AC4F8687
| AC4F8687 | |
|---|---|
| Short name: | GMDC |
| Long name: | Geometric data container |
The Geometry Data Container format is the 3D mesh of The Sims 2 files. GMDC is part of the SceneGraph Resource Collection set of files, more commonly known as RCOL. This complex file format stores information such as vertices, normal vectors, UV texture mapping coordinates, and bone joints, and morphs. It is a very important file to modding efforts, as its central to creating new objects in the game.
The file specification for GMDC follows. The format uses the standard RCOL file header, and data chunks conform to the standard RCOL chunk header structure.
Contents |
The File Structure
REF reference: RCOL file header and index ; Depending on the RCOL index, other RCOL chunks ; may appear before the GMDC chunk 7BITSTR block name (cGeometryDataContainer) DWORD block ID DWORD block version REF reference: read a cSGResource chunk here REF reference: Elements section (P1) REF reference: Linkages section (P2) REF reference: Groups section (P3) REF reference: Model section (P4) REF reference: Subsets section (P5) ; Depending on the RCOL index, other RCOL chunks ; may appear after the GMDC chunk
The Elements (P1) Section
The first section of a GMDC file is the Elements chunk. This section stores the actual vertices, normals, UV coordinates, morphs, etc.
DWORD element count ; 32bit count ; Elements LOOP ; repeat previous value times DWORD References Array Size ; Size of element array that can be referenced in Referenced Array List DWORD Element Identity ; See table 1 below DWORD Identity repetition ; logs how many times this identity has been used DWORD Block Format ; Determines the format of the element values list DWORD Set Format ; Determines the format of values in the element list ; Element Value List block DWORD Block size ; The size of the following data block in bytes LOOP element value list ; repeat by formula 1 below LOOP value set ; repeat by formula 2 below IF (GMDC version = 4) WORD ; Single value from a value set ELSE IF (GMDC version < 4) DWORD ; Single value from a value set ENDLOOP ENDLOOP ; Reference Array (links to entries by references# in another element - generally automatic associations) DWORD count LOOP ; repeat previous count value times IF (GMDC version = 4) WORD ; Single Reference Array Entry ELSE IF (GMDC Version < 4) DWORD ; Single Reference Array Entry ENDLOOP ENDLOOP
Table 1 : Element Identities
| 0x1C4AFC56 | Blend Indices |
| 0x5C4AFC5C | Blend Weights |
| 0x7C4DEE82 | Target Indices |
| 0xCB6F3A6A | Normal Morph Deltas |
| 0xCB7206A1 | Colour |
| 0xEB720693 | Colour Deltas |
| 0x3B83078B | Normals List |
| 0x5B830781 | Vertices |
| 0xBB8307AB | UV Coordinates |
| 0xDB830795 | UV Coordinate Deltas |
| 0x9BB38AFB | Binormals |
| 0x3BD70105 | Bone Weights |
| 0xFBD70111 | Bone Assignments |
| 0x89D92BA0 | Bump Map Normals |
| 0x69D92B93 | Bump Map Normal Deltas |
| 0x5CF2CFE1 | Morph Vertex Deltas |
| 0xDCF2CFDC | Morph Vertex Map |
Table 2: Block Formats
| 0x00 | 1xdword | float |
| 0x01 | 2xdword | float |
| 0x02 | 3xdword | float |
| 0x04 | 4xbyte | byte |
Table 3: Set Groups (formats)
| 0x00 | Main (Used by the main [first] Vertex group and intermediate blend groups) |
| 0x01 | Norms (Used by the main normals, and target indices) |
| 0x02 | UV (Used by UV coordinates and Deltas) |
| 0x03 | Secondary (Secondary groups used by the later elements in files, deltas, bones, etc) |
Reading the element value list
To read the element value list, use the following code:
'' Read blockFormat
'' ...
'' Determine set length
int setLength = 1;
switch (blockFormat)
{
case 0x00:
case 0x04:
setLength = 1:
break;
case 0x01:
setLength = 2;
break;
case 0x02:
setLength = 3;
break;
}
'' Determine list length
int listLength = blockSize / setLength / 4;
'' Read list
for (int i=0; i<listLength; i++)
{
'' Read single set
for (int j=0; j<setLength; j++)
{
if (blockFormat == 0x04)
{
'' Read a 32bit integer
}
else
{
'' Read a float
}
}
}
The "Target Indices" sections seem to only appear in the Elements section, and flag the inclusion of Morph Delta(s), Morph Normal(s) and a Morph map. For multiple morph models, there would be 'n' Morph Delta sections, then 'n' Morph normals sections, then a single morph map, which is mapped into sets of 4 bytes. Each byte value, if zero, means the corresponding vertice is left at its explicit location. For the first morph, you read the value of the least-significant byte in the morph map. Zeroes mean that vertice has no morph. Placing a number value (1, 2 or 3) into a byte flags the corresponding vertice and normal to be modified by adding the delta value from morph delta and morph normal (if present) (n-1). For a second morph, the second byte (reading big-endian) is used, again, a 1 would mean take the delta values from the first morph data section, or a 2 from the second one. That leaves room for 4 morphs in the morph map. Esentially, the map is designed to read by 'column' and use the value-1 as an index for which data block, at that offset, to look for the proper delta value.
As of this editing, leaving all the data blocks empty in a Target Index block still results in a loadable file that will morph from thin to fat in the game. However, the data are definitely vectors, and indexes, but I haven't figured out whether the indexes are to vertices or to triangles. After reproducing a complete model, even using the original tangent normals (0x89D92BA0 : Bump Map Normals) from the original mesh, bumpmapping won't work without this data. Until this mystery is unraveled, complete game meshes can be produced with all the features except alpha layer bumpmapping.
The Linkages (P2) Section
The second section in a GMDC contains data to link elements from section one, to groupings of those elements, defined in section 3 (P3). In some cases, three additional blocks other than the main index may be populated. These blocks contain extra indices of vertices, normals, and UV's for a subset mesh, defined later on in section 5 (P5).
DWORD count LOOP ; repeat "previous count" times DWORD index count LOOP ; index, Block A IF (GMDC Version = 4) WORD index value ELSE IF (GMDC version < 4) DWORD index value ENDLOOP DWORD referenced array size (max element reference array size) DWORD active elements for this link (active element #'s) DWORD Submodel vertex count LOOP ; Block B IF (GMDC Version = 4) WORD subset index value ELSE IF (GMDC version < 4) DWORD subset index value ENDLOOP DWORD Submodel normals count LOOP ; Block C IF (GMDC Version = 4) WORD normals index value ELSE IF (GMDC version < 4) DWORD normals index value ENDLOOP DWORD Submodel UV count LOOP ; Block D IF (GMDC Version = 4) WORD UV index value ELSE IF (GMDC version < 4) DWORD UV index value ENDLOOP ENDLOOP
The Groups (P3) Section
The third section in GMDC is the groups section. Groups collect elements from section one, through linkages in section 2, to form components like faces of a mesh.
DWORD count LOOP ; repeat "previous count" times DWORD primitive type DWORD link index 7BITSTR name of object DWORD face count LOOP ; Array of vertices that make the faces. Items are read sequentially in groups of three to form a face. Repeat "face count" times IF (GMDC version = 4) WORD vertex reference ELSE IF (GMDC version < 4) DWORD vertex reference ENDLOOP DWORD opacity amount ; 0xFFFFFFFF = full opacity, 0x0 = full transparency, < 16 for shadows IF (GMDC version != 1) DWORD subset count LOOP ; repeat "subset count" times IF (GMDC version = 4) WORD model subset reference ELSE IF (GMDC version < 4) DWORD model subset reference ENDLOOP ENDLOOP
The last subset version maps the value used in the 0xFBD70111 (Bone Assignments) section to the standard values used by other parts of the game. For example, a bone value of 4(from P1) would be used as an index to retrieve a value from the fifth element of this array that represents the real bone number, as used in other parts of the game. In creating a new GMDC, making an array that uses a series of 0, 1, 2, 3, ... makes a legitimate map, so long as you use the "real" bone values in the Bone Assignments section.
The Model (P4) Section
There is only one model per GMDC, so the next section does not have an outer loop. The model contains information to rotate and transform the mesh, as well as a bounding mesh for the whole model. The mesh stored in the model section is composed of vertices and the faces formed with them. In the face list, each sequential set of 3 values represents a face. The face is defined by using the vertices at the positions in the vertex list specified in the 3 face values.
DWORD transform block count LOOP ; repeat "transform block count" times DWORD quaternion x ; Rotation quaternion: x plane amount DWORD quaternion y ; Rotation quaternion: y plane amount DWORD quaternion z ; Rotation quaternion: z plane amount DWORD quaternion w ; Rotation quaternion: focal point DWORD transform x ; Transform: x amount DWORD transform y ; Transform: y amount DWORD transform x ; Transform: z amount ENDLOOP DWORD name pairs count LOOP ; repeat "name pairs count" times (this is equal to the number of targets located in P1 (the first target is usually a pair of NULL names). 7BITSTR blend group name 7BITSTR assigned element name ENDLOOP DWORD vertex count ; if zero, no mesh, continue to next section (used when model has no bones or joints) IF (vertex count > 0) DWORD face count LOOP ; repeat "vertex count" times DWORD vertex x DWORD vertex y DWORD vertex z ENDLOOP LOOP ; repeat "face count" times IF (GMDC version = 4) WORD ELSE IF (GMDC version < 4) DWORD END LOOP
You can reduce the resultant size if this part by consolidating duplicate vertices (since normals and UVs are not elements), as long as you adjust the correct index value in the face reference list.
The "Name Pairs" are used by the game to identify links to the morphs for animation purposes. Inclusion of full morph data without duplicating the name pairs referenced by the animations will not render.
The Subset (P5) Section
Subsets are parts of the full mesh, and are associated with bones (joints) and other components of the model.
DWORD subset count ; a standard Sims2 skeleton has 65 joints, although many are not used by the vertices. Other values indicate animated meshes with joint or target areas, but are processed in the same manner. LOOP ; repeat 'subset count' times DWORD vertex count ; if zero, blank section IF (vertex count > 0) DWORD face count LOOP ; repeat "vertex count" times DWORD vertex x DWORD vertex y DWORD vertex z ENDLOOP LOOP ; repeat "face count" times IF (GMDC version = 4) WORD ELSE IF (GMDC version < 4) DWORD END LOOP END LOOP
Reading the GMDC
Geometry
To read the geometry, you start with the group. From the link indexed in the group, you read the elements. The vertex list element is the position of the vertices. The face list in the P3(groups) is an array of vertices read in groups of 3 to form faces. The normals element is a list of normal vectors for the vertices. Texture map coordinates stored in a referenced element as well(in [U,V]). These are all standard elements of a group, but bumpmap normals may also be present(mostly body meshes).
Blends
The Blends are defined in the models section and used in animations. Blend zero alot of times seems to be null, but actually is just as valid as the others(although all of its vertices may have 0.0 deltas). For Each blend, there is a target index element(although the target index may be empty). While most meshes only have 1 or 2, there are some like the Sim face mesh that have 27.
A Morph is a change in a vertex(position, normals, UV coords, and/or bumpmaps). There can be up to four of them per vertex
The Morph Map element maps Blend ids to the Morph elements. The rows are vertices, columns are Morphs, and values are blends. No matter how many blends are present(even with the face at 27) there is always just 1 map.
This article is imported from the old MTS2 wiki. It's original page, with comments, can be found at http://old_wiki.modthesims2.com/AC4F8687
