MD2 (file format)

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MD2 is a model format used by id Software's id Tech 2 engine and is thus used by 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[edit]

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

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 indices to the vertices and texture coordinates.

At offset ofs_frames frame data is stored, each frame has a short header followed by a number of vertex and surface normal indices, 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 array. 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; these vectors can be found in the frame's header. Alternatively, you can set the translation/scale matrix with model's values before rendering the model's frame (e.g. if using OpenGL); please note that scaling using glScale may de-normalize the surface normals.

Example[edit]

This is an example of how to read a single frame and display it, written in pseudocode.

 loop while $(int)index is less than $(int)num_tris
   loop while $(int)j is less than 3
     texture_function_s $(float)texture_coordinates[ $(short)triangle[ $(int)index ].textureindex[j] ].s / skinwidth
     texture_function_t $(float)texture_coordinates[ $(short)triangle[ $(int)index ].textureindex[j] ].t / skinheight

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

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

See also[edit]

Resources[edit]