SkinPlusPlus

Python bindings written in c++, for working with skin data in DCC's.

Disclaimer • Key Features • Usage • Performance • How To Compile • Roadmap • Personal Info

Disclaimer

This software (SkinPlusPlus) is provided "as is", without any warranty. The authors or copyright holders will not be liable for any damages or claims related to the software or its use.

Key Features

• Save and load skin data with speed

  • Logic is written in c++ but exposed with python bindings

• Work directly with numpy ndarrays

  • Use of Pybind11 means there is minimal copying of data to pass the data from Python to the respective c++ SDK.

• Currently supported DCCs:

  • 3DsMax:
    • 2024 - Python310
    • 2023 - Python39
    • 2022 - Python37
    • 2021 - Python37
  • Maya:
    • 2024 - Python310
    • 2023 - Python39
    • 2022 - Python37

Usage

PySkinData is a c++ struct exposed to Python as the class SkinData. This struct contains five separate data attributes:

• bone names (str)
• vertex bone weights (float64)
• vertex bone ids (int)
• vertex positions (float64)
• vertex indices (int)

This struct allows the data to be typed correctly. The c++ backend uses Eigen matrices and exposes them to Python via Pybind11 as numpy arrays.

Due to the relationship between Eigen and Pybind11, there is no performance hit when passing arrays to and from c++.

This results in a reduction in the number of iterable structures the data needs to be stored in to convert back and forth btween numpy and the c++ SDK get and set weight functions.

🔥 This means it is fast 🔥

Take 3DsMax as an example, to get from a numpy ndarray to 3DsMax SDK Tab it requires the following steps:

• ndarray -(copy)-> py list -(copy)-> mxs Array -(copy)-> Tab -> set weights.

Compared to the SkinPlusPlus approach:

• ndarray -(reference)-> Eigen Matrix -(copy)-> Tab -> set weights.

The native approach runs multiple copy operations in Python to get the data into a MaxScript Array so it can be passed to c++. SkinPlusPlus has no copy operations in Python.

SkinData provides attribute access to the raw data with the following properties:

• SkinData.bone_names
• SkinData.weights
• SkinData.bone_ids
• SkinData.positions
• SkinData.vertex_ids

Performance

Performance benchmarks are done on a mesh with 507,906 vertices, each with 6 influences.

3DsMax 2022

Get Skin Data

Method	Time-secs	x Faster	% Faster
pymxs -> numpy array	68.231	base	base
maxscript -> numpy array	47.859	001.426x	00142.56%
SDK function publish -> numpy array	12.800	005.330x	00533.06%
skin_plus_plus -> numpy array	00.335	203.631x	20363.10%

Set Skin Data

Method	Time-secs	x Faster	% Faster
pymxs <- mxs.Array	10.008	base	base
maxscript <- mxs.Array	08.258	01.211x	0121.18%
SDK function publish <- mxs.Array	07.368	01.358x	0135.82%
SDK struct primative <- mxs.Array	05.838	01.714x	0171.43%
SDK primative <- mxs.Array	05.694	01.757x	0175.76%
skin_plus_plus <- np.ndarray	00.184	54.345x	5434.57%

Maya 2022

Get Skin Data

Method	Time-secs	x Faster	% Faster
maya.cmds -> numpy array	81.572	base	base
pymel -> numpy array	04.647	017.550x	01755.08%
skin_plus_plus -> numpy array	00.524	155.810x	15580.99%

Set Skin Data

Note that set data in Maya is done on a mesh with 7938 vertices as cmds is too slow for 500k vertices

Method	Time-secs	x Faster	% Faster
maya.cmds <- np.ndarray	11.458	base	base
OpenMaya (api2) <- np.ndarray	00.103	110.968x	11096.80%
skin_plus_plus <- np.ndarray	00.025	466.319x	46631.94%

How To Compile

Dependencies

The c++ backend has 3 main dependencies

• Pybind11
  • Exposes c++ logic to python, circumventing native SDK mechanisms
• Eigen
  • Matrix library for c++, provides extremely performant backend for numpy
• fmt
  • Allows for easy string formatting in c++

Roadmap

• Include Vertex Positions

  • This will enable features for applying skin data to different topologies

• Support multiple DCCs

  • 3DsMax
  • Maya
  • Unreal
  • Blender
  • MotionBuilder
  • Houdini

• Send data between DCCs

  • Make skin data serialisable
  • Pass data between DCC using local servers
  • This will provide a foundation for a DCC agnostic skinning pipeline

• Expand toolkit to include functions other than get and set.

Personal Info

Webbie techanimdad.com  ·  GitHub @munkybutt