Skin Binding

1. Parenting -- Skin geometries are parented to joints. Skin geometries are not deformed.

2. Rigid bind -- All points of skin geometries are grouped into clusters. Each cluster is attached to a single joint, i.e., each point of a skin geometry is influenced by a single joint. To apply rigid bind, select the skin geometries and the joint chain, select Skin -> Bind Skin -> Rigid Bind. Editing Clusters below for editing cluster membership.

3. Rigid bind with a lattice on a joint (or bone) -- A lattice deformation is applied to a specified joint or bone. To apply rigid bind with a lattice, apply rigid bind first. Select a joint and go to Skin -> Edit Rigid Skin -> Create Flexor. In the Create Flexor window, select "lattice" as Flexor Type. Select the location(s) where you want to use lattices. Set S, T, and U divisions of a lattice. Click on Create.

4. Rigid bind with a sculpt object on a bone (or joint) -- A sculptor (a sphere) is applied to a specified bone of joint. To apply a sculptor, apply rigid bind first. Select a joint and go to Skin -> Edit Rigid Skin -> Create Flexor. In the Create Flexor window, select "Sculpt" as Flexor Type. Translate and scale the sculptor and sculptStretchOrigin together in order to decide how much the skin is deformed. To animate the sculptor, set driven keys between the joint's z-rotation (driver) and sculptor's x- and z-scalings (driven).

5. Smooth bind -- All points of skin geometries are influenced by a number of joints. How much each point should be influenced by each joint is specified by the weight. The total weight for each point should add up to 1. To apply smooth bind, select skin geometries and the joint chain, select Skin -> Bind Skin -> Smooth Bind. See Editing Skin Weights below.

6. Smooth bind with an influence object -- A NURBS or polygonal geometry sitting just below a skin geometry can create muscle bulges. Apply smooth bind first. Parent an influence object to the joint above. Select the bound skin first and the influence object second, and then apply Skin -> Edit Smooth Skin -> Add Influence. To animate the influence object, use set driven keys. See Set Driven Key below.

7. Indirect bind -- A lattice deformer is applied to geometry and the lattice is bound to the skeleton.

(See skin.mb for examples for Methods 1 - 7).

Editing Clusters
When you bind a geometry or a lattice to a skeleton a cluster (a set of points) is created for each joint in the skeleton. As you move or rotate joints, the clusters react accordingly. You can edit cluster membership as follows:
1. Select a joint.
2. Select Deform -> Edit Membership Tool
3. Dragging the marquee around points while pressing the right mouse button and the shift key adds the points to the set. Dragging the marquee around points while pressing the right mouse button and the control key deletes the points from the set.

Editing Skin Weights
1. Select skin geometries and press 5 to apply smooth shading.
2. Go to Skin -> Edit Smooth Skin -> Paint Skin Weights Tool.
3. In Brush tab of the tool, set the Radius (U).
4. In Influence tab, select the joint for which you want to paint weights.
5. In Paint Weights tab, select Paint Operation and set Value, and paint.

Set Driven Key
1. Apply smooth bind to the skin geometry (geometries) and bones.
2. Place an influence object under the skin geometry.
3. Parent the influence object to joint1.
4. Select the skin geometry and the influence object. Select Skin -> Edit Smooth Skin -> Add Influence.
5. Open the options window for Set Driven Key by selecting the small square box next to Set under Animate -> Set Driven Key.
6. Select joint2 in one of the panels (e.g., a front view panel) and click on "Load Driver" in Set Driven Key options window. The joint should appear in the Driver part (upper part) of the Set Driven Key options window.
7. Select roateZ in the list of the joint's attributes in the upper right quarter of Set Driven Key options window.
8. Select the influence object in one of the panels and click on "Load Driven" in Set Driven Key options window. The object should appear in the Driven part (lower part) of the Set Driven Key options window.
9. Select scaleX in the list of the object's attributes in the lower right quarter of Set Driven Key options window. Click on Key.
10. Select scaleZ in the list of the object's attributes. Click on Key.
11. Select the IK of the leg and bend the knee joint by moving the IK up.
12. Scale up the influence object in X and Z.
13. Select scaleX in the list of the object's attributes. Click on Key.
14. Select scaleZ in the list of the object's attributes. Click on Key.
15. Move the IK of the leg. The muscle bulges should occur.