Robust Weight Transfer

Overview

Robust Weight Transfer is a skin weight transfer tool based on the SIGGRAPH Asia 2023 paper “Robust Skin Weights Transfer via Weight Inpainting”.

Unlike conventional weight transfer tools, it can robustly transfer weights even when the source and target mesh shapes do not perfectly match. For unmatched vertices, the “Weight Inpainting” algorithm estimates appropriate weights from surrounding weight information.

Basic Operation

1. Find the closest point on the source mesh for each target vertex.
2. Perform matching based on distance and normal angle thresholds. Vertices that don’t match due to thresholds become candidates for Weight Inpainting.
3. Transfer source weights directly to matched vertices, and assign Weight Inpainting estimated weights to unmatched vertices.
4. Apply smoothing if needed (optional).
5. Seam vertices normally have separate weights, but you can optionally average weights of vertices at the same position (optional).

Launch

Launch the tool from the dedicated menu or with the following command.

import faketools.tools.rig.robust_weight_transfer.ui
faketools.tools.rig.robust_weight_transfer.ui.show_ui()

Usage

1. Standard Weight Transfer

1. Select the source mesh (with skinCluster) and click Set
2. Select the target mesh and click Add Selected
3. Click Transfer

2. Partial Transfer

1. Set the source mesh
2. Select the vertices you want to transfer on the target mesh
3. Click Add Selected (displayed in blue in the list)
4. Click Transfer

3. Matching Verification

1. Set source and target
2. Click Search to verify matching results
3. Click Select Unmatched to check unmatched vertices
4. Adjust Distance Ratio or Angle as needed
5. Click Transfer

※ If all target geometry and vertices are unmatched, weight transfer will not be performed.

4. Garment Seam Processing

1. Add all clothing parts (body, collar, sleeves, etc.) to targets
2. Turn on Average Seam Weights
3. Click Transfer

Options

Source

Set the mesh to transfer weights from.

1. Select a mesh with skinCluster
2. Click the Set button

Targets

Set the meshes or vertices to transfer weights to.

• Add Selected: Add selected meshes or vertices to the list
• Remove: Remove selected items from the list
• Clear: Clear all targets
• Select: Select the target in the viewport

About Partial Transfer: When you add selected vertices, weights are transferred only to those vertices. They are displayed in blue in the list, with the vertex count shown as [123 vtx].

Settings

Configure matching parameters.

About Distance Ratio: Smaller values result in stricter matching. 0.05 means matching within 5% of the diagonal length.

About Expand Boundary: At the boundary between matched and unmatched vertices, weights from vertices that barely passed the threshold can introduce noise. Setting this value to 1 or higher will also treat vertices within N edge rings around unmatched vertices as “unmatched”, making them candidates for Weight Inpainting interpolation. This removes noise at the boundary and results in smoother weight transitions.

• 0: No expansion (default, original behavior)
• 1-5: Expand the boundary by the specified number of edge rings

※ An error will occur if expansion causes all vertices to become unmatched.

About Flip Normals: Turn this on when normals are flipped between source and target (e.g., clothing lining).

About Use Deformed Source / Use Deformed Target: Use when transferring weights in a pose other than bind pose. With both enabled, matching is performed based on the current pose shapes.

Post Processing

Configure processing applied to weights after transfer.

About Smoothing: Weight smoothing options after transfer. Smooths weights estimated by Weight Inpainting for more natural results.

About Seam Weights: Options for averaging seam vertex weights. This option is useful when the mesh is divided into multiple parts. Averages weights of vertices at the same position for consistent weights.

Use Cases: - When clothing collar and body are separate meshes with seam vertices at the same position - When vertices are split at UV seams but at the same position

Status

Displays matching results.

• Matched: Number and percentage of matched vertices
• Unmatched: Number and percentage of unmatched vertices (estimated by Weight Inpainting)

Action Buttons

Basic Workflow

Preset Menu

Save and load settings as presets.

• Save Settings…: Save current settings as a preset
• Edit Settings…: Edit or delete presets
• Reset Settings…: Reset all settings to defaults
• Preset name: Load a saved preset

Note: Source and Targets are not included in presets.

Technical Details

Weight Inpainting Algorithm

Weights for unmatched vertices are solved as an optimization problem using a Laplacian matrix. This computes smoothly interpolated weights from surrounding weight information.

Dependencies

• numpy: Numerical computation
• scipy: Sparse matrix operations
• robust-laplacian: Fast Laplacian computation (optional, fallback implementation available)

If robust-laplacian is not installed, the built-in fallback implementation is used.

Troubleshooting

Low Match Rate

• Increase Distance Ratio (e.g., 0.05 → 0.1)
• Increase Angle (e.g., 30 → 45)
• Try turning on Flip Normals

Weights Not Smooth

• Increase Smoothing Iterations
• Increase Smoothing Alpha

Issues with Deformed State

• Turn on both Use Deformed Source and Use Deformed Target
• Or return to bind pose before transfer

Seam Averaging Not Working

• Increase Position Tolerance (e.g., 0.0001 → 0.001)
• Verify vertices are actually at the same position