Muscle constraints are configured with the Muscle Properties SOP node and the Muscle Constraint Properties Vellum SOP node. These nodes take incoming solid muscle geometry, add or modify attributes, and then pass the data downstream.

Then the Muscle Vellum Solver SOP node applies these attribute values to either physical properties or attachment constraints in the following ways:

• Muscles are attached to bones firmly in areas designated as Muscle Ends.

• Muscles are attached with a springy sliding attachment to bones in areas designated to have Muscle to Bone attachments.

• Muscle are attached to other muscles with a springy attachment via the Muscle to Muscle attachment.

• Muscles are attached to other muscles with a firm, non-sliding attachment in areas designated to have Muscle Glue attachments.

In all cases, a firm attachment means it has a very high stiffness and will resist forces that try to pull it away from the rest position. Any other attachment is subject to a stiffness and damping ratio property that can affect its responsive and springy behavior.

Tissue constraints are configured with the Tissue Properties SOP node. This node takes the incoming tissue geometry, adds and/or modifies its attributes, and then passes the data downstream. The Tissue Vellum Solver SOP node then uses these attribute values to create the necessary constraints.

Tissue is constrained in the following ways:

• All core points are firmly attached to the muscle and bone input geometry.

• The interior surface of the tissue layer (tissue solid) is attached to the exterior surface of the core layer (core surface).

• The exterior surface of the tissue layer (tissue surface) is attached with a sliding attachment to the muscle and bone input geometry.

• A distance limiting attachment also exists to restrict the exterior surface (tissue surface) from sliding too far.

In all cases, a firm attachment means it has a very high stiffness and will resist forces that try to pull it away from the rest position. Any other attachment is subject to a stiffness and damping ratio property that can affect its responsive and springy behavior.

Skin constraints are configured with the Skin Properties SOP node. This node takes the incoming skin geometry, adds and/or modifies its attributes, and then passes the data downstream. The Skin Vellum Solver SOP node then uses these attribute values to create the necessary constraints.

Skin is constrained in the following ways:

• All interior skin (skin solid) points are attached and slide over the input tissue (tissue surface) geometry.

• Exterior skin (skin surface) points have a separate sliding attachment to the tissue (tissue surface) geometry.

• A distance limiting attachment also exists to restrict the skin surface from sliding too far.

Two separate attachment constraints exist for the skin pass so that you can adjust them independently. You can use the solid point attachment (on the skin solid) to adhere or loosen the connection between skin and the underlying tissue. If loosened enough, the skin can appear more like a loose fitting jacket surrounding the tissue. You can also use the exterior surface attachment (on the skin surface) to force the polygonal exterior to tighten itself up against the tissue and press deeper into crevices.