rasterizeHTML.js by cburgmer

API

Draw a page/an HTML string/a Document to the canvas.

rasterizeHTML.drawURL( url [, canvas] [, options] [, callback] )
rasterizeHTML.drawHTML( html [, canvas] [, options] [, callback] )
rasterizeHTML.drawDocument( document [, canvas] [, options] [, callback] )

See the full documentation here. Examples are collected here.

How it works

For security reasons rendering HTML into a canvas is severly limited. Firefox offers such a function via ctx.drawWindow(), but only with Chrome privileges (see https://developer.mozilla.org/en/Drawing_Graphics_with_Canvas).

As described in http://robert.ocallahan.org/2011/11/drawing-dom-content-to-canvas.html and https://developer.mozilla.org/en/HTML/Canvas/Drawing_DOM_objects_into_a_canvas however it is possible by embedding the HTML into an SVG image as a <foreignObject> and then drawing the resulting image via ctx.drawImage().

To cope with the existing limitations, rasterizeHTML.js will load external images, fonts and stylesheets and store them inline via data: URIs or inline style elements respectively.

Demo

Limitations

SVG is not allowed to link to external resources, as such all used resources need to be embedded using data: URIs. However resources can only be loaded if from the same origin, unless CORS is used.

The code is tested under Firefox, Chrome & Safari. However IE is not supported so far (IE10 doesn't load HTML inside an SVG).

At the time of writing it seems that the individual browsers still have some issues with rendering SVGs with embedded HTML to the canvas. See the wiki for a list of known issues and do add your findings there.

Example code

<!DOCTYPE html>
<html>
<head>
    <title>rasterizeHTML.js example</title>
    <script type="text/javascript" src="rasterizeHTML.allinone.js"></script>
</head>
<body>
    <canvas id="canvas" width="400" height="200"></canvas>
    <script type="text/javascript">
        var canvas = document.getElementById("canvas");

        rasterizeHTML.drawHTML('Some <span style="color: green">HTML</span> with an image <img src="someimg.png" />', canvas);
    </script>
</body>
</html>