Look At IK

LookAt IK can be used on any character or other hierarchy of bones to rotate a set of bones to face a target.
Note that if LookAtIK does not fit you requirements, you can also use AimIK, that is very similar, but provides a different set of parameters, to make characters (especially non-biped) look at targets.

Getting started:

• Add the LookAtIK component to the root GameObject. That GameObject's forward axis will be the forward direction.
• Assing Spine, head and eye bones to the component.
• Press Play.

Getting started with scripting:

public LookAtIK lookAt;

void LateUpdate () {
    lookAt.solver.IKPositionWeight = 1f; // The master weight
    
    lookAt.solver.IKPosition = something; // Changing the look at target

    // Changing the weights of individual body parts
    lookAt.solver.bodyWeight = 1f;
    lookAt.solver.headWeight = 1f;
    lookAt.solver.eyesWeight = 1f;

    // Changing the clamp weight of individual body parts
    lookAt.solver.clampWeight = 1f;
    lookAt.solver.clampWeightHead = 1f;
    lookAt.solver.clampWeightEyes = 1f;
}

Adding LookAtIK in runtime:

• Add the LookAtIK component using GameObject.AddComponent().
• Call LookAtIK.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:

• target - the target Transform. If assigned, solver IKPosition will be automatically set to the position of the target
• weight - the master weight of the solver (multiplies all the other weights)
• bodyWeight - the weight of rotating the spine bones
• headWeight - the weight of rotating the head bone
• eyesWeight - the weight of rotating the eye bones
• clampWeight - clamping rotation of the spine bones. 0 is free rotation, 1 is completely clamped to zero effect
• clampWeightHead - clamping rotation of the head bone. 0 is free rotation, 1 is completely clamped to zero effect
• clampWeightEyes - clamping rotation of the eye bones. 0 is free rotation, 1 is completely clamped to zero effect
• clampSmoothing - the number of sine smoothing iterations applied to clamping to make it smoother
• spineWeightCurve - normalized weight distribution between the spine bones. The first spine bone is at "time" 0, the last spine bone is at 1
• head - the head bone
• spine - the spine bones in descending order (parents first), bones can be skipped
• eyes - the eye bones

Script References:

• Solver
• Component