MD2 is a model format used by id Software

Id Software

Id Software is an American video game development company with its headquarters in Richardson, Texas. The company was founded in 1991 by four members of the computer company Softdisk: programmers John Carmack and John Romero, game designer Tom Hall, and artist Adrian Carmack...

's id Tech 2 engine and is thus used by Quake II

Quake II

Quake II, released on December 9, 1997, is a first-person shooter computer game developed by Id Software and distributed by Activision. It is not a sequel to Quake; it merely uses the name of the former game due to Id's difficulties in coming up with alternative names.The soundtrack for Quake II...

 as well as many other games, most of them using this engine, including SiN and Soldier of Fortune. The format is primarily used for animated player models although it can also be used for static models. Unlike more recent character model formats, MD2 animations are achieved via keyframes on a per-vertex level; the keyframes are stored within the model file and the engine interpolates between them to create a smooth animation.

File format

An MD2 file begins with a fixed length header followed by static model data such as texture coordinates.
Dynamic data such as vertices

Vertex (computer graphics)

A vertex in computer graphics is a data structure that describes a point in 2D or 3D space. Display objects are composed of arrays of flat surfaces and vertices define the location and other attributes of the corners of the surfaces.-Application to object models:In computer graphics, objects are...

 and normals

Surface normal

A surface normal, or simply normal, to a flat surface is a vector that is perpendicular to that surface. A normal to a non-flat surface at a point P on the surface is a vector perpendicular to the tangent plane to that surface at P. The word "normal" is also used as an adjective: a line normal to a...

 are stored within a number of file chunks called frames (or key-frames) which each have their own short headers.

In defining the file structure several data types will be referred to.

int (4 bytes), short (2 bytes), and char (1 byte)

MD2 Header

Offset	Data type	Name	Description
0	int	ident	Magic number. Must be equal to "IDP2"
4	int	version	MD2 version. Must be equal to 8
8	int	skinwidth	Width of the texture
12	int	skinheight	Height of the texture
16	int	framesize	Size of one frame in bytes
20	int	num_skins	Number of textures
24	int	num_xyz	Number of vertices
28	int	num_st	Number of texture coordinates
32	int	num_tris	Number of triangles
36	int	num_glcmds	Number of OpenGL OpenGL OpenGL is a standard specification defining a cross-language, cross-platform API for writing applications that produce 2D and 3D computer graphics. The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes from simple primitives. OpenGL... commands
40	int	num_frames	Total number of frames
44	int	ofs_skins	Offset to skin names (each skin name is an unsigned char[64] and are null terminated)
48	int	ofs_st	Offset to s-t texture coordinates
52	int	ofs_tris	Offset to triangles
56	int	ofs_frames	Offset to frame data
60	int	ofs_glcmds	Offset to OpenGL commands
64	int	ofs_end	Offset to end of file

At the offset ofs_st there are num_st of this structure:

Data type	Name
short	s
short	t

The texture coordinates are multiplied by the texture's size and so are always integers.

To recover the floating-point texture coordinates as used by common 3D display API's such as OpenGl, divide the texture coordinates by the respective size dimensions of the texture:

sfloat = (float)s / texturewidth
tfloat = (float)t / textureheight

At offset ofs_tris there are num_tris of the following structure

short vertexindex[3]
short textureindex[3]

These are indexes to the vertexs and texture coordinates and tell the engine reading the file how to build primitives from the data.

At offset ofs_frames frame data is stored, each frame has a short header followed by a number of vertex and Surface-normal indexes, the frame header structure is like this:

float scale[3]
float translate[3]
char name[16]

Then there is num_xyz of this structure:

unsigned char v[3]
unsigned char lightnormalindex

Each vertex is stored as an integer. To recover the floating-point vertex coordinates, the MD2 reader multiplies each coordinate by the scaling vector for the current frame and then adds the frame's translation vector:

float x = (v[0] * scale[0]) + translate[0]
float y = (v[1] * scale[1]) + translate[1]
float z = (v[2] * scale[2]) + translate[2]

The frames scale and translation vector can be found in the frame's header.

Example

This is an example of how to decompress a single frame and display it. Its not in any specific programming language to try and make it easy for every one to interpret. variables have $ before them and their type

loop while $(int)index is less than $(int)num_tris

texture_function_s $(float)texture_coordinates[ $(short)triangle[ $(int)index ].textureindex[0] ].s / skinwidth
texture_function_t $(float)texture_coordinates[ $(short)triangle[ $(int)index ].textureindex[0] ].t / skinheight

normal_function $(unsigned char)vertex[ $(short)triangle[ $(int)index ].vertexindex[0] ].lightnormalindex

vertex_function_x ($(unsigned char)vertex[ $(short)triangle[ $(int)index ].vertexindex[0] ].v[0] * scale[0]) + translate[0]
vertex_function_y ($(unsigned char)vertex[ $(short)triangle[ $(int)index ].vertexindex[0] ].v[1] * scale[1]) + translate[1]
vertex_function_z ($(unsigned char)vertex[ $(short)triangle[ $(int)index ].vertexindex[0] ].v[2] * scale[2]) + translate[2]

$(int)index = $(int)index + 1
end loop

Resources

• The Quake II's MD2 file format
• [ftp://ftp.idsoftware.com/idstuff/source/quake2.zip Quake2 Source]