CustomCollider2D.SetCustomShape

When calling CustomCollider2D.SetCustomShape (the NativeArray version), the colliders seem to update visually in the scene inspector. However, the colliders don't seem to collide until I do something like disable and reenable the gameobject holding the CustomCollider2D. It's as if Unity knows they are there, but box2d doesn't, but that's just a guess.

When using SetCustomShapes (plural), everything works as expected. It seems that either SetCustomShape (singular) isn't updating everything internally, or there is some other API I'm supposed to be calling to force the refresh?

This all comes up as part of an investigation on the best way to update a 'bunch' of colliders in a dynamic environment. Imagine, for example only, a large maze 128 on a side. The maze is constantly changing and the walls of the maze of made of squares, each a collider. The number of walls change over time and the walls that are 'active' also change.

In one update model, SetCustomShapes is used and it's native arrays are populated in a job. The job scans what walls are visible (these walls are not gameobjects, just structs in another nativearray), and populates the PhysicsShape2Ds and vertices that SetCustomShapes uses. So if one wall changes, the whole bag of colliders gets rebuilt.

The other model is to prepopulate colliders (128*128 of them in this example) and have them shoved off somewhere (way off at like -10000, -10000). They sit there and wait for walls to be added or removed. For each wall added/ removed, that collider (each is either just a circle or a square) is moved from it's -10000 spot to the correct spot in the maze. This is done with SetCustomShape (singular). Footnote; if the parked colliders at -10000 overlap, there is a large delay when the customcollider2d first updates. If the parked colliders don't overlap, there is no delay. I assume this has to do with the tree hashing in box2d, but that's just a guess.

The second model doesn't work unless I force the CustomCollider2D to 'update' after any call to SetCustomShape. Disabling and enabling the CustomCollider2D is 'expensive'.

So, is this a minor bug or am I missing a 'Refresh' API when using SetCustomShape?
Secondly, what's the best model? Update everything or created parked colliders and bring them into and out of service using SetCustomShape (singular)?

 

Colliders do not collide (I know, seems counter-intuitive)... rather it is Rigidbodies (and Rigidbody2Ds) that collide.

Rigidbodies only collide when they move or rotate, generally speaking. Rigidbodies left alone will soon fall asleep, unless kept awake.

If you need an RB to notice that all of a sudden you have built a freeway straight through his yard, you need to generally get the RB to do an update.

One easy way is to always tell a quiescent non-moving RB to go to their current location.

Code (csharp):

1. myRigidbody.MovePosition( myRigidbody.position);

Obviously if you're moving the RB around you don't need to do that. But the act of doing the above SHOULD inform the RB that he needs to reconsider his position and the implications therein.

I think you still run into trouble if you build a collider entirely AROUND an RB: only the edges of the collider are checked, generally speaking.

 

In my example/test, there is a Rigidbody2D moving around the maze. It 'collides' fine with the CustomCollider2D walls so long as I use SetCustomShapes to create the CustomCollider2D physics shapes. If I use SetCustomShape (singular), it doesn't, unless I disable/enable the CustomCollider2D after calling SetCustomShape.

--edit--
I think I'm just fooling myself. Neither SetCustomShape nor SetCustomShapes seem to update the active colliders unless I disable and enable the containing Gameobject after any changes. If SetCustomShape(s) is called in Awake or Start, life if good. But updates made later update in the scene visually (the green collider lines move), but RigidBody2D's don't seem to interact with them.

Note that it doesn't make a difference if I have a RigidBody2D (static) on the object with the CustomCollider2D. Also note that the kind of changes I am making is to the vertices of the colliders. They are all 4 vertex polygons (squares basically).

 

I've created a simple reproduction case that I think captures what I am seeing. It was created using a vanilla 2D URP Core project template in Unity 2021.3.1. I've attached the project, but it's as simple as updating a CC2D with the script below. The project just has a RigidBody2D sprite object with a CircleCollider2D attached. That object just 'falls' down the y axis under the influence of gravity. It will pass through the first piece of the collider geometry and then stop at the second piece. The gizmo in the scene view draws both of the collider rectangles correctly. It just appears that the first rectangle isn't 'live' until I disable and re-enable the CC2D. I've also attached a screenshot showing the circle resting on the lower rectangle after having passed through the first rectangle shape.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using Unity.Collections;
5.  
6.  
7. public class TestScript : MonoBehaviour {
8.  
9.     private CustomCollider2D cc2d;
10.     private int updateCount;
11.  
12.     public void Awake() {
13.         cc2d = GetComponent<CustomCollider2D>();
14.     }
15.  
16.     //This is a contrived example used to demonstrate that subsequent updates to the CC2D vertices don't seem to completely update physics collisions.
17.     //The scene view will show a green collider rectangle for where the collider should be, but the RigidBody2D circle in this project will not collide with it.
18.     //If the CC2D is disabled/enabled after then vertices change, then the collision happens as expected.
19.     //In the original test case, the vertices move around according to game logic and are updated in a Job with Burst, etc.  That has been removed here since it isn't necessary
20.     //to reproduce the behavior.
21.     public void FixedUpdate() {
22.         if (updateCount == 0) {
23.             var shapes = new NativeArray<PhysicsShape2D>(1, Allocator.Temp);
24.             var vertices = new NativeArray<Vector2>(4, Allocator.Temp);
25.             //This first update seems to apply properly.
26.             //This can also be done in Awake or Start rather than on the first update.
27.             shapes[0] = new PhysicsShape2D() { shapeType = PhysicsShapeType2D.Polygon, vertexCount = 4, vertexStartIndex = 0 };
28.             vertices[0] = new Vector2(100, 100);
29.             vertices[1] = new Vector2(100, 101);
30.             vertices[2] = new Vector2(101, 101);
31.             vertices[3] = new Vector2(101, 100);
32.             cc2d.SetCustomShapes(shapes, vertices);
33.         } else {
34.             var shapes = new NativeArray<PhysicsShape2D>(2, Allocator.Temp);
35.             var vertices = new NativeArray<Vector2>(8, Allocator.Temp);
36.  
37.             //Subsequent updates to the first 4 vertices don't seem to properly apply, not unless the cc2d is disabled and re-enabled.
38.             //Note that the scene view shows the green collider at the propery location, the circle will not collide with it, however.
39.             shapes[0] = new PhysicsShape2D() { shapeType = PhysicsShapeType2D.Polygon, vertexCount = 4, vertexStartIndex = 0 };
40.             vertices[0] = new Vector2(-10, -10);
41.             vertices[1] = new Vector2(-10, -9);
42.             vertices[2] = new Vector2(10, -9);
43.             vertices[3] = new Vector2(10, -10);
44.  
45.             //This geometry does update properly and the circle will collide with it as the circle falls. Presumably, subsequent updates
46.             //to these vertices would not apply, same as with the first set of vertices above.
47.             shapes[1] = new PhysicsShape2D() { shapeType = PhysicsShapeType2D.Polygon, vertexCount = 4, vertexStartIndex = 4 };
48.             vertices[4] = new Vector2(-10, -15);
49.             vertices[5] = new Vector2(-10, -14);
50.             vertices[6] = new Vector2(10, -14);
51.             vertices[7] = new Vector2(10, -15);
52.             cc2d.SetCustomShapes(shapes, vertices);
53.         }
54.  
55.  
56.         //If the collider is disabled/enabled, then the changes to the vertices seem to apply and the circle starts colliding with CustomCollider2D again.
57.         //So uncomment the following line and everything will work as expected.  THe ball will collider with the upper (first 4 vertices) part of the collider.
58.         //cc2d.enabled = false; cc2d.enabled = true;
59.  
60.         updateCount++;
61.     }
62. }

 

Thanks for taking a look. I've created bug report and attached the CC2D.zip project to it. It is Case 1425289.

 

Ah, interesting. Makes sense and not what I was guessing might cause it. Your explanation also points out something I have not considered, but seems notable and sensible... a CustomCollider2D creates a single AABB for itself, not one for each shape within the collider (Wrong, see below). Totally sensible, I'd just not thought about that and the performance impacts that might have for a CC2D with scattered shapes over a 'larger' area.

 

It's all good... and CustomCollider2D is a great addition to Unity. Good to know about the shapes and AABB as well. I've updated my post above to not have incorrect information for people of the future that stumble across it.

I had not noticed that about being able to turn on AABB gizmos. I've turned that on and I can definitely see different AABBs for each shape within a CC2D.

 

In a related problem/observation, I have noticed that if I do not call 'RigidBody2D.simulated=false' prior to making updates to a CustomCollider2D via SetCustomShapes(), then Physics2D.FindNewContactsTask takes longer and longer eventually grinding the whole game to a halt.

Setting 'RigidBody2D.simulated=false' before updating the CustomCollider2D and then calling "'RigidBody2D.simulated=true' after the call to SetCustomShapes() skirts this problem. I don't know if this indicates an internal issue that can be improved, or if the docs need updating. But just calling SetCustomShapes (a lot, like every frame) on a CustomCollider2D with a RigidBody2D present on the same object will eventually grind the Physics2D sim to an effective halt.

I'm using Unity 2022.2.0b13, and updating the CustomCollider2D every frame with roughly 100 shapes and 400 vertices, via the CustomCollider2D.SetCustomShapes(NativeArray<PhysicsShape2D> shapes, NativeArray<Vector2> vertices) API in this test.

 

I tried a number of options. Here is what I determined:
Requires Multithreading to be enabled in the Physics2D settings.
Requires Unity 2022. I used 2022.2.0b13. Does not reproduce in Unity 2021.

I've attached a project that reproduces the problem, but this is the only script. Note, this is a bespoke test case created from scratch to reproduce this problem.

Code (CSharp):

1.  
2. using System.Collections;
3. using System.Collections.Generic;
4. using UnityEngine;
5. using Unity.Jobs;
6. using Unity.Mathematics;
7. using Unity.Burst;
8. using Unity.Collections;
9.  
10. public class TestScript : MonoBehaviour {
11.  
12.     private CustomCollider2D cc2d;
13.     private Rigidbody2D rb2d;
14.     private int len;
15.  
16.     private void Awake() {
17.         cc2d = GetComponent<CustomCollider2D>();
18.         rb2d = cc2d.attachedRigidbody;
19.         len = 100;
20.     }
21.  
22.     private void Update() {
23.         //For testing. Geometry was originally created in a job but simplified here for this reproduction case.
24.         NativeArray<PhysicsShape2D> shapes = new NativeArray<PhysicsShape2D>(len, Allocator.TempJob);
25.         NativeArray<Vector2> vertices = new NativeArray<Vector2>(4*len, Allocator.TempJob);
26.         for(int i = 0; i < len; i++) {
27.             shapes[i] = new PhysicsShape2D { shapeType = PhysicsShapeType2D.Polygon, vertexCount = 4, vertexStartIndex = i * 4 };
28.             vertices[i * 4] = new Vector2(i, 0);
29.             vertices[i * 4 + 1] = new Vector2(i, 1);
30.             vertices[i * 4 + 2] = new Vector2(i + 1, 1);
31.             vertices[i * 4 + 3] = new Vector2(i + 1, 0);
32.         }
33.  
34.         //Set to false then true after the update to skirt the problem.
35.         //rb2d.simulated = false;
36.         cc2d.SetCustomShapes(shapes, vertices);
37.         //rb2d.simulated = true;
38.  
39.         shapes.Dispose();
40.         vertices.Dispose();
41.     }
42.  
43. }
44.  

 

Excellent and thanks for your rapid attention

 

For each shape, it does produce an AABB and entry in the broadphase. Not the shapes you were making, but the specific shapes you were replacing, were the issue. Your initial shape was somewhere around 100,100.

 

Another anomaly with CustomCollider2D. Again, could just be me or a setting I have missed.

A CustomCollider2D attached to a child object does not seem to be positioned properly, unless the child object has a RigidBody2D attached. This does not appear to be the case for any of the other Collider2Ds (like PolygonCollider2D).

I've attached an image that shows a unit with a child offset from the origin. If I attach a RigidBody2d to the child and then move the child around, the CustomCollider2D follows the child as expected (and like all of the other Collider2Ds do). Without a RigidBody2D, the collider appears anchored at the origin regardless of the position of the child.

I observed this after switching from a PolygonCollider2D to CustomCollider2D (which I'm determined to eventually harvest the performance advantages from).

 

Ok, got it. So in the example image above, when using a custom collider, I need to offset and reapply the collider geometry if/when the child transform changes position relative to its parent. For 'fixed' position child transforms, this would be a one time thing.

For confirmation; regarding rotations (and scale), it appears this is not necessary? The CustomCollider2D geometry appears to be tracking the child transform rotations and scale without having to reapply updated geometry to the CustomCollider2d. I can rotate a child transform around the z axis in the editor and the customcollider2d tracks the changes.