wave6-zero-data-enableable-signal

Zero-Data Enableable Signal — Inter-System Signaling

Intent

Use a zero-field IEnableableComponent as a single-bit signal between producer and consumer systems, avoiding event queues and DynamicBuffer cleanup overhead.

Use When

• One system signals another that a condition occurred (repositioning needed, UI dirty, AI alert)
• Signal is boolean (happened / not happened) and carries no data payload
• Producer and consumer are on different systems with defined execution order

Avoid When

• Signal must carry a data payload — use a separate IComponentData field or DynamicBuffer element
• Multiple independent signals of same type can occur in the same frame — a single bit cannot distinguish count; use DynamicBuffer for counted/multi-signal
• Multiple producers write to the same entity's signal — last write wins; use DynamicBuffer for multi-producer scenarios

Senior Pattern

// Zero-size signal component:
public struct RepositionNeeded : IComponentData, IEnableableComponent { }

// Baker: add signal component (starts disabled):
public override void Bake(TeamAuthoring authoring)
{
    var entity = GetEntity(TransformUsageFlags.None);
    AddComponent<RepositionNeeded>(entity);
    SetComponentEnabled<RepositionNeeded>(entity, false);
}

// Producer system — sets signal:
[UpdateInGroup(typeof(SimulationSystemGroup))]
[BurstCompile]
public partial struct TeamEventSystem : ISystem
{
    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        foreach (var (teamData, entity) in
            SystemAPI.Query<RefRO<TeamData>>().WithEntityAccess())
        {
            if (teamData.ValueRO.NeedsReposition)
                SystemAPI.SetComponentEnabled<RepositionNeeded>(entity, true);
        }
    }
}

// Consumer system — reacts and MUST clear signal:
[UpdateInGroup(typeof(SimulationSystemGroup))]
[UpdateAfter(typeof(TeamEventSystem))]
[BurstCompile]
public partial struct RepositionSystem : ISystem
{
    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        foreach (var (transform, entity) in
            SystemAPI.Query<RefRW<LocalTransform>>()
                     .WithAll<RepositionNeeded>()
                     .WithEntityAccess())
        {
            // handle repositioning
            DoReposition(ref transform.ValueRW);

            // MUST clear signal — consumer owns signal clearing:
            SystemAPI.SetComponentEnabled<RepositionNeeded>(entity, false);
        }
    }
}