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Wallhacking is the changing of wall properties in first-person shooters. Most wallhacks are used to make a map's walls at least partially transparent, allowing players to see through opaque objects. Wallhacking is usually considered cheating, analogous to maphacking in real-time strategy games, and can lead to kicks and bans from online game servers if discovered.

Many FPS games provide weapons such as grenades that can kill unseen players, but such explosives rely on splash damage rather than direct hits. However, in a game like Call of Duty 4: Modern Warfare, certain guns can shoot through walls, rifles in particular. This allows them to see the enemy and kill them instantly, unseen.

Other types of wallhack include "wallwalk", in which players become able to see through and walk through walls. Sometimes referred to as "ghostmode", this hack enables sneak attacks on anyone walking by the wall, as the player inside the wall is essentially invisible.

Contents 1 History 2 Methodology 3 References 4 See also

[edit] History

The first wallhack to appear was for Quake by id Software and simply an exploit/extension of the intent to provide transparency only to certain textures^[1][2] -- like lava and water -- which in the software version and original GL versions of Quake were opaque. The methodology employed was to alter (VIS) the map file to have transparent walls -- in addition to lava and water -- rather than make use of an external program or software patch. Generally, only games released after the second-generation Quake-engine games detect and block direct modification to game content to prevent that method of wallhacking, as GL-capable video cards had reached a mass-market price-point.

[edit] Methodology

Valve's Half-Life brought wallhacks into more common use, with both Team Fortress Classic and Counter-Strike modifications for which wallhacks were available. The earliest wallhack for Half-Life — and similar games — worked by making everything partially transparent. Since game engines rarely do accurate occlusion checking and instead rely on the graphics hardware's depth buffer to do so, the player was able to see through walls to the objects that would normally not be visible. The major drawback of this method was a lack of clarity — some players found that the transparency of every surface made it hard to discern individual objects to the extent that they would occasionally walk into walls or try to shoot players through a wall. This is known as the Flautz-style wallhack after first encountered in a cheat by a programmer known as Flautz.

Slightly later wallhacks for Half-Life worked by hooking into the game engine's call to the OpenGL API function glBegin to check if the engine was about to render a triangle or a quad -- game entities and player characters are drawn with triangles, while level geometry is drawn with quads. If the wallhack detected a triangle was about to be rendered, it would call glDisable(GL_DEPTH_TEST) to prevent the graphics hardware from performing a depth-buffer comparison before rendering each pixel. In this way, the wallhack would cause game characters and game entities to appear on top of all map geometry (walls, floors and ceilings) regardless of their logical position within the world. One drawback of this method was that the lack of depth-testing on game entities and characters meant they were often rendered incorrectly, with the back-most polygons of a model being rendered before the front-most ones because they were sent through the graphics pipeline last. This is often known as the XQZ-style wallhack because it was first popularized in a cheat called XQZ2.

The most recent Half-Life wallhacks produce an effect almost identical to the XQZ-style wallhack without the visual corruption by taking advantage of the render queue of Half-Life-based mods. Half-Life renders all map geometry first, then game entities and characters. Thus, there is a period of time when map geometry is fully rendered but rendering of entities has not begun. The wallhack effect is achieved by clearing the depth buffer at this point, so that all game entities are then drawn onto what the graphics hardware believes is a clear screen. Depth-testing is not disabled, so the game entities and characters are still depth-checked against each other, but are not depth-tested against the game world, since that information has been cleared from the depth buffer. The result is that game entities and characters appear on top of map geometry regardless of their logical position within the game — but because they are still depth-tested against each other, there is no corruption of entity models as there is with the XQZ-style wallhack. Because of their similarity and lack of corruption, this method is known as Perfect XQZ.

Wallhacks for other games, such as Quake 3 or Battlefield 1942, usually use similar methods to those used in Half-Life. Even in games that use shaders for all rendering instead of the fixed-function pipeline, the GPU still handles depth-testing internally for most operations and the same techniques remain relevant. Advances in the way scenes are ordered and sent through the render pipeline may require slight changes in wallhack methods in order to differentiate between map geometry and game objects. Both OpenGL and Direct3D provide similar depth buffer and depth-testing functionality and neither one is significantly easier or harder to wallhack.

In 2001, ASUS released drivers for their graphics cards which allowed wallhacking. ^[3]

[edit] References

[edit] See also

• Aimbot
• Occlusion culling
• Cheating in online games
• Exploit (online gaming)