Hair simulation with Unity 2D Animation

Hair.cs

using System;
using System.Collections.Generic;
using Sirenix.OdinInspector;
using UnityEngine;
using UnityEngine.U2D;

namespace Son.Modules
{
    public class Hair : MonoBehaviour
    {
        [SerializeField] private Transform origin;
        [SerializeField] private SpriteRenderer _renderer;

        [SerializeField, Range(0f, 10f)] private float gravity;
        [SerializeField, Range(0f, 1f)] private float gravityFallout;
        [SerializeField] private Vector2 damp;

        [SerializeField, Range(0f, 1f)] private float updateInterval = .125f;

        [SerializeField, FoldoutGroup("Data", order: 1)] private List<Transform> bones = new List<Transform>();
        [SerializeField, FoldoutGroup("Data")] private List<Point> points = new List<Point>(8);

        private float lastUpdate;

        private bool flipped;
        private bool onFlip;
        private bool lastFlipped;

        private void Start()
        {
            foreach (var point in points)
                point.Position = origin.TransformPoint(point.StartOffset);
        }

        private void Update()
        {
            flipped = origin.forward.z < 0f;
            onFlip = flipped != lastFlipped;
            lastFlipped = flipped;

            if (updateInterval < Time.time - lastUpdate || onFlip)
            {
                Simulate(onFlip ? 1f : Time.time - lastUpdate);
                lastUpdate = Time.time;
            }
        }

        [Button(size: ButtonSizes.Medium)]
        public void Initialized()
        {
            bones.Clear();
            points.Clear();

            var spriteBones = _renderer.sprite.GetBones();
            var spriteBoneByName = new Dictionary<string, SpriteBone>();
            foreach (var bone in spriteBones)
                spriteBoneByName[bone.name] = bone;

            foreach (var child in origin.GetChildRecursive())
            {
                if (spriteBoneByName.ContainsKey(child.name))
                    bones.Add(child);
            }

            for (int i = 0; i < bones.Count; i++)
            {
                var spriteBone = spriteBoneByName[bones[i].name];
                var startOffset = i < bones.Count - 1 ? bones[i + 1].position : bones[i].position + Vector3.down * spriteBone.length;
                points.Add(new Point() { StartOffset = origin.InverseTransformPoint(startOffset),  Gap = spriteBone.length });
            }
        }

        private void Simulate(float interval)
        {
            Vector2 parentPos = origin.position;

            for (int i = 0; i < points.Count; i++)
            {
                var point = points[i];
                var gravity = this.gravity * (1f - (float)i / points.Count * gravityFallout); // 꼬리 쪽으로 갈수록 더 펄럭거리도록 조정.
                var newPos = point.Position + point.Velocity * damp + gravity * interval * Vector2.down;
                var clampedOffset = Vector2.ClampMagnitude(newPos - parentPos, point.Gap);

                var lastPos = point.Position;
                point.Position = parentPos + clampedOffset;
                point.Velocity = point.Position - lastPos;
                if (onFlip) // 좌우반전 되었을 때, 너무 펄럭이지 않도록 조정.
                    point.Velocity = Vector2.ClampMagnitude(point.Velocity, .1f);

                parentPos = point.Position;
            }

            for (int i = 0; i < points.Count; i++)
            {
                Vector2 direction = points[i].Position - bones[i].position.V2();
                float angle = Mathf.Atan2(direction.y, direction.x) * Mathf.Rad2Deg;
                bones[i].rotation = flipped ? Quaternion.Euler(180f, 0f, -angle) : Quaternion.Euler(0f, 0f, angle);
            }
        }

        [Serializable]
        public class Point
        {
            public Vector2 Position { get; set; }
            [field: SerializeField] public Vector2 StartOffset { get; set; }
            [field: SerializeField] public float Gap { get; set; }
            public Vector2 Velocity { get; set; }
        }
    }
}