Firstwall

Every sector has one of its walls specially designated as its firstwall, which controls the orientation of the sector's floor and ceiling. The firstwall is important for three major reasons:

1. When the floor or ceiling texturing is set to "relative", the texture will be placed parallel to the firstwall.
2. Ceiling and floors slope upwards and downwards from the firstwall.
3. In the blastable wall effect, the game engine closes the hole at the start of the level by lowering the ceiling to the floor at the firstwall.