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Browsers have poor support of image formats. Actually only GIF, JPG, PNG and WebP are supported.

I would like to had a new one : JBIG2

From the end user point of view, he will only download and install a chrome extension and his browser will be able to decode the new image format.

From the web developer point of view, new format will be transparent and compatible with tag img, canvas and css. To display JBIG2 images, he still uses :

<img src=“path/to/myImage.jbig2”>

or

var myImage = new Image();
myImage.addEventListener( 'load', function() {
    // insert in canvas, when image is loaded
});
myImage.src = 'path/to/myImage.jbig2';

or

.my-class {
    background-image: url( “path/to/myImage.jbig2”);
}

The problem isn’t the decoder itself. I foresee to use this one JBig2dec written in C language.

The problem is how to implement a new image decoder? In Chrome, when we have to run C code the best solution is to use Native Client Extension.

And even better, I can read on this NaCl web page :

Graphics, audio, and much more: Run native code modules that render 2D and 3D graphics, play audio, respond to mouse and keyboard events, run on multiple threads, and access memory directly all without requiring the user to install a plugin.

Multimedia applications: Codecs for processing sounds, images, and movies can be added to the browser in a Native Client module.

But unfortunately there is no documentation neither sample to implement a 2D graphic decoder. I just guess that I need to register an hook for the minetype image/jbig2.

Does anyone know how to implement a new image format decoder with NaCl ?

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Laurent Trillaud
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  • According to the documentation “**Codecs for processing** sounds, **images**, and movies **can be added to the browser in a Native Client module**”, the NaCl is made to build codecs. But as far I know the documentation and examples of graphics codec are missing. The perfect solution is really implement just an image decoder into NaCl and let the rendering as usual to the browser. – Laurent Trillaud May 15 '14 at 09:27

1 Answers1

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Yes, I think the solution you've described will mostly work, though you may need to load the image using an <embed src="..." type="image/jbig2"> instead of <img>.

Basically, you will:

  1. Compile the JBig2 decoder using the Native Client SDK
  2. Add the PPAPI plugin entry point. See any of the examples in the NaCl SDK, or the tutorial here.
  3. In your derived Instance class, implement the virtual function HandleDocumentLoad. This function will be called when your Native Client plugin is used as a mimetype loader. You can use the URLLoader object that is passed to read your JBig2 file.
  4. Create a 2D graphics context, and display the contents of the decoded image in it. Take a look at the Graphics2D example in the NaCl SDK (examples/api/graphics2d).
  5. Make a Chrome extension that registers itself as a JBig2 Native Client mimetype handler (as you've already found).
binji
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  • Thank you for your answer, but it not exactly what I need. It could be a workaround. I agree with all your 5 points excepted the 4. I don’t want to create a new 2D graphics context making a kind of ‘hole’ in the web page. I want to keep the 2D context (canvas) of the web developer because he can use high level Canvas framework like [KineticJS](http://kineticjs.com/). The point 4 should be : “Give the decoded image data to the browser to build his Image object”. But how? – Laurent Trillaud May 15 '14 at 09:22
  • I guess that I have a workaround for the point 4 with the [communication between Javascript and NaCl modules](https://developer.chrome.com/native-client/devguide/tutorial/tutorial-part1#communication-between-javascript-and-native-client-modules) but it solve only the feature Javascript, not the html and css calls, and the web developer have not the same code to load native format images and JBig2. – Laurent Trillaud May 15 '14 at 09:25