ChristmasSomething.cs

using UnityEngine;

/// <summary>
/// [WIP] 行き当たりばったりでクリスマスっぽい何かを作っている
/// </summary>
[RequireComponent(typeof(MeshRenderer))]
public class ChristmasSomething : MonoBehaviour
{
    [SerializeField]
    private Vector2Int _texSize = new Vector2Int(300, 300);

    private Renderer _renderer;

    [SerializeField]
    private float _radius = 40f;

    private Texture2D _canvas;

    [SerializeField]
    private Color32 _baseColor = new Color32(0, 0, 0, 255);

    [SerializeField]
    private Color32 _addColor = new Color32(255, 255, 255, 255);

    [SerializeField]
    private int _interval = 10;

    [SerializeField]
    private int _maxParallelDrawCount = 10;

    [SerializeField]
    private Transform _camTransform;

    void Start()
    {
        _renderer = GetComponent<MeshRenderer>();
        _canvas = new Texture2D(_texSize.x, _texSize.y);
        _renderer.material.mainTexture = _canvas;
        for (int x = 0; x < _texSize.x; x++)
        {
            for (int y = 0; y < _texSize.y; y++)
            {
                _canvas.SetPixel(x, y, _baseColor);
            }
        }

        _canvas.Apply();
    }


    void Update()
    {
        transform.Rotate(new Vector3(0.3f, 1f, 0), Time.deltaTime * 20f);

        bool isApplyed = false;
        FadeOut();

        if (_interval < 1)
        {
            _interval = 1;
        }

        if (Time.frameCount % _interval == 0)
        {
            int count = Random.Range(1, _maxParallelDrawCount);
            for (int i = 0; i < count; i++)
                Draw(Random.Range(0, _texSize.x), Random.Range(0, _texSize.y), _radius * Random.Range(0.6f, 1f));
            _canvas.Apply();
            isApplyed = true;
        }

        if (isApplyed == false)
            _canvas.Apply();
    }

    void LateUpdate()
    {
        _camTransform.LookAt(Vector3.zero);
        _camTransform.RotateAround(Vector3.zero, Vector3.up, -Time.deltaTime * 20f);
    }

    void FadeOut()
    {
        for (int x = 0; x < _texSize.x; x++)
        {
            for (int y = 0; y < _texSize.y; y++)
            {
                var color = _canvas.GetPixel(x, y);

                var result = Color.Lerp(color, _baseColor, color.b * 0.1f);

                _canvas.SetPixel(x, y, result);
            }
        }
    }

    void Draw(int cx, int cy, float radius)
    {
        for (int x = 0; x < _texSize.x; x++)
        {
            for (int y = 0; y < _texSize.y; y++)
            {
                var xx = x - radius;
                var yy = y - radius;

                float distance = Mathf.Sqrt(xx * xx + yy * yy);
                if (distance >= radius)
                    continue;

                _canvas.SetPixel(x + cx, y + cy, _addColor);
            }
        }
    }
}