A way to create random-noise background image (png) with javascript?

问题

The new layout of YouTube added a background random-noise which I like very much, having seen almost exactely the same effect on other sites, so I plan to use the same technique in my webpage prototypes, or at least have this "trick" in my toolbox for future use.

The image is like this (taken from http://g.raphaeljs.com/barchart.html):

Now Youtube accomplishes the (embarrassingly identical) same effect by embedding the image in source code:

(on Youtube main page, right click background to display it, then right click the image and "display image properties" [ffox]):

data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAJUAAACVCAAAAAB0....lotsofdata

I tried to discover where this line of code is in the source code, but due to the dynamic creation, I couldn't.

So, my question is: "Is there a way to apply a tiled background to a page, using a png image generated algorithmically CLIENT-SIDE?" (preferrably with javascript)

I am very beginner in webdev and javascript, but I like to base my learning around defined problems to be solved, so this would be a nice way to learn something

Thanks for reading!

UPDATE:

For anyone interested in tile texture generation using javascript, I found this, which seems very interesting:

http://somethinghitme.com/projects/canvasterrain/

http://somethinghitme.com/projects/canvasterrain/js/canvasTerrain.js

回答1:

To generate image client-side, I suggest you to have a look to HTML5 canvas element.

You can draw on a canvas with Javascript (even if the canvas element is hidden), and so generate anything you want (including a simple noise tile).

Resource to learn Canvas drawing : https://developer.mozilla.org/en/Drawing_Graphics_with_Canvas

After that, you can export your canvas as URL with the method toDataURL (a string like "data:image/png;base64....") which is interpreted by browsers like a traditionnal url for an image, so you can set it as css background for your body element.

Warning 1 : Canvas is supported by all modern browsers and you can emulate it on IE with ExplorerCanvas - but I don't know if ExplorerCanvas support .toDataURL()

Warning 2 : Canvas is resolution-dependant, so I suggest you to generate a little tile (32*32, or 64*64) and repeat it

Edit : An example of tiled background : http://jsfiddle.net/SfzPc/12/

Edit 2 : An completed example with a noisy background : http://jsfiddle.net/SfzPc/14/

回答2:

You can use CSS to display this image:

#someimageselector {
    background: white url('data:image/png;base64,iVBOR...lots of data') repeat scroll left top;
}

You can change the initial color of your background by editing the value white.

To set CSS with JavaScript, set the background property of an element:

document.getElementByID("someimageselector").background = 'white url(data:image/png....';

回答3:

There are two jQuery plugin libraries that do exactly what you are looking for: NoiseGen and Noisy. Haven't used either yet but they both look pretty good.

NoiseGen

Project: http://primegap.net/2011/10/20/noisegen-generate-background-noise-with-jquery/
Demo: http://www.lucaongaro.eu/demos/noisegen/

Noisy

Project: https://github.com/DanielRapp/Noisy
Demo: http://rappdaniel.com/other/noisy-sample/

回答4:

Fyi: Base64 is binary data represented as a string. Most likely the original image still came out of Photoshop and was later encoded into Base64. This technique helps having less http-requests per page view, as the actual image data can be saved and cached inside the css or html document.

来源：https://stackoverflow.com/questions/8580541/a-way-to-create-random-noise-background-image-png-with-javascript

标签

javascript

html

png

background-image

client-side