The article mentioned above is located at http://willyg302.wordpress.com/2012/11/04/2d-visibility/.
More precisely, I have few shapes drawn on canvas some of them are complex made by arc and similar methods. Thus I don't have a simpel way how to describe one shape with an equation where I can store only a few parametrs (i.e. circle is described as centerX, centerY, radius with these I can easily draw it but with more complex shapes I don't have such information) therefore I thought about storing the whole canvas data by pixels with context.getImageData.data, then using method described in the article (polar transformation, ..., back to cartesian system) and putting the whole scene into canvas with canvas.putImageData method.
Or if anyone has tried to create dynamic shadows in different way in html5+js I'd appreciate your suggestions about these as well (I do it currently in similar way as is described in http://ncase.me/sight-and-light/, though I'm experiencing some troubles with concave shapes :( ).
This is getting awfully long, I hope I explained myself well enough.
Thank you very much for any advice you can share and I'm sorry that my post grew so large, although I'm asking just one question.
EDIT: Forgot to mention, I'm looking only for 2d solution.