Window Instances allow you to freely place planes into a room and act as a "portal".
The idea is borrowed from Dxtre3D, which did not have "Toggle Opacity" option for walls but instead you would place these portals yourself.
They are complementary to regular portals, and can be used to implement arched roofs (like in Lara's Home Pool) or multiple portals on the same wall.
They are not physical and only cosmetic, which means you can't traverse between rooms.
Window Instances allow you to freely place planes into a room and act as a "portal". The idea is borrowed from Dxtre3D, which did not have "Toggle Opacity" option for walls but instead you would place these portals yourself. They are complementary to regular portals, and can be used to implement arched roofs (like in Lara's Home Pool) or multiple portals on the same wall. They are not physical and only cosmetic, which means you can't traverse between rooms.
This issue is used for discussion