Player stuck on ledge after restoring savefile

In games based on the Doom engine it is possible for the player to become stuck in ledges when restoring their game from a save file. This is due to a difference in how the Z coordinate is chosen for spawning the player from a save, and how it is determined at runtime when the player moves between sectors.

During normal motion, the player will be set to the highest floor height contacted by any part of the player's bounding box. This keeps the player from becoming stuck into any lower sidedefs of contacted linedefs and makes for natural motion through the level. However, when a save file is restored, the player is simply placed at the floor height of the sector in which the player's midpoint is located, ignoring any other sectors contacted. This can result in becoming stuck and is particularly an issue when saving while in contact with tall or narrow ledges, such as those found in, a place that many players first encountered this bug.

Many source ports repair this by doing a full bounding box test for contacted sectors after spawning the player from a save.

Trivia

 * It is possible to obtain the ordinarily impossible secret #4 in by saving while in contact with the teleporter but with the player's midpoint in the secret sector and then loading the save. In Nessus, it is similarly possible to use this technique, in conjunction with a jump through an arch-vile (present solely in the Ultra-Violence and Nightmare! skill levels), to register the map's only secret.