bouncy balls!! v1.1

You have some transparency within the world background along the edges. You can probably avoid this by not using the 'clear' method on the background image. Greenfoot will automatically tile any image smaller than the size of the world when set to the background.

Okay. I downloaded it and checked it out. I seems to be okay on the download. Maybe it is the particular version of greenfoot you are using.

An extreme example can be seen here: http://www.greenfoot.org/scenarios/12156 I think it has something to do with the size of the world. But as you say, it only happens here on greenfoot.org, not offline in the program.

@Super_Hippo, your scenario does not have the source published, so all that is possible is to see the result -- not what may be causing it. As I have not ever had any issues similar to what you all are experiencing, I am wondering if it could be related to the operating systems we are using.

In my scenario, the blue boxes in the background can move outside the world. Only in the world boundaries, the moving objects are displayed correctly. I don't know how it is done, but I could think of the following: Every time the world gets repainted, the 'image' is cleared and then, the background image and all the objects are painted on it. Outside the world, the 'clearing of the image' does not happen. Usually, this shouldn't be a problem because it isn't visible, but in our case it is visible. So objects which are there (or close to the edges) are painted but not removed and create colored 'lines' when they are moving. It could be a bug on this website. Like a minimum size of the world and if the world is actually smaller, the rest will be filled with something that we can see (and you can't for some reason). I am using Windows and Internet Explorer 11. (Windows 10 for a few days, but it was the same on 8.1. The new browser 'Edge' doesn't work because it doesn't support plugins.)

The way that the images of the actors remain along the edges, it is acting like the background image is not completely covering the world canvas but the actors still being painted there -- like the edges of the world background image are transparent. If a discussion thread were started on this issue, we could try different codes that I could suggest to attempt to resolve the issue.