[grumblestumble]

I'm using fabricjs for annotations as well and it's a great library. The biggest downfall of using canvas as a renderer as opposed to svg is that it doesn't look great if you provide zoom controls. Lovely crisp SVG paths rendered as pixels on a canvas :/

[secondtimeuse]

I think you can implement programmatic zoom on canvas in fabricjs as well. E.g. See this http://www.eraseimage.com/ use mouse zoom on the left canvas.