Natural Collisions

In DOTS Dynamic Bone Natural collision referes to collisions using Unity's Unity.Physics package components/data. Instead of creating and storing custom data, DOTS Dynamic Bone uses the Unity.Physics.PhysicsCollider in its physics calculations. This allows a DOTS Dynamic Bone Particle to collide with any other entity that contains a Unity.Physics.PhysicsCollider and the best part is that it is very easy to use.

In order to use Natural collision just set the Use Natural Colliders setting to true on any DOTS Dynamic Bone Component. You can also add Natural collision to an already existing Bone by adding a DOTSDynamicBoneNaturalCollider_Tag to your DOTSDynamicBone Entity. This tag let's the Natural collision system know you want to use it. Also be sure to set UseNaturalColliders on the DOTS Dynamic Bone Entity to true and to make sure the collider property in the Particle's DynamicBuffer is not null. If you only want only some Particles to take part in the collision then you can leave the Particle's collider data null which will process the Particle noramlly.

Here's an example oh how to add a DOTS Dynamic Bone Entity to the Natural collision system:

public class DOTSDynamicBoneAddCollisionSystemExample : SystemBase
{
    protected override void OnUpdate()
    {

        Entities.
            WithName("AddBoneToCollisionSystemJob")
            .WithoutBurst()
            .WithAll<DOTSDynamicBone_AddToCollisionSystem_Tag>()
            .WithNone<DOTSDynamicBone.Collision.DOTSDynamicBoneNaturalCollider_Tag>()
            .ForEach((Entity e,ref DOTSDynamicBone.DOTSDynamicBone boneData,ref DynamicBuffer<DOTSDynamicBone.Particle> particles)=> {
                // set the UseNaturalColliders property to true
                boneData.UseNaturalColliders = true;

                // let's add the Unity.Physics.PhysicsCollider to each respective particle.
                // let's also disable collision calculations for every Particle who ith index is divisiable by 2 just because we can. 
                for(int i = 0; i < particles.Length; i++)
                {
                    DOTSDynamicBone.Particle p = particles[i];

                    p.m_ExcludeFromCollision = i % 2 == 0;  // exclude from collision if i mod 2 == 0

                    // if the m_TransformEntity has a PhysicsCollider then set it
                    unsafe
                    {
                        if (HasComponent<Unity.Physics.PhysicsCollider>(p.m_TransformEntity))
                        {
                            Unity.Physics.PhysicsCollider col = GetComponent<Unity.Physics.PhysicsCollider>(p.m_TransformEntity);

                            if (col.IsValid && col.Value.IsCreated)
                                p.collider = col.ColliderPtr;
                            else p.collider = null;
                        }
                        else p.collider = null;
                    }

                    particles[i] = p;
                }

                // these two functions are not Burstable. this addition and removal should be done
                // elsewhere. This is just an example.
                EntityManager.AddComponentData(e, new DOTSDynamicBone.Collision.DOTSDynamicBoneNaturalCollider_Tag { });
                EntityManager.RemoveComponent<DOTSDynamicBone_AddToCollisionSystem_Tag>(e);

            })
            .Run();

    }
}
public struct DOTSDynamicBone_AddToCollisionSystem_Tag : IComponentData { }
public struct DOTSDynamicBone_RemoveFromCollisionSystem_Tag : IComponentData { }