Question Convert Rigidbody.AddForceAtPosition to Unity Physics.

I'm writing a buoyancy system for Unity Physics by converting a rigidbody one I got.

I'm not sure how to convert this. I can't find anything on how to add force at position.

Code (CSharp):

1.  // apply drag relative to water
2.         var forcePosition = _rb.position + _forceHeightOffset * Vector3.up;
3.         _rb.AddForceAtPosition(Vector3.up * Vector3.Dot(Vector3.up, -velocityRelativeToWater) * _dragInWaterUp, forcePosition, ForceMode.Acceleration);
4.         _rb.AddForceAtPosition(transform.right * Vector3.Dot(transform.right, -velocityRelativeToWater) * _dragInWaterRight, forcePosition, ForceMode.Acceleration);
5.         _rb.AddForceAtPosition(transform.forward * Vector3.Dot(transform.forward, -velocityRelativeToWater) * _dragInWaterForward, forcePosition, ForceMode.Acceleration);

 

Unity.Physics.Extensions has some extension methods for applying impulses. To apply forces, use force * deltaTime to get impulse

Code (CSharp):

1. using Unity.Collections;
2. using Unity.Entities;
3. using Unity.Jobs;
4. using Unity.Physics.Extensions;
5. using Unity.Transforms;
6.  
7. [UpdateBefore(typeof(BuildPhysicsWorld))]
8. public class ImpulseAtPointSystem : SystemBase
9. {
10.     protected override void OnUpdate()
11.     {
12.         Entities.ForEach((DynamicBuffer<ImpulseAtPoint> impulses, ref PhysicsVelocity velocity, in PhysicsMass mass, in Translation translation, in Rotation rotation) =>
13.         {
14.             NativeArray<ImpulseAtPoint> impulseArray = impulses.AsNativeArray();
15.             for (int i = 0; i < impulseArray.Length; i++)
16.             {
17.                 velocity.ApplyImpulse(mass, translation, rotation, impulseArray[i].Impulse, impulseArray[i].Point);
18.             }
19.             impulses.Clear();
20.         }).ScheduleParallel();
21.     }
22. }

 

Thanks.

I did this.

Code (CSharp):

1. //Do Physics
2.                 if (_inWater)
3.                 {
4.                     forces.Clear();
5.                     forces.Add(Vector3.up * Vector3.Dot(Vector3.up, -velocityRelativeToWater) * _dragInWaterUp);
6.                     forces.Add(localToWorld.Right * Vector3.Dot(localToWorld.Right, -velocityRelativeToWater) * _dragInWaterRight);
7.                     forces.Add(localToWorld.Forward * Vector3.Dot(localToWorld.Forward, -velocityRelativeToWater) * _dragInWaterForward);
8.  
9.                     var forcePosition = position + _forceHeightOffset * Vector3.up;
10.  
11.                     for (int i = 0; i < forces.Count; i++)
12.                         AddForceAtPosition(ref physicsMass, ref translation,ref rotation, ref physicsVelocity, PhysicsWorldExtensions.GetRigidBodyIndex(physicsWorld, entity), forces[i],forcePosition, ForceMode.Acceleration);
13.                 }
14.  
15.   private void GetImpulseFromForce(ref PhysicsMass mass, float3 force, UnityEngine.ForceMode mode, float timeStep, out float3 impulse, out PhysicsMass impulseMass)
16.         {
17.             var unitMass = new PhysicsMass { InverseInertia = new float3(1.0f), InverseMass = 1.0f, Transform = mass.Transform };
18.  
19.             switch (mode)
20.             {
21.                 case UnityEngine.ForceMode.Force:
22.                     // Add a continuous force to the rigidbody, using its mass.
23.                     impulseMass = mass;
24.                     impulse = force * timeStep;
25.                     break;
26.                 case UnityEngine.ForceMode.Acceleration:
27.                     // Add a continuous acceleration to the rigidbody, ignoring its mass.
28.                     impulseMass = unitMass;
29.                     impulse = force * timeStep;
30.                     break;
31.                 case UnityEngine.ForceMode.Impulse:
32.                     // Add an instant force impulse to the rigidbody, using its mass.
33.                     impulseMass = mass;
34.                     impulse = force;
35.                     break;
36.                 case UnityEngine.ForceMode.VelocityChange:
37.                     // Add an instant velocity change to the rigidbody, ignoring its mass.
38.                     impulseMass = unitMass;
39.                     impulse = force;
40.                     break;
41.                 default:
42.                     impulseMass = mass;
43.                     impulse = float3.zero;
44.                     break;
45.             }
46.         }
47.  
48.  
49.  
50.         private void AddForceAtPosition(ref PhysicsMass physicsMass, ref Translation translation,ref Rotation rotation, ref PhysicsVelocity velocity, int entityIndex, float3 force, float3 position, ForceMode mode = ForceMode.Force)
51.         {
52.  
53.            GetImpulseFromForce(ref physicsMass,force, mode, deltaTime, out float3 impulse, out PhysicsMass impulseMass);
54.            velocity.ApplyImpulse(impulseMass, translation, rotation, impulse, position);
55.         }
56.