用Unity ECS DOTS做一个烟花，附代码

以下是用 Unity ECS DOTS 实现的简单烟花示例代码：

using System.Collections.Generic;
using Unity.Collections;
using Unity.Entities;
using Unity.Mathematics;
using Unity.Transforms;
using UnityEngine;

public class FireworkSystem : SystemBase
{
    private EntityQuery fireworkQuery;
    private EntityQuery explosionQuery;

    protected override void OnCreate()
    {
        fireworkQuery = GetEntityQuery(typeof(Firework), typeof(Translation), typeof(Velocity));
        explosionQuery = GetEntityQuery(typeof(Explosion), typeof(Translation));
    }

    protected override void OnUpdate()
    {
        // 更新烟花位置和速度
        Entities.With(fireworkQuery).ForEach((ref Translation translation, ref Velocity velocity) =>
        {
            velocity.Value += new float3(0, -9.81f, 0) * Time.DeltaTime;
            translation.Value += velocity.Value * Time.DeltaTime;
        }).Run();

        // 检查烟花是否需要爆炸
        Entities.With(fireworkQuery).ForEach((Entity entity, ref Firework firework, ref Translation translation) =>
        {
            if (translation.Value.y <= firework.Height)
            {
                // 生成爆炸粒子
                var explosionEntity = EntityManager.CreateEntity(typeof(Explosion), typeof(Translation));
                EntityManager.SetComponentData(explosionEntity, new Translation { Value = translation.Value });
                EntityManager.DestroyEntity(entity);
            }
        }).Run();

        // 更新爆炸粒子位置和寿命
        Entities.With(explosionQuery).ForEach((Entity entity, ref Explosion explosion, ref Translation translation) =>
        {
            explosion.Lifetime -= Time.DeltaTime;
            if (explosion.Lifetime <= 0)
            {
                EntityManager.DestroyEntity(entity);
            }
            else
            {
                var size = explosion.Size * (1 - explosion.Lifetime / explosion.MaxLifetime);
                translation.Value += explosion.Velocity * Time.DeltaTime;
                EntityManager.SetComponentData(entity, new Scale { Value = size });
            }
        }).Run();
    }
}

public struct Firework : IComponentData
{
    public float Height;
    public float3 Velocity;
}

public struct Explosion : IComponentData
{
    public float Lifetime;
    public float MaxLifetime;
    public float3 Velocity;
    public float Size;
}

public struct Velocity : IComponentData
{
    public float3 Value;
}

public class FireworkSpawner : MonoBehaviour
{
    public GameObject fireworkPrefab;

    private void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            var mousePosition = Input.mousePosition;
            var worldPosition = Camera.main.ScreenToWorldPoint(new Vector3(mousePosition.x, mousePosition.y, 10));
            SpawnFirework(worldPosition);
        }
    }

    private void SpawnFirework(float3 position)
    {
        var fireworkEntity = GameObjectConversionUtility.ConvertGameObjectHierarchy(fireworkPrefab, World.Active);
        EntityManager.SetComponentData(fireworkEntity, new Translation { Value = position });
        EntityManager.SetComponentData(fireworkEntity, new Firework { Height = Random.Range(5f, 15f), Velocity = new float3(Random.Range(-5f, 5f), Random.Range(5f, 15f), Random.Range(-5f, 5f)) });
        EntityManager.AddComponentData(fireworkEntity, new Velocity());
    }
}

这个示例中，我们定义了 `Firework` 和 `Explosion` 两个组件，分别表示烟花和爆炸粒子。在 `FireworkSpawner` 中，我们监听鼠标左键点击事件，然后在鼠标位置生成一个烟花。在 `FireworkSystem` 中，我们使用 `Translation` 和 `Velocity` 组件来更新烟花的位置和速度，并且在烟花达到一定高度时生成爆炸粒子。爆炸粒子的位置和大小会随时间变化，当寿命结束时，会自动销毁。