Ah, man, with the colors, I thought this was obvious, but it doesn't quite fit the url. But you can still copy, paste in the box:

(1-sqrt(pow(7.5-x,2)+pow(7.5-y,2))/8)*(y-7.5)

Pokeball.

edit Actually, there's no fixed length, so https://tixy.land/?code=%281-sqrt%28pow%287.5-x%2C2%29%2Bpow...