GP Transfer Weights

Client: Personal project

My Role: Tool Developer, UI/UX Designer

The Production Challenge: The “Broken” Rigging Workflow for 2D/3D

In modern animation pipelines, integrating 2D elements (like those created with Blender’s Grease Pencil) with 3D rigs is a powerful but notoriously difficult workflow. While you can parent a Grease Pencil object to a 3D armature, you cannot directly skin it or transfer mesh weights to it.

This creates a critical bottleneck:

• Lack of Deformation: 2D elements remain rigid. They can follow a character’s arm, but they cannot bend with the arm.
• Manual, Frame-by-Frame Adjustments: Artists are forced into tedious, time-consuming manual adjustments to make 2D elements deform, killing efficiency and artistic flow.
• Pipeline Disconnection: The 2D and 3D workflows remain fundamentally separate, preventing the creation of truly integrated, deformable characters and effects.

I faced this exact problem and decided to build the solution.

The Solution: A Python-Powered Bridge for Weight Transfer

GP Transfer Weights is a custom Blender extension I developed to solve this challenge. It is a production-focused tool that creates a seamless bridge between a 3D character’s mesh and a 2D Grease Pencil object’s strokes.

How it Works (The Technical Approach):

The addon uses Blender’s Python API (bpy) to perform a series of sophisticated calculations:

1. Vertex Proximity Analysis: For each point in the Grease Pencil object, the script finds the closest vertices on the target 3D mesh surface.
2. Barycentric Weight Interpolation: It doesn’t just copy the weight from the single nearest vertex. To ensure smooth, organic deformations, it calculates the weight based on the relative influence of the three closest mesh vertices (the vertices of the closest polygon face).
3. Weight Data Transfer: The interpolated weight values are then programmatically assigned to the corresponding Grease Pencil points, storing them in a custom data layer.
4. Armature Modifier Integration: The addon ensures that Blender’s standard Armature modifier can then read this newly created weight data, allowing the Grease Pencil object to deform with the 3D rig as if it were a native part of the mesh.
5. Grease Pencil v3 compatibility: since Blender 4.3, Grease Pencil data structure is completely new and the API removed some functions. My extension takes care of the issue and works in Blender 4.2 and in 4.3 and higher.

This entire process, which would be impossible to do manually, is executed with a single click.

The Result: A Unified & Efficient Production Workflow

GP Transfer Weights transforms a broken workflow into an efficient and artist-friendly one.

• True Deformation: 2D Grease Pencil elements now bend, stretch, and deform organically along with the 3D rig, enabling truly integrated 2D/3D character animation.
• Massive Time Savings: The one-click solution eliminates hours of manual tweaking and frame-by-frame animation.
• New Creative Possibilities: Artists can now create complex effects like 2D frame by frame animated details that move on top of 3D objects, or stylized motion graphics that are perfectly synced to a character’s performance.

This project is an example of my core philosophy: identifying deep-seated pipeline problems and building robust, elegant technical solutions to solve them.