Blender Auto Rig Hierarchy Operator

auto_rig_hierarchy.py

import bpy
from mathutils import Vector, Matrix

#Create the armature
def create_armature(object, collection):
    armature_data = bpy.data.armatures.new(object.name)
    armature = bpy.data.objects.new(object.name, armature_data)
    armature.matrix_basis = object.matrix_basis
    collection.objects.link(armature)
    return armature

#Create the bones
def bone_from_hierarchy(object, armature, parent_bone = None):
    #Create a bone parented and disconnect to its parent
    bone = armature.data.edit_bones.new(object.name)
    bone.parent = parent_bone
    bone.use_connect = False

    #Get its transformation matrix inside the armature from the object matrix
    matrix = armature.matrix_world.inverted() @ object.matrix_world

    #Place head and tail
    bone.head = matrix @ Vector()
    bone.tail = matrix @ Vector((0.0, 0.0, 1.0))

    if 'stop_rig' in object.keys():
        return

    #Recurse through the children objects
    for child in object.children:
        bone_from_hierarchy(child, armature, bone)

#Parent the objects to the armarture
def parent_from_hierarchy(object, armature):

    name = object.name

    #Get the pose bone
    bone = armature.pose.bones[name]

    #Keep the object position
    matrix_world = object.matrix_world.copy()

    #Parent it
    object.parent = armature
    object.parent_type = 'BONE'
    object.parent_bone = name

    #Make so we can unparent and keep object's position
    bone_matrix = Matrix.Translation(bone.tail - bone.head) @ bone.matrix
    object.matrix_parent_inverse = (armature.matrix_world @ bone_matrix).inverted()

    #Assigns its position
    object.matrix_world = matrix_world

    if 'stop_rig' in object.keys():
        return

    #Recurse through the children
    for child in object.children:
        parent_from_hierarchy(child, armature)

def make_bone_hierarchy(object):
    if object:
        armature = create_armature(object, object.users_collection[0])
        #Enter edit mode for the armature in order to create edit bones
        bpy.context.view_layer.objects.active = armature
        bpy.ops.object.mode_set(mode='EDIT')
        bone_from_hierarchy(object, armature)
        #Back to object mode
        bpy.ops.object.mode_set(mode='OBJECT')
        #bpy.context.view_layer.objects.active = object
        #Parent the objects to the armature
        parent_from_hierarchy(object, armature)


def main(context):
    root = context.active_object
    make_bone_hierarchy(root)


class SimpleOperator(bpy.types.Operator):
    """Tooltip"""
    bl_idname = "object.auto_rig_hierarchy"
    bl_label = "Auto Rig Hierarchy"

    @classmethod
    def poll(cls, context):
        return context.active_object is not None

    def execute(self, context):
        main(context)
        return {'FINISHED'}


def register():
    bpy.utils.register_class(SimpleOperator)


def unregister():
    bpy.utils.unregister_class(SimpleOperator)


if __name__ == "__main__":
    register()