This video I made shows what it looks like with and without stencil buffer portals.
https://www.youtube.com/watch?v=_SjYeNLr0Jo
I have a new way to use the stencil buffer to hide geometry.
The sectors have a stencil buffer shader with comp not equals and the portals ref is the same as the sectors.
Render queue had to be changed for each portal and sector.
Stenciling is a 2D effect.
The map came from a portal rendering tutorial video.
https://www.youtube.com/watch?v=HQYsFshbkYw