Switch

Switches are implemented using wall texture names that are built-in to the Doom rendering engine. At initialization time, the engine finds each texture name listed in the “Off” column below (in the TEXTURE1 or TEXTURE2 lump), and links it with the name in the “On” column. When a linedef using a switch texture has a type that can be activated, the texture is replaced by its counterpart when used.

Switches in Doom follow the convention of having a name prefixed by SW1 (for the “Off” version) and SW2 (for the “On” version). However, this is purely a convention; the engine works with a hardcoded list of names, and a pair of custom textures named, for example, SW1DUMMY and SW2DUMMY will not be considered as a switch.

Switches follow a tiered system: all switches present in the shareware version of Doom are expected to be found in the full version; and all switches present in the registered version are expected to also be found in Doom II. However, since a few Doom switches were not used in the Doom II levels, they were replaced by dummies, despite the needed patches for their definition being actually present in DOOM2.WAD.

Animated switches are possible, if a switch texture (on, off, or both) is included in an animation range. This effect is notably used in Final Doom, where to achieve it the textures have not been sorted alphabetically.

Doom switches
The following codes are used in the “Version” column above:
 * S - Shareware
 * R - Registered/Ultimate Doom
 * C - Commercial &mdash; Doom II

Source

 * Unofficial Doom Specs