MAXON Cinema 4D - Clean up joint's weights for AR compatibility

klts-joints-weights-ar-cleanup-20190214.py

# MAXON Cinema 4D
# Clean up joint's weights for AR compatibility
#
# This script will set to zero the weights of all but 4
# joints/bones for each point in the selected Weight tag.
# As a result, the weights will be unnormalized. So you'll
# probably want to normalize all weights after using this
# script.
#
# NB: The weights table in the Weight Manager UI tab
#     won't update automatically after using the script.
#     Please click inside the Weight Manager tab to see
#     the updated values.

import c4d
import operator

def main():
    active_doc = c4d.documents.GetActiveDocument()
    doc_sel = active_doc.GetSelection()
    sel_len = len(doc_sel)
    
    if sel_len != 1 or  doc_sel[0].GetTypeName() != 'Weight' :
        c4d.gui.MessageDialog('''Error: Please select a single Weight tag.
There is currently {0} object(s) selected.'''.format(sel_len))
        return
        
    weight_tag = doc_sel[0]
    
    active_doc.StartUndo()
    active_doc.AddUndo(c4d.UNDOTYPE_CHANGE, weight_tag)

    mesh_obj = weight_tag.GetObject()
    joint_count = weight_tag.GetJointCount()
    for point_id in range(mesh_obj.GetPointCount()):
        joint_weights = {joint_id: weight_tag.GetWeight(joint_id, point_id)
                         for joint_id in range(joint_count)}
        new_weights = sorted(joint_weights.items(),
                                key=operator.itemgetter(1),
                                reverse=True)
        for joint_id in range(4, joint_count):
            joint_to_prune_id = new_weights[joint_id][0]
            new_weights[joint_id] = (joint_to_prune_id, 0.0)
        new_weights = dict(new_weights)
        for joint_id in range(joint_count):
            weight_tag.SetWeight(joint_id, point_id, new_weights[joint_id])
    
    active_doc.EndUndo()

if __name__=='__main__':
    main()