Domvas

Overview

Domvas implements the missing piece that connects the DOM and Canvas. It gives to the ability to take arbitrary DOM content and paint it to a Canvas of your choice.

Usage

var canvas = document.getElementById("test");
var context = canvas.getContext('2d');

domvas.toImage(document.getElementById("dom"), function() {
    context.drawImage(this, 20, 20);
});

Syntax

domvas.toImage(domElement, readyCallback, width, height, left, top);

readyCallback's 'this' and first argument points to a valid, preloaded image node that you can simply draw to your canvas context.

How it works

Domvas uses a feature of SVG that allows you to embed XHTML content into the SVG – and as you might know, the actual SVG can be used as a data uri, and therefore behaves like a standard image.

I have written about this technique in 2008 when I brought CSS transforms to browsers that did not have them. It took a little more experimentation to transform it into a reusable plugin: HTML content needs to be serialized to XML, and all styles have to be inlined.

Caveats

• Internet Explorer is not supported, as it doesn't support the foreignObject tag in SVG.
• For whatever reason, Opera is failing. I am not sure why. If a Opera pal is reading this, get in touch!
• SVG's foreignObject is subject to strong security – meaning any external content will likely fail (i.e. iframes, web fonts)
• The DOM object is not linked, but copied – if you change the style of the DOM object, it will not automatically update in Canvas
• Content outside the bounding box of the element will be cut of per default if painted to Canvas. Don't worry though, simply pass a more comfortable offset to the toImage function (see above)

Credits / License

©2012 Paul Bakaus. Licensed under MIT. Reach out on Twitter!