Renders HTML into the browser's canvas.
See the API.
$ npm install rasterizehtml
Then include a script tag with
node_modules/rasterizehtml/dist/rasterizeHTML.allinone.js or require through browserify.
var canvas = document.getElementById("canvas"); rasterizeHTML.drawHTML('Some ' + '<span style="color: green; font-size: 20px;">HTML</span>' + ' with an image <img src="someimg.png">', canvas);
How does it work
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
In addition SVG is not allowed to link to external resources and so rasterizeHTML.js will load external images, fonts and stylesheets and store them inline via data: URIs (or inline style elements respectively).
All resources (HTML page, CSS, images, fonts and JS) that are needed for drawing the page can only be loaded if from the same origin, unless techniques like CORS are used. I.E.
drawURL() can only load pages from the same domain as the current page and all draw methods can equally only embed styling and images from that domain.
The code is tested under Firefox, Chrome & Safari.
There's basic support for Microsoft Edge, however it will not work under any version of Internet Explorer.
Also the individual browsers still have some issues when rendering SVGs with embedded HTML to the canvas.
Import type definitions as follows:
import * as rasterizeHTML from 'rasterizehtml';
npm test. There's also a vagrant image that installs all necessary build dependencies.
For tests against individual browsers open
test/SpecRunner.html, for integration tests under Safari open
test/manualIntegrationTestForWebkit.html (under Chrome you will either need to start the browser passing in the option
--allow-file-access-from-files or load the page through a local webserver).
Where is it used?
- CSS Critic, a lightweight tool for regression testing of Cascading Style Sheets