MotionBuilder uses the HumanIK 4.5 middleware library to perform Character solving.
The CharacterSolverSelector menu, located in the Character Settings pane, lets you select the HumanIK 4.5 solver. See Character Solver selector.
Autodesk® HumanIK® animation middleware is a run-time full-body inverse kinematics (IK) solver. It is also a run-time retargeting engine for characters of differing size, proportions and skeletal hierarchy.
HumanIK offers developers a modular component for the development of their animation tool-chain and run-time game engine.
HumanIK is a highly modular, multi-threaded library, optimized for use with the following platforms:
Designed for integration into animation engines, HumanIK works in unison with third-party solvers and middleware components, such as physics and simulation engines. See Switching to HIK solving.
What is new in HumanIK 4.5 release
Following are the changes in the HumanIK 4.5 solver: