Skin PLG (RW Section)

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Skin PLG
RenderWare Stream Section
Vendor	Criterion Games
Module	Toolkit
Module ID	0x000001
Identifier	0x16
Chunk ID	0x00000116
Versions	All
Hierarchy
Parents: Geometry (Extension)
Children: None
Extensions: None
File Format

Skin is an additional RenderWare plugin for geometry section. It is used to hold information about skinned model.

Structure

The structure starts with a 4-byte value, where each individual byte contains a counter and the last byte being used for padding.

1b - BYTE - numBones: Overall number of bones in the skeleton.
1b - BYTE - usedBones: Number of bones affected by the skin.
1b - BYTE - maxVertexWeights: Maximum number of non-zero weights per vertex.
1b - BYTE - Padding

The third counter can be any value from 0 to 4. If it equals zero, the engine attempts to figure out this number by looking into each weight array (see below) and counting the non-zero weights. It then takes the largest number from the results.

The counters are followed by multiple arrays that contain information about how vertices of a mesh relate to bones. The number of vertices is obtained from the parent geometry section.

Xb - BYTE[usedBones]       - A list of bone indices, that are affected by the skin.
Xb - BYTE[numVertices][4]  - A list that maps all vertices to (up to) four bones of the skeleton.
Xb - FLOAT[numVertices][4] - A list that weights each vertex-bone mapping.

Next, a list of transformation matrices for each bone is provided:

Xb - Bone[numBones]      - Bone transformations

Where Bone is defined as follows:

struct Bone {
    DWORD unused;            // Only stored if version < 0x37000 && maxVertexWeights == 0
    FLOAT transform[4][4];   // Skin-to-Bone transform.
};

Bone Group Remapping

As indicated above by the usedBones counter, a mesh (stored within the parent geometry) may not affected by all bones in the skeleton. Some platforms only support a certain number of bones at once. Thus RenderWare can split up a skeleton into groups, where group-indices must be mapped to the actual bone indices. Those groups are stored in a run-length encoded fashion.

For all RenderWare-based GTA games, this feature is typically unused. Thus the following values are usually set to zero.

4b - DWORD  - boneLimit: the maximum number of bones per group. (?)
4b - DWORD  - numGroups: the number of bone groups.
4b - DWORD  - numRemaps: the number of bone remappings.

If there are any groups (numGroups > 0), the counters are followed by three arrays:

Xb - BYTE[numBones]           - boneRemapIndices: an array of all bone indices where each element identifies a bone of the skeleton
Xb - BoneGroup[numGroups]     - boneGroups (see below)
Xb - BoneRemap[numRemaps]     - boneRemaps (see below)

Where BoneGroup and BoneRemap is defined as follows:

struct BoneGroup {
    BYTE firstBone;            // Index of first bone in boneRemaps array.
    BYTE numBones;             // Number of bones in boneRemaps that define the mesh (starting from firstBone).
};

struct BoneRemap {
    BYTE boneIndex;            // Index of the bone in boneRemapIndices.
    BYTE indices;              // The number of elements of the boneRemapIndices that are included by the group in boneRemapIndices.
};

See also

• IFP Animation Package