You can watch Shrek as a desktop wallpaper via the Steam Workshop
Wallpaper Engine is one of the most popular utilities available via Steam. It's a tool that lets you run animated or interactive desktop wallpapers, and download those made by the community from the Steam Workshop. I bought it at the weekend because I was bored.
One of the first community-made wallpapers I found? Shrek, the movie, in its entirety.