You can create an object and use it to influence the shape of smooth skin. The object, called an influence object, acts like a surgical implant against which the skin deforms. For example, you can create a sphere and use it to simulate a muscle or bone that bulges as you pose the character in certain positions. You can also use an influence object to smooth deformation and maintain volume in regions that collapse while bending.
In the next steps, you’ll use a cylinder to give Sven's forearm better structure. To use an influence object, the skeleton must be in the bind pose—the original pose at which the skin was bound to Sven.
To return the skeleton to the bind pose
- Click the Select Tool and cancel the selection of Sven.
- Turn off
Modify > Evaluate Nodes > IK Solvers.
After you use an IK handle to pose a character, you must do this step before you can return the skeleton to the bind (T-stance) pose.
- Select back_root, the root of the skeleton.
- Select
Skin > Go To Bind Pose.
- Select the ikHandleLeftArm in the Hypergraph. Use the Move Tool to move the handle manipulator slightly in any direction. When you release the mouse, note that the arm does not move and that the IK handle manipulator snaps back to the desired position at the end of the joint chain. Repeat this step for any other IK handles you posed previously.
- Turn on
Modify > Evaluate Nodes > IK Solvers.
You must do this step to enable the IK solvers so you can manipulate IK handles in the scene again.
To position a cylinder to be used as an influence object
-
-click Sven’s surface (anywhere but on the skeleton) and select
Actions > Template from the marking menu.
By making Sven a template, you won’t accidentally select Sven in subsequent steps.
- Create a cylinder (select Create > Polygon Primitives > Cylinder) and name it forearm_influence.
- Scale the and move the cylinder similarly to how it is positioned in this top and front view.
To make the cylinder an influence object
- In the Outliner, select Sven and Shift-select forearm_influence.
- Select
Skin > Edit Influence > Add Influence >
. In the
Add Influence Options, select
Edit > Reset Settings, and then click the
Add button.
Maya completes the operation within a few moments. To ensure the influence object stays in the correct position at the forearm, you will parent it to the left_elbow joint.
- In the
Hypergraph, Shift-select forearm_influence, forearm_influenceBase, and left_elbow joint, in that order.
The order of selection is important. The parent object should be selected last.
- Press p to parent the forearm nodes under the left_elbow joint.
The forearm_influence nodes appear in the skeleton hierarchy below the left_elbow joint.
The forearm_influenceBase is known as a base object. It stores vertex position information for the influence object. The reason for parenting the base object to the left_elbow joint is so that the influence object’s vertices stay in the correct position at the forearm whenever the forearm moves to a new position. Other than this step, you do not work with the base object.
- Right-click Sven and select Actions > Untemplate. It is easier to see subsequent skin deformations when Sven is displayed with smooth shading rather than as a template.
- From the menus at the top of the top view, turn off Show > Joints to avoid having the joints obstruct your view of the skin.
- Use each arm’s IK handle (ikHandleLeftArm and ikHandleRightArm) to pose the arms in the following position.
The left elbow (right in picture) looks more natural than the right elbow. To tune the elbow’s deformation during bending, change the position, scale, and rotation of forearm_influence.
Don't worry if the influence object pokes through the skin. It won’t be displayed when you render animations.