This is an old post, but wanted to share my two cents.
I generated the shape based on a “generator” found on Shadertoy: https://www.shadertoy.com/view/MlySzw
The code inside the Custom Node is something like this:
float PI = 3.141592f;
float2 TWO_PI = 6.28318f;
float2 center = 2.0f * (uv - centerOffset);
uv = center;
float a = atan2(uv.x, uv.y) + PI;
float r = TWO_PI / sides;
float d = cos(floor(0.5 + a / r) * r - a) * length(uv);
return smoothstep(0.41, 0.4, d);
Hope this helps anyone!
Cheers!