Exit Portals are meshes, you put for each thing, where you can see the outdoor world. They force light from outdoor to come through them, which speeds up renders. Partly significantly.
They simply need to be planes, which are as big as the (for example) window frame and their normal need to point inside the room.
You need to cover every single opening, where light from outdoor floats into the room, because every window, you forget, will render black.
It's supposed to be used with BiDir, but it also works without BiDir (with some different effects)
