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JavaScript <canvas> to (Animated) GIF 23 July 2010

This is the GIF which was generated from the canvas.

This is the raw canvas element saved as a non-animated PNG

I’ve tried this before but it didn’t work. <canvas> can’t do toDataURL('image/gif'), and the primitive GLIF library couldn’t do much so I never had the opportunity to test my gif-merging code that I had. But I’m at it again, this time, porting it from the AS3GIF library, an awesomely comprehensive bitmap to binary gif encoder that even supports LZW compression (and the patent has luckily expired. Yay!). AS3Gif is supposed to “play and encode animated GIFs”, but since web pages can usually natively play GIFs fine, it’s only a port of the GIFEncoder portions of the library. And it works really well. The rest of this post is copied from the Github readme. Interesting how the w2_embed/anonybot embed post was a blog post turned into readme, this is a readme turned into blogpost. I’ll start with a link to the Github repo anyway:

Basic Usage

Since it pretty much is GIFEncoder, you could consult the as3gif how-to page

But there are some differences so I’ll cover it here anyway.!

This is the GIF which was generated from the canvas.

You first need to include the JS files. It’s probably best if you include it in this order, but it shouldnt’ matter too much.

<script type="text/javascript" src="LZWEncoder.js"></script>
<script type="text/javascript" src="NeuQuant.js"></script> 
<script type="text/javascript" src="GIFEncoder.js"></script>

If you want to render the gif through an inline <img> tag or try to save to disk or send to server or anything that requires conversion into a non-binary string form, you should probably include b64.js too.

<script type="text/javascript" src="b64.js"></script>

Simple enough right? Now to convert stuff to GIF, you need to have a working or at least some imageData-esque array.

<canvas id="bitmap"></canvas> 
  var canvas = document.getElementById('bitmap'); 
  var context = canvas.getContext('2d'); 
  context.fillStyle = 'rgb(255,255,255)'; 
  context.fillRect(0,0,canvas.width, canvas.height); //GIF can't do transparent so do white 
  context.fillStyle = "rgb(200,0,0)"; 
  context.fillRect (10, 10, 75, 50); //draw a little red box

Now we need to init the GIFEncoder.

var encoder = new GIFEncoder();

If you are making an animated gif, you need to add the following

encoder.setRepeat(0); //0 -> loop forever //1+ -> loop n times then stop 
encoder.setDelay(500); //go to next frame every n milliseconds

Now, you need to tell the magical thing that you’re gonna start inserting frames (even if it’s only one).


And for the part that took the longest to port: adding a real frame. encoder.addFrame(context);

In the GIFEncoder version, it accepts a Bitmap. Well, that doesn’t exist in Javascript (natively, anyway) so instead, I use what I feel is a decent analogue: the canvas context. However, if you’re in a situation where you don’t have a real <canvas> element. That’s okay. You can set the second parameter to true and pass a array as your first argument. So in other words, you can do encoder.addFrame(fake_imageData, true)as an alternative. However, you must do an encoder.setSize(width, height); before you do any of the addFrames if you pass a array. If you pass a canvas context, then that’s all okay, because it will automagically do a setSize with the canvas width/height stuff.

Now the last part is to finalize the animation and get it for display.

var binary_gif = //notice this is different from the as3gif package! 
var data_url = 'data:image/gif;base64,'+encode64(binary_gif); 


Each of the files exposes a single global (see, at least it’s considerate!). But since there’s three files, that means that there’s three globals. But two of them are more of supporting libraries that I don’t totally understand or care about enough to document. So I’m just gonna document GIFEncoder.

new GIFEncoder() This is super parent function. You really don’t need the new keyword because It’s not really even using any special inheritance pattern. It’s a closure that does some var blah = exports.blah = function blah(){ for no good reason. Anyway, it returns an object with a bunch of methods that the section will be devoted to documenting. Note that I’ve never tested more than half of these, so good luck.

Boolean start() This writes the GIF Header and returns false if it fails.

Boolean addFrame(CanvasRenderingContext2D context) This is the magical magic behind everything. This adds a frame.

Boolean addFrame(CanvasPixelArray image, true) This is the magical magic behind everything. This adds a frame. This time you need you pass true as the second argument and then magic strikes and it loads your canvas pixel array (which can be a real array, I dont care and I think the program has learned from my constant apathy to also not care). But note that if you do, you must first manually call setSize which is happily defined just below this one.

void setSize(width, height) Sets the canvas size. It’s supposed to be private, but I’m exposing it anyway. Gets called automagically as the size of the first frame if you don’t do that crappy hacky hack.

void setDelay(int milliseconds) the number of milliseconds to wait on each frame

void setDispose(int code) Sets the GIF frame disposal code for the last added frame and any subsequent frames. Default is 0 if no transparent color has been set, otherwise 2. I have no clue what this means so I just copypasted it from the actionscript docs.

void setFrameRate(Number fps) Sets frame rate in frames per second. Equivalent to setDelay(1000/fps). I think that’s stupid.

void setQuality(int quality) Sets quality of color quantization (conversion of images to the maximum 256 colors allowed by the GIF specification). Lower values (minimum = 1) produce better colors, but slow processing significantly. 10 is the default, and produces good color mapping at reasonable speeds. Values greater than 20 do not yield significant improvements in speed. BLAH BLAH BLAH. Whatever

void setRepeat(int iter) Sets the number of times the set of GIF frames should be played. Default is 1; 0 means play indefinitely. Must be invoked before the first image is added.

void setTransparent(Number color) Sets the transparent color for the last added frame and any subsequent frames. Since all colors are subject to modification in the quantization process, the color in the final palette for each frame closest to the given color becomes the transparent color for that frame. May be set to null to indicate no transparent color.

ByteArray finish() Adds final trailer to the GIF stream, if you don’t call the finish method the GIF stream will not be valid.

String stream() Yay the only function that returns a non void/boolean. It’s the magical stream function which should have been a getter which JS does support but I didnt’ feel like making it a getter because getters are so weird and inconsistent. Like sure there’s the nice pretty get thing but I think IE9/8 doesn’t implement it because it’s non standard or something and replaced it with a hideously ugly blah blah. So Anyway, it’s a function. It returns a byteArray with three writeByte functions that you wouldn’t care about and a getData() function which returns a binary string with the GIF. There’s also a .bin attribute which contains an array with the binary stuff that I don’t care about.


The process isn’t really the fastest thing ever, so you should use WebWorkers for piecing together animations more than a few frames long. You can find the rest of the WebWorkers section on the actual readme, because the rest is just a huge block of code with comments.

ShinyTouch/JS 28 August 2009

Yay for yet another demo that strives to mix an mash almost everything HTML5 related! ShinyTouch in JS dumps the stuff from a <video> tag with ogg encoded video (well, almost all video from linux is ogg encoded so it’s just whatever format i got first from cheese). It gets dumped into <canvas> and getImageData does it’s magic.

Interestingly, if you don’t use the video and just do data from a raw image, you get upwards of 125fps on V8. Adding the video, it ceases to work on Chromium (maybe a linux thing? this tells me it’s just linux, but you can never be so sure).

//At this point, run away as the algorithm gets messy and hackish

So the thing just searches from right to left up to down within the quad. When it finds a column of something that fits the rgb range of the finger that is larger than a certain threshold, it checks for a reflection from the point. If it detects a reflection then yay! it throws the data at the perspective warper (based on a python one which is based on a C# one and though it would probably be easier to port from C# to JS making long chains of derivative work is fun). If there wasnt a reflection then it logs that and if that number is larger than some othe rthreshold then it kills the scanning and goes on with it’s life. The reflection algorithm just takes the point 5 pixels to the right and assumes that would be a reflection if there was one and a point 15px above and 5px to the left (nasty stuff) and takes the hue value from their RGB values. It takes the absolute value of the difference of the hue values multiplied by 100 (or 200 in the python version) and compares it with a preset configuration variable.

So now that that horrible algorithm which was just whatever came to my little totally untrained mind first. But it works semi-decently, at least for me. But you can hopefully see how nasty it’s inner workings are and it inspires people to clean it up. It’s quite a bit more readable than the Python version and only 200 lines of JS so it won’t be too hard to understand.

But since HTML5 has no Video capture thing for webcams, and my webcam doesn’t work with flash so I can’t use that canvas<-flash webcam bridge i built, uh, almost 2 years ago. So now you just get to gaze at my finger moving for like 20 seconds!

Freemovie/JS Pure Javascript SWF Generator 17 August 2009

I’m making a crude python script that translates PHP to JS rather hideously. It probably will not work on any other codebase. It was a script quickly hacked together to one purpose.

Freemovie is

FreeMovie is an SWF generator library written in PHP and ported to Ruby. FreeMovie can be used to develop Web and desktop aplications. Speaking of the Ruby port, I can’t find it. So if anyone finds it, I think it might be useful somewhere. Found it in the CVS, it’s really incomplete compared to the PHP version.

The machine translated code (Not entirely autogenerated, I wrote a line or two of it) is not too hideous, the tabbing is slightly off, but it’s at least mostly readable. It was a lot worse 2 hours ago (half of the lines had indentation, other without any, debugging comments everywhere saying useless and distracting things).

The translator is only 107 lines of (hideous code, though the language is beautiful, I guess if you loved JS enough, you could try running the program though skulpt) python (+ 20 or so in another file to change chr() to String.fromCharCode, etc). After that, it uses 6 PHP compatibility functions and 5 from the PHP.js project to cover the features that I’m too lazy to put in the compiler or are just not features in JS.

The above demo generates a flash image entirely client-side, though the resulting base64 encoded data is sent to be decoded on the server since you can’t load a SWF from a data-url. If someone finds out how, it would be cool to tell me.

A big issue though, is that for some odd reason half the shapes don’t work. The ones in the demo work, but all filled shapes, and the circles/arcs do not work.

ShinyTouch ideas 13 July 2009

One potential I see for shinytouch is the ability for it to be embedded in a flash application which can be embedded into a web page. Then there could be a web 2.0 style JS API for awesome canvas tag based creations. Or it could just be used to interact with another flash application or game. The reason why this is more likely able to be used as such is because setup for this is so easy that this could actually convince people to do it. With other systems you really have to convince people really well to be dedicated enough to set up the hardware whatever it is. At that point, the software is the easy part and the audience is more than glad to go through the hassle of downloading, running, configuring, and maybe even compiling. But with shinytouch aiming at a different, larger and overall lazier (myself included in this group) audience. This means that it is really important to lower the entry barrier to the lowest possible level. I think being able to just move the webcam a little bit, go to a website and follow simple directions to use their own touchscreen is a very potentially attractive concept. It could even spawn more interest in the touchscreen, natural user interface communities. This is really what I want he project to end up like. It seems quite practical to me. How do you feel about this?

(note that this is my second post entirely from my iPhone)

Future updates to the Ajax Animator 12 April 2009

okay, so recently something really awesome happened. Google App Engine will now support Java. The great thing about this, it that decent flash export may happen because of that (yay!) and possibly actionscript later on.

Flash Export 21 July 2008

Okay, i’ve done it. You can now export to flash. But the problem now is that I’m still using the uber limited freemovie library, which is both outdated and incapable of anything besides the rectangles and lines.

For now, I haven’t installed the server files yet so it wont work until I do, but by the time you read this, I may have already done it.

Ajax Animator 20 May 2007

Ajax Animator
Ajax Animator

Gmail revolutionized email by offering a web based equivalent to Outlook and Thunderbird, except this was completely web based. No more Installing. So did Google Docs and Spreadsheets, or Zoho office, or etc, they had entirely free and web based clones of Microsoft Office or OpenOffice. Or Microsoft Windows, then there is Linux and now there is desktoptwo eyeos and youos. I think of it as a development cycle, somebody makes something that is expensive, then something free, then something entirely Web based. Now, what about Flash. According to adobe, 97% of all people who browse the Internet have flash player installed. By far larger than the amount of people who have outlook, thunder bird, Microsoft office, or Openoffice installed. Flash also accounts for a large percent of So why isn’t there a freeware open source replacement to this $400 software? There are though, UIRA, F4L, QFlash, KDSFlash, and more, but they are early in development. So when is the third generation web 2.0 equivalent for animation software coming? This is what I want to develop. This is a project to make an open-source browser based Flash Authoring system.

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