage id of “square”, and we decide not to attach a class to it. Flash CS3 reminds us that it will create one for us, and if we code inside the Flash IDE, we can happily write: var s:Sprite = new square(); addChild(s);However, FDT will show an error, because it doesn’t have a clue what you’re talking about. To solve this, use getDefinitionByName("square"), as shown in the following example:

package {
import flash.display.MovieClip;
import flash.display.Sprite;
import flash.utils.getDefinitionByName;
public class Application extends MovieClip {
private static const LINKAGE_SQUARE:String = "square";
public function Application () {
var s:Sprite = new (getDefinitionByName(LINKAGE_SQUARE))();
addChild(s);
}
}
}