Animated walls 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 "First" column below (in the TEXTURE1 or TEXTURE2 lump), and links it with all following texture names up to and including the name in the "Last" column. At rendering time, a linked texture name in a sidedef of a wall is changed to the next linked name about three times a second, wrapping around to "First" after "Last". (Scrolling walls are another form of animation; any wall with any texture can be made scrolling by assigning the appropriate linedef type.)
Technical list of animated flats
In the Doom games, the built-in animated walls are:
|BLODGR1||BLODGR4||R||4||Green slime oozing from PIPE6 wall|
|BLODRIP1||BLODRIP4||R + 2||4||Blood oozing from PIPE1 wall|
|FIREBLU1||FIREBLU2||R + 2||2||Fire on blue wall|
|FIRELAV3||FIRELAVA||R + 2||2||Fire on red wall1|
|FIREMAG1||FIREMAG3||R + 2||3||Fire on brown wall|
|FIREWALA||FIREWALL||R + 2||3||Brush fire|
|GSTFONT1||GSTFONT3||R + 2||3||Blood flowing from mouth of green stone gargoyle|
|ROCKRED1||ROCKRED3||R + 2||3||Red rock|
|SLADRIP1||SLADRIP3||S + R||3||Green slime draining from grate|
|SFALL1||SFALL4||2||4||Green slime falls|
|DBRAIN1||DBRAIN4||2||4||Similar to lava, used for the exposed brains of the final boss|
- There is a FIRELAV2 texture in the IWADs, but due to its position it is not in the sequence defined by the table.
- There are no WFALL textures in the Doom or Doom II IWADs, though John Romero released a set of waterfall textures during the 2015 Doom source data release. The Plutonia Experiment defines some waterfall textures (though these are simple palette swaps of BFALLx), and TNT: Evilution has a set of multi-purpose textures.
- PWADs can replace the TEXTURE1 and TEXTURE2 lumps, as well as individual wall patches. Thus the number of frames, and of course the description, can vary from the table above.
The following codes are used in the "Version" column above:
In Heretic, the built-in animated walls are: