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Extracting Meshes

This page covers how mesh extraction works under the hood and what to expect from the output.

How Extraction Works

The tool reads the BoneWeight data on each vertex of your mesh. Every vertex in a SkinnedMeshRenderer stores up to four bone influences (indices and weights). When you select a bone and click extract:

  1. The tool collects the bone index for your selected bone (and optionally its children)
  2. It scans every vertex and marks those influenced by any of those indices
  3. It then iterates over every triangle — if any vertex in a triangle is influenced by the selected bone, the whole triangle is kept or removed (depending on whether you're keeping or removing that region)
  4. A new Mesh asset is created from the filtered triangle data and saved to disk

The source mesh is never modified. The new mesh is a copy with a subset of the original triangles.

What the Output Looks Like

The extracted mesh:

  • Retains all original vertex data (positions, UVs, normals, tangents, blend shapes, bone weights)
  • Retains the same submesh structure as the source
  • Is saved as a .asset file in your project

Open edges

Because the tool simply removes triangles, the cut boundary will have open (non-watertight) edges. This is expected — see Limitations for details on when this matters and when it doesn't.

Assigning the Extracted Mesh

After saving, assign the new mesh to a SkinnedMeshRenderer on your character:

  1. Select a SkinnedMeshRenderer component in the Inspector
  2. In the Mesh field, assign your new .asset file
  3. Make sure the SkinnedMeshRenderer's Bones array still points to the original rig — the new mesh shares the same bone indices

Tip

Because the extracted mesh shares bone indices with the original, it will animate correctly when bound to the same skeleton.

Child Bone Inclusion

The Include Child Bones toggle controls whether child bones of the selected bone are included in the extraction query.

Selecting the Head bone also captures geometry influenced by:

  • Jaw / chin bones
  • Eye bones
  • Eyebrow bones
  • Ear bones
  • Any accessory bones parented to the head

Only vertices directly influenced by the selected bone are extracted. Useful when you want a precise, minimal extraction without pulling in adjacent geometry.

Read/Write Requirement

Unity's Mesh API requires a mesh to have Read/Write Enabled before vertex and triangle data can be accessed at edit time. If your mesh doesn't have this flag set:

  • Use the 🔧 Enable Read/Write on Source Mesh button in the tool
  • Or enable it manually: select the FBX/model asset → Inspector → Model tab → check Read/Write Enabled → Apply