Code is not perfect. A central control instance is missing. Still some Bugs in the game: In the upper half of the screen, change the rows very lately, then it will work.
realy funny game.
But on hint:
There is a Greenfoot mehtod in the class GreenfootImage called mirorHorizontaly or something like that. If you use this the frog will not be upside down.
http://www.greenfoot.org/files/javadoc/greenfoot/GreenfootImage.html
on this webside there are all GreenfootImage mehtods.
2012/9/6