modifiedMM/MultipleMaids/IK.cs

using UnityEngine;

public class IK
{
    private TBody body;
    private Quaternion defHipQ;
    private Quaternion defKneeQ;
    private float defLEN1;
    private float defLEN2;
    private Vector3 knee_old;
    private Vector3 vechand;

    public void Init(Transform hip, Transform knee, Transform ankle, TBody b)
    {
        body = b;
        defLEN1 = (hip.position - knee.position).magnitude;
        defLEN2 = (ankle.position - knee.position).magnitude;
        knee_old = knee.position;
        defHipQ = hip.localRotation;
        defKneeQ = knee.localRotation;
        vechand = Vector3.zero;
    }

    public void Porc(Transform hip, Transform knee, Transform ankle, Vector3 tgt, Vector3 vechand_offset)
    {
        knee_old = knee_old * 0.5f + knee.position * 0.5f;
        Vector3 normalized1 = (knee_old - tgt).normalized;
        knee_old = tgt + normalized1 * defLEN2;
        Vector3 normalized2 = (knee_old - hip.position).normalized;
        knee_old = hip.position + normalized2 * defLEN1;
        new Quaternion().SetLookRotation(normalized2);
        hip.transform.rotation =
                Quaternion.FromToRotation(knee.transform.position - hip.transform.position, knee_old - hip.transform.position)
                * hip.transform.rotation;
        knee.transform.rotation =
                Quaternion.FromToRotation(ankle.transform.position - knee.transform.position, tgt - knee.transform.position)
                * knee.transform.rotation;
    }
}