best approach to Lock Angular Axes (X and Z) on Physics Entities

Hello Everyone,

im looking for a good way to Lock X and Z Angular Axes for some Dynamic bodies (Pure Enities). (Characters)
why does the Unity PhysicsBody do not support it like the Old Rogidbody ?

Thank you.

 

In the Physics Mass IComponentData, there's a float3 field called InverseInertia. Set the X and Z components of that field to 0 to lock rotation around those axes.

 

AFAIK Unity Physics doesn't have an authoring component to set up rotation locking, so I made one myself:

Code (CSharp):

1. [DisallowMultipleComponent, RequiresEntityConversion, RequireComponent(typeof(PhysicsBodyAuthoring))]
2. public class FreezeRotationAuthoring : MonoBehaviour
3. {
4.     public bool3 Flags;
5. }
6.  
7. [UpdateAfter(typeof(PhysicsBodyConversionSystem))]
8. public class FreezeRotationConversionSystem : GameObjectConversionSystem
9. {
10.     protected override void OnUpdate()
11.     {
12.         Entities.ForEach((FreezeRotationAuthoring freezeRotation) =>
13.         {
14.             Entity entity = GetPrimaryEntity(freezeRotation.gameObject);
15.             PhysicsMass mass = DstEntityManager.GetComponentData<PhysicsMass>(entity);
16.             if (freezeRotation.Flags.x)
17.                 mass.InverseInertia.x = 0f;
18.             if (freezeRotation.Flags.y)
19.                 mass.InverseInertia.y = 0f;
20.             if (freezeRotation.Flags.z)
21.                 mass.InverseInertia.z = 0f;
22.             DstEntityManager.SetComponentData(entity, mass);
23.         });
24.     }
25. }

 

Thank you!

 

What does

InverseInertia

do? Is it

1 / Inertia

?

 

@starikcetin Pretty much. It's common for physics engines to opt for inverse values for mass and inertia for performance.

 

Upon further inspection, this is not the case. If you check the "Override Default Mass Distribution" toggle in PhysicsBodyAuthoring, a float3 field called "InertiaTensor" will be visible. You can lock rotation around an axis by setting the corresponding component of that field to Infinity.