(If you have not read Portals, please do so now before reading this article.)
Linked portals are a powerful feature which make it possible to connect two separate areas of a map via the floor/ceiling or one-sided linedefs, allowing the player to see, shoot, and even move seamlessly from one area into another. They are used similarly to two-way portals, apart from the fact that you can pass through them. They can be used to create 3D architecture and room-over-room effects, with very few limitations.
# Class Trig Description 358 Ext -- Apply linked portal to like-tagged ceilings 359 Ext -- Apply linked portal to like-tagged floors 360 Ext -- Linked portal anchor line for special 358 361 Ext -- Linked portal anchor line for special 359 376 Ext -- Apply linked portals to like-tagged lines 377 Ext -- Anchor line for special 376
Linked portals have their own specific sub-set of terminology used to describe certain aspects and behaviors.
Unlike the basic portal types, which were rendered and could cover height variances (much like the doom sky), linked portals form an actual map structure. The Portal Plane refers to an X/Y plane that bisects the sector(s) that contain the portal. The z-position of the portal is fixed, and should be the same height on both sides of the linked portal.
Beyond the Plane
Map architecture is said to be beyond the portal plane when its vertical height is equal to or beyond the portal height--that is, at or above a ceiling portal plane or at or below a floor portal plane. When map architecture is beyond a portal plane, the portal will display at the height of the plane.
Inside the plane
Map architecture is said to be inside the portal plane when its vertical height is not beyond the portal plane--that is, below a ceiling portal or above a floor portal. Any architecture that is inside the portal plane will render normally and will obscure rendering of the portal.
Linked portals use trigger and anchor lines (much like anchored portals) to determine an X and Y offset from one part of the map to another, but there are specific requirements unique to linked portals:
- Linked portals must be two-way, meaning the upper area must reference the lower area and visa versa.
- Linked portals have specific behavior relating to z-coordinates of the portal plane.
Setup (Doom line specials)
Refer to Zarkyb's linked portals tutorial for in-depth information on usage.