Lag clipping


Lag clipping is a glitch which occurs in versions of Doom based on the Atari Jaguar version, including Doom 64. Due to changes in how player logic is handled which separate that handling from the rest of the game loop, causing the game to lag (that is, run at a lower frame rate than the version's target, which varies by version) causes clipping operations to be performed on the player at a lower than normal rate. As a result, the player can move through otherwise solid walls, and occasionally through multiple widely spaced walls at a time, when sufficient lag is generated. The more lag, the larger the distance becomes in which the player's motion may ignore intervening linedefs.

A lag clip is usually performed by firing a hitscan weapon (the shotgun or super shotgun, the latter being available in the Sony PlayStation port and in Doom 64) at point blank against a wall. The resulting overlapping bullet puff sprites which spawn cause lag both via mobj processing and through increased overdraw in the renderer.

Lag clips are useful for taking shortcuts in the game, and can also be exploited to trigger another console-exclusive glitch, linedef deletion. In addition, a lag clip is a critical part of triggering an early victory condition in Doom 64 which causes the game to end after MAP30: The Lair.