Continous Movement Preloader

1

I’ve been seeing this nice little effect on a few sites, how would you go about making a continous moving preloader, any links to tutorials or a site that has it open-sourced would be great. Heres a great example below, I can make the pixel art, Im just not technical with the AS thats needed, so coding examples would be great too.

http://www.soleilnoir.net/