DOTS/ECS spawn random prefab from array

News & General Discussion
1

Hello!
I’m trying to spawn random prefabs onto my map every X seconds using ECS, but components are only able to hold basic types and not arrays.

How do I access an array of prefabs in my spawner system and instantiate them?
If I could attach the script to an empty gameobject and drag-n-drop my prefabs onto a public array that would be ideal!

Anyone knows how to do?

2

This belongs in the DOTS forum.

How I’m doing it:

The following is my control script.

    void Start()
    {
        em = World.DefaultGameObjectInjectionWorld.EntityManager;
        var settings = GameObjectConversionSettings.FromWorld(World.DefaultGameObjectInjectionWorld, blobAssetStore);
        settings.ConversionFlags = GameObjectConversionUtility.ConversionFlags.AssignName;
        weaponEntity = GameObjectConversionUtility.ConvertGameObjectHierarchy(weaponMainLowPrefab, settings);
        enemyEntity = GameObjectConversionUtility.ConvertGameObjectHierarchy(enemyPrefab, settings);
    }

    Entity CreateEnemy(int state, int X, int Y)
    {
        var instance2 = em.Instantiate(enemyEntity);
        var actionThreshold = 1f;
        var health = 100f;
        switch (state)
        {
            case 0:
                actionThreshold = 0.1f;
                health = 100f;
                break;
        }
        switch(mapStart)
        {
            case Starts.RegularGrowth:
                health = 10f;
                break;
        }
        var position = positionMapping[X, Y];

        var we = new EnemyEntity()
        {
            actionThreshold = actionThreshold,
            actionValue = 0,
            health = health,
            lerp = 0f,
            mapCorner0 = mapCorners[0],
            mapCorner1 = mapCorners[2],
            newPosition = position,
            oldPosition = position,
            state = state,
            weaponEntity = weaponEntity,
            X = X,
            Y = Y
        };
        em.SetComponentData(instance2, new Translation { Value = position });
        em.SetComponentData(instance2, new Rotation { Value = quaternion.identity });
        em.SetComponentData(instance2, we);
        return instance2;
    }

The prefabs must already have the components, with the [GenerateAuthoringComponent] tag above the struct, and a ConvertToEntity component (with ConvertAndDestroy selected).

The following is the enemy system.

var weaponCreation = new NativeQueue<WeaponCreationStruct>(Allocator.TempJob);
        var parallel = weaponCreation.AsParallelWriter();
Entities
                .WithName("EnemySystem")
            .WithBurst(Unity.Burst.FloatMode.Default, Unity.Burst.FloatPrecision.Standard, true)
            .ForEach((Entity entity, int nativeThreadIndex, ref Translation translation, ref Rotation rotation, ref EnemyEntity enemy, in LocalToWorld localToWorld) =>
            {
                        parallel.Enqueue(new WeaponCreationStruct()
                        {
                            velocity = localToWorld.Forward * 55 /** velocity*/,
                            entity = enemy.weaponEntity,
                            weaponEntity = new WeaponEntity(WeaponType.MainLow, enemy.mapCorner0.x, enemy.mapCorner1.x, enemy.mapCorner0.y, enemy.mapCorner1.y),
                            position = front, // any lower and it collides with the player when the player moves
                            rotation = frontDir,
                        });
            }).ScheduleParallel()
        Dependency.Complete();
        if (weaponCreation.Count > 0)
        {
            int count = weaponCreation.Count;
            for (int i = 0; i < count; i++)
            {
                var current = weaponCreation.Dequeue();
                var instance = EntityManager.Instantiate(current.entity);
                EntityManager.SetComponentData(instance, new Translation { Value = current.position });
                EntityManager.SetComponentData(instance, new Rotation { Value = current.rotation });
                EntityManager.SetComponentData(instance, new Unity.Physics.PhysicsVelocity() { Linear = current.velocity });
                EntityManager.SetComponentData(instance, current.weaponEntity);
            }
        }