Used by the routines at DEC_DZ_AND_UPDATE_UVZ and MOVE_PLAYER.

Every moving object's move comes through here: the robot's from MOVE_PLAYER, everything else's from DEC_DZ_AND_UPDATE_UVZ. It takes the steps in U, V and Z (+$09 to +$0B) and shortens each where the object would otherwise end up below the floor, through a wall, or inside another object, then writes them back. The code is Knight Lore's and Pentagram's.

The axes are done one at a time, Z first, then U, then V, and each test counts the moves already accepted on the earlier axes and the later ones as zero. That is what lets a blocked move slide: walking diagonally into a wall keeps the part of the move that runs along it.

While it works, bit 1 of +$07 is set, which makes the object scans (IS_OBJECT_NOT_IGNORED) pass over the object itself; found already set, it returns at once. Bits 0-2 of +$0C are cleared at the start and set for each axis whose move was cut.