Quick and dirty Maya skin load/save

mayaskin.py

# Relies on https://github.com/christophercrouzet/banana.maya

import collections
import json

from maya import OpenMaya, OpenMayaAnim, cmds

import banana.maya
banana.maya.patch()


Data = collections.namedtuple('SkinData', (
    'shape',
    'influences',
    'weights',
))


def apply_data(data):
    skin_group = list(data.influences)
    skin_group.append(data.shape)
    skin = cmds.skinCluster(tuple(str(dag) for dag in skin_group),
                            bindMethod=1)
    dg_skin = OpenMayaAnim.MFnSkinCluster.bnn_get(skin[0])

    deformer_set = OpenMaya.MFnSet(dg_skin.deformerSet())
    selection = OpenMaya.MSelectionList()
    deformer_set.getMembers(selection, True)
    if selection.length() != 1:
        raise RuntimeError("One and only one geometry is expected.")

    dagp_shape = OpenMaya.MDagPath()
    components = OpenMaya.MObject()
    selection.getDagPath(0, dagp_shape, components)

    indices = OpenMaya.MIntArray()
    indices.setLength(len(data.influences))
    for i in xrange(indices.length()):
        indices.set(i, i)

    weights = OpenMaya.MDoubleArray()
    weights.setLength(len(data.weights))
    for i in xrange(weights.length()):
        weights.set(data.weights[i], i)

    dg_skin.setWeights(data.shape, components, indices, weights)
    cmds.skinPercent(dg_skin, dagp_shape, normalize=True)
    dag = OpenMaya.MFnTransform(data.shape.bnn_parent())
    dag.findPlug('inheritsTransform').setBool(False)


def get_data(skin, rounding=4):
    deformer_set = OpenMaya.MFnSet(skin.deformerSet())
    selection = OpenMaya.MSelectionList()
    deformer_set.getMembers(selection, True)
    if selection.length() != 1:
        raise RuntimeError("One and only one geometry is expected.")

    dagp_shape = OpenMaya.MDagPath()
    components = OpenMaya.MObject()
    selection.getDagPath(0, dagp_shape, components)

    dagp_influences = OpenMaya.MDagPathArray()
    skin.influenceObjects(dagp_influences)
    influences = tuple(OpenMaya.MFnTransform(dagp_influences[i])
                       for i in xrange(dagp_influences.length()))

    weights = OpenMaya.MDoubleArray()
    util = OpenMaya.MScriptUtil()
    ptr_unit = util.asUintPtr()
    skin.getWeights(dagp_shape, components, weights, ptr_unit)

    influence_count = util.getUint(ptr_unit)
    if influence_count == 0:
        raise RuntimeError("No influence found for this component.")

    return Data(
        shape=dagp_shape,
        influences=influences,
        weights=tuple(round(weights[i], rounding)
                      for i in xrange(weights.length()))
    )


def load(filename):
    with open(filename) as f:
        datas = json.load(f)

    if not datas:
        return ()

    return tuple(Data(
        shape=OpenMaya.MDagPath.bnn_get(data['shape'],
                                        types=[OpenMaya.MFn.kShape]),
        influences=tuple(OpenMaya.MFnTransform.bnn_get(name)
                         for name in data['influences']),
        weights=data['weights']
    ) for data in datas)


def save(filename, datas):
    out = tuple({
        'shape': data.shape.partialPathName().split('|')[-1],
        'influences': tuple(dag.name() for dag in data.influences),
        'weights': data.weights
    } for data in datas)

    with open(filename, mode='w') as f:
        json.dump(out, f)


def save_example():
    filename = '/path/to/file.json'

    # Save the selected skin clusters into the file.
    skin_datas = []
    selection = OpenMaya.MSelectionList()
    OpenMaya.MGlobal.getActiveSelectionList(selection)
    for i in range(selection.length()):
        node = OpenMaya.MObject()
        selection.getDependNode(i, node)
        if node.hasFn(OpenMaya.MFn.kSkinClusterFilter):
            data = get_data(OpenMayaAnim.MFnSkinCluster(node))
            skin_datas.append(data)

    save(filename, skin_datas)


def load_example():
    filename = '/path/to/file.json'

    # Load the skin clusters saved within the file.
    skin_datas = load(filename)
    for skin_data in skin_datas:
        apply_data(skin_data)