【Dots之003】SystemAPI.Query相关基础笔记

1、SystemAPI.Query

注：SystemAPI.Query只能作为foreach中in的的子句

SystemAPI.Query<RefRO<LocalTransform>>().WithAll<Obstacle>()

解析：对于每个具有LocalTransform和Obstacle的Entity；都会将LocalTransform的只读引用返回给查询结果

SystemAPI.Query<RefRW<LocalTransform>, RefRW<Velocity>>().WithAll<Ball>()

解析：查询具有LocalTransform,Velocity,Ball组件的Entity,将LocalTransform和Velocity的可读写引用返回，用于可读可修改

2、LocalTransform

不设置默认的Scale和Rotation属性

state.EntityManager.SetComponentData(player, new LocalTransform());

可以看到默认都是设置为0；

设置的默认属性以后：

 state.EntityManager.SetComponentData(player, new LocalTransform{Position = new float3{x = obstacleTransform.ValueRO.Position.x + config.PlayerOffset,y = 1,z = obstacleTransform.ValueRO.Position.z + config.PlayerOffset},Scale = 1, // If we didn't set Scale and Rotation, they would default to zero (which is bad!)Rotation = quaternion.identity});

给Entity添加LocalTransform需要设置默认的Scale和Rotation;上面的代码中没有设置，得到的结果会如下：

现在就是正常的状态了；

3、Unity.Mathematics.Random

首先根据情况决定是否需要设置一个随机种子；然后在进行调用；

var rand = new Random(123);
//随机一个值
float random_one = rand.NextFloat(0, 100);
//随机一个2为向量
float2 random_v2 = rand.NextFloat2(new float2(0, 0), new float2(100, 100));
//随机一个方向
random_v2 = rand.NextFloat2Direction();

4、EntityQuery

获取或者创建与查询描述匹配的EntiyQuery
如果System中没有匹配的EntityQuery，那么就Create一个；如果有就直接Get

//描述同时具有Obstacle和LocalTransform组件的EntityQuery
var obstacleQuery = SystemAPI.QueryBuilder().WithAll<LocalTransform, Obstacle>().Build();

5、IEnableableComponent

组件继承IEnableableComponent，可以起到开启和关闭组件的作用；而不需要把该组件从Entity上面移除；
1、启用组件：SetComponentEnabled(entity,true);
2、关闭组件：SetComponentEnabled(entity,false);

 public override void Bake(PlayerAuthoring authoring){var entity = GetEntity(TransformUsageFlags.Dynamic);AddComponent<Player>(entity);  AddComponent<Carry>(entity);//设置是否启用ComponentDataSetComponentEnabled<Carry>(entity, false);}public struct Carry : IComponentData, IEnableableComponent{}

3、如果通过IJobEntity的方式来处理组件的启用与否，可以参考下面的这种方式：

 	[WithAll(typeof(Turret))][WithOptions(EntityQueryOptions.IgnoreComponentEnabledState)][BurstCompile]public partial struct SafeZoneJob : IJobEntity{public float SquaredRadius;// Because we want the global position of a child entity, we read LocalToWorld instead of LocalTransform.void Execute(in LocalToWorld transformMatrix, EnabledRefRW<Carry> shootingState){//组件的启用状态shootingState.ValueRW = math.lengthsq(transformMatrix.Position) > SquaredRadius;}}

EnabledRefRW后面的类型必须要继承IEnableableComponent；