aibis-dream/Assets/Scripts/SceneManagement/SubwayHandStrap.cs

using UnityEngine;

namespace AibisDream
{
    [RequireComponent(typeof(SpriteRenderer))]
    public sealed class SubwayHandStrap : MonoBehaviour
    {
        [SerializeField] private SubwayCarMotion carMotion;
        [SerializeField] private float length = 0.42f;
        [SerializeField] private float gravity = 9.81f;
        [SerializeField] private float dampingRatio = 0.16f;
        [SerializeField] private float maxAngle = 25f;
        [SerializeField] private float maxAngularSpeed = 180f;
        [SerializeField] private float maxIntegrationStep = 1f / 120f;

        [Header("Instance Variation")]
        [SerializeField] private bool randomizeOnAwake = true;
        [SerializeField] private float lengthVariation = 0.03f;
        [SerializeField] private Vector2 dampingRatioRange = new Vector2(0.14f, 0.18f);
        [SerializeField] private float initialAngleRange = 0.5f;

        [Header("Pivot")]
        [SerializeField] private Vector3 hangPointLocalOffset;

        private SpriteRenderer spriteRenderer;
        private Vector3 restLocalPosition;
        private float angle;
        private float angularVelocity;
        private float baseLength;

        public float Angle => angle;

        public float Length => length;

        private void Awake()
        {
            spriteRenderer = GetComponent<SpriteRenderer>();
            restLocalPosition = transform.localPosition;
            baseLength = length;

            if (hangPointLocalOffset == Vector3.zero && spriteRenderer.sprite != null)
            {
                hangPointLocalOffset = new Vector3(0f, spriteRenderer.sprite.bounds.max.y, 0f);
            }

            if (carMotion == null)
            {
                carMotion = GetComponentInParent<SubwayCarMotion>();
            }

            if (randomizeOnAwake)
            {
                RandomizeInstance();
            }

            ApplyPose();
        }

        private void Update()
        {
            float remainingTime = Time.deltaTime;
            while (remainingTime > 0f)
            {
                float step = Mathf.Min(remainingTime, maxIntegrationStep);
                Simulate(step);
                remainingTime -= step;
            }

            ApplyPose();
        }

        private void RandomizeInstance()
        {
            Random.State previousState = Random.state;
            Random.InitState(GetInstanceID());

            length = baseLength * Random.Range(1f - lengthVariation, 1f + lengthVariation);
            dampingRatio = Random.Range(dampingRatioRange.x, dampingRatioRange.y);
            angle = Random.Range(-initialAngleRange, initialAngleRange);
            angularVelocity = 0f;

            Random.state = previousState;
        }

        private void Simulate(float deltaTime)
        {
            float safeLength = Mathf.Max(0.01f, length);
            float angleRadians = angle * Mathf.Deg2Rad;
            float angularVelocityRadians = angularVelocity * Mathf.Deg2Rad;
            float naturalFrequency = Mathf.Sqrt(gravity / safeLength);
            float accelX = carMotion != null ? carMotion.AccelX : 0f;

            float angularAcceleration =
                -(gravity / safeLength) * Mathf.Sin(angleRadians)
                - (accelX / safeLength) * Mathf.Cos(angleRadians)
                - 2f * dampingRatio * naturalFrequency * angularVelocityRadians;

            angularVelocityRadians += angularAcceleration * deltaTime;
            angularVelocity = Mathf.Clamp(angularVelocityRadians * Mathf.Rad2Deg, -maxAngularSpeed, maxAngularSpeed);
            angle += angularVelocity * deltaTime;

            ClampAngleLimit();
        }

        private void ClampAngleLimit()
        {
            if (Mathf.Abs(angle) <= maxAngle)
            {
                return;
            }

            float limitSign = Mathf.Sign(angle);
            angle = limitSign * maxAngle;

            if (Mathf.Sign(angularVelocity) == limitSign)
            {
                angularVelocity = 0f;
            }
        }

        private void ApplyPose()
        {
            Quaternion rotation = Quaternion.Euler(0f, 0f, angle);
            transform.localRotation = rotation;
            transform.localPosition = restLocalPosition + hangPointLocalOffset - rotation * hangPointLocalOffset;
        }
    }
}