Implement OnUpdate() to perform the major work of this system.
By default, the system invokes OnUpdate() once every frame on the main thread.
To skip OnUpdate if all of the system's [EntityQueries] are empty, use the
[RequireMatchingQueriesForUpdateAttribute]. To limit when OnUpdate is invoked, you can
specify components that must exist, or queries that match specific Entities. To do
this, call M:Unity.Entities.ComponentSystemBase.RequireForUpdate@@@@1 or
ComponentSystemBase.RequireForUpdate
in the system's OnCreate method. For more information, see [ShouldRunSystem].
Use [IJobEntity] or SystemAPI.Query for common iteration patterns. You can also instantiate and schedule an IJobChunk instance;
implement other Unity.Jobs interfaces or perform work on the main thread. If you call EntityManager methods
that perform structural changes on the main thread, be sure to arrange the system order to minimize the
performance impact of the resulting [sync points].
[sync points]: xref:concepts-structural-changes
[C# Job System]: xref:JobSystem
[IJobEntity]: xref:Unity.Entities.IJobEntity
[EntityQueries]: xref:Unity.Entities.EntityQuery
[RequireMatchingQueriesForUpdateAttribute]: xref:Unity.Entities.RequireMatchingQueriesForUpdateAttribute
[ShouldRunSystem]: xref:Unity.Entities.ComponentSystemBase.ShouldRunSystem