Canvas on the Background

I was reading the documentation about -webkit-gradient on the Apple HTML documentation site and I stumbled across something that I had never seen before. I thought it was so cool, that I decided to write a blog post about it.

With the introduction of CSS3 into many top-line browsers there is now the ability to manipulate the background-image of any element, specifically gradients and svg. One of the things that is missing is canvas as an element for the background.

In 2008! WebKit introduced(http://webkit.org/blog/176/css-canvas-drawing/) a CSS attribute value called -webkit-canvas(id). When attached to a background style allows you the developer to have programatic access to the background-image through canvas. Believe me when I say "This is Powerful".

I must warn that this is specific to WebKit only at the moment. I would love to see other browsers add this support in as it is super powerful.

So lets see this in action.

In this post I will do one simple sample (http://html5samples.appspot.com/backgroundCanvas.html) and all it will do is draw a square into the background of a div:

<html>

<head>

<style>

div {

background: -webkit-canvas(test);

float:left;

width: 100;

height: 100;

}

</style>

function onLoad() {

var ctx = document.getCSSCanvasContext("2d","test", 100,100);

ctx.fillStyle = "blue";

ctx.fillRect(10,10,90,90)

}

(function() {

document.addEventListener("DOMContentLoaded", onLoad);

})();

</script>

</head>

<body>

</body>

</html>

Pretty cool! Well actually the concept is cool, that demo is pretty ugly :) You can do some pretty awesome demos with this. You could have a game or some super cool animation running in the background. I think you could get around the lack of background-opacity support in CSS3.

I will do some more samples soon.

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