Player model in ET

Each character used in ET is assigned in characters of pak0.pk3. There are some files to define a character, they refer what class it is, what mesh it uses, what animation group it uses, what mesh it uses when it is undressed, what model its head is.

The mdm is a mesh data file for player models. mdm includes the surfaces and tags. The surface is a geometric data of model or polygon data. Skinning the surfaces with textures, the model appears in ET. The tag is a position info to attach another model to this model. The tag has its position and degree at each frame.

The mdx is a animation data file which contains bone structure and frames. The bone is a skeltal model data. Each bone has its length and its parent bone. The frame is a 3D-position data of the bones. one of the mdx frames have slightly different bone position compared with the previous frame. Thus a series of those frame will make an animation of a action. Ordinarily the mdx has several(or massive) number of animations in it.

A combination of mdm and mdx makes the polygons live, act, be a player.

This system is extremely good for sharing the animations which are used by the similar models. For example, ET only has one mdx( precisely there are more but they are a little ) to be used by the player models, 5 classes of allies and axis team. If we need to create the animation data for each model as like RtCW, The file size will be more bigger and memory requirements will be higher.

MDM Data Structure

[MDM]
  |
  |--[MDM HEADER]
  |
  |--[Surface]
  |     |
  |     |--[Header]
  |     |--[Vertex]
  |     |--[Triangle]
  |     |--[Collapsemap]
  |     |--[Bone Reference]
  |     :
  |
  |--[Tag]
  |    :
  |
  |--[EOF]


[MDX]
  |
  |--[MDX HEADER]
  |
  |--[Frame]
  |     |
  |     |--[Frame State]
  |     |--[Compressed Bone Frame]
  |     :
  |
  |--[Bone]
  |    :
  |
  |--[EOF]

Detail Data Structure

MDM HEADER

Surface

MDM SURAFCE VERTEX is a vertex data of this surface.

Weight is a element to determine where the vertex is. The vetex potision is calculated by summation of the multiple of the weight and its position of each bone.

Triangle is combinations of 3 vertex indices to buld a polygon.

Collapsemap data is not specified yet. Reference Bone data is the continuous number of the bone index. They are int32 and their amount is same as the number of Number of Reference Bones in Surface Header.

Tag

MDX HEADER

MDX Header refers the version, numbers and offset of the frame and bone structure of this mdx.

MDX FRAME

Frame is a state of the skeltal model at a moment. It can be the scene of firing Panzer, or dying by the head shot, or Nazi salutling. There are 2 sections in Frame, Frame State and Compressed Bone Frame. Frame State refers the bounding box of this model at this frame and a base position which will be used as the parent bone by the root bone. Compressed Bone Frame is the bone position data at this frame. "Compressed" means that each data is not 32bit, but 16bit.

The Compressed Bone Frame follows after Frame State. It will repeat same times as the number of bones.

To know the bone position, you have to summation the vectors which are calcurated by using ( Parent Distance, 0 , 0 ) as a start vector, rotating it with Offset Angles.

To convert angles to radian, just do this: Radian = 2 * 3.14 * Angle / 65536.0

MDX BONE

Bone Structure is like a puppet. A puppet has joints and fixed-length bones. Bones in ET is so. The meshed are attached around the bones. If a bone moves, mesh moves. If a bone is rotated, mesh is rotated as well.

References and Thanks

http://mojo.gmaxsupport.com/Articles/MDSFileFormat.html

Chris Cookson speced the mds, and this is extremely helpful for ET modder as well. Thanks that great documents.