モジュール小物とグリッドスナップ

using UnityEngine;

public class PropScatter : MonoBehaviour
{
    [SerializeField] private GameObject[] prefabs;
    [SerializeField] private int count = 120;
    [SerializeField] private float radius = 40f;
    [SerializeField] private LayerMask groundMask;
    [SerializeField] private Vector2 scaleRange = new Vector2(0.8f, 1.4f);

    [ContextMenu("Scatter")]            // right-click the component → Scatter
    public void Scatter()
    {
        Clear();

        for (int i = 0; i < count; i++)
        {
            Vector2 flat = Random.insideUnitCircle * radius;
            Vector3 from = transform.position + new Vector3(flat.x, 50f, flat.y);

            // drop a ray straight down to find the ground
            if (!Physics.Raycast(from, Vector3.down, out RaycastHit hit, 200f, groundMask))
                continue;

            // skip cliffs — props on a vertical wall look broken
            if (Vector3.Angle(hit.normal, Vector3.up) > 30f) continue;

            GameObject prefab = prefabs[Random.Range(0, prefabs.Length)];
            GameObject go = Instantiate(prefab, hit.point, Quaternion.identity, transform);

            go.transform.rotation = Quaternion.Euler(0f, Random.Range(0f, 360f), 0f);
            go.transform.localScale = Vector3.one * Random.Range(scaleRange.x, scaleRange.y);
        }
    }

    [ContextMenu("Clear")]
    public void Clear()
    {
        for (int i = transform.childCount - 1; i >= 0; i--)
            DestroyImmediate(transform.GetChild(i).gameObject);
    }
}