Very cool. Shows the versatility of OO design and a good greenfoot design. There is a small bug. If you overlap the two small worlds and click back and forth between them they get "stuck" so that you can't move the bottom one. You have to go to the top one and drag it a bit to unstick them. It happens if they are not overlapped, but it's harder to tell when it's not working. Also, it has to be running. You can drag the screens when it's paused, but the "top" window doesn't change and it doesn't get stuck.

@m_p_v_13, the problem was appearing when the mousePressed object was not dragged (when the object was just clicked on). The object was being selected, but not de-selected. I changed 'mouseDragEnded' to 'mouseClicked' to fix it.

Cool. Works well. it would be good if you could move the wombat around rather than just see him spin on and off screen. Also, something to shoot in the ship sequence would be good! The DoctorProfessor is out! BOOM!

Your programm did help me, but know we have another problem: We want to have several levels and the actors should be able to go into a new level at different time (in the minor wolrds). Do you have an idea, how this could work or it is even possible?

@Game/maniac, it was not intended to be a game -- just a sample world. The Wombat world was a sample of a gridded (cell size greater than one) world and the Space world was a sample of a pixel cell-sized world. Originally I did not even have the asteroids in it; and DoctorProfessorYoshi wrote that it would be nice to be able to shoot at something. So, I added asteroids and a counter (and gave the wombat user-key control).

I currently am using a lot of the code from this project but I have the problem that I cannot click actors in the world (which I need), so would it be possible to remove the code that enables the user to move around the PIP elements and if then how?