[Python] BVH animation skinning

I am fairly new to Blender and retargeting methods, however I am looking for a way to skin bvh declared motion.

I imported a skin and fbx format animation from Mixamo, which means that armatures in fbx files containing skin and action are the same.

Since my goal is to make it work with bvh, I converted action fbx to bvh file.

However, when I attempt to transfer animation, skin from the fbx is deformed. I am a bit confused as I haven't found too much information on how to do it properly.

I would be very grateful for any help!

my current code:



import bpy
import sys
import numpy as np
import argparse
import os

def clean_scene():
bpy.ops.object.select_all(action='SELECT')
bpy.ops.object.delete()

def load_fbx(source):
bpy.ops.import_scene.fbx(filepath=source)

def load_bvh(source):
bpy.ops.import_anim.bvh(filepath=source)
return source.split('/')[-1][:-4]

def extract_weight(me):
verts = me.data.vertices
vgrps = me.vertex_groups

weight = np.zeros((len(verts), len(vgrps)))
mask = np.zeros(weight.shape, dtype=int)
vgrp_label = vgrps.keys()

for i, vert in enumerate(verts):
for g in vert.groups:
j = g.group
weight[i, j] = g.weight
mask[i, j] = 1

return weight, vgrp_label, mask

def clean_vgrps(me):
vgrps = me.vertex_groups
for _ in range(len(vgrps)):
vgrps.remove(vgrps[0])

def load_weight(me, label, weight):
clean_vgrps(me)
verts = me.data.vertices
vgrps = me.vertex_groups

for name in label:
vgrps.new(name=name)

for j in range(weight.shape[1]):
idx = vgrps.find(label[j])
if idx == -1:
continue
for i in range(weight.shape[0]):
vgrps[idx].add(, weight[i, j], 'REPLACE')

def set_modifier(me, arm):
modifiers = me.modifiers
for modifier in modifiers:
if modifier.type == 'ARMATURE':
modifier.object = arm
modifier.use_vertex_groups = True
modifier.use_deform_preserve_volume = True
return

modifier = modifiers.new(name='Armature', type='ARMATURE')
modifier.object = arm
modifier.use_vertex_groups = True
modifier.use_deform_preserve_volume = True

def adapt_weight(source_weight, source_label, source_arm, dest_arm):
dest_bone_names = {bone.name for bone in dest_arm.data.bones}

# Check for exact matches only
missing_bones = [name for name in source_label if name not in dest_bone_names]
if missing_bones:
print("\n[ERROR] The following vertex group names were not found in the destination armature bones:")
for name in missing_bones:
print(f" - {name}")
raise ValueError("Aborting weight transfer due to missing bones.")

# Proceed with safe mapping
weight = np.zeros((source_weight.shape[0], len(dest_arm.data.bones)))
dest_bone_index = {bone.name: i for i, bone in enumerate(dest_arm.data.bones)}

for j, name in enumerate(source_label):
idx = dest_bone_index[name]
weight[:, idx] += source_weight[:, j]

return weight

def main():
parser = argparse.ArgumentParser()
parser.add_argument('--fbx_file', type=str, required=True, help='path of skinned model fbx file')
parser.add_argument('--bvh_file', type=str, required=True, help='path of animation bvh file')

if "--" not in sys.argv:
argv = []
else:
argv = sys.argv[sys.argv.index("--") + 1:]

args = parser.parse_args(argv)

clean_scene()

load_fbx(args.fbx_file)
source_arm = bpy.data.objects['Armature']
source_arm.scale = [1.0, 1.0, 1.0]

bvh_name = load_bvh(args.bvh_file)
dest_arm = bpy.data.objects[bvh_name]
dest_arm.scale = source_arm.scale

bpy.context.view_layer.update()

meshes = [obj for obj in bpy.data.objects if obj.type == 'MESH']

for mesh in meshes:
weight, label, _ = extract_weight(mesh)
weight = adapt_weight(weight, label, source_arm, dest_arm)
load_weight(mesh, dest_arm.data.bones.keys(), weight)
set_modifier(mesh, dest_arm)
bpy.context.view_layer.update()


# source_arm.hide_viewport = True

if __name__ == "__main__":
main()

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