Other Portals with only one camera?

I have some idea how it's possible to do teleporting portals with only one camera.

The level is sector based.

You have two sectors that are invisible and both behind portal plane object and with one portal you copy the other sector and put it's transform behind the portal and other rooms are copied.

When you enter the invisible sector behind the portal you are teleported to the real one.

I think I can use portal planes for clipping geometry or a scan line renderer.

I'm thinking about visibility portals and teleporting portals.

 

But why do it that way?

That method sounds super limiting on where portals can be placed, requires duplicating large numbers of objects, and more. All for what reason though? To avoid having another camera? Why would that matter?

 

Exactly. A second camera simply renders the scene again from a different perspective. Thanks to frustum culling, objects outside the view frustum won't be rendered anyways. I can highly recommend this talk by the valve employee Dave Kircher. He does all the technical parts in that talk.