Creates a Unity.Physics Mesh Collider from a Unity.CompositeCollider2D in Entities exp1.0 without using SubScenes

TilemapData.cs

public class TilemapData : IComponentData
{
  public Grid Grid;
  public Tilemap CollisionMap;
}
	
public struct TilemapData_TAG : IComponentData {}

TilemapDataAuthoring.cs

// Runtime conversion. DO NOT PUT IN SUB-SCENE.
public class TilemapDataAuthoring : MonoBehaviour
{
	public Grid Grid;
	public Tilemap CollisionMap;

	public PhysicsCategoryTags BelongsTo;
	public PhysicsCategoryTags CollidesWith;

	private void Awake()
	{
		var entityManager = World.DefaultGameObjectInjectionWorld.EntityManager;

		var entity = entityManager.CreateEntity();
		entityManager.SetName(entity, "TILEMAP_DATA");
		entityManager.AddComponent<TilemapData_TAG>(entity);

		entityManager.AddComponentData(entity, new TilemapData
		{
			Grid = Grid,
			CollisionMap = CollisionMap
		});

		entityManager.AddComponentData(entity, new Translation { Value = float3.zero });
		entityManager.AddComponentData(entity, new Rotation { Value = quaternion.identity });
		entityManager.AddComponentData(entity, new Scale { Value = 1f });
		entityManager.AddComponent<LocalToWorld>(entity);

		var compositeCollider2D = CollisionMap.GetComponent<CompositeCollider2D>();
		var collisionMesh = compositeCollider2D.CreateMesh(false, false);
		var vertices = new NativeArray<Vector3>(collisionMesh.vertices, Allocator.Temp);
		var triangles = new NativeArray<int3>(collisionMesh.triangles.Length / 3, Allocator.Temp);

		var ii = 0;
		for(var i=0; i<collisionMesh.triangles.Length; i += 3)
		{
			triangles[ii++] = new int3(
				collisionMesh.triangles[i],
				collisionMesh.triangles[i+1],
				collisionMesh.triangles[i+2]
			);
		}

		var meshBlob = Unity.Physics.MeshCollider.Create(
			vertices.Reinterpret<float3>(),
			triangles,
			new CollisionFilter
			{
				BelongsTo = BelongsTo.Value,
				CollidesWith = CollidesWith.Value
			}
		);

		entityManager.AddComponentData(entity, new PhysicsCollider
		{
			Value = meshBlob
		});
		entityManager.AddSharedComponent(entity, new PhysicsWorldIndex());
	}
}