Sectors and Portals

Sectors and Portals

Sectors

A sector is a room: a closed mesh with its normals facing inward, which the engine tests points against to know where you are. Add ▸ 4DS ▸ Sector builds one.

The export refuses a sector that:

• does not enclose a volume,
• is not closed (it names how many open edges there are), or
• has outward-facing normals.

Portals

A portal is the opening between two sectors: a flat outline of at most eight corners, parented to its sector and named after it with _portal1, _portal2 and so on. Add ▸ 4DS ▸ Portal builds one on the selected sector.

The eight-corner limit is real — the outline is stored in a fixed slot of eight, so a ninth does not fit.

Their own switches

Sectors and portals carry a panel of their own. Two bits belong to the engine and are refused on export if you set them: the Parsing and Prepared bits, which the game sets at load time for its own bookkeeping.

Seeing them in Blender

A sector is drawn as a wireframe in cyan and a portal in purple, and the Sectors box in the 4DS Model tab carries a pair of switches for each:

	What it does
Solid	Shows the faces rather than the wires. A sector is filled by its own display; a portal is drawn filled by the overlay, which is what lets it keep its place in the depth of the scene.
In Front	Draws them over whatever stands in front of them, so a room can be seen from outside the building.

Their colors are shown by setting the viewport to color objects by object, which is what a sector's cyan and a portal's purple live on - a viewport colors by material until it is told otherwise, so filling either of them asks for that once.

A portal lies flat in a wall of the sector it belongs to, so the two surfaces are in the same place and would fight over every pixel. A filled portal is brought a hair toward whoever is looking - not into the room, because it has to win that wall from either side of it - and it is drawn both ways round, since a portal has no front: in the file it is a ring of points and the plane they lie in, with no faces at all, and the game walks the same portal from either side.

What a sector shows follows the scene as it changes. Whether a sector-typed mesh counts as a portal comes from its name and the sector it hangs off, and both can change at any moment, so parenting one under a sector or renaming it is picked up straight away, and so is opening a file saved before these switches existed.

Tip

A mission scene is the best reference: import one, and look at how its sectors and portals are arranged.