Unity DOTS纯ECS写一个类似UGUI的EventSystem(实现IPointerDownHandler/IPointerUpHandler/IBeginDragHandler等)_unity ipointerdownhandler

这篇文章主要展示下在Unity的ProjectTiny环境中用纯ECS代码实现UGUI里的EventSystem，包括常用的IPointerDownHandler、IPointerUpHandler、IBeginDragHandler、IDragHandler、IEndDragHandler、IPointerEnterHandler、IPointerExitHandler、IPointerClickHandler等功能。

虽然ProjectTiny里有自带的Button等UI，但是它的点击事件并不是通用的，无法随便给想要的2D entity加上点击事件。不过ProjectTiny提供了最基本的InputSystem，可以获得输入数据。根据这些数据，再处理下，就可以实现UGUI里的那几个Handler了，然后就可以让任意的2D entity(带RectTransform的entity)响应按下抬起点击滑动等事件，还有游戏中常用的鼠标滑动到物品icon上就弹出一个tip，滑出icon后tip消失(也就是IPointerEnter/IPointerExit的功能)。

需要注意一点，由于IComponentData中不能存放NativeList这种Container，所以用的是IBufferElementData，跟数组用法差不多，可以动态增长，但是增删比较麻烦。也可以直接在System里用一个NativeList来存放数据，但是这样不够ECS，而且数据不多，遍历几遍数组对性能影响不会太大。

看代码。代码只是展示一下实现方法，可以继续优化。

using Unity.Entities;
using Unity.Jobs;
using Unity.Mathematics;
using Unity.Transforms;
using Unity.Tiny.UI;
using Unity.Tiny;
using Unity.Tiny.Input;
using Unity.Tiny.Rendering;
using Unity.Collections;

namespace wangtal.EventSystem {
   
    public interface IPointerDownHandler {
   }

    public interface IPointerUpHandler {
   }

    public interface IPointerClickHandler {
   }

    public interface IPointerEnterHandler {
   }

    public interface IPointerExitHandler {
   }

    public interface IBeginDragHandler {
   }

    public interface IDragHandler {
   }

    public interface IEndDragHandler {
   }

    public interface ICancelHandler {
   }

    internal struct PointerEventData : IBufferElementData {
   
        internal enum TriggerState : byte {
   
            None = 0 << 0,
            PointerDown = 1 << 0,
            PointerUp = 1 << 1,
            PointerClick = 1 << 2,
            BeginDrag = 1 << 3,
            Drag = 1 << 4,
            EndDrag = 1 << 5,
            PointerEnter = 1 << 6,
            PointerExit = 1 << 7
        }

        public TriggerState State;

        public int PointerId;

        public Entity Target;

        // 当前位置
        public float2 Position;

        // 滑动间隔
        public float2 Delta;

        // 按下时的位置
        public float2 PressPosition;
    }

	public class InputSystemGroup : ComponentSystemGroup
    {
   
        const int MaxTriggerEvent = 10;

        protected override void OnCreate()
        {
   
            base.OnCreate();
            var entity = EntityManager.CreateEntity();
            var buffer = EntityManager.AddBuffer<PointerEventData>(entity);
            for (int i = 0; i < MaxTriggerEvent; i++) {
   
                PointerEventData data = new PointerEventData {
   
                    State = PointerEventData.TriggerState.None, PointerId = -1, Target = Entity.Null, Position = float2.zero, Delta = float2.zero, PressPosition = float2.zero
                };
                buffer.Add(data);
            }
        }
    }

	[UpdateInGroup(typeof(InputSystemGroup))]
    unsafe public class EventSystem : SystemBase
    {
   
        private ScreenToWorld screenToWorld;

        private InputSystem inputSystem;

        protected override void OnCreate()
        {
   
            base.OnCreate();

            screenToWorld = World.GetExistingSystem<ScreenToWorld>();
            inputSystem = World.GetExistingSystem<InputSystem>();
        }

        protected override void OnUpdate()
        {
   
            var input = inputSystem;
            Entities.ForEach((Entity entity, ref DynamicBuffer<PointerEventData> eventDatas) => {
   
                PointerEventData* p = (PointerEventData*)eventDatas.GetUnsafePtr();
                for (int i = 0; i < eventDatas.Length; i++, p++) {
   
                    ref var eventData = ref UnsafeUtility.AsRef<PointerEventData>(p);//eventDatas[i];
                    if (eventData.State == PointerEventData.TriggerState.PointerDown ||
                        eventData.State == PointerEventData.TriggerState.PointerUp ||
                        eventData.State == PointerEventData.TriggerState.BeginDrag ||
                        eventData.State == PointerEventData.TriggerState
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