WAD3 Structure: Difference between revisions

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==Introduction==
#redirect [[WAD#Technical_specifications]]
The following file specification concerns the [[WAD3]] file format used {{valve|4|addtext='s}} famous {{goldsrc|4|nt=1}}. The file extension is "[[.wad]]". Contrary to the [[BSP30|BSP]] v30 file format that has been derived from the [[Quake 1]] [[BSP29|BSP]] (v29) format, the [[WAD3]] format is tecnically fully compatible with [[Quake]]'s [[WAD2]] files. [[WAD]] files are used to store game related files in some kind of archive. Somehow they seem to contain only textures, although they are capable of holding different kinds of data.
 
This file spec uses constructs from the C programming language to describe the different data structures used in the [[WAD]] file format. Architecture dependent datatypes like integers are replaced by exact-width integer types of the C99 standard in the ''stdint.h'' header file, to provide more flexibillity when using x64 platforms. Basic knowledge about textures in the [[BSP]] file is recommended.
{{Tint|color=green| #include <stdint.h>}}
 
== Directory entries ==
The directory of a [[WAD]] file is basically an array of structures. Every archived file has an associated entry in this directory:
<source lang=cpp> #define MAXTEXTURENAME 16
 
typedef struct _WADDIRENTRY
{
    int32_t nFilePos;            // offset in WAD
    int32_t nDiskSize;          // size in file
    int32_t nSize;              // uncompressed size
    int8_t nType;                // type of entry
    bool bCompression;          // 0 if none
    int16_t nDummy;              // not used
    char szName[MAXTEXTURENAME]; // must be null terminated
} WADDIRENTRY;
  </source>
 
The first value is the offset of the raw data of the archived file within the [[WAD]] file followed by the size of data used by the it in its current form. Additionally ''nSize'' stores the size of original file, if it has been compressed. This is indicated by the bCompression boolean value. If it is false, no compression is used which is mostly the case. The ''nType'' member would give as information about the type of file, that is associated with this entry. As [[WAD]] files usually contain only textures, this information may be ignored. The ''nDummy'' short integer is not used when loading textures and i have not found any information about this member. Finally the entry contains a name for the file which can be a string of maximum 16 chars including the zero termination. In case of textures, this is the name referred by the ''BSPMIPTEX'' structs of the [[BSP]] file.
 
==Files in a WAD File - Textures==
The actual files in the [[WAD]] archive, the textures, also start with a file header which may look familiar:
 
<source lang=cpp> #define MAXTEXTURENAME 16
#define MIPLEVELS 4
typedef struct _BSPMIPTEX
{
    char szName[MAXTEXTURENAME];  // Name of texture
    uint32_t nWidth, nHeight;    // Extends of the texture
    uint32_t nOffsets[MIPLEVELS]; // Offsets to texture mipmaps BSPMIPTEX;
} BSPMIPTEX;</source>
 
This struct equals the one of the [[BSP]] file exactly. The name of the texture as not needed actually, as it equals the file name in the directory entry. The next members are of particular interest. They give the size of the texture in pixel as well as the offsets into the raw texture data. The first value of the offset array points to the beginning of the original texture relativly to the local header (the ''BSPMIPTEX'' struct). From this point follows a ''nWidth'' * ''nHeight'' bytes long array of indexes (0-255) pointing to colors in a color table. The other three offsets are used the same way, but with the diference that the width and height of the image are cut in half with every further offset. These represent the so-called [[mipmap]] levels of the original image. After the last byte of the fourth [[mipmap]] there are two dummy bytes followed by the actual color table consisting of an array of triples of bytes (RGB values) with 256 elements. The indexes of the image are plugged into the color table array to receive the corresponding RGB color value for the pixel.
 
== External Links ==
* [https://hlbsp.sourceforge.net/index.php?content=waddef WAD3 Specifications] at Source Forge
[[Category:GoldSrc]]

Latest revision as of 21:50, 5 December 2023

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