870 Part VIII Character Animation

Summary

Building characters is a process that requires several different steps, and this chapter has presented a single approach. Other methods exist, and you should find one that works for you. This chapter covered the following topics:

How to create a character’s structure

A modeling approach using subobjects and smoothing

A method for connecting body parts

A simple way to create hair

This knowledge now prepares you to rig the character with bones that can be used to animate it.

Rigging Characters

Alinked hierarchy attaches, or links, one object to another and makes transforming the attached object by moving the

one it is linked to possible. The arm is a classic example of a linked hierarchy — when the shoulder rotates, so do the elbow, wrist, and fingers. Establishing linked hierarchies can make moving, positioning, and animating many objects easy.

A bones system is a unique case of a linked hierarchy that has a specific structure. You can create a structure of bones from an existing hierarchy, or you can create a bones system and attach objects to it. A key advantage of a bones system is that you can use IK Solvers to manipulate and animate the structure.

After you’ve created a system of bones, you can cover the bones with objects that have the Skin modifier applied. This modifier lets the covering object move and bend with the bone structure underneath. The process of attaching a model to a bones systems and skin is called rigging.

Building a Bones System

In some instances, establishing a hierarchy of objects before linking objects is easier. By building the hierarchy first, you can be sure of the links between objects. One way to build this hierarchy is to use a bones system. A bones system consists of many bone objects that are linked together. These bone objects are normally not rendered, but you can set them to be renderable, like splines. You can also assign an IK Solver to the bones system for controlling their motion.

To create a bones system, select Create Systems Bones IK Chain and click in a viewport to create a root bone, click a short distance away to create another bone, and repeat this a few more times. Each subsequent click creates another bone linked to the previous one. When you’re finished adding bones, right-click to exit bone creation mode. In this manner, you can create a long chain of bone objects all linked together.

These bones are actually linked joints. Moving one bone pulls its neighbors in the chain along with it. Bones can also be rotated, scaled, and stretched. Scaling a bones system affects the distance between the bones.

To branch the hierarchy of bones, simply click the bone where you want the branch to start while still in bone creation mode. A new

35C H A P T E R

In This Chapter

Building a bones system

Setting bone parameters and IK Solvers

Making linked objects into bones system

Using the Skin modifier

872 Part VIII Character Animation

branching bone is created automatically. Click the Bones button again to create a new bone. Then continue to click to add new bones to the branch.

Figure 35-1 shows the rollouts that are available for creating bones.

Figure 35-1: The Bone rollouts lets you specify which bones get assigned an

IK Controller.

Assigning an IK Solver

In the IK Chain Assignment rollout, you can select from four different IK Solvers: History Dependent, IKHISolver, IKLimb, and SplineIK Solver. You can assign each of these solver types to children and to the root bone using the available options. You need to select both the Assign to Children and the Assign to Root options to assign the IK Controller to all bones in the system. If the Assign to Children option is deselected, then the Assign to Root option is disabled.

Cross-	Chapter 37, “Using Inverse Kinematics,” presents details on each of these IK Solvers.
Reference

Setting bone parameters

The Bone Parameters rollout includes parameters for setting the size of each individual bone, including its Width and Height. You can also set the percentage of Taper applied to the bone.

Fins can be displayed on the front, back, and/or sides of each bone. For each fin, you can specify its size and start and end taper values. Including fins on your bones makes correctly positioning and rotating the bone objects easier. Figure 35-2 shows a simple bones system containing two bones. The first bone has fins.

Chapter 35 Rigging Characters 873

Figure 35-2: This bone includes fins that make understanding its orientation easier.

At the bottom of the Bone Parameters rollout is an option to Generate Mapping Coordinates. Bones are renderable objects, so this option lets you apply texture maps to them.

Tutorial: Making a simple puppet using bones

Starting simply, a good example is a puppet. The bones system for the puppet can be built first. If you specify the IK Solver before building the bones, then you’re ready to animate the puppet after it is finished.

To create a simple puppet out of bones, follow these steps:

1.Select Create Systems Bones IK Chain and in the IK Chain Assignment rollout, select IK Limb from the IK Solver drop-down list. To be able to see the orientation of each bone, enable the Side Fins.

2.In the Front viewport, click where you want the head bone to start and click again where the neck will be, then continue to click to form the spine, pelvis, right thigh, right lower leg, and foot bones. Then right-click to end the bones chain.

3.While still in Bones mode, click the pelvis bone in the Front viewport and drag to the left to form the left thigh bone. Continue to click to form the left lower leg and left foot bones. Right-click to end the chain.

4.Form the right arm bones by clicking the head bone and clicking consecutively to form the right upper arm, right lower arm, and hand bones. Right-click to end the chain.