Handling Shape Keys with Skeleton in Blender

When working with MakeHuman models in Blender where shape keys modify the mesh but the skeleton doesn't follow, there are a few more efficient approaches than manually calculating offsets for 900+ bones:

Recommended Approaches

1. Automatic Weight Transfer

Instead of manually calculating offsets, you can use Blender's weight transfer functionality:

PYTHONCopied
import bpy

def transfer_weights_after_shapekey():
    obj = bpy.context.active_object
    
    # Store original shape key values
    original_values = {}
    if obj.data.shape_keys:
        for key in obj.data.shape_keys.key_blocks:
            original_values[key.name] = key.value
            
    # Create a temporary copy with applied shape keys
    temp_obj = obj.copy()
    temp_obj.data = obj.data.copy()
    bpy.context.collection.objects.link(temp_obj)
    
    # Apply shape keys to the temporary object
    for key_name, value in original_values.items():
        if key_name != "Basis" and value > 0:
            # Apply the shape key influence
            temp_obj.shape_key_remove(temp_obj.data.shape_keys.key_blocks[key_name])
    
    # Transfer weights from original to morphed mesh
    obj.select_set(True)
    temp_obj.select_set(True)
    bpy.context.view_layer.objects.active = temp_obj
    bpy.ops.object.data_transfer(use_reverse_transfer=True, data_type='VGROUP_WEIGHTS')
    
    # Clean up
    bpy.data.objects.remove(temp_obj)

2. Use an Armature Modifier with Shape Keys

Make sure your armature modifier is applied after the shape keys in the modifier stack. This way, the deformation from shape keys happens first, then the armature deforms the already-morphed mesh.

3. Consider a Corrective Smooth Modifier

If the issue is that bones aren't positioned correctly after shape key application:

PYTHONCopied
# Add a corrective smooth modifier after shape keys are applied
def add_corrective_smooth():
    obj = bpy.context.active_object
    corrective = obj.modifiers.new(name="Corrective", type='CORRECTIVE_SMOOTH')
    corrective.factor = 1.0
    corrective.iterations = 5
    
    # Move it after the armature in the stack
    while obj.modifiers[-1].name != "Corrective":
        bpy.ops.object.modifier_move_up(modifier="Corrective")

4. For Production: Consider Baking Shape Keys to Bone Positions

For a more permanent solution, you could create a script that:

1. Analyzes which vertices are affected by each shape key
2. Determines which bones influence those vertices
3. Creates bone position drivers based on shape key values

This is more complex but would be the most efficient runtime solution.

Final Note

Given the complexity of a 900+ bone rig, I recommend starting with approach #2 (checking modifier order) as it's the simplest solution that often resolves this issue without additional scripting.