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Help with DynamicBuffer of Entities

Discussion in 'Data Oriented Technology Stack' started by Plummers, May 20, 2020.

  1. Plummers

    Plummers

    Joined:
    Oct 29, 2015
    Posts:
    31
    Hi,
    I have a Formation which moves around and then I have the units "in the formation" which move to the position of their Formation entity.

    Formation #1 << 20 units
    Formation #2 << 16 other units
    etc..

    Currently a Formation does not know its units. The units know their Formation.

    Question. Now I have a situation where a Formation needs to select a specific unit from its formation.

    Is a dynamic buffer the way to go and can I do this:
    "public DynamicBuffer<Entity> units" and have this on my formation?

    Many thanks for any advice and help, still working out how best to use DOTS.
     
  2. DreamingImLatios

    DreamingImLatios

    Joined:
    Jun 3, 2017
    Posts:
    2,517
    If you want to use dynamic buffers you need to define an IBufferElementData.
     
  3. quabug

    quabug

    Joined:
    Jul 18, 2015
    Posts:
    63
    `ISharedComponentData` seems fit to your need.
    Create something like
    Code (CSharp):
    1. public struct Formation : ISharedComponentData
    2. {
    3.     public int Value;
    4. }
    And `SetFilter` for your query to iterate each entities which have specific `Value` of `Formation`.

    `DynamicBuffer` also works but need to more attention on lifecycle of each entity.
     
  4. Plummers

    Plummers

    Joined:
    Oct 29, 2015
    Posts:
    31

    Thanks quabug. I'm getting a burst error when I try setting this as the unit is instantiated:

    commandBuffer.AddSharedComponent(entityInQueryIndex, unit, new FormationID { Value = 1 });

    Can I set each group of formation units a new Value? So first formation every unit has shared FormationID Value = 1, 2nd formation = 2 etc...

    [Error]
    Burst error BC1001: Unable to access the managed method `object.Equals(object)` from type `FormationID`

    Thanks again
     
  5. quabug

    quabug

    Joined:
    Jul 18, 2015
    Posts:
    63
    https://docs.unity3d.com/Packages/c.../api/Unity.Entities.ISharedComponentData.html
    "ISharedComponent implementations must implement IEquatable<T> and GetHashCode()."

    Yes, that is a shared component used for.
    https://docs.unity3d.com/Packages/com.unity.entities@0.10/manual/shared_component_data.html
    "Shared components are a special kind of data component that you can use to subdivide entities based on the specific values in the shared component (in addition to their archetype)."
     
  6. Plummers

    Plummers

    Joined:
    Oct 29, 2015
    Posts:
    31
    Thanks for all your help quabug.

    Found out the reason was you can't add sharedcomponentdata with burst enabled. So got it working now.
     
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