Try now, Xiao ... I think it might be better. The ending doesn't work (you can keep clicking) but the shapes (including the blue ovals) should now scroll smoothly. I actually pre-draw an array with every single size I need (80, in the current version) and then just pull images from that array. Saves a ton of processing mid-game (youll notice a delay when you click to start). Almost ready to start building game logic!

I do plan to share this! I can offer no timeline, but ultimately I try to share everything I create, for the benefit of my students, and educators and students everywhere :)

Thanks Dan, It turns out that this wasn't the actual problem. I was getting a javascript error that made it seem like setColorAt was getting a null object. It turned out that I was hitting an object limit. Once I simplified some of my classes to maintain a spritesheet rather than a number of arrays of GreenfootImage, it eliminated the problem. This is the scenario I'm working on, if you're interested: https://www.greenfoot.org/scenarios/25314

I like that you took the initiative to put this up on the Gallery! I know it took some extra work. Thanks! I'm going to use this as an exemplar for future years :)