Author Archive for hristo

Finally got around to revive the links here

I can only say I’m sorry that I took so incredibly long to bring this place back to normal. I think all the sources and .swf-s are back online, if you spot something wrong please let me know.

Cheers! h

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My blog got exploded

Sorry guys, had some wordpress issues with the automatic update to WP3 because of the wp-tuner plug-in … you know, my blog has never been the fastest loading website ever, so at some point I had installed the darn thing to see what was going wrong and where.

Now, I didn’t understand much about what was going wrong and where, but instead got to explode my blog with the plugin during the WP3 update. Everything would have been great if once that I was facing the blank screen of death I had decided to put some minimal effort in debugging it manually (which I ended up doing anyway, and honestly, it took like 10 minutes – wp-tuner had left some stuff in the wp-config.php – but hey, how could I know it was THAT easy) instead of just trying to rollback things with mediatemple’s 1-click WP installer.

So, thanks to the brilliantly written 1-click install, all sources and flash files and images and everything is dust. I’ll fix everything this weekend, but now I need to go do some work. Thanks for reading this non-updated blog anyway! I’ve got a couple of things I’d like to share, and maybe I’ll get in blogging mood this weekend, now that I have to patch up everything anyway.

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Producing video with flash/air: png sequence rendering from swf playback

I’ve been quite busy at school here in Barcelona. Busy in fun ways too: recently I put flash to good use in a ‘creative project’ my mates and I had to pull through in the last couple of days before exams kicked in. We hacked together this short animation to welcome freshmen to next year’s csr classes:

View on Vimeo.

You have to love flash – you can pull out quite some tricks in no time. All scenes were done in flash authoring, and the swf files were rendered with camera shake and flicker to png sequences by a small air app. The non-flash part was simply to put everything in an avi container, compress it and mux it with audio, stuff that was done with virtualdub and megui.

Rendering swf playback to an image sequence

When working with video, I personally enjoy image sequences because they’re so easy to manage. My uncontested favourite format for image editing is png, mostly because it’s compact and lossless. In the case of dumping video frames from flash, it also has the advantage of compressing very well rasterised vector graphics.

The app I put together is some sort of a batch processor that you compile with the rendering ‘script’ inlined in its code; its beyond simple but worked so well that I thought about posting it here in case someone needs to do something similar.

Here’s the cleaned-up api:

public class PNGSequenceRenderer extends Sprite
	 * Sets the dimensions of the input swf material.
	 * @param	width (pixels)
	 * @param	height (pixels)

	public function setInputSize ( width : Number, height : Number ) : PNGSequenceRenderer;

	 * Sets the dimensions of the outputed png sequence.
	 * @param	width (pixels)
	 * @param	height (pixels)

	public function setOutputSize ( width : uint, height : uint ) : PNGSequenceRenderer;

	 * Sets the scale mode for the output, either 'show all' or 'no border'.
	 * @param	showAll true for 'show all', false for 'no border'.

	public function setScaleMode ( showAll : Boolean ) : PNGSequenceRenderer;

	 * Sets the level of camera shake. ( e.g. 0 - disabled, 1 - moderate, 2 - heavy. )
	 * @param	factor Camera shake amount.

	public function setCameraShake ( factor : Number = 0 ) : PNGSequenceRenderer;

	 * Sets the level of flicker. ( e.g. 0 - disabled, 1 - moderate, 2 - heavy. )
	 * @param	factor Level of shutter flicker.

	public function setFlicker ( factor : Number = 0 ) : PNGSequenceRenderer;

	 * Sets the output background transparency and fill color.
	 * @param	transparency Whether to draw on a transparency-enabled BitmapData.
	 * @param	color Background color for rendering.

	public function setBackground ( transparency : Boolean = false, color : uint = 0 )
		: PNGSequenceRenderer;

	 * Enqueues a scene for rendering.
	 * @param	url The location of the movie to render.
	 * @param	cameraShakeMultiplier Local camera shake adjustment.
	 * @param	flickerMultiplier Local flicker adjustment.
	 * @param	from First frame to render.
	 * @param	to Frame upon which to end the scene early.

	public function enqueueScene ( url : String, cameraShakeMultiplier : Number = 1,
		flickerMultiplier : Number = 1, from : uint = 0, to : uint = 0xffffff )
		: PNGSequenceRenderer;

	 * Begins loading scenes and outputing frames in the specified folder.
	 * @param	outputFolder The folder where all outputed files are to be put.
	 * If no other limit is specified, each scene is rendered until a pink
	 * (solid #ff00ff) frame is reached.

	public function render ( outputFolder : String ) : void;

How to

What you do with this is to extend your app from the Renderer class, and put together the rendering script in the constructor body, something like:

public class Main extends PNGSequenceRenderer
	public function Main () : void
		setCameraShake ( 1 );
		setFlicker ( 1 );
		setInputSize ( 800, 400 );
		setOutputSize ( 853, 480 );
		enqueueScene ( 'C:\\prj\\swfs\\scene01.swf' );
		enqueueScene ( 'C:\\prj\\swfs\\scene02.swf' );
		render ( 'C:\\prj\\output\\' );

Compiling the project for the air 1.5 target will launch the adl and run your app, which will begin loading and playing your scenes one by one, and dumping the png sequence in the output folder. During the process you’ll be getting some basic feedback on the screen, mainly which scene and frame is being rendered.

Note: Before you jump into testing it out, remember to have a pink solid fill frame (#ff00ff) at the end of each scene, as the renderer expects a frame with a pink middle pixel in order to proceed with the queue. Also, compile in release mode as the PNG encoder runs twice to three times faster without debug stuff in the bytecode.

Once you have the image sequences ready, you can edit them in virtually any video editing software package (if you need to), and then package everything in a video container. The latter will come out pretty voluminous, so you’ll need to compress it with a codec, such as h.264. Finally, you mux it with the audio and you are ready for distribution.

For the windows crowd, virtualdub is a great piece of software for playing with video, and also pulls off the packaging of the sequences into a container with a couple of mouse clicks. Also, check out megui for the video and audio compression and muxing, it makes it all real easy.


The code requires the PNGEncoder class from as3corelib, as well the standard normal output Park-Miller prng class (described here and used for the flicker and camera shake effects).

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Hello everyone, I haven’t posted for a while; I’ve been passing exams, writing a thesis, working and travelling at the same time, so that’s my excuse. I’ll hit back at you when I sit down and finally start working on some more fun stuff, which will be quite soon actually.


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Speedy Voronoi diagrams in as3/flash

Voronoi diagram is a decomposition of space, here a 2d plane, on a nearest neighbour basis. The diagram splits the plane in regions, each corresponding to a site (a point of interest), and containing all the points closer to this site than to any other.

Voronoi diagrams have many applications, in fields as different as botanics and astrology. A few examples of computer graphic uses for Voronoi diagrams include procedural generation of organic forms, crazy image compression, beautiful fractals, noise, etc.

What got me in Voronoi mood however is seeing this this algorithmic collage by Santiago Ortiz from Bestiario. The work’s sheer visual impact shows off the one quality of Voronoi diagrams I appreciate the most – they look awesome. Watching the masks move for a couple of minutes got me terribly into porting Steve Fortune’s algorithm for Voronoi decomposition: I had to see for myself how much stuff could happen on the screen before the player choked.

Fortune’s algorithm

Fortune’s algorithm, ideally, computes a Voronoi diagram in O(NlogN) time, where N is the number of sites, or the minimum possible time for the job, as O(NlogN) is the time-complexity of optimal sorting algorithms. It sweeps through the plane, maintaining a front of parabolas that progressively traces out the diagram, by spliting and adding curves for each site encountered, and removing arcs whenever a region vertex is determined with certainty. The Wikipedia article has it all explained pretty well, but if you need additional info, give this and this articles a try.

I began with this c++ implementation, which is a simplified take on the algorithm. The latter uses a binary tree for the composition of the beachline, whilst here we’ve got a double linked list. However, I do think that the double-link approach would do better for most visual applications in flash, where the cost of not having quick lookup of beachline parabolas might be offset by not having to reogranise the tree, and by the low overall number of particles. I ended up modifying and optimising most of the code however, and I bet this is the reason for the artifacts that show up every now and then in the last of the three demos.

Below you have a demo showing off 1000 regions, in line with nodename‘s mona-lisa tessalator:

Then 2000 points going around with their speed determined by the values of an image:

Finally, a simple audio visualiser: 

Anyway, this really is just a study of how quickly the regions of a diagram can shape up without cheating. There is no bounding box intersection, nor sophisticated output options. Clearly, output of an optimal and informative data structure will be worth the performance kick, and if I get to do my graph theory homework, I’ll be coming back to this.


Fortune’s algorithm is already well implemented and made available by astatic, also nodename shows it off with his Voronoi toy, even though you don’t see the sources. You get a different tool for the same job by HIDIHO!, he goes through Delaunay triangulation, and then translates to a Voronoi decomposition, the two being dual graphs.


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