Procedural Animation & IK

Overview

Procedural animation and Inverse Kinematics for dynamic, responsive character motion. Foot IK, look-at, hand placement, and runtime motion adaptation.

When to Use

•Use for foot IK on uneven terrain
•Use for look-at/head tracking
•Use for weapon/item holding
•Use for dynamic leaning/tilting
•Use for procedural locomotion

Architecture

code

┌─────────────────────────────────────────────────────────────┐
│                  ANIMATION PIPELINE                         │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│  ANIMATION CLIP      IK LAYER         FINAL POSE           │
│  ┌──────────┐      ┌──────────┐      ┌──────────┐         │
│  │ Base     │─────▶│ Foot IK  │─────▶│          │         │
│  │ Motion   │      │ Hand IK  │      │ Blended  │         │
│  │ (Clip)   │      │ Look At  │      │ Output   │         │
│  └──────────┘      └──────────┘      └──────────┘         │
│        ↑                 ↑                                  │
│  [Animator]      [OnAnimatorIK]                            │
│                                                             │
└─────────────────────────────────────────────────────────────┘

IK Types

Type	Use Case	Unity Method
Foot IK	Ground adaptation	`SetIKPosition/Rotation`
Hand IK	Weapon hold, grab	`SetIKPosition/Rotation`
Look At	Head tracking	`SetLookAtPosition/Weight`
Hint	Elbow/Knee direction	`SetIKHintPosition`

Common Techniques

Technique	Description
Foot Placement	Raycast ground, adjust feet
Body Offset	Lower body on slopes
Procedural Lean	Tilt body during turns
Head Look	Track target with head
Two-Bone IK	Arms reaching for objects

Best Practices

•✅ Use Animation Rigging package for complex setups
•✅ Blend IK weights smoothly (lerp)
•✅ Cache raycast results
•✅ Use layers for IK in Animator
•✅ Validate IK targets exist
•❌ NEVER set IK weight to 1 instantly
•❌ NEVER skip ground checks for foot IK
•❌ NEVER apply IK without base animation

Few-Shot Examples

Example 1: Foot IK

User: "Add foot IK for terrain adaptation."

Agent:

csharp

private void OnAnimatorIK(int layerIndex)
{
    // Left foot
    if (Physics.Raycast(_leftFoot.position + Vector3.up, 
        Vector3.down, out var hitL, 2f, _groundMask))
    {
        _animator.SetIKPositionWeight(AvatarIKGoal.LeftFoot, 1f);
        _animator.SetIKRotationWeight(AvatarIKGoal.LeftFoot, 1f);
        _animator.SetIKPosition(AvatarIKGoal.LeftFoot, 
            hitL.point + Vector3.up * _footOffset);
        _animator.SetIKRotation(AvatarIKGoal.LeftFoot,
            Quaternion.LookRotation(transform.forward, hitL.normal));
    }
    // Repeat for right foot
}

Example 2: Look At Target

User: "Make character look at target."

Agent:

csharp

[SerializeField] private Transform _lookTarget;
[SerializeField] private float _lookWeight = 0.8f;

private void OnAnimatorIK(int layerIndex)
{
    if (_lookTarget != null)
    {
        _animator.SetLookAtWeight(_lookWeight, 0.3f, 0.7f, 0.5f, 0.5f);
        _animator.SetLookAtPosition(_lookTarget.position);
    }
}

Example 3: Procedural Lean

User: "Add lean during movement."

Agent:

csharp

private void Update()
{
    float turnInput = Input.GetAxis("Horizontal");
    float targetLean = -turnInput * _maxLeanAngle;
    _currentLean = Mathf.Lerp(_currentLean, targetLean, 
        Time.deltaTime * _leanSpeed);
    
    _spine.localRotation = Quaternion.Euler(0, 0, _currentLean);
}

Animation Rigging Package

For complex rigs, use Unity's Animation Rigging:

•Multi-Aim Constraint
•Two-Bone IK Constraint
•Chain IK Constraint
•Twist Correction

Related Skills

•@advanced-character-controller - Movement integration
•@cinemachine-specialist - Camera follow
•@juice-game-feel - Motion polish