Limb IK

LimbIK extends TrigonometricIK to specialize on the 3-segmented hand and leg character limb types.

LimbIK comes with multiple Bend Modifiers:

• Animation: tries to maintain bend direction as it is in the animation
• Target: rotates the bend direction with the target IKRotation
• Parent: rotates the bend direction along with the parent Transform (pelvis or clavicle)
• Arm: keeps the arm bent in a biometrically natural and relaxed way (also most expensive of the above).
• Goal: bends the arm towards the "Bend Goal" Transform.

NOTE: Bend Modifiers are only applied if Bend Modfier Weight is greater than 0.

The IKSolverLimb.maintainRotationWeight property allows to maintain the world space rotation of the last bone fixed as it was before solving the limb.
This is most useful when we need to reposition a foot, but maintain its rotation as it was animated to ensure proper alignment with the ground surface.

Getting started:

• Add the LimbIK component to the root of your character (the character should be facing its forward direction)
• Assign the limb bones to bone1, bone2 and bone3 in the LimbIK component (bones can be skipped, which means you can also use LimbIK on a 4-segment limb).
• Press Play

Getting started with scripting:

public LimbIK limbIK;

void LateUpdate () {
    // Changing the target position, rotation and weights
    limbIK.solver.IKPosition = something;
    limbIK.solver.IKRotation = something;
    limbIK.solver.IKPositionWeight = something;
    limbIK.solver.IKRotationWeight = something;

    // Changing the automatic bend modifier
    limbIK.solver.bendModifier = IKSolverLimb.BendModifier.Animation; // Will maintain the bending direction as it is animated.
    limbIK.solver.bendModifier = IKSolverLimb.BendModifier.Target; // Will bend the limb with the target rotation
    limbIK.solver.bendModifier = IKSolverLimb.BendModifier.Parent; // Will bend the limb with the parent bone (pelvis or shoulder)

    // Will try to maintain the bend direction in the most biometrically relaxed way for the arms. 
    // Will not work for the legs.
    limbIK.solver.bendModifier = IKSolverLimb.BendModifier.Arm; 
}

Adding LimbIK in runtime:

• Add the LimbIK component via script
• Call LimbIK.solver.SetChain()

Component variables:

• fixTransforms - if true, will fix all the Transforms used by the solver to their initial state in each Update. This prevents potential problems with unanimated bones and animator culling with a small cost of performance

Solver variables:

• bone1 - the first bone (upper arm or thigh)
• bone2 - the second bone (forearm or calf)
• bone3 - the third bone (hand or foot)
• target - the target Transform. If assigned, solver IKPosition and IKRotation will be automatically set to the position of the target
• positionWeight - the weight of solving to the target position (IKPosition)
• rotationWeight - the weight of solving to the target rotation (IKRotation)
• bendNormal - normal of the plane defined by the positions of the bones. When the limb bends, the second bone will always be positioned somewhere on that plane
• AvatarIKGoal - the AvatarIKGoal of this solver. This is only used by the "Arm" bend modifier
• maintainRotationWeight - weight of maintaining the rotation of the third bone as it was before solving
• bendModifier - a selection of automatic modifiers of the bend normal
• bendModifierWeight - the weight of the bend modifier