Hi, I completely agree with Gertjan and I recommend the reading of "Book of shaders" (http://www.bookofshaders.com)
You are a very good explanation for how it works. Here is the page for circle
https://thebookofshaders.com/07/
You just have to replace u_resolution with resolution, u_mouse with mouse and u_time with time and it works in Isadora.
I am preparing a patch with all the book sample in Isadora, I will post it when ready.