Bug Ball with rigidbody is stuttering/jittering

Hi, I'm moving a ball with AddForce, but as you can see in the video the ball begins to stutter if it is moving fast. It isn't very noticable in the editor, but very much on my phone. I'm unsure if it's the Cinemachine camera or the script of the ball that is causing the problem.

Here's the script:

Code (CSharp):

1.     private void Update()
2.     {
3.         if (Input.touchCount > 0)
4.         {
5.             Touch touch = Input.GetTouch(0);
6.  
7.             switch (touch.phase)
8.             {
9.                 case TouchPhase.Began:
10.                     startPosition = touch.position;
11.                     break;
12.                 case TouchPhase.Moved:
13.                     // The force on the x axis is calculated...
14.                     // by how far away the finger is from the starting point
15.                     xForce = touch.position.x - startPosition.x;
16.  
17.                     // Limit x-axis force to prevent advantages from longer screens
18.                     if (xForce > maxXForce)
19.                     {
20.                         xForce = maxXForce;
21.                     }
22.                     else if (xForce < -maxXForce)
23.                     {
24.                         xForce = -maxXForce;
25.                     }
26.                     break;
27.             }
28.  
29.  
30.             fingerDown = true;
31.         }
32.         else
33.         {
34.             fingerDown = false;
35.         }
36.     }
37.  
38.     private bool OnGround()
39.     {
40.         Vector3 rayOrigin = transform.position;
41.         float rayDistance = 0.8f;
42.         LayerMask layerMask = LayerMask.GetMask("Ground");
43.         RaycastHit hit;
44.         if (Physics.Raycast(rayOrigin, Vector3.down, out hit, rayDistance, layerMask))
45.         {
46.             slopeNormal = hit.normal;
47.             // Calculates the angle along z axis
48.             slopeAngle = Vector2.Angle(Vector3.up, slopeNormal);
49.  
50.             return true;
51.         }
52.  
53.         return false;
54.     }
55.  
56.  
57.     private void FixedUpdate()
58.     {
59.         if (fingerDown && move)
60.         {
61.             // Calculations to make it more responsive
62.  
63.             // calculate the direction we want to move in and our desired velocity
64.             float targetSpeed = (xForce * sideSpeed);
65.             // calculate the difference between current velocity and desired velocity
66.             float speedDif = targetSpeed - rb.velocity.x;
67.             // Change acceleration rate depending on situation
68.             float accelRate = (Mathf.Abs(targetSpeed) > 0.01f) ? acceleration : decceleration;
69.             // Applies acceleration to speed difference, then raises to a set power so acceleration increases with higher speeds
70.             // finally multiplies by sign to reapply direction
71.             float movement = Mathf.Pow(Mathf.Abs(speedDif) * accelRate, velPower) * Mathf.Sign(speedDif);
72.  
73.  
74.             // Making the ball move along a slope
75.            
76.             if(OnGround())
77.             {
78.                 forceDirection = Vector3.ProjectOnPlane(new Vector3(movement, 0, 0), slopeNormal);
79.             }
80.             else
81.             {
82.                 forceDirection = new Vector3(movement, 0, 0);
83.             }
84.  
85.             // Makes the ball move from left ot right
86.             rb.AddForce(new Vector3(forceDirection.x, forceDirection.y, 0));
87.         }
88.  
89.         // Move forward
90.         if (move)
91.         {
92.             if (rb.velocity.z < maxForwardSpeed)
93.             {
94.                 rb.AddForce(Vector3.forward * forwardSpeed * Time.fixedDeltaTime);
95.             }
96.         }
97.  
98.  
99.     }

 

Make sure your rigidbody is using interpolation. Otherwise your ball's transform will only be updated in frames where FixedUpdate() is called.

 

Yes it is set to "interpolate"

 

Alright so I should remove the fixedDeltaTime?

 

Do you see some more errors in the script? I'm not sure if I put the correct things inside Update() or FixedUpdate(). I tried moving the "// Calculations to make it more responsive" inside the Update() method, but that didn't help.

 

It's hard to tell in the video, but I think the issues are in Cinemachine. @Gregoryl could you break down the differences between fixedUpdate, LateUpdate and the other option in Cinemachine. I think this is one of the times that's an issue.

How/Why I think this: I put my finger over the ball whilst watching the video, so that I wasn't distracted by its judder, and could still detect the same sort of pattern of judders in the geometry passing by.

 

I tried turning off interpolation and now the stuttering is gone

 

Can someone else explain why this works for this problem?

I'd have thought that interpolation on would be the saving grave, not turning it off. But what do I know?

 

Last time I checked Cinemachine the "SmartUpdate" option just checked if the target GameObject has a rigidbody or not to decide whether update the camera in Update or FixedUpdate. It didn't checked whether the Rigidbody has interpolation enabled or not. Even if CM does that now, this approach wouldn't work when the target GameObject is a child GameObject of the Rigidbody object.

As for a proper solution to the stuttering problem, I'd try forcing Cinemachine to update the camera in the Update method and enable interpolation in the Rigidbody.

 

Correct, it must have been an older version of Cinemachine (in Unity 2019), sorry. I recall seeing the code that just checked for the presence of a Rigidbody in order to use FixedUpdate or LateUpdate. Glad to know this part has improved!