Write to referenced Entity's component data

I have an Entity reference in a component and I'm trying write new values to one of the referenced entity's components. However, I just don't seem to be able to achieve it. I'm sure I'm just missing something obvious.
I have the following components
...on the 'wheel':

Code (CSharp):

1. public struct TorqueControl : IComponentData
2. {
3.     public float AppliedTorque;
4.     public float3 Axis;
5. }

...and on the player entity

Code (CSharp):

1. public struct BallMoveControl : IComponentData
2. {
3.     public Entity BallEntity;
4.     public float Torque;
5.     public float BoostTorque;
6. }

The idea is that the following system uses the Entity reference in the BallMoveControl to update the data in the TorqueControl (and no, the logic is not complete yet):

Code (CSharp):

1. using Unity.Collections;
2. using Unity.Entities;
3. using Unity.Mathematics;
4. using UnityEngine;
5.  
6. [UpdateBefore(typeof(ApplyTorqueSystem))]
7. public class PlayerMoveSystem : SystemBase
8. {
9.     Entity cameraEntity;
10.  
11.     [NativeDisableParallelForRestriction]
12.     public ComponentDataFromEntity<TorqueControl> tcGroup;
13.  
14.     protected override void OnStartRunning()
15.     {
16.         Entities.WithAll<Camera, Transform>().WithoutBurst().ForEach((Entity entity) =>
17.         {
18.             cameraEntity = entity;
19.         }).Run();
20.     }
21.  
22.     protected override void OnUpdate()
23.     {
24.         Transform trans = EntityManager.GetComponentObject<Transform>(cameraEntity);
25.         quaternion camRotation = new quaternion();
26.         camRotation = math.quaternion(trans.rotation.x, trans.rotation.y, trans.rotation.z, trans.rotation.w);
27.         float vAxis = Input.GetAxis("Vertical");
28.         float hAxis = Input.GetAxis("Horizontal");
29.         bool sprint = Input.GetButton("Sprint");
30.  
31.         tcGroup = GetComponentDataFromEntity<TorqueControl>();
32.  
33.         Entities.WithAll<IsPlayerTag>().WithoutBurst().ForEach((ref BallMoveControl bmc) =>
34.         {
35.             if (vAxis != 0 || hAxis != 0)
36.             {
37.                 // create force vector (in camera space)
38.                 float3 axis = new float3(vAxis, 0f, -hAxis);
39.  
40.                 // transform into world space
41.                 axis = math.rotate(camRotation, axis);
42.  
43.                 // Remove y component
44.                 axis.y = 0;
45.  
46.                 if (tcGroup.Exists(bmc.BallEntity))
47.                 {
48.                     tcGroup[bmc.BallEntity].Axis = axis;
49.                     tcGroup[bmc.BallEntity].AppliedTorque = sprint ? bmc.BoostTorque : bmc.Torque;
50.  
51.                     // Using the following in debug shows that the correct component data is being retrieved
52.                     // but it is obviously being copied and not written back to the source:
53.  
54.                     //TorqueControl localTC = tcGroup[bmc.BallEntity];
55.                     //localTC.Axis = axis;
56.                     //localTC.AppliedTorque = sprint ? bmc.BoostTorque : bmc.Torque;
57.                 }
58.             }
59.         }).Run();
60.  
61.     }
62. }

As it stands this won't even compile as "the return value of tcGroup[bmc.BallEntity] can't be modified because it is not a variable". This is obviously why using the commented code doesn't work, even though it runs.

What am I doing wrong or am I taking the wrong approach completely?

 

Make the tcGroup local and add WithNativeDisableParallelForRestriction(tcGroup) to your Entities call.

EDIT: Re-reading it I noticed that you are using Run(), in this case I don't think you need the WithNativeDisableParallelForRestriction(tcGroup) at all.

EDIT 2: Noticed also that you are not writing back to the tcGroup:

Code (CSharp):

1. TorqueControl localTC = tcGroup[bmc.BallEntity];
2. localTC.Axis = axis;
3. localTC.AppliedTorque = sprint ? bmc.BoostTorque : bmc.Torque;
4. tcGroup[bmc.BallEntity] = localTC;

 

SystemBase has GetComponent and SetComponent methods which let you not worry about ComponentDataFromEntity.

 

Thanks! My main mistake was sorted by your Edit 2 - I wasn't writing the values back. I really ought to brush up on my 'by reference' vs 'by value'!
As for your first comment, I was always intending to use ScheduleParallel (even if it is not really required for this system) - I just switched to Run() to make sure things weren't being processed out of order somehow.

Is there an alternative to WithNativeDisableParallelForRestriction for using SetComponent in a ForEach with ScheduleParallel? If so, it looks like that would give the cleanest code. Otherwise this is what I ended up with:

Code (CSharp):

1. using Unity.Entities;
2. using Unity.Mathematics;
3. using UnityEngine;
4.  
5. [UpdateBefore(typeof(ApplyTorqueSystem))]
6. public class PlayerMoveSystem : SystemBase
7. {
8.     Entity cameraEntity;
9.  
10.     protected override void OnStartRunning()
11.     {
12.         Entities.WithAll<Camera, Transform>().WithoutBurst().ForEach((Entity entity) =>
13.         {
14.             cameraEntity = entity;
15.         }).Run();
16.     }
17.  
18.     protected override void OnUpdate()
19.     {
20.         Transform trans = EntityManager.GetComponentObject<Transform>(cameraEntity);
21.         quaternion camRotation = new quaternion();
22.         camRotation = math.quaternion(trans.rotation.x, trans.rotation.y, trans.rotation.z, trans.rotation.w);
23.         float vAxis = Input.GetAxis("Vertical");
24.         float hAxis = Input.GetAxis("Horizontal");
25.         bool sprint = Input.GetButton("Sprint");
26.  
27.         ComponentDataFromEntity<TorqueControl> tcGroup = GetComponentDataFromEntity<TorqueControl>();
28.  
29.         Entities.WithAll<IsPlayerTag>().WithNativeDisableParallelForRestriction(tcGroup).ForEach((ref BallMoveControl bmc) =>
30.         {
31.             if (vAxis != 0 || hAxis != 0)
32.             {
33.                 // create force vector (in camera space)
34.                 float3 axis = new float3(vAxis, 0f, -hAxis);
35.  
36.                 // transform into world space
37.                 axis = math.rotate(camRotation, axis);
38.  
39.                 // Remove y component
40.                 axis.y = 0;
41.  
42.                 if (tcGroup.Exists(bmc.BallEntity))
43.                 {
44.                     TorqueControl localTC = tcGroup[bmc.BallEntity];
45.                     localTC.Axis = axis;
46.                     localTC.AppliedTorque = sprint ? bmc.BoostTorque : bmc.Torque;
47.                     tcGroup[bmc.BallEntity] = localTC;
48.                 }
49.             }
50.             else
51.             {
52.                 // I don't like the way this runs all the time when there isn't player input, but it has to be reset somehow!
53.                 if (tcGroup.Exists(bmc.BallEntity))
54.                 {
55.                     TorqueControl localTC;
56.                     localTC.Axis = new float3(0f, 0f, 0f);
57.                     localTC.AppliedTorque = 0f;
58.                     tcGroup[bmc.BallEntity] = localTC;
59.                 }
60.             }
61.         }).ScheduleParallel();
62.  
63.     }
64. }

 

Unless you have thousands of entities with the IsPlayerTag component, ScheduleParallel seems completely unnecessary. Just use Schedule and then you can use SetComponent just fine.