Difference between revisions of "WAD"

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"Virtual" lumps (such as '''F_START''') only exist in the directory, having a size of 0. Their offset value therefore is nonsensical (often 0).
 
"Virtual" lumps (such as '''F_START''') only exist in the directory, having a size of 0. Their offset value therefore is nonsensical (often 0).
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It is therefore possible for more than one lump to have the same offset value.
  
 
==Lump order==
 
==Lump order==

Revision as of 17:47, 16 March 2006

WAD (which, according to the Doom Bible, is an acronym for "Where's All the Data?" [1]) is the file format used by Doom and all Doom-engine-based games for storing data. A WAD file consists of a header, a directory, and the data that makes up the resources stored within the file. WADs can be either IWADs or PWADs.

Header

A WAD file always starts with a 12-byte header. It contains three values:

Bytes Content
0x00-0x03 The ASCII string "PWAD" or "IWAD". Defines whether the WAD is a PWAD or an IWAD.
0x04-0x07 An integer specifying the number of lumps in the WAD.
0x08-0x0b An integer holding a pointer to the location of the directory.

All integers are 4 bytes long in x86-style little-endian order. Their values can never exceed 231-1, since Doom reads them as signed ints.

Directory

The directory associates names of lumps with the data that belong to them. It consists of a number of entries, each with a length of 16 bytes. The length of the directory is determined by the number given in the WAD header. The structure of each entry is as follows:

Bytes Content
0x00-0x03 An integer holding a pointer to the start of the lump's data in the file.
0x04-0x07 An integer representing the size of the lump in bytes.
0x08-0x0f An ASCII string defining the lump's name. Only the characters A-Z (uppercase), 0-9, and [ ] - _ should be used in lump names (an exception has to be made for some of the Arch-Vile sprites, which use "\"). The string must be null-padded up to 8 bytes long where necessary.

Tools should not assume the lump-order in the WAD to be sorted by their byte offset into the WAD.

"Virtual" lumps (such as F_START) only exist in the directory, having a size of 0. Their offset value therefore is nonsensical (often 0).

It is therefore possible for more than one lump to have the same offset value.

Lump order

The majority of lumps have no restrictions on where they must be located in WAD files, although there are typically some guidelines to make the file easily readable by other people. For certain lumps, however, the location is crucial.

Map data lumps

A map in Doom is made up of several lumps, each containing specific data required to construct and execute the map. The first lump gives the internal name of the map. In Doom, this had to be in the form ExMy or MAPxx, where x and y could not exceed 4 and 9 respectively (Ultimate Doom), and xx could not exceed 32 (Doom 2/Final Doom). Other than defining the name of the map, the lump is usually empty but can contain data. The level name marks the start of this map. In order to work properly, the following lumps must follow immediately after the the level name:

  • THINGS: A lump listing all the Things present in this map, their X, Y, and Z coordinates, starting angles, type, flags, special, and args. As with all of these lumps, this list will be generated by your level editor and should generally be left alone. Note: The standard Doom format does not contain Z and args.
  • LINEDEFS: A list of linedefs, defined by their starting and ending vertices, flags, type, tag, args, and front and back sidedefs (if any). Note: The standard Doom format does not contain args.
  • SIDEDEFS: A list of the sidedefs that are linked to the linedefs. These contain the data for what textures appear where on the side of each line, their X and Y offsets, and what sector this side of the linedef belongs to.
  • VERTEXES: A list of each vertex in the map, using X and Y coordinates.
  • SEGS: A list of line segments called "segs" that connect to form subsectors. Created by a node builder.
  • SSECTORS: A list of subsectors, created by a node builder.
  • NODES: The node tree which Doom uses to speed up the rendering process. Similar to a vismap in modern 3D games (such as Quake 3). Created by a node builder.
  • SECTORS: Defines the floor and ceiling heights and textures, as well as light value, tag, and type of each sector in your map.
  • REJECT: Optionally compiled by the node builder, this lump contains data about which sectors are visible from which other sectors. Originally, Doom used this to optimize the game speed by skipping AI routines for enemies whose target was in a rejected sector. Some modern source ports do not require this lump any more; ZDoom for example has been designed to work even without this lump present. For compatibility purposes, an empty (0-filled) REJECT lump should be included if nothing else. The REJECT lump can also be used to create certain special effects (sectors into which enemies cannot see, for example) if modified carefully.
  • BLOCKMAP: Collision-detection information which determines whether objects in a map are touching.
  • BEHAVIOR: Not originally a part of Doom, the BEHAVIOR lump was first used in Hexen and contains the compiled scripts that this map will use. Vanilla Doom and other ports designed for Doom only will crash when this lump is present because Hexen format levels are not compatible with Doom format levels. This lump must be present for Hexen format levels since it is the only way to tell if a map is in Hexen or Doom format.

Flats, Sprites, and Patches

These three resources must be located between special marker lumps so that Doom knows what it is looking at. Other than defining the beginning and end of a graphics section, these lumps contain no data and are 0 bytes long.

The markers consist of names X_START and X_END, where X is the first 1 or 2 letters of the appropriate resource. For example, sprites should be located between S_START and S_END markers. SS_START and SS_END are usually used for user WAD files. Similarly, flats are F_START and F_END (FF_START and FF_END in user WAD files). Patches are not required to have any markers. Some lump management utilities require P_START and P_END.

Miscellaneous

Some lumps are known by their names and apply to the game as a whole. Some of these are:

  • Sound effects
  • Music
  • PLAYPAL: Color palettes for various situations.
  • COLORMAP: Map to adjust pixel values for reduced brightness.
  • ENDOOM: Text displayed when vanilla Doom exits.
  • TEXTURE1, TEXTURE2, PNAMES: Data defining the wall textures.
  • DEMOs: Recorded games, auto-played before any level is started.