Key Concept: Twist

• “Twistâ€? is a special type of rotation

  • Easy to explain, hard to model
  • Only relevant to chains, not single xforms
  • Perfect example of a non-physical “spaceâ€?

• Move twist rotations out of hierarchy

  • 2 DOF chain plus 1 DOF twist bones
  • Last bone is still 3-DOF to drive twist

• Distribute twist based on last joint

  • Use first euler to control “twistâ€? bones
  • Expressions or drivers
    • Constraints only on “stiffâ€? chains
  • ï?Œâ€œTwist and Shoutâ€? Game Developer, April '04