multiple boxes for floor and a bouncy sphere problem

Hi
I have a problem where i have a floor composed of boxes (lets say 10 boxes perfectly in a row), thats 10 entities with a box collider each

i send a bouncy ball forward but sometimes it seems to get 2 collisions (1 hitting the top of a box and at the same time also colliding with the "corner" of the next box.

It makes the bouncy ball jump backwards because of this.
Is there anything i can do to prevent this? its "impossible" to hit the corner of the next box as the alignment is perfect for the boxes.

The normal of the wrong bounce comes out as this ( i am sending the sphere forward on x axis only)
float3(-0.4347691f, 0.900542f, 0f)

Thanks!!

 

Yeah this is expected because of the predictive contacts.Your options are:
1. Switch to Havok physics, which has a solution for this called "welding".
2. Try to come up with a fixup for contacts (using IContactsJob) by for example casting a sphere in the velocity direction and seeing if it will actually hit the provided normal. Some context for this can be found here https://forum.unity.com/threads/sph...se-on-contact-with-mesh-collider-edge.889963/.
3. Wait a little while longer as we will try to provide the sample code for 2 in the coming releases, but I can't set the date or anything since it's still in early prototyping phase.

 

It seems 1) is the easiest? is there any info how to do this?

 

Check out the simple quick start guide here: https://docs.unity3d.com/Packages/com.havok.physics@0.3/manual/quickstart.html
Contact point welding setup is touch on here: https://docs.unity3d.com/Packages/com.havok.physics@0.3/manual/configuration.html
There is a test scene in the Samples you can play with the configuration.

 

ok i will have a look steve thanks!
just to make sure i understand correctly
1. enable welding for (floor body tags) in havok config
2. add the custom tag (floor body) on terrain floor objects
3. no changes to sphere?

 

Yes, that should do it.

 

i am using custom code, where do i put this body tag? do i add a new componentData or somewhere that exists already?

 

Add PhysicsCustomTags component data to your entities that need welding and that's it.

 

it doesnt seem to work much better, even on the first bounce it will sometimes shoot up even though it had a forward velocity. the problem doesnt seem to appear as often though

Is this welding technique supposed to minimize or eliminate the problem?

Code (CSharp):

1.   if (PixelData.TypeId == BlockType.Terrain)
2.         {
3.             Unity.Physics.PhysicsCustomTags tagData = new Unity.Physics.PhysicsCustomTags() { Value = PhysicsManager.Instance.TerrainBlocksBodyTag.Value };
4.             dots.EntityManagerRef.AddComponentData<Unity.Physics.PhysicsCustomTags>(dots.ECSEntity, tagData);
5.         }

when i create terrain blocks i add this as discussed


my settings are as simple as this

EDIT: i noticed that my bowling balls now move on the floor nicely without any hiccups that i had before. The forward bouncy ball however does not seem to work as well, any ideas?

 

Maybe look at Bevel Radius and see if increasing it helps? To avoid penetrations to some extent... Also, do you need it to be bouncy? It could be that restitution causes problems as well...

 

It seems the restitution is causing this problem, i guess welding can't fix this problem?


Is it possible to use SimulationCallbacks and disable certain collisions whos normal is not Vector3.up for example?
I had a look at a sample, i didnt see anything about normals or impulses

 

Yes, it is possible. Implement an IContactsJob, you'll get a ModifiableContactHeader and ModifiableContactPoint and you can tweak their normals. If you know your normals should all be pointing up, it should be fairly easy to do. Check ModifyNarrowphaseContactsBehaviour in the samples, it does some magic with normals, although it's probably too complicated for your case.