Green flag. It takes a while to render... If you don't want to wait, just hold click the screen to view the final result (it's just a screenshot).
Basically, each pixel scans all the way around itself to see how close it is to the shape it's rendering from—the closer it is, the brighter the pixel. Because each pixel has to scan all around itself, it takes a long time. It's not perfect though... there were some comprimises in quality to make it faster.
