_             /////    /////   //////  /////   /////
  __ _ _   _  ___ | | _____    //        //  //  //     //      //
 / _` | | | |/ _ || |/ / _ \    /////   /////   ////// //       /////  3.2
| (_| | |_| | (_|||   (  __/       //  //      //     //           //
 \__, |\__,_|\___||_|\_\___|  /////   //      //////   /////  /////

The Most Unofficial Quake Technical Specification.
by Olivier Montanuy, with contributions from
Brian Martin, Raphaël Quinet, John Wakelin, David Etherton and others
April 1, 1996

Warning: This citation is morally challenged.

Ben là, je viens de terminer de lester le corps, tu vois ? [...] Tu vois, il y a un barème quand tu lestes un corps, c'est-à-dire tu fais trois fois son poids. Normalement un homme moyen, comme cette victime-ci, c'est trois fois son poids. Et sinon, par exemple, ça change, hein. Tu vois, pour les enfants ou pour les nains, ça change. Pour un enfant, c'est [...] quatre fois son poids.
-- Body handling specifications, by Ben,
in "C'est Arrivé Près de Chez Vous" ("Man Bites Dog")

List of Contents

1. Introduction
1.1 Legal warning
1.2 Thanks
1.3 A word from the authors.
1.4 For more informations.
1.5 Typing conventions.
2. The PACK files
2.1 The PACK file format
2.2 The Resources files
2.3 The Sound files
2.4 The Code lump
3. The Level Map Models
3.1 Description of .BSP files
3.2 The format of .BSP files
3.3 Level layout definition
3.4 Bsp tree definition
3.5 Pre-calculated geometric entries
3.6 Entities definitions
3.7 Additional informations
4. The Entity Alias Models
4.1 Presentation of Alias Models
4.2 Animating Alias Models
4.3 The Format of .MDL files
5. The Sprites models
5.1 General description of Sprites
5.2 The Format of .SPR files
6. New WAD file
6.1 The format of WAD2 files
6.2 Format of status bar pictures
6.3 Format of console lumps
6.4 Format of palettes
7. The Level Maps
7.1 Description of .MAP files
7.2 The format of .MAP files

1. Introduction

1.1 Legal Warning

Quake and Doom are trademarks of id Software Inc., Mesquite, Texas. This document is not a publication of id Software, who should not be associated with it. id Software will not answer any questions related to this document.

This document is Copyright (C) 1996 by Olivier Montanuy.
All rights reserved.

Permission to use, copy and distribute unedited copies of this whole document is hereby granted, provided that no fee is charged for the use or availability of this document (other than the normal connection costs for on-line services, if applicable). The above copyright notice and this permission notice must be left intact in all copies of this document. Short excerpts of this document may be quoted in discussion groups or mailing list articles, as long as a reference to the full document is given.

Commercial distribution of this document, in whole or in part, requires prior agreement with the author. Commercial distribution includes any means by which the user has to pay either for the support (e.g. book, newsletter or CD-ROM) or for the document itself. Unauthorized commercial distribution is prohibited.

Disclaimer: this document describes the Quake file formats as we understand them, but we cannot guarantee that anything is correct. In fact, we could be totally wrong. We cannot be held responsible for any consequences of the use or misuse of the information contained herein. You have been warned.

1.2 Thanks

A lot of thanks to:

Contributors to this document:

1.3 A word from the authors

This document is an updated version of the Unofficial Quake Specs 3.1, adapted for the Quake Shareware release. This release is not compatible with the previous Quake Test1 release. The .BSP and .MDL file formats have changed.

Though this document is largely the result of hacking, it has been checked against the C code of the Quake utility. Some details could not be guessed by hacking. But the C code is so... special, that it's sometime easier to look at the bytes.

You will need some working knowledge of 3D geometry to understand this specification, and a good deal of patience too, because some (if not all) explanations may not be crystal clear.

Please do not make any full-featured editor working with the Quake shareware release.

Last, if you enjoyed editing Quake, don't forget to support id Software and to buy their products. Help feed John and Mike as they work on the next generation game engine!

The authors.

1.4 For more informations

1.4.1 How to get the last version of the specifications?

The latest version of this document will always be available on the official Quake-editing support site, www.gamers.org.

You will also find it at the following locations:

Other sites will also have a copy of this document (according to the distribution rights stated above) but we cannot guarantee that those sites will have the most recent version. Usually, we upload the new versions on www.stud.montefiore.ulg.ac.be first, then on the other sites on the same day.

1.4.2 Informations about 3D rendering

1.4.3 Cool Quake related pages

1.4.5 Newsgroups

1.5 Typing conventions

All the code structures are written in C, because C is all we talk. Well, it could have been worse. We could have written that specification in French.

0xABCD   = hexadecimal number ABCD, in C convention.
char     = 8 bit signed integer,
u_char   = 8 bit unsigned integer (BYTE),
short    = 16 bit signed integer,
u_short  = 16 bit unsigned integer (WORD),
long     = 32 bit signed integer,
u_long   = 32 bit unsigned integer (DWORD),
float    = 32 bit single precision real (floating point).

2. The PACK files

2.1 The PACK files format

The PACK format is used to emulate a Unix directory arborescence, and to avoid putting some hundreds of files on the user's disk. It is not a compressed format, and it's very similar to the WAD format of DOOM.

2.1.1 The PACK Header

The PACK file starts with a header, that indicates where to find the directory, and the size of that directory. The number of entries can be deduced by dividing by sizeof(pakentry_t) = 0x40

typedef struct
{ u_char magic[4]= "PACK";     // Name of the new WAD format
  long diroffset;              // Position of WAD directory from start of file
  long dirsize;                // Number of entries * 0x40 (64 char)
} pakheader_t;

2.1.2 The PACK Directory

The PACK directory is made of a list of consecutive entries, each with the following format:

typedef struct
{ u_char filename[0x38];       // Name of the file, Unix style, with extension,
                               // 50 chars, padded with '\0'.
  long offset;                 // Position of the entry in PACK file
  long size;                   // Size of the entry in PACK file
} pakentry_t;

At offset diroffset in the PACK file, you will find:

pakentry_t dir[dirsize/sizeof(pakentry_t)];   // Directory

The directory is preferably placed at the end of the PACK file, but it could actually be anywhere. The entries could also be scattered all around the PACK file, leaving large gaps. If you write a PACK hacking utility, you must take care not to introduce too many empty space. Also, you should never assume that the entries are stored in the same order as in the directory (they could be in reverse order, for example). If you want to add some data after the last entry, make sure that you are really at the end of the file.

Since PACK files are a bit like WAD, it is possible to use the same tricks that were used by tools such as DeuSF and NWT to modify the PACK file reversibly. It is hoped, however, that Quake is flexible enough so that this trick is not needed.

2.1.3 Determining the type of PACK Entries

Contrary to the WAD2 files, there is no tag giving the type of each entry. However, they can be safely recognized by the extension, and it's the method used by Quake itself.

.WAV Sound files (RIFF/WAVE)
.BSP levels (map and textures)
.MDL 3D models (Alias)
.SPR Sprite models
.DAT Pseudo-code
.RC Resources
.CFG Config Files
.LMP Lump files
.LMP End screen
.WAD WAD2 file

2.2 The resources files (.RC)

Those files are ordinary Text, in Unix format (LF only, no CR), so they won't display correctly under DOS if you are using an old editor. They contain only settings and definitions.

2.3 The sound files (.WAV)

The sound files are ordinary 16-bit RIFF WAVE files (the format commonly used under Microsoft Windows, and now supported by many utilities under different operating systems).

2.4 The code lump (.DAT)

The .DAT file contains some semi-compiled machine independent P-code, instead of the Quake programming language .QC files.

This file contains the behavior associated to each of the entities. For instance, this file contains the frame table that defines how and when each frame of the Alias Models must be displayed.

This file also contains the light styles used to animate the Faces of the BSP models. Those light styles can be found as strings, among the other character strings.

Here is a very partial description of that data lump. The only interesting part is the list of text strings, because it gives the names of possible spawning sequences for the Entities.

typedef struct
{ long offset;
  long size;
} codentry_t;

typedef struct
{ long  version;               // 3
  long  program;               // offset to start of P-CODE
  codentry_t  table12;         // table of 1 long and 4 short (frames?)
  codentry_t  table12;         // table of 3 long
  codentry_t  table12;         // table of 3 long
  codentry_t  table64;         // Table of 16 long
  codentry_t  strings;         // Character strings, separated by '\0'
  codentry_t  numeric;         // Constants and variable
} codehead_t;

Do not attempt to decompile the QC code: most probably, this language is still totally unstable, so any efforts to hack would be a waste. And id Software will probably provide examples of source code, not only compiled stuff.

2.5 The lump file (.LMP)

There are three kinds of lumps: Palette, colormap, pictures.


This is the game the color palette:

struct { u_char Red, u_char Green, u_char Blue} Palette[256];


This is the precalculated color map, made of 32 tables. each table contains 256 indexes to the actual colors in the colormap.

u_char ColorIndex[32][256];

Phen light level is light and the color is color, the games uses the color index:
c = ColorIndex[ ((light>>3)&0x1F)][color].


These are simple flat pictures, with indication of width and height, that are used for menus, status bar and the like.

typedef struct
{ long width;
  long height;
  u_char Color[width*height];                                       
} picture_t;

2.6 The end screen (.BIN)

A classical DOS text screen, 80x25 with color tags. Same as the end screen in DOOM.

2.7 The config file (.CFG)

A simple text file, that contains the default configuration of keys.

3. Level Map Models

3.1 Description of .BSP Files

3.1.1 General description of level BSP Maps

The BSP maps are meant to be generated automatically. They are described here only for the purpose of helpin you write a BSP generation tool. If you are only interested in building Quake editors, please read the description of Level Maps instead.

The level BSP maps are stored in files with extension .BSP (for Binary Space Partition Tree). Those files need not necessarily contain level maps, they can also contain the definition of any entity that is not supposed to be modified during game play.

Since a BSP based model requires the calculation of a BSP tree, and this calculation is tedious, these models are not used to store definitions of monsters, players, or anything that can change shape during game play. But you could use them for a model of a big rock, because that rock isn't gonna be modified...

Moreover, there are no frames associated to a BSP based model, contrary to what happens for Alias models: it's just one single big frame. So you cannot animate them.

3.1.2 Description of the contents of .BSP files

The .BSP files contain all the information that is needed to display a level correctly, for the obvious reason that those files are meant to be distributed individually, or associated in multi-level maps without causing trouble. In DOOM, you had to take care that all the needed textures were available. Now, the textures are in the level itself.

One disadvantage of that format is that, contrary to DOOM, you cannot have a single set of textures for all your levels, or re-use textures in another level. Now guess why Quake will come on CD-ROM.

Here are the contents of levels:

  1. A list of entities that are present in the level.
  2. A description of the level map, in term of faces, edges, vertices, and textures on the faces. Actually, there might be more faces than really needed, because of the BSP tree that splits them.
  3. Some enormous amount of data to accelerate the rendering of levels, and which must be calculated off-line: a set of planes, models, BSP nodes, clip nodes, BSP leaves, visibility lists, and edge lists, face lists.

The format of level is pretty complicated, don't be disappointed if you don't understand everything on first try. Maybe you can imagine how hard it has been to hack it out of the BSP map.

3.2 The Format of BSP files

Beware: the description below is valid only for the version 0x1C of the BSP file format, used in Quake Shareware version, 22 June 96. Previous version of Quake used different formats. Future versions might differ again.

A BSP file starts with some sort of directory, of fixed size. As a matter of fact, the entries in a BSP file are always at the same place in the directory.

Here is the description of one directory entry:

typedef struct                 // A Directory entry
{ long  offset;                // Offset to entry, in bytes, from start of file
  long  size;                  // Size of entry in file, in bytes
} dentry_t;
Here is the BSP header itself, made of a version tag, and 15 entries:
typedef struct                 // The BSP file header
{ long  version;               // Model version, must be 0x17 (23).
  dentry_t entities;           // List of Entities.
  dentry_t planes;             // Map Planes.
                               // numplanes = size/sizeof(plane_t)
  dentry_t miptex;             // Wall Textures.
  dentry_t vertices;           // Map Vertices.
                               // numvertices = size/sizeof(vertex_t)
  dentry_t visilist;           // Leaves Visibility lists.
  dentry_t nodes;              // BSP Nodes.
                               // numnodes = size/sizeof(node_t)
  dentry_t texinfo;            // Texture Info for faces.
                               // numtexinfo = size/sizeof(texinfo_t)
  dentry_t faces;              // Faces of each surface.
                               // numfaces = size/sizeof(face_t)
  dentry_t lightmaps;          // Wall Light Maps.
  dentry_t clipnodes;          // clip nodes, for Models.
                               // numclips = size/sizeof(clipnode_t)
  dentry_t leaves;             // BSP Leaves.
                               // numlaves = size/sizeof(leaf_t)
  dentry_t lface;              // List of Faces.
  dentry_t edges;              // Edges of faces.
                               // numedges = Size/sizeof(edge_t)
  dentry_t ledges;             // List of Edges.
  dentry_t models;             // List of Models.
                               // nummodels = Size/sizeof(model_t)
} dheader_t;

All the offsets are counted from the start of the BSP files. The size can be 0, if the entry is not present. It must not be negative.

Basic data types

Before we start with the level entry structure, you will need to understand the following data types:

typedef float scalar_t;        // Scalar value,

typedef struct                 // Vector or Position
{ scalar_t x;                  // horizontal
  scalar_t y;                  // horizontal
  scalar_t z;                  // vertical
} vec3_t;

typedef struct                 // Bounding Box, Float values
{ vec3_t   min;                // minimum values of X,Y,Z
  vec3_t   max;                // maximum values of X,Y,Z
} boundbox_t;

typedef struct                 // Bounding Box, Short values
{ short   min;                 // minimum values of X,Y,Z
  short   max;                 // maximum values of X,Y,Z
} bboxshort_t;

scalar_t is a scalar value, that is used to represent X,Y,Z coordinates, or distances. It is a 32bit, single precision floating point number, and it can be expected that in later version it will be replaced by some fixed point number, as is typical in DOS games (because the floating point unit of Intels just amazingly sucks).

vec3_t is a 3D vector, that is used to represent either 3D position in space, or vectors normal to planes. Usually, 3D positions in space will be integer values, though they are coded in floating point. Maybe a hint that the final engine will work only with integer of fixed point values, like DOOM did.

boundbox_t is a set of two vec3_t, that represents a bounding box in 3D space. The first vec3_t stores the minimum values, the second one stores the maximum values. These bounding boxes, though less elegant than a center point and a distance, allow for greater processing speed.

bboxshort_t is a set of six short integer, that represent a condensed form of boundbox_t, the ordinary bounding box.

3.3 Level layout definition

The basic level entries are those that define the geometrical structure of the level; i.e. those are the only ones a level editor should ever bother about.

Actually, this is not totally true, because those entries are intricately related to the BSP tree format, so an intermediate format shall be used, before calculating the BSP tree and the pre-calculated entries.

3.3.1 The Definitions of Models

The name Model refers here to either a big zone, the level, or smaller independent parts inside that zone, like the grid bars on level TEST1, that open with a push on the switch.

The level map is divided in one or more Models, which are independent areas, roughly bounded by two sets of Clip Nodes, and organised internally around a BSP Tree, that contains the BSP Leaves, which are the actual areas where entities can be found (like the sectors in DOOM).

typedef struct
{ boundbox_t bound;            // The bounding box of the Model
  vec3_t origin;               // origin of model, usually (0,0,0)
  long node_id0;               // index of first BSP node
  long node_id1;               // index of the first Clip node
  long node_id2;               // index of the second Clip node
  long node_id3;               // usually zero
  long numleafs;               // number of BSP leaves
  long face_id;                // index of Faces
  long face_num;               // number of Faces
} model_t;

About the Models

The first model is the whole level itself. The other models, smaller, represent door, switches, bars, that might move around the level.

A typical BSP model is only made of one single model, and only the level maps may eventually need more than one model.

About the different fields

The numleafs field is the number of leaves in the BSP tree. It is used to determine how much room each visilists requires when decompressed (better not put a wrong number there).

The node_id field is an index to the first node of the BSP tree that splits the model.

The bnode_id and bnode_id2 field is an index to the first node of two BSP tree that are used for early collision detection. There used to be only one of these trees. The purpose of the second tree is unknown (maybe it's not for collision detection after all).

The face_id and face_num fields refer to all the consecutive faces in the face list that belong to a given model.

Unknown fields

The purpose of the four zero fields is unknown. Apparently, it's not a good idea to use another value than 0 there.

3.3.2 List of Vertices

The vertices definitions are used for Edges, which are part of faces.

The order of vertices in the list is irrelevant.

typedef struct
{ float X;                    // X,Y,Z coordinates of the vertex
  float Y;                    // usually some integer value
  float Z;                    // but coded in floating point
} vertex_t;

The vertices are only used for texture mapping.

There must be only one given vertex definition, for any point in 3D space.

3.3.3 The Edges

This structure stores a list of pairs of indexes of vertices, each pair defining an edge of a face. That edge will generally be used by more than one face (two or three is typical).

Edges are referenced in List of edges, that represent the actual list of edges contained in each face. The edges are not directly referenced in faces, otherwise the face structure could not have a fixed size.

typedef struct
{ u_short vertex0;             // index of the start vertex
                               //  must be in [0,numvertices[
  u_short vertex1;             // index of the end vertex
                               //  must be in [0,numvertices[
} edge_t;

Note that the first edge in the list is never used: as a matter of fact, the List of Edges uses positive or negative numbers to indicate the edge sense, so number zero would be unsuitable.

3.3.4 The Texture Informations

The texture informations define how the textures are rendred on the faces (i.e. the Wall, Floors, Ceilings, Sky, and Water areas).

Since those surfaces can be of complex shape, they are split in simple convex Faces. But then, all those faces have a reference to the same texture information.

typedef struct
{ vec3_t   vectorS;            // S vector, horizontal in texture space)
  scalar_t distS;              // horizontal offset in texture space
  vec3_t   vectorT;            // T vector, vertical in texture space
  scalar_t distT;              // vertical offset in texture space
  u_long   texture_id;         // Index of Mip Texture
                               //           must be in [0,numtex[
  u_long   animated;           // 0 for ordinary textures, 1 for water 
} surface_t;

Texture orientation

The orientation of the texture, on the face, is defined by two vectors S and T) and two offsets along these vectors, distS and distT.
See the explanation of Texture Mapping below.

The animated field is just a boolean that is set to 1 when the texture is to be used with a swirling animated texture, like water, slime or lava. If it is not set to 1 with those textures, the game crashes, complaining that surface extent is invalid.

Mips mapping

The textures are rendered by using Mip Mapping: depending on the distance from the face to the player, a different texture is used for texture mapping, so as to reduce aliasing.

Since the Mip Mapping uses distance as a trigger, the bounding box of all face vertices (i.e. the face extent) must be smaller than 256, for any coordinate. Otherwise it would not be possible to select a Mip Mapping valid for all the texture.

Once the right texture is chosen, the face is rendered as an ordinary texture-mapped convex face.

Texture names

The Mip texture are referenced by texture_id, so that more than 256 textures can be used in a level. But it is expected that the more texture you use, the slower the game will be, so do not use more than 64 without very good reasons.

Depending on the name of the texture, a face will look like a sky, or a wall or floor (that can eventually be animated).

3.3.5 The Face

The face are convex polygons that cover the original surfaces (convex polygons are more convenient for 3D rendering, especially in hardware).

typedef struct  
{ u_short plane_id;            // The plane in which the face lies
                               //           must be in [0,numplanes[ 
  u_short side;                // 0 if in front of the plane, 1 if behind the plane
  long ledge_id;               // first edge in the List of edges
                               //           must be in [0,numledges[
  u_short ledge_num;           // number of edges in the List of edges
  u_short texinfo_id;          // index of the Texture info the face is part of
                               //           must be in [0,numtexinfos[ 
  u_char typelight;            // type of lighting, for the face
  u_char baselight;            // from 0xFF (dark) to 0 (bright)
  u_char light[2];             // two additional light models  
  long lightmap;               // Pointer inside the general light map, or -1
                               // this define the start of the face light map
} face_t;

The faces that lie in the same plane must be stored consecutively, because they will be referenced as a list in the definition of models.

Light level of the faces

The lightmap field is an offset into the Light Maps. If there is no light map, this pointer is -1.

The baselight field gives the base light level for the face, that is the minimum light level for the light map, or the constant light level in the absence of light map. Curiously, value 0xFF codes for minimum light, and value 0 codes for maximum light.

The typelight field indicates the kind of lighting that should be applied to the face:

Note that if you use values 1 to 8, you may wish to set baselight to 0.

Texture mapping

(Warning: texture mapping is totally different from early versions of the BSP model. Forget about those early versions.)

To paint a face with a given texture, it is required that a position (s,t) in texture space be associated to each vertex in 3D space.

But that would make a lot of data, because a given vertex is often used by more than one face, and each one require a special (s,t) coordinate. So it has been prefered to store only the S and T vectors, and to calculate the (s,t) coordinates on the fly, probably when loading the level.

For a given face, the (s,t) coordinates are calculated from the Vertex coordinates and the Texture definitions by a simple dot product with the S and T vectors:

s = dotproduct(Vertex,vectorS) + distS;    
t = dotproduct(Vertex,vectorT) + distT;

In theory, vectorS and vectorT should be orthogonal vectors, and always lie in the face plane (or rather, the face plane), so as to avoid any distortion when mapping the texture onto the face.

Actually, those two vectors are often chosen among the coordinate axis themselves (or their opposite), so that textures in adjacent wall remain naturally aligned, despite the possibly different orientation of the walls. There is distortion of course, but it's limited.

Also, though the skies are ordinary wall textures, they are drawn in a very special way, that make them look like skies. That is probably the same trick as in DOOM: it doesn't take the player position into account when texture mapping, only the orientation of view, so that the sky appears to be far away.

Unknown field

There is one short integer that has not been identified, and experiment showed that its value seems to be ignored by the engine. However, it is safer to put value 0xFFFF there, because this is the default value used in almost every face.

3.3.6 The Mip Textures

The Mip textures definitions are used only in Texture info, and are referenced by index, not by name.

The Mip Texture definition is a structured file, that contains a list of individual Mip Textures, each one accessed via an offset.

typedef struct                 // Mip texture list header
{ long numtex;                 // Number of textures in Mip Texture list
  long offset[numtex];         // Offset to each of the individual texture
} mipheader_t;                 //  from the beginning of mipheader_t

Each individual texture is also a structured entry, that indicates the characteristics of the textures, and a pointer to scaled down picture data.

typedef struct                 // Mip Texture
{ char   name[16];             // Name of the texture.
  u_long width;                // width of picture, must be a multiple of 8
  u_long height;               // height of picture, must be a multiple of 8
  u_long offset1;              // offset to u_char Pix[width   * height]
  u_long offset2;              // offset to u_char Pix[width/2 * height/2]
  u_long offset4;              // offset to u_char Pix[width/4 * height/4]
  u_long offset8;              // offset to u_char Pix[width/8 * height/8]
} miptex_t;

The Mip texture header is generally followed by (width * height) * (85 / 64) bytes, that represent the color indexes of the textures pixels, at different scales. Do not rely on that size however, rather consider the offsets described below.

The pixels are accessed by offsets, with offset1 (resp. 2, 3, 4) pointing to the beginning of the color indexes of the picture scaled by 1 (resp. 1/2, 1/4, 1/8). These offsets are relative to the beginning of miptex_t.

The name of the texture is rather irrelevant, except that:

An individual Mip texture occupies 33% more space than a simple flat texture would. This is the cost of anti-aliasing.

3.4 Bsp tree definition

These are the entries that are related to the BSP tree that is used for rendering the level.

3.4.1 The BSP tree Nodes

The BSP tree nodes are used to partition one model (from the List of models) into a set of independent convex BSP tree Leaves.

All the BSP tree nodes are stored in that same BSP tree node structure, Though there is in fact one BSP tree per model. But of course no index should point to nodes that are part of another BSP tree.

typedef struct
{ long    plane_id;            // The plane that splits the node
                               //           must be in [0,numplanes[
  u_short front;               // If bit15==0, index of Front child node
                               // If bit15==1, ~front = index of child leaf
  u_short back;                // If bit15==0, id of Back child node
                               // If bit15==1, ~back =  id of child leaf
  bboxshort_t box;             // Bounding box of node and all childs
  u_short face_id;             // Index of first Polygons in the node
  u_short face_num;            // Number of faces in the node
} node_t;

Organisation of the BSP tree

The BSP tree nodes are part of a BSP tree, valid only inside a given model.

The front (resp. back) value is the equivalent of the right (resp. left) of node, in DOOM. Actually, even in DOOM it was the front (resp. back) of a linedef, if it had been extended vertically.

If the bit 15 is not set, as detected by (value & 0x8000) == 0, then the number is the index to the front (resp. back) child node.

If the bit 15 is set, then the child is in fact a BSP tree leaf, and the index of this leaf is obtained by inverting all the bits of front (resp. back).

In particular, the value -1 translates into leaf index 0. But actually it means that there is no leaf. Leaf 0 is a dummy leaf, contains no faces, and has a special type (-2) that means the BSP tree rendering must stop.

The role of BSP tree nodes

The nodes are the Quake equivalent of the DOOM nodes and also of the DOOM blockmaps. They are parts of a 3D BSP tree, not a 2D BSP tree like in DOOM.

The nodes are used for level display, placements of entities and second-level collision detections.

The front child node (and all the nodes below it) is entirely contained in the half-space that is in front of the split plane.

The back child node (and all the nodes below it) is entirely contained in the half-space that is in the back of the split plane. (The 'front' and 'back' of a split planes are defined by the plane equation giving a positive or negative result for any given vertex.)

The Bounding Boxes of nodes

The Bounding box of the node is presented in a packed format, bboxshort_t, that only contains short integer instead of floats.

That bounding box slightly exagerates the actual size of the node and all it's childs. Each bounding box boundary seems to be rounded to the next multiple of 16, so that the bounding box is at least 32 units larger than it should be.

That means that the level coordinates must all remain roughly between -32700 and +32700.

3.4.2 The BSP Tree Leaves

The BSP tree leaves are children of BSP tree Nodes and indicate which faces are contained inside a BSP tree leaf.

typedef struct
{ long type;                   // Special type of leaf
  long vislist;                // Beginning of visibility lists
                               //     must be -1 or in [0,numvislist[
  bboxshort_t bound;           // Bounding box of the leaf
  u_short lface_id;            // First item of the list of faces
                               //     must be in [0,numlfaces[
  u_short lface_num;           // Number of faces in the leaf  
  u_char sndwater;             // level of the four ambient sounds:
  u_char sndsky;               //   0    is no sound
  u_char sndslime;             //   0xFF is maximum volume
  u_char sndlava;              //
} dleaf_t;

The first leaf (index 0) is always totally solid, so that in the BSP tree nodes, a value of zero points to a solid leaf (i.e. a leaf that need not be rendered).

The BSP tree leaf contains a reference to a set of consecutive entries in the list of faces.

The bounding box must contain all the faces in the leaf.

The leaf contains an index to the Visibility Lists that describe which other leaves are visible from that leaf. If this index is -1, then all the other leaves are visible.

The tree leaves are the Quake equivalent of the sectors in DOOM. You can imagine them as rooms, or part of rooms, where the monsters, players and object will be placed.

Actually the tree leaves are the equivalent of the Sub Sectors: each sector in DOOM is decomposed by the BSP into smaller and simpler convex sub sectors, that contain only part of the sector lines.

Technically, each tree leaf, made of some faces and bound by the BSP node split lines, appears in 3D space as a convex polytope.

Leaf types

The type field describes what happens when the player is into that precise leaf. Here are the known values (negative):

Note that this field is only taken into account when the player is in the leaf, so if you're in a leaf full of water you'll see the world blurred, but players outside will see you perfectly.

3.4.3 The List of Faces

This structure stores a list of indexes of faces, so that a list of faces can be conveniently associated to each BSP tree leaf.

u_short lface[numlface];   // each u_short is the index of a Face

The list of faces is only used by the BSP tree leaf. This intermediary structure was made necessary because the faces are already referenced by Nodes, so a simple reference by first face and number of faces was not possible.

3.4.4 The List of Edges

This structure stores indexes of edges, possibly inverted, so that faces can be reconstituted.

short lstedge[numlstedge];

All the edges in a face are stored consecutively, with the correct orientation so that all the vertices in the face are walked clockwise.

But since the edges are used for more than one face, there is a trick to ensure that the edge of a given face is always referenced with the correct orientation:

The fact that all edges are walked in a clockwise order is critical for the face rendering process (rasterisation).

The faces are made of just one closed set of edges, or contour. Those edges seem to be always stored in the right order.

3.4.5 Visibility Lists

(Thanks to David Etherton for determining the precise formula)

The visibility lists are used by BSP Leaves, to determine which other leaves are visible from a given BSP Leaf.

The Visibility list can be of size 0, in that case it will not be used. The game will crawl if there is no visibility list in a level.

u_char vislist[numvislist];    // RLE encoded bit array

Basically, the visibility list is an array of bits. There is one such array of bits for each BSP Leaf. They are all stored in the vislist array, and each leaf has an index to the first byte of it's own array

The bit number N, if set to 1, tells that when laying in the tree leaf, one can see the leaf number N.

The only complication is that this bit array in run-length encoded: when a set of bytes in the array are all zero, they are coded by zero followed by the number of bytes is the set (always more than 1).

Normally, the size of the bit array associated to a leaf should be (numleafs+7)/8, but in fact due to the run lenght encoding, it's usually much less.

When the player is in a leaf, the visibility list is used to tag all the leaves that can possibly be visible, and then only those leaves are rendered.

Here is an example of decoding of visibility lists:

// Suppose Leaf is the leaf the player is in.
v = Leaf.vislist;
for (L = 1; L < numleaves; v++)
    if (visisz[v] == 0)           // value 0, leaves invisible
        L += 8 * visisz[v + 1]    // skip some leaves
    else                          // tag 8 leaves, if needed
        for (bit = 0x80; bit > 0; bit = bit / 2, L++)
            if (visisz[v] & bit)

There is no necessity to unpack the visibility list in memory, because the code to read them is fast enough.

If you put a few badly placed zero bits in the visibility lists, some of the leaves will turn into totally grey areas, and that's rather funny. If you put all bits to zero for a given leaf, then every player in that sector will become temporarily blind: he will get a fully grey screen. I wonder what use you can make of this in level design, though. If only it had been black...

The visibility list structure is the Quake equivalent of the REJECT map of DOOM, except that now it's also used for level rendering. It eliminates leaves that can't be seen, whereas in DOOM it was just use to speed up monster line of sight calculations.

3.5 Pre-calculated geometric entries

Those entries can all be automatically calculated from the Level layout definition, and are not related to the Bsp tree definition.

Do not confuse the Clip Nodes with the BSP tree nodes, they are not used for the rendering of the level.

3.5.1 List of Planes

The plane definitions are used for faces, BSP Nodes, Clip Nodes.

The order of planes in list is irrelevant.

typedef struct
{ vec3_t normal;               // Vector orthogonal to plane (Nx,Ny,Nz)
                               // with Nx2+Ny2+Nz2 = 1
  scalar_t dist;               // Offset to plane, along the normal vector.
                               // Distance from (0,0,0) to the plane
  long    type;                // Type of plane, depending on normal vector.
} plane_t;

Plane types:

The planes are used as split planes in the BSP tree nodes, and as reference plane in the faces.

They are the Quake equivalent of the DOOM Linedefs and Segments.

The planes are defined by a normal vector and a distance. This normal vector must be of norm 1.

The plane equations are used for distance calculation and to determine if a given vertex (of a face, or an entity) is on the front side or the back side of the plane.

Some of the planes, especially the first ones in the list, are not associated to any face, but rather to BSP nodes split planes. So they show numsurf = 0.

There must be only one given plane definition, for any plane in 3D space. That's because the calculations of the translation and rotation of plane normal vector are cached, so if you put redundant planes definitions you'll contribute to slowing down the engine. Definitely not an option.

3.5.2 The Clip Nodes

This structure is used to give a rough and somewhat exaggerated boundary to a given model. It does not separate models from each others, and is not used at all in the rendering of the levels

Actually, the clip nodes are only used as a first and primitive collision checking method.

The clip nodes are much simpler than the BSP nodes, so it makes collision detection faster, most of the time. In the same idea, DOOM defined a BLOCKMAP for faster collision detection.

typedef struct
{ u_long planenum;             // The plane which splits the node
  short front;                 // If positive, id of Front child node
                               // If -2, the Front part is inside the model
                               // If -1, the Front part is outside the model
  short back;                  // If positive, id of Back child node
                               // If -2, the Back part is inside the model
                               // If -1, the Back part is outside the model
} clipnode_t;

The engine starts from the top bound node as defined in the Model.

There is no bounding box defined for those nodes, because the bounding box is that of the model bounding boxes.

If you modify a clip node, for instance by changing the plane definitions or by putting -1 values for each child, then the model becomes totally pass-through. That's a very funny special effect.

The Clip Nodes do not tightly bound a model, so you should never use planes from the model as clip node split planes. Actually, the clip node planes should be distant from the model by at least 16 in X,Y, and 24 in Z.

Also take care that the Clip Node planes should be oriented toward the exterior of the model, not the interior. If you change the orientation, then the player can go through the model as if it did now exist... even falling through the floor.

3.5.3 The Light Maps

The light maps are special arrays that indicate the brightness of some points in the Mip Texture pictures.

Different light maps can be associated to each face, so that two faces with similar textures can still look different, depending on the light level.

The light maps are simply:

u_char lightmap[numlightmap];  // value 0:dark 255:bright

Light levels

The u_char value that the lightmap gives at any point is directly a light level value, from 0 to 255. If you put zero, it will be utter darkness, and if you put 255 if will be totally bright.

The formula for calculating light level is something like:

light(X,Y,Z) = lightmap(X,Y,Z) * lightstyle(typelight, time) - baselight
where, as a rough explanation:

Note that the textures's color and light are translated into a final color by using a pre-calculated color palette. Direct RGB calculations would be too costly and not very suitable for 256 color displays. This is the same trick as used when gouraud shading the Alias models.

Translation of lightmaps into 3D space

Well the exact formula seems rather hard to determine experimentally, so don't expect this explanation to be accurate.

The size and layout of a lightmap, on texture space, is not related to the texture but only to the face extent, in 3D space. You can change the texture without having to recalculate light maps.

Each light maps seem to be stored as a simple

u_char light[width*height];
where width and height are determined by the extents of the faces's bounding box, i.e. the bounding box of all the vertices contained in that face (or, rather, all the Edges).

Since such a bounding box is essentially 3D, and the lightmap is only 2D, one coordinate has to be discarded. The coordinate to remove depends on the orientation of the face's plane, as given by the Plane Type.

This mapping from 3D to 2D, by discarding one coordinate, is exactly the same as the one used for Texture Mapping the faces. You can probably consider the lightmaps as ``alpha-channel textures'' which modify the intensity of the real textures on which they are applied.

Note that the extents of the bounding box (i.e. the difference between maximum and minimum values) must be divided by 16 to give the width and height, because a lightmap value is only calculated every 16 steps, for every coordinate.

Calculating only every 16 steps make the radiosity calculation 256 times less tedious, and ensures that the lightmap will look nice and smooth on the face (because bilinear interpolation is used between known lightmap values).

Unknown Fields

I'm aware that the above explanation is rather obfuscated, and may not cover all cases. It's savagely hacked out of some experimental results and some considerations on the convenience of calculations.

Note also that the lightmap are oriented in regard to the 3D coordinates, and do not seem to care about the face orientation. So if you modify a lightmap, chances are that your modifications will happen is some unexpected place (like, at the bottom instead of at the top...).

Last, in case you wonder where the lightstyle table is defined, the answer is: no idea.

3.6 Definition of entities

(Thanks to John Wakelin who wrote most of this section)

The entities define the monsters, things, but also the positions in space where something must happen. So they are the Quake equivalent of both the THINGS and the LINEDEF types from DOOM.

The entities are defined in the .BSP file in a series of simple text blocks as shown below.

The entity definitions are made up of a series of specific details that define what each is, where it starts, when it appears etc. Each specific is followed by a modifier that arguments it. All definitions have the classname specific that identifies that entity. The classname specifics relate intimately with the code lump and are the names of functions written in Quake C.

3.6.1 Format of entities definitions

I have chosen the terms ``specific'' and ``arg'' for the two different parts of each detail of the definition. These terms may or may not suit but, they will have to do until we learn what id calls them.

Line feeds (ASCII 0x0a) separate each definition and each line in the definition. Spaces (ASCII 0x20) separate specifics from args. I tried changing them around and it does not seem to matter what separates them as long as it is white space.

The specifics and args are contained within double quotes. Each definition is bounded by curly braces.

Like so:

    "<specific>" "<arg>"
    "<specific>" "<arg>"

3.6.2 Possible specifics

specifics args Description
classname <name> Type of entity to be defined (mandatory)
origin # # # coordinates of where it starts in space
angle # direction it faces or moves (sometimes in degrees)
light # used with the light classname (how bright?)
target <t#> Matches a targetname & would appear to work
targetname <t#> like a linedef tag
wad <filename> ??? - The world
spawnflags # Used to flag the definition of an object that is to be different than the default behavior or type for a classname. See item_health for a good example of this
model *# Tag to a moving shape/model (see Models)

The following specifics are found only with the models.

specifics args Description
speed # How fast the model is moved
wait # How long a pause between completion of movement and return to the original position (in seconds I think)
lip # Seems to be a means of adjusting the starting position of model
style # I am guessing that it is like the spawnflag arg in that it may determine a different than default type.
dmg # How much damage the model causes when it shuts on you?

3.6.3 Classnames

The following classnames are the name of a function in the Code Lump.

Note these are only the names that are known to work currently, but later versions of Quake will probably use different names.

Classnames Associated specifics Description
worldspawn wad ??? Pointer to a .wad file
angle -
light origin Light source
light Brightness -sometimes no light level is specified (default?)
info_player_start origin Player starting coordinates
angle -
info_player_deathmatch origin Deathmatch start coordinates
angle -

Weapons - take the origin additional specific (and sometimes angle but I don't see why)

weapon_supershotgun Double barrel
weapon_nailgun Nailgun
weapon_supernailgun Chain Nailgun
weapon_grenadelauncher Grenade Launcher
weapon_rocketlauncher Rocket Launcher
weapon_lightning Lightning Gun (?)
weapon_superlightning Chain Lightning Gun (?)

These monsters appear to take the origin and angle specifics, but they might also take other specifics as well.

monster_knight Slashes at you with sword
monster_demon1 Jumps on you... then server crashes (out of area???)
monster_wizard Shoots ``caco'' lightning balls at you ... deadly aim
monster_shambler terrifying 10 foot tall beast with 3 clawed hands
monster_ogre Chainsaw *and* nailgun
monster_army looks like an untexture-mapped player
monster_tarbaby Blobbish thing that jumps up at you when close
monster_fish Swims after you ... should prob be in water
monster_serpent Looks like an untexture mapped stingray (crashes)
monster_dragon Nice looking Wayvern ... (crashes)
monster_vomit Untextured blob ... scary and fast
monster_zombie Untextured humaniod ... (crashes)

Items - Take the origin and spawnflags additional specifics

item_health 25% with spawnflag 1(default)
100% with spawnflag 2
13% with spawnflag 3 (huh?)
item_armor1 100% Armor (blue)
item_armor2 150% (yellow)
item_armorInv 200% (red) - why didn't they use spawnflags here?
item_shells Shotgun shells (ammo for shotguns)
item_spikes Nine inch Nails (ammo for nailguns)
item_rockets Rockets (ammo for grenade and rockt launchers)
item_cells (ammo for lightning weapons presumably)
item_key I assume it is a key but the game crashes hard if it is hacked in
misc_barrel exploding barrel filled with lava
misc_explobox exploding tall gray box
misc_explobox2 exploding short square box

These entities are always associated with models via targetnames.

info_teleport_destination origin Teleport landing coordinates
angle -
targetname Same as trigger target
path_corner origin -
target Where the train came from
targetname Where to send it next
These are used to define the path of a func_train such as the one above the main room in test2.

Models - These classnames are used with the model-type of entities

func_door door
func_door_secret secret door
func_button button
func_plat Lifts
func_train Sliding platforms
func_dm_only Teleporters that only show up in deathmatch (may work with other things but, no examples here)
trigger_teleport teleporter entrance (walk-over)
trigger_multiple Multiple actions that are activated by a walk over rather than button type of switch.
func_illusionary illusion: visible, but cannot be touched.

Note: The term model specifies an entity that controls the actions of a model and its parameters. Do not confuse it with ordinary entity models.

The model numbers (*x) comes from the order in which the models are stored in the models structure.

The first model (*0) is a bounding box that defines the extents of the whole world. The rest (starting at *1) make up the models.

The models are defined by a bounding box of the max and min(x,y,z). Therefore they are always parrallel to the horizontal planes. This would seem to exclude any ramp-like structures that move.

The specific classname, eg. func_button, tells Quake what type of action to set up for this model. The rest of the specifics in the model definition are arguments to the function refered by the classname and define things like: what direction to move, how long to wait between multiple actions, what tag to use to associate the action with another model, how much damage it will inflict if it closes on you, etc.

For more information, take a look in appendix A, that contains a list of known models.

3.7 Additional Informations

3.7.1 Texture names

(Thanks to Stephen Crowley for experimenting with the names)

The names of textures can contain up to 16 characters.

The animation of the texture is entirely determined by it's name: there are three special names, that make different animations. All the other names mean that the texture is not animated.

Here are the animated textures:

Currently, no other combination works.

When displaying an animated texture, the lightmap and light levels are not taken into account. Those textures are always rendered at full brightness, probably because the face cache would be saturated if every animation frame had to fit into it.

Note that sky textures have an extent that make them too big to display as an ordinary wall texture, and that if you turn an ordinary texture into a sky texture, it will look fairly weird.

Also, for some strange reason, bit 4 of the face flags is set when the texture is supposed to be animated. If you replace an animated texture by an ordinary texture, and forget to set this bit to zero, then there will be an error like: SurfExtent>256.

3.7.2 Texture Anti-aliasing

This is an attempted explanation for the curious structure of the Mip Texture.

The sampling theorem states that when you sample any signal (sound, picture, anything) the highest frequency contained in this signal must be at most one half of the sampling frequency. If there is any frequency above that, the sampling process will map it into a lower frequency, thus creating a terrible mess into the sampled signal. This mess is called Aliasing.

When you try to display a picture on a smaller space, you increase all the frequencies contained in that picture, and thus risk Aliasing. That's basically what happened in DOOM at long distance.

Now, all you need is only to low-pass filter the picture, with a cut frequency equal to half the sampling frequency. Easy! But... There is no DSP on the video memory, so those calculations would take too much time. It's much easier to pre-calculate 4 scaled down pictures, that can be used across the most common range of scales:
infinity-1, 1-1/2, 1/2-1/4, 1/4-1/8.
Below 1/8, there will be some aliasing...

4. The Entity Alias Models

(Thanks to Brian Martin who clarified most of this section)

Alias models can be used for entities, like players, objects, or monsters. Some entities can use sprite models (that are similar in appearance to those of DOOM, though the structure is totally different) or even maybe models similar to those of the levels.

Importing models from 3DS or the likes is now quite easy. You'll just have to work out a few things on your own (like calculation of the vertex normals, matching them with the vertex normal table, finding the bounding area of the object, and scaling the vertices to 8-bit values).

4.1 Presentation of Alias Models

You need not bother too much about the way Alias Models are rendered, just keep in mind that the more simple the model, the faster the game will be.

Here is an attempt at describing what the different parts of the model represent. This description is a bit outdated, though.

First imagine a wireframe model of the entity, made of triangles. This gives the general shape of the entity. For instance, imagine you have the general shape of a cow, made of triangles in 3D space.

The 3D vertices define the position of triangles, and contrary to level models, there is no need for elaborate stuff like nodes, planes, faces. Only triangles and vertices.

Now, there is something missing: the skin. A cow without skin looks pretty ugly.

Imagine that you have a flat carpet made of the skin of an unlucky cow. All you need to do is put some parts of this carpet at the relevant place on the wireframe model of the cow, and you'll get a fairly realistic (though a bit polygonal) cow. Actually, you will need two carpets: one for the upper part and one for the lower part.

For each triangle in the wireframe model of the cow, there will be a corresponding triangle cut from the skin picture. Or, in other words, for each 3D vertex of a triangle, there will be a corresponding 2D vertex positioned on the skin picture.

It is not necessary that the triangle in 3D space and the triangle on the skin have exactly the same shape (in fact, it is not possible for all triangles) but they should have shapes roughly similar, to limit distortion and aliasing.

By the way: there is no Mip mapping on the Alias models, so they don't look very good in distance, which is not too bad since they are constantly supposed to be moving or changing. If you want then to look fine, do them with BSP models. But then they won't move.

4.2 Animating Alias models

The Alias Model animation is based on frames (in DOOM, sprites were also animated by frames). So the deformations are defined once and for all, and there is no skeletal model or any similar physical model involved in the deformations... well, at least not in real time.

Once the general shape of the model (for instance, a cow) is defined, and the skin is mapped correctly on that shape, animation is pretty straightforward: just move the triangles around and it will seem to move.

To move the triangle, you need only modify the position of the 3D vertices that are part of it. For instance, to move the leg of the cow, you will move the vertices that define the endpoints of the legs. You will also move the other vertices a bit, so that the movement looks less mechanical.

Chances are that creating a fine looking animation is gonna be a very tough job, a bit like with the DOOM sprites. I would bet that the quality of the animation will be the most critical point.

Note that the animation consists only in changing vertex positions (and that's why there is one set of vertices for each animation frame).

The skin of the cow is not modified, neither are the definition of the triangles. If you want blood stains to appear on the skin, you'll have to hide the original triangle, by reducing it or by putting another triangle in front.

As remarked by Bernd Kreimeier, this method is similar to the trick squids use when they want to change color: their skin is made os small areas, of two different colors, and they can reduce or enlage them at will.

Along the same idea, if you want parts of the models, like head, weapons and the like, to go flying away when they are cut, then they must be defined using parts of the skin that are separate from the parts used for the body.

Or you can use separate models, like the player gibs, but then the original part must be reduced to a very small size.

4.3 Alias Model .MDL file format

The .MDL files are collection of lumps, but contrary to .BSP files there are no pointers to access the lumps directly, and it is suspected that there will be, in future versions of the models.

Once you have the file header, you can find all the other parts, just by calculating their position in the file.

A Model file contains:

  1. A skin texture, that describes the color of the skin and clothes of the creature, or whatever it can be wearing.
  2. A list of skin vertices, that are just the position of vertices on the skin texture.
  3. A list of triangles, the describe the general shape of the model.
  4. A list of animation frames.
    Each frame holds a list of the 3D vertices and the index of the precalculated vertex normal.

4.3.0 Alias Model Header

Here is the format of the .MDL file header:

typedef struct
{ long id;                     // 0x4F504449 = "IDPO" for IDPOLYGON
  long version;                // Version = 6
  vec3_t scale;                // Model scale factors.
  vec3_t origin;               // Model origin.
  scalar_t radius;             // Model bounding radius.
  vec3_t offsets;              // Eye position (useless?)
  long numskins ;              // the number of skin texture
  long skinwidth;              // Width of skin texture,
                                            must be multiple of 8
  long skinheight;             // Height of skin texture
                               //           must be multiple of 8
  long numverts;               // Number of vertices
  long numtris;                // Number of triangles surfaces
  long numframes;              // Number of frames
  long synctype;               // 0= synchron, 1= random
  long flags;                  // 0 (see Alias models)
  scalar_t size;               // average size of triangles
} mdl_t;

The size of this header is 0x54 bytes (84).

4.3.1 Alias Model Skins

The model skins are flat pictures that represent the texture that should be applied on the model. There can be more than one skin, though usually there is only one.

The structure of model skins

The structure of the skin is similar to the structure of Sprites textures.

You will find the first skin just after the model header, at offset baseskin = 0x54. There are numskins skins to read.

Each of these model skins is either a single picture (type=0) or a group of pictures (type!=0).

If the skin is made of a single picture, the structure is:

typedef struct
{ long   group;                // value = 0
  u_char skin[skinwidth*skinheight]; // the skin picture
} skin_t;

If the skin is made of a group of pictures, the structure is:

typedef struct
{ long group;                  // value = 1
  long nb;                     // number of pictures in group
  float time[nb];              // time values, for each picture
  u_char skin[nb][skinwidth*skinheight]; // the pictures 
} skingroup_t;                                                 

The skin pictures

The skin pictures are a table of u_char, which represent an index in a color table. It is suspected that index 0xFF is not a color, but an indication of transparency.

The width of skins must be a multiple of 4, to ensure long word alignement.

Those pictures are usually made of at least two pieces: one is used for the front of the model, the other for the back of the model.

Actually, there may be as many pieces as there are independent parts in the model. For instance, for the player, there are two pieces that defines the body, and two others that define the gun.

Note that the back skin of a given model part must be on the same height, but translated width/2, relatively to the front skin part. The back skin part must also be inverted along the vertical axis.

This design is used to allow the correct rendering of a seamless skin texture, using Skin Vertices with onseam == 0x20, on the skin border.

4.3.2 Alias Model Skin Vertices

A .MDL file is made of a list of vertices. To each of these vertices corresponds a 3D position, a normal, and a position on the skin picture, for texture mapping.

The list of skin vertices indicates only the position on texture picture, not the 3D position. That's because for a given vertex, the position on skin is constant, while the position in 3D space varies with the animation.

The list of skin vertices is made of these structures:

typedef struct
{ long onseam;                 // 0 or 0x20
  long s;                      // position, horizontally
                               //  in range [0,skinwidth[
  long t;                      // position, vertically
                               //  in range [0,skinheight[
} stvert_t;

s and t are (X,Y) position on the skin picture.

onseam is a flag, and if non zero it means that the vertex is on the boundary between the skin part that is applied on the front of the model, and the skin part that is applied on the back of the models (i.e. on the edge).

If a vertex is onseam, but is part of a triangle that is on the back side of the model (facesfront is 0), then skinwidth/2 must be added to s so as to find the actual value of s.

The skin vertices are stored in a list, that is stored at offset offset baseverts = baseskin + skinsizes:

stvert_t vertices[numverts];

skinsizes is the sum of the size of all skin pictures.

4.3.3 Alias Model Triangles

An Alias Model is made of a set of triangle facets, with vertices at the boundaries. Triangles should all be valid triangles, not degenerates (like points or lines).

Only vertices index are stored in triangles. the normal vector of the surface is reconstituted from the vertex position.

Here is the structure of triangles:

typedef struct
{ long facesfront;             // boolean
  long vertices[3];            // Index of 3 triangle vertices
                               // in range [0,numverts[
} itriangle_t;

Note that the index of a given vertex is the same in the skin vertex table and in the frame table.

At offset basetri = baseverts + numverts * sizeof(stvert_t) in the .MDL file, you will find:

itriangle_t triangles[numtris];

The boolean facesfront indicates if the triangle is part of the front or the back skin. 1 means that it is on the front skin, 0 means that it is on the back skin.

When the triangle is on the back skin, then any skin vertex that is on the skin seam (as indicated by onseam=1) must have it's s coordinate increased by skinwidth/2.

As a matter of fact, on the skin picture, the back skin is always situtated at the same level as the front skin, but moved by skinwidth/2 to the right (check this, with any model).

The following code might make this easier to understand:

  for(j=0; j < numtris; j++)
    for(i=0; i < 3 ; i++)
      vertex = triangles[j].vertices[i]
      s = vertices[vertex].s;
      t = vertices[vertex].t;
      if( (vertices[vertex].onseam) && (!triangle[j].facesfront))
        s += skinwidth / 2;
      /* use s and t as the coordinates of the vertex*/

4.3.4 Alias Model Frames

An Alias Model contains a set of animation frames, which can be used in relation with the behavior of the modeled entity, so as to display it in various postures (walking, attacking, spreading its guts all over the place...).

This frame structure is rather complex to figure out, because:

The frame vertices

Each frame vertex is defined by a 3D position and a normal for each of the vertices in the model.

typedef struct
{ u_char packedposition[3];    // X,Y,Z coordinate, packed on 0-255
  u_char lightnormalindex;     // index of the vertex normal
} trivertx_t;

To get the real X coordinate, from the packed coordinates, multiply the X coordinate by the X scaling factor, and add the X origin. Both the scaling factor and the origin can be found in the Model Header.

The formula for calculating positions is:

vec3_t position[i] = ( scale[i] *  packedposition[i] ) + origin[i]
Where scale, and origin can be found as vectors in the Model Header.

The vertex normals

The lightnormalindex field is an index to the actual vertex normal vector. This vector is the average of the normal vectors of all the faces that contain this vertex.

This information is necessary to calculate the Gouraud shading of the faces, but actually a crude estimation of the actual vertex normal is sufficient. That's why, to save space and to reduce the number of computations needed, it has been chosen to approximate each vertex normal.

The ordinary values of lightnormalindex are comprised between 0 and 161, and directly map into the index of one of the 162 precalculated normal vectors that can be found in Appendix B.

Value 255 is sometimes used in models, but this is a bug. Only values 0 through 161 should be used.

The simple frames

The simple frames can come standalone or in groups (see below). They always have the same structure:

typedef struct
{ trivertx_t min;              // minimum values of X,Y,Z
  trivertx_t max;              // maximum values of X,Y,Z
  char name[16];               // name of frame
  trivertx_t frame[numverts];  // array of vertices
} simpleframe_t;

The size of each simple frame is sizeframe = 0x18 + numverts * trivertx_t;.

The number of vertices is numverts, and to each of the vertex declared here corresponds a Skin Vertex with the same index.

The frame header contains two vertex definitions, min and max, that define a bounding box around the whole frame: all the other vertices must be inside that bounding box.

However, that bounding box is only used for collision detection, so if you make it smaller than it should be the model will still display fine, but you can get very close to it before hitting it.

To get the floating point values corresponding to min and max, treat them as if they were ordinary vertex positions.

The frames

These are the actual animation frames, made of a single frame, or a group of single frames, with timing indication.

The beginning of the frames can be found in the .MDL file, at offset baseframes = basetri + numtris * sizeof(itriangle_t);.

Each frame must be read separately, since they may not have a constant size.

If the frame is made of one simple frame:

{ long type;             // Value = 0
  simpleframe_t frame;         // a single frame definition

If the frame is made of a group of simple frames:

{ long type;                   // Value != 0
  trivertx_t min;              // min position in all simple frames
  trivertx_t max;              // max position in all simple frames
  float time[nb]               // time for each of the single frames
  simpleframe_t frames[nb];    // a group of simple frames

Unknown fields

The first filed of the header is always zero, and there's no explanation for it. It cannot be a time stamp, since frame animations is in fact coded in the Code lump.

The lightnormalindex of min and max have irrelevant values, and are apparently not used. They only pad the structure to 4 bytes.

5. The Sprite models

(Thanks to Raphaël Quinet who wrote most of this section)

General description of Sprites

The sprites are used in Quake to represent objects that could not be rendered properly using polygons (because of a shape with too many small details) or that were not worth the trouble of using polygons (they render faster than Alias models or BSP based models).

The sprites are essentially designed for stuff like explosions, fire, magical effect, or the like. They can also be used for simple objects that have a vertical axis of rotation, like torches or barrels.

The format of the sprites is rather simple. Basically, this is a list of 2D pictures (flat bitmaps) organized in lumps.

Some frames are grouped in animation sequences, that start with the first picture in the animation and automatically proceed to the next, at the time values indicated in the beginning of the sequence.

5.2 The Format of .SPR files

The sprite files (.SPR) begin with a header, which is immediately followed by the list of frames. There are no pointers to the individual pictures, which means that the engine probably reads and parses the whole file once and for all, because the only way to access a given picture is to read all previous frames and know their width and height.

5.2.1 Sprite file header

Here is the format of the .SPR file header:

typedef struct
{ char name[4];                // "IDSP"
  long ver1;                   // Version = 1
  long type;                   // See below
  float radius;                // Bounding Radius
  long maxwidth;               // Width of the largest frame
  long maxheight;              // Height of the largest frame
  long nframes;                // Number of frames
  float beamlength;            // 
  long synchtype;              // 0=synchron 1=random
} spr_t;

The size of this header is 0x24 bytes.

Type of sprites:

5.2.2 Sprite frames

There are two types of frames. Most of them contain a single picture, but some of them (in s_torch.spr and shots.spr) contain multiple pictures associated with floating point values.

The first kind of frames are marked with a leading (long) zero, followed by the picture data:

  long group;                 // Always 0 for single-picture frames
  picture pic;                 // Picture data, see below

The second kind of frames are marked with a leading 0x1 or 0x10000000, followed by the number of pictures, a list of floating point values, and a list of pictures:

  long group;                  // not zero (0x1 or 0x10000000)
  long npics;                  // Number of pictures
  float times[npics];          // 0.0, 0.2, 0.3, ...
  picture pic[npics];          // Pictures

The times are offsets that describe when the corresponding picture shall be displayed, relative to an animation frame that repeats regularly. 0.0 means start of the animation frame, and 1.0 is the end. So if you have npics pictures, and want a regular sequence of pictures, you will start from 0.0 and regularly increase the dates by 1/npics.

By the way... the above is just a wild guess. But what the heck can it be, if it's not time stamps?

5.2.3 Pictures

The format of each individual picture is given below. It contains the X and Y offsets, the width and height of the picture, followed by the list of pixels. The reference to the Quake palette is implicit and the value 0xFF denotes a transparent pixel.

typedef struct
{ long ofsx;                   // horizontal offset, in 3D space
  long ofsy;                   // vertical offset, in 3D space
  long width;                  // width of the picture
  long height;                 // height of the picture
  char Pixels[width*height];   // array of pixels (flat bitmap)
} picture;

6. The WAD2 files

The WAD2 format is only used for the graphic .WAD, that stores general information like the palette and the status bar items.

It is believed that this format was the original distribution file intended for Quake, but since then id Software probably realised they needed a file format that allowed a more direct mapping of their development directories, so they chose the PACK format instead.

6.1 The format of WAD2 files

The structure of the WAD2 files is almost exactly the same as that of DOOM's PWAD and IWAD files. Only the size of the directory entries is a bit different.

6.1.1 The WAD2 file header

typedef struct
{ u_char magic[4];             // "WAD2", Name of the new WAD format
  long numentries;             // Number of entries
  long diroffset;              // Position of WAD directory in file
} wadhead_t;

6.1.2 The WAD directory

The entries in the WAD2 directory are a bit bigger than in PWAD and IWAD:

typedef struct
{ long offset;                 // Position of the entry in WAD
  long dsize;                  // Size of the entry in WAD file
  long size;                   // Size of the entry in memory
  char type;                   // type of entry
  char cmprs;                  // Compression. 0 if none.
  short dummy;                 // Not used
  char name[16];               // 1 to 16 characters, '\0'-padded
} wadentry_t;

At offset diroffset in file, you will find the WAD directory itself:

wadentry_t dir[numentries];        // like in DOOM

This directory then contains pointers to all the entries in the WAD2 file, and like with PACK file there can be large amounts of unused data, if one is not careful enough when building WAD2 files.

6.1.3 Determining the type of directory entries

The field type in the directory identifies the entry. It's a single byte, which give 256 possibilities. Only 3 are currently used.

0x40= '@'= Color Palette
0x42= 'B'= Pictures for status bar
0x44= 'D'= Used to be Mip Texture
0x45= 'E'= Console picture (flat)

6.2 Format of status bar pictures

The pictures will probably used for everything concerning the status bar (animations, numbers, ...). They are not used for sprites, countrary to DOOM.

These files are just like DOOM flats, but with a header to indicate width and height.

typedef struct
{ long width;                  // Picture width
  long height;                 // Picture height
  u_char Pixels[height][width]
} pichead_t;

6.3 Format of console lumps

The console lumps are just flat pictures, similar to DOOM flats, without any formatting, and using one byte per pixel. The color palette is that of the PALETTE lump.

The console background:

char  Screen [200][320];       //This means it's a 320x200 array
The console characters:
char  CChars [128][128];       //This means it's a 128x128 array

6.4 Format of Palettes

All the pictures, textures, sprites and Alias model skins use color indexes in a 256-color table, and it can be expected that only a limited set of color palettes will be used. Maybe just one. At least, it's pretty sure that there is only one color palette for all the textures.

This format is Exactly the same as in DOOM:

struct RGB {char R; char G; char B;} Palette[256];
Internally, the color palette is translated into a much bigger structure, that takes into account the light level, just like in DOOM. This structure depends on the number of colors available on the display, so it might be calculated by the engine at startup.

7. The Level Map files

7.1 Description of Map Files

7.1.1 General description of the Map format

The Map format describes a single level of Quake, in a very robust and very simple manner. This format is meant to be used by Quake editors, though you can edit it by hand (provided you've got special 3D hardware in your brain).

The Map cannot directly be used by Quake: Once complete, it must be transformed into a BSP Level Map. This transformation is known to require a lot of processing power, a lot of memory, and a lot of time.
Those tools calculate the BSP tree, the set of visibility lists, the shadows on each textures, and put the textures into the level BSP file.

This is rather complicated, but the advantage is that there is no possibility to create invalid level layout, by mistake.

Appendix A. Model Examples

These examples of the model types may help to explain their use a little better. They were extracted from the three levels included in QTEST1.

A.1 Map TEST1

ModelsModel Bounding box Co-ordinates
  "model" "*1"
  "angle" "-2"
  "classname" "func_door"
  "targetname" "t2"
min: x = 412, y = 1352, z = -144
max: x = 428, y = 1368, z =  -24

  "model" "*2"
  "angle" "-2"
  "classname" "func_door"
  "targetname" "t2"
min: x = 448, y = 1352, z = -144
max: x = 464, y = 1368, z =  -24

  "model" "*5"
  "classname" "func_button"
  "target" "t2"
min: x = 500, y = 1240, z = -104
max: x = 512, y = 1256, z =  -88

These are the columns that block the path to the teleport. *1 is the left column (looking from outside the room by the button) and *2 is the one one the right. *5 is the button that lowers the two columns.

Note the targetname t2 for both columns and the same one for the button (model *5) This is what ties the button to the lowering of the columns.

The angle specific here describes the direction to move the column. Changing it to "0" moves the column to the right instead of down (looking at it from by the button). The angle is in degrees for objects moving parallel to the normal line of sight but for movements perpendicular to this ``horizontal plane'', "-1" and "-2" are used for up and down respectively.

Note: When the angle of model *1 was changed to "-1", it moved up instead of down... After jumping through the teleporter the column could be seen protruding though the floor upstairs. This is important in that it showed that the model was in fact a 3D object that is simply being moved in the manner defined and not just some textures being manipulated in such a way as to make them appear to be solid.

ModelsModel Bounding box Co-ordinates
  "model" "*3"
  "target" "t1"
  "classname" "trigger_teleport"
min: x = 244, y = 1576, z = -136
max: x = 284, y = 1624, z =  -40

  "targetname" "t1"
  "angle" "90"
  "origin" "448 1028 16"                   
  "classname" "info_teleport_destination"
  "light" "250"
(Not a model, just a target)

Model *3 is the teleporter. The target specific points it to the info_teleporter_destination entity with the same tag (t1).

ModelModel Bounding box Co-ordinates
  "model" "*4"
  "classname" "func_door_secret"
  "angle" "180"
min: x = 448, y = 668, z =   8
max: x = 512, y = 684, z =  88

This is the ``secret'' door that leads out onto the ledge with the 100% health. Again the angle just tells the function which way to move it.

ModelModel Bounding box Co-ordinates
  "model" "*6"
  "classname" "func_door"
  "angle" "180"
  "spawnflags" "1"
  "targetname" "t3"
  "speed" "175"
  "wait" "8"
min: x = -304, y = 1360, z = -16
max: x =  -64, y = 1472, z =  -4

  "model" "*7"
  "classname" "func_button"
  "target" "t3"
  "angle" "-2"
  "lip" "4"
  "wait" "10"
min: x = -400, y = 1564 z =  -4
max: x = -344, y = 1616 z =   4

These are the bridge to the 150% armor and the button on the floor that causes it to extend. Note the lip arg in model *7, this defines the starting position in some way related to the surface that the model is being moved into or out of.

It is also notable that the buttons are activated by touch (walking over this one is as good as bumping model *5. Presumably you could put a button on the ceiling and have the player jump up into it.

A.2 Map TEST2

There are a lot of models/models in test2 (lots of moving stuff) and it is here that we start to see some of the real possibilities inherent in the engine.

ModelModel Bounding box Co-ordinates
  "model" "*7"
  "speed" "200"
  "classname" "func_door"  
  "angle" "0"
  "targetname" "t3"
  "spawnflags" "4"
  "dmg" "1000"
min: x = 1112, y = -1024, z =   0
max: x = 1240, y =  -832, z = 112

  "model" "*9"
  "speed" "200"
  "dmg" "1000"
  "targetname" "t3"
  "angle" "180"
  "spawnflags" "4"
  "classname" "func_door"
min: x = 2120, y = -1024, z =   0
max: x = 2248, y =  -832, z = 112

These are the walls that make up the two crushing traps on either side of the starting room that allow you to kill anyone who goes for the yellow armor in the cages.

Here is the first use of the dmg arg that defines how badly it hurts you if it closes on you. There are some doors that will hurt you slightly (3-5%) if they catch you as they are closing. There might be a default dmg value for certain types of doors but, clearly, setting this at 1000 as it is here, will kill you in one hit.

ModelModel Bounding box Co-ordinates
  "model" "*11"
  "target" "t4"
  "classname" "func_train"  
min: x = 1792, y = -1064, z = 304
max: x = 1888, y =  -984, z = 320
  "target" "t5"
  "targetname" "t4"
  "origin" "1792 -1064 304"
  "classname" "path_corner"
(Not a model, just a target)
  "target" "t4"
  "targetname" "t5"
  "classname" "path_corner"
  "origin" "1472 -1064 304"
(Not a model, just a target)

This is that sliding platform that goes back and forth above the starting room and carries you to the grenade-launcher and back again.

The model is the ferry itself and I have included it's two path_corners that define the extents of its route. The thing to note here is how the targets are set up pointing to each other's targetname to keep the platform moving to and fro. I imagine that if you were to set up a series of these corners, that just kept pointing to the next one in line, that you could have one of these things follow a long complex path through the level.

ModelModel Bounding box Co-ordinates
  "model" "*1"
  "classname" "func_door"
  "angle" "180"
  "targetname" "t1"
min: x = 1392, y = -1272, z = -16
max: x = 1696, y =  -840, z =  -4

  "model" "*2"
  "classname" "func_door"
  "angle" "0"
min: x = 1696, y = -1272, z = -16
max: x = 2000, y =  -840, z = -4

  "model" "*3"
  "classname" "func_button"
  "angle" "90"
  "target" "t1"
min: x = 1288, y = -832, z = 16
max: x = 1336, y = -816, z = 56

  "model" "*4"
  "spawnflags" "4"
  "targetname" "t1"
  "classname" "func_door"
  "angle" "270"
  "wait" "4"
min: x = 1632, y = -1408, z = -16
max: x = 1760, y = -1288, z =  -4

  "model" "*5"
  "classname" "func_door"
  "spawnflags" "4"
  "angle" "90"
  "targetname" "t1"
  "lip" "0"
  "wait" "4"
min: x = 1632, y = -824, z = -16
max: x = 1760, y = -688, z =  -4

  "model" "*8"
  "target" "t1"
  "angle" "90"
  "classname" "func_button"
min: x = 2024, y = -832, z = 16
max: x = 2072, y = -816, z = 56

Models *1 and *3 somehow define the targetname for model *2.

These are all the definitions that handle the two buttons in the yellow armor cages and the four floor surfaces that they cause to open. Notice that there are only five target/targetname specifics (t1) in the group.

Every once in a while, when calling two models into action, one of the targetnames will be missing. It turns out that you can wrap at least one targetname-less model in between two models that are targeted at one another. Quake, apparently, will assume that you mean to apply the action to the middle one as well.

ModelModel Bounding box Co-ordinates
  "model" "*25"
  "targetname" "t15"
  "angle" "180"
  "classname" "func_door"
min: x = 2336, y = -568, z = 32
max: x = 2400, y = -552, z = 96

  "model" "*26"
  "classname" "func_door"
min: x = 2400, y = -568, z = 32
max: x = 2464, y = -552, z = 96

  "model" "*27"
  "target" "t15"
  "classname" "trigger_multiple"
min: x = 2336, y = -616, z = 56
max: x = 2464, y = -560, z = 64

Here is another example of the dropped targetname whilst wrapping, using the trigger_multiple classname. This is the small double doors that let you out of the secret room with the red armor. Model *27 is walk-over activated (as are all triggers) and opens the doors when you approach them.

ModelModel Bounding box Co-ordinates
  "model" "*31"
  "classname" "func_plat"  
min: x = 1248, y = -704, z = 160
max: x = 1392, y = -576, z = 320

func_plats are the elevator/lifts that automatically rise as you step on them. If they have the angle arg included it would seem to be an indicator of the direction from which it is activated.

A.3 Map TEST3

ModelModel Bounding box Co-ordinates
  "model" "*5"
  "classname" "func_dm_only"  
min: x = 1184, y = -960, z = -48
max: x = 1200, y = -848, z =  48

  "model" "*6"
  "classname" "func_dm_only"
min: x = -576, y = -496, z = -40
max: x = -560, y = -400, z =  64

Map three is the only one that has these ... these models are obviously the two teleporters that are only available during deathmatch.

Appendix B. Table of normal vectors

This table is used in the Entity models to code the normal vector of each vertex, in each frame (the lightnormalindex value).

Since it doesn't seem to be derived from a regular polygon, there is no known formula to calculate it, so we can only list here all the values.

Take care to normalise all those vectors to 1, before using them.

To select the right vector from the list, just take the one whose dot product with the actual normal vector of the vertex gives the greater positive result. It's not too important that it differs a bit from the actual normal vector of the vertex, Gouraud shading tollerates a fair bit of imprecision.

Note: since this table is defined in the QBSP source, you had better get it from there (in file anorms.h). The table below was hacked out before QBSP was released.

vector_t normals[162]=