Resolved Resizing colliders at runtime and in jobs with burst.

So recently I've been working on a project that requires me to be able to resize the colliders of prefabs that I'm instantiating in an ICollisionEventsJob but the only way I've found to do that is by first getting the collider pointer and changing the geometry of it via unsafe code. Preferably I would like to avoid unsafe code if possible but if not I would at least want to be able to use it in parallel safely and efficiently.

So in my project, I am using a CommandBuffer as a parallel writer in the ICollisionEventsJob which I then use to instantiate and initialize an entity during a specific type of collision. Problem is that I need to change the size of the instantiated entity dynamically, but just changing (for instance) the CompositeScale component doesn't affect the collider's size as it is baked in at the start of the simulation.

I looked around for a fix and I stumbled upon an example scene by (I presume) Unity which uses code like this:

Code (CSharp):

1. unsafe
2. {
3.     // grab the sphere pointer
4.     SphereCollider* scPtr = (SphereCollider*)collider.ColliderPtr;
5.     oldRadius = scPtr->Radius;
6.     newRadius = math.lerp(oldRadius, radius.Target, 0.05f);
7.     // if we have reached the target radius get a new target
8.     if (math.abs(newRadius - radius.Target) < 0.01f)
9.     {
10.          radius.Target = radius.Target == radius.Min ? radius.Max : radius.Min;
11.     }
12.  
13.     // update the collider geometry
14.     var sphereGeometry = scPtr->Geometry;
15.     sphereGeometry.Radius = newRadius;
16.     scPtr->Geometry = sphereGeometry;
17. }

To change the collider size. Now the problem with this is that it requires that you either have access to the collider of the entity or that you know how to make a new one from scratch, both things of which I don't know how to do.

Getting access to the entity's collider might at first seem like a fairly easy task but not in this case. (In my understanding) you have to use a ComponentDataFromEntity<PhysicsCollider> to get access to the PhysicsCollider component of an entity. To make one of those I have to have access to a system and create one right after I created the new entity. Problem is that a system is a reference type, which does not play nicely with jobs. Also, I am unsure whether burst plays nicely with unsafe code or not.

So really, in my mind, there is only one solution which is to create a new collider from scratch which I do not know how to do in code. However, to me, even that seems like a roundabout and inefficient way of doing it. I would really appreciate any kind of help, thanks.

 

Unfortunately, we currently don't support collider runtime scaling. We have it in sight as an important feature, though.

You can use

public static unsafe BlobAssetReference<Collider> Create(...)

to create a collider and

public unsafe void Initialize(...)

to change existing one. The key part is setting up the *Geometry struct for the shape. Going into the physics code often helps if you're not sure about what some things do or what to pass in.

Unsafe code does look a bit intimidating, but it just requires you to know exactly what you're doing and it will serve you well (Burst won't complain).

The following samples might be useful:
Assets/Demos/5. Modify/5b. Change Collider Size.unity
Assets/Demos/5. Modify/5c. Change Collider Type.unity
Assets/Demos/5. Modify/5g. Change Collider Filter.unity

Please let me know if this helps.

 

I get a bit confused with this statement that collider runtime scaling is not supported. In my thread here https://forum.unity.com/threads/collider-create-performance.1055930/ I change the geometry of an already created collider like this:

Code (CSharp):

1. unsafe
2. {
3.     BoxCollider* bcPtr = (BoxCollider*)collider.GetUnsafePtr();
4.     BoxGeometry boxGeom = bcPtr->Geometry;
5.     boxGeom.Size = size;
6.     bcPtr->Geometry = boxGeom;
7. }

Is this different to runtime scaling?

 

I think you need to rebuild the PhysicsMass (PhysicsMass.CreateDynamic) after you change the size of a collider
just changing the collider alone is not enough

 

@Shinyclef , sorry for the confusion. You can change the whole geometry, I meant that we don't support changing scale only. Currently, scale is baked into the geometry, so the way you're going is the only one right now.

@argibaltzi, that's correct, thank you! You should update entity's PhysicsMass component with

PhysicsMass.CreateDynamic(collider.MassProperties, mass) 

.

 

Sorry for the late reply.

I'm sorry but I don't think I understand how those two functions work; Initialize
and BlobAssetReference<Collider>.Create. Create takes either a byte[] (byte[] of what?) or a collider (But that seems kinda backwards to me) or a void* and length (Again, to what?). Also I don't really understand where you're finding this "Initialize" function, could you elaborate? Sorry if I seem brazen I would just like to understand.

I do understand @argibaltzi point, but again, I'm unsure as to how I'm supposed to go about getting a new collider.

 

you need to study the samples and do some experiments to understand how things work

 

Hi, juliusensen.
I use this way to rescale the collider. This code is working fine in the level editor. I'm not 100% sure is it the right way to do it in the actual game or not.

Code (CSharp):

1. EntityManager manager = World.DefaultGameObjectInjectionWorld.EntityManager;
2. Entity ent = manager.CreateEntity();
3.  
4. SphereGeometry sphere = new SphereGeometry
5. {
6. Center = float3.zero,
7. Radius = 100
8. };
9. BlobAssetReference<Unity.Physics.Collider> colliderRef = Unity.Physics.SphereCollider.Create(sphere);
10.  
11. manager.AddComponentData(ent, new PhysicsCollider { Value = colliderRef });
12.  

Or you can use this way, mentioned above. Not tested it, but looks like it will work fine.

Code (CSharp):

1. EntityManager manager = World.DefaultGameObjectInjectionWorld.EntityManager;
2.         Entity ent = manager.CreateEntity();
3.  
4.         PhysicsCollider collider = manager.GetComponentData<PhysicsCollider>(ent);
5.         unsafe
6.         {
7.             SphereCollider* bcPtr = (SphereCollider*)collider.Value.GetUnsafePtr();
8.             SphereGeometry sphereGeom = bcPtr->Geometry;
9.             sphereGeom.Center = float3.zero;
10.             sphereGeom.Radius = 100;
11.             bcPtr->Geometry = sphereGeom;
12.         }

And quick guess about jobs. Probably it won't work, but may be it will push you to the right solution. It is pseudocode and I have no time to test this approach.

Code (CSharp):

1. void OnUpdate()
2. {
3. NativeList<Entity> entities = new NativeList<Entity>();
4.         EntityCommandBuffer buffer = new EntityCommandBuffer();
5.         InstantiateJob instJob = new InstantiateJob()
6.         {
7.             buffer = buffer,
8.             entities = entities
9.         };
10.         var instHandle = instJob.Schedule();
11.         instHandle.Complete();
12.  
13.         buffer.Playback(World.EntityManager);
14.         var data = GetComponentDataFromEntity<PhysicsCollider>();
15.  
16.         ResizeColliderJob resizeJob = new ResizeColliderJob
17.         {
18.             radius = 200,
19.             dataFromEntity = data,
20.             entities = entities
21.         };
22.         var resizeHandle = resizeJob.Schedule(entities.Length, 4);
23.         resizeHandle.Complete();
24.  
25.         entities.Dispose();
26. }
27. public struct InstantiateJob : ICollisionEventsJob
28. {
29.     public EntityCommandBuffer buffer;
30.     public NativeList<Entity> entities;
31.  
32.     public void Execute(CollisionEvent collisionEvent)
33.     {
34.         Entity tempEnt = buffer.Instantiate();
35.         entities.Add(tempEnt);
36.     }
37. }
38.  
39. public struct ResizeColliderJob : IJobParallelFor
40. {
41.     public float radius;
42.     public ComponentDataFromEntity<PhysicsCollider> dataFromEntity;
43.     public NativeList<Entity> entities;
44.  
45.     public void Execute(int index)
46.     {
47.         unsafe
48.         {
49.             Unity.Physics.SphereCollider* sPtr = (Unity.Physics.SphereCollider*)dataFromEntity[entities[index]].ColliderPtr;
50.             var sphereGeometry = sPtr->Geometry;
51.             sphereGeometry.Radius = radius;
52.             sPtr->Geometry = sphereGeometry;
53.         }
54.     }
55. }

 

Thanks so much! The first method works perfectly for what I'm trying to do.

 

it's nice to hear that. I'm glad I could help