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CSkSkinInfo

Overview

CSkSkinInfo defines how each vertex in a mesh is influenced by bones from the skeleton.
It determines how meshes deform when animated. Each vertex stores a small list of bones and their respective weights.
This block appears in animated DRS assets and is generated automatically when the model has an armature with vertex groups.

In the WriteOrder defined in drs_definitions.py, it appears for: - AnimatedUnit - AnimatedObjectCollision - AnimatedObjectNoCollision

It is not used for static objects without a skeleton.

Structure

Field Type Description
version int32 Internal version number for the format.
vertex_count int32 Number of vertices with weight data.
vertex_data List[VertexData] One entry per vertex, containing bone indices and weights.

VertexData

Field Type Description
bone_indices List[int] Bone IDs influencing this vertex. The IDs reference the bones from CSkSkeleton.
weights List[float] Normalized influence weights for each bone index (usually up to 4 per vertex).

Authoring & In-Game Behavior

When exporting from Blender, the create_skin_info() function in drs_utility.py gathers the skin data like this:

  1. Vertex Source:
    A unified list of all mesh vertices is created (from the exported mesh). Vertices are matched by position using rounding and KD-tree lookup to ensure each Blender vertex connects to the correct exported vertex.

  2. Bone Mapping:
    Blender’s vertex groups are matched to bones in the armature.
    The mapping uses the bone names from CSkSkeleton to find the correct bone ID.
    Each vertex group name must exactly match its bone name to export correctly.

  3. Weight Handling:
    Each vertex can store up to 4 influences. If more are found, only the 4 highest weights are kept.
    Weights are then normalized to ensure their total equals 1.0.

  4. Import Behavior:
    When importing, the tool recreates vertex groups in Blender based on stored bone indices and weights, matching the bones from the linked skeleton.
    Missing bones or mismatched names are skipped but logged for visibility.

In-game, this data ensures that mesh vertices follow the correct bones as they animate. Missing or invalid weights can cause visible stretching or collapsing of the model.

Validation Rules

Rule Why it matters
Each vertex has ≤ 4 influences Game engine expects a fixed small number for performance.
Weights per vertex sum to 1.0 Prevents visual deformation errors.
Each bone index exists in CSkSkeleton Ensures valid bone links for animation.
Vertex match succeeds during export Prevents missing weight assignments.

Cross-References

  • Skeleton: CSkSkeleton — provides the bone hierarchy and IDs used here.
  • Mesh: CDspMeshFile — contains the vertices that the weights are applied to.
  • Joint Mapping: CDspJointMap — connects mesh joints to the correct bones.
  • Write Order: Listed for animated objects in drs_definitions.py.

Nice to know

  • This block is written only when a mesh has vertex groups and a valid armature.
  • If bone names don’t match exactly between Blender and the skeleton, those weights are skipped and logged.
  • Removing unused vertex groups before export helps reduce unnecessary data and warnings.