The following concept overview will be covering Wrap Skinning for the purpose of actual muscle/bone deformation of the skin.

The basic concept is:

Skeleton Joints driving Bones driving Muscle movement/shape driving Skin deformation.

Skeleton Joints>>Geometry Bones>>Geometry Muscle>>Geometry Skin

With wrap skinning we:

Bind the Bones to the Joints
Wrap influence the bones & muscle to the skin
SetDriven Key the muscle deformation to translation of the IKhandle.

Overview of Steps

Modeling:
Model an arm or other apendage
Model the bones for the apendage
Model the muscle tissue


Placement:
Situate the bones properly within the Skin (Arm) model
Situate the muscle tissue

Rig:
Draw a 3 joint skeleton within the bones
Rigid Bind the joints to the bones
Select the Skin then the Bones and create a wrap relationship
Then Add Influence the muscle tissue
Create clusters on the muscle tissue that allow for flexed position shaping
SetDriven Key the IKhandle.ty to the cluster.t (using the axis needed for proper deformation)



Relaxed Position:

Below is a simplified example of skin, bone and muscle structure in an un-flexed position




Flexed Position:

Below is a simplified example of skin, bone and muscle structure in a flexed position




Closing:

This is not an anatomically correct example of bone & muscle structure.
The sole purpose is to relay the concept, thus some of the deformation is incorrect and many muscles have been left out. (ex. elbow)

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