Code

There is an error in your link.

I guess I was mistaken. I does take you to a scenario (even with the final "o" character. Just go to the linked page and click on the big green "Open in greenfoot" link (above and to the right of the scenario frame).

Apparently, you have that code. Although, are you sure that is the code you need. That code will only scroll the background image of the world without scrolling (moving) any actors with the background. Also, it will only work when the initially set background image (cropped to world window size) is to wrap during scrolling.

Then you want to look at the paint method of the ScrollWorld class.