The easiest way is to alternate one variable e.g. "a = 1-a" <- this will make 'a' alternate between 0 and 1.
If you then use 'a' as a radius to a circle, you'll get a solid disc, because you'll get alternating points on the center and on the circle. The trick is to make sure you get an even spread across the curve, because else you'll be using an unnecessarily big line width. For blend modes, maximum or replace should work fine.
use in "per point"
u=bnot(u);X=i*2-1;y=if(u,v,0)
Line scopes
u=bnot(u) is the important part, so is if(u,...
If(u,point from where top(or bottom) of the scope, to the other side)