Used by the routine at FIRST_PILLAR.

Only the player's legs, record 0, can use a doorway, and only while their graphic is one of 16 to 47 -- which leaves out the puff he becomes when he dies -- and bit 3 of the flags is set. In the doorway (IS_NEAR_TO, with the limits the pillar gives), bit 0 of the legs' flags is set: while it is, the collision code (ADJ_FOR_OUT_OF_BOUNDS) lets him past the line of the wall, and PLAYER_LEGS clears it again at the end of his next update. Then one of four routines (SCREEN_MOVE_TBL), by the way he faces, decides whether he is wholly past the wall he faces.

This is Knight Lore's doorway check and its exit check in one. Knight Lore marks the player in the doorway from the arch and decides the exit in the player's own move; Pentagram leaves the move alone (EXIT_STUB) and decides here, from the player's position after his move rather than from his position plus the step. The room's half-sizes (ROOM_EXTENT) are pushed for the four, because the dispatch uses HL.