Fill closed spline

Hello
Is there a way to fill a closed spline with a colour? - Something similar to the curve mask node but using nulls as the points instead.
I have a four point extruded spline with the nulls of the spline attached to sound modifiers but I’d like there to be a 2D fill in the same shape as the closed spline behind it. What would be the best approach?
Thanks,
Aaron

HI Did you have any luck with this? after the same thing…