3ds Max 2012 Bible - Kelly L. Murdock [409]
Coloring bones
Bones, like any other objects, are assigned a default object color, and materials can be applied from the Material Editor. For each separate bone, its object color can be changed in the Modify panel or in the Bone Tools panel.
You can also apply a gradient to a bone chain using the Bone Tools palette. This option is available only if two or more bones are selected. The Start Color is applied to the chain's head, and the End Color is applied to the last selected child. The colors are applied or updated when the Apply Gradient button is clicked. Figure 38.5 shows a long, spiral bone chain with a white-to-black gradient applied.
FIGURE 38.5
A white-to-black gradient was applied to this spiral bone chain.
Adjusting fins
The Fin Adjustment Tools rollout includes the same parameters as those found in the Bone Parameters rollout. You can specify the dimensions and taper of a bone and its fins. But you can also specify that the parameters are applied using Absolute or Relative values. Relative values are based on the parameters of the bone that is above the current bone in the chain.
This rollout also includes Copy and Paste buttons that you can use to copy the bone parameters from one bone to another.
Making objects into bones
You can make any object act like a bone. To make an object into a bone, you need to open the Object Properties rollout in the Bone Tools panel. The Object Properties rollout includes a setting for Bone On. If enabled, the object acts like a bone. When the Bone On/Off option is enabled, the remaining Bone controls become available. The Auto-Align option causes the pivot points of adjacent bones to be aligned automatically. The Freeze Length option causes a bone to keep its length as the bones system is moved. If the Freeze Length is disabled, you can specify a Stretch type. None prevents any stretching from occurring, and Scale changes the size along one axis, but Squash causes the bone to get wider as its length is decreased and thinner as it is elongated. You can also select to stretch an axis and choose whether to Flip the axis.
You can use the Realign button to realign a bone: click the Reset Stretch button to normalize the stretch value to its current value.
Forward Kinematics versus Inverse Kinematics
Before you can understand IK, you need to realize that another type of kinematics exists: forward kinematics. Kinematics solutions work only on a kinematics chain, which you can create by linking children objects to their parents.
Cross-Reference
Chapter 9, “Grouping, Linking, and Parenting Objects,” covers linking objects and creating kinematics chains. •
Forward kinematics causes objects at the bottom of a linked structure to move along with their parents. For example, consider the linked structure of an arm, where the upper arm is connected to a forearm, which is connected to a hand, and finally connected to some fingers. Using forward kinematics, the lower arm, hand, and fingers all move when the upper arm is moved.
Having the linked children move with their parent is what you would expect and want, but suppose the actual object that you wanted to place is the hand. IK enables child objects to control their parent objects. So, using IK, you can drag the hand to the exact position you want, and all other parts in the system follow.
Forward kinematics in Max involves simply transforming linked hierarchies. When you move, rotate, or scale a linked hierarchy, the children move with the parent, but the child object also can be transformed independent of its parent.
Creating an Inverse Kinematics System
Before you can animate an IK system, you need to build and link the system, define joints by positioning pivot points, and define any joint constraints you want.
Building and linking a system
The first step in creating an IK system is to