gltf-skin-anim-viewer.py

A super-simple, ugly looking, CPU-side skinning implementation in Python. It uses pygltflib to load files, moderngl to render, and numpy+numba for skinning. For some reason numba wanted scipy for the numpy dot product. To installed required packages:

pip install -r /path/to/requirements.txt

To run:

python gltf-skin-anim-viewer.py

The core stuff

In skin_animator.py you'll find how to implement it CPU-side. Leaving the GPU implementation as an exercise to the reader.

The basics of it is to sort the nodes in parent-first order, which happens in the loader. Then you're free to apply each parent's transform the all the kids:

node.transform = np.dot(parent_node.transform, node.transform)

Each time you animate a step, you'll need to get the bone transformation for each bone. And yeah, "bone" and "joint" means the same thing in this nomenclature...

joint_matrix = np.dot(node.transform, inverse_bind_matrix.reshape((4,4)).T)

Then you just apply each animated bone with some weights to the vertices.

I highly recommend a blog post from the game developer lisyarus, where he take you through the ropes.

Result

— Yuck! Did you model that?
— Absolutely not.

Licence

MIT