Invisible wall

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An invisible wall is a video game term for a boundary that limits where a player can go, but doesn't appear in game as any kind of visible obstacle; it's as if someone built a glass wall in an open area—you can't see the wall, but it's there. The term can also be applied to minor obstacles, ones that appear to be a nuisance and could be bypassed if encountered in real life, but are treated as impassable obstructions in the game. For example, in some games the main character cannot swim, so any water is an obstacle, including small puddles of water, even though in real life one could walk right through such an obstacle. Other examples include short fences or moderately sized rocks.

In 2D games, the screen itself was an "invisible wall", as a character could not go off screen; if the game world extended past the visible screen, then it would scroll when the player tried to go in that direction, otherwise the player would be stopped.

In 3D games, developers would draw beyond the boundary of the playable world in order to give some background and to create the illusion of an expansive world. However, actually creating the world itself is a time consuming task, so developers would limit where the player could go, since there is really nothing out there. Developers could build a realistic obstacle to keep players in the boundaries of the game world, but sometimes this can be tedious and having random objects in the way can destroy the illusion of a large world; as such, some developers take the quick route, and simply bar players from going in a particular direction with an invisible wall.

In some games however, both 2D and 3D, those imposed boundaries can sometimes be broken either by cheating, or as a result of a programming bug or glitch. The results may vary: either the player will be able to move in an "unreachable" or "auxiliary" area of the game used e.g. for allowing objects to move "inside" the main playfield or containing unused items or portions of a level. More often, the game will encounter an error and crash, or an overflow-wraparound effect may occur, making the player appear in a random or opposing part of the game's world. This can also be a form of cheating.

Some examples include:

• In the 3D First person shooter game Doom, using a "no clipping" cheat enables the player to freely move not only around the visible part of the current map, but even beyond it, at least up to the limit imposed by the coordinate system of the game itself, which is the only true "invisible barrier". In the latter case, the first person perspective display becomes corrupt, while the map mode still correctly tracks the player's movements.

• In the famous Super Mario Bros. NES game, a hidden world can can be accessed by exploting a game glitch allowing the player to reach a normally hidden and unreachable although the boundary actually visible in this case.

• In the vertically scrolling NES game Front Line, due to a programming glitch the player can continue moving sideways of the screen beyond the intended "playfield" area, causing the graphic tiles to become corrupted and enabling the player to slip past most enemies, who won't follow him into the glitchy "void". The actual "invisible wall" is not where the player is (normally) supposed to be playing, but extends farther to the left and right sides of the screen.

• Also, in the game Battlefield 1942, while a player is normally prevented from exiting a map's boundaries with a timed death penalty, in certain circustances those barriers can be violated (e.g. by using the free flying camera mode, using an unusually high speed vehicle or finding an unusually "thin" boundary area) and will result in a map wrap-around effect (the player will emerge on the oppossing part of the map).

• In the 2005 shooter Mercenaries: Playground of Destruction, "resricted areas" were constantly bombed areas keeping the player from reaching the edge of the map. However, with use of the in-game invincibility code or anything rendering the player invincible, they could venture into these areas to find the landscape simply ends, with an invisible wall preventing the player from exiting the game's boundaries.