Table of Contents

Fix physics jitter

Beginner Programmer

Warning

Bullet Physics is being phased out. We no longer plan to support or expand its features as our focus shifts to Bepu Physics. We recommend transitioning to Bepu Physics for access to the latest updates and ongoing improvements.

In Stride, there is no default smoothing applied to entities that are attached to physics entities. This can cause noticeable jitter, especially if the camera is attached to a character component.

In this tutorial, we will explore how to add smoothing to an entity using a SyncScript.

Note

You can also decrease the FixedTimeStep in the physics settings configuration to achieve more accurate physics simulations. For example, changing it from 0.016667 to 0.008 will increase accuracy but at the cost of higher CPU usage.

Code to handle smoothing between two entities

The following code is all that's needed to smoothly attach two entities. Ensure that you unparent the entity you are trying to smooth, otherwise the transform processor will override this script.

[ComponentCategory("Utils")]
[DataContract("SmoothFollowAndRotate")]
public class SmoothFollowAndRotate : SyncScript
{
    public Entity EntityToFollow { get; set; }
    public float Speed { get; set; } = 1;

    public override void Update()
    {
        var deltaTime = (float)Game.UpdateTime.Elapsed.TotalSeconds;
        var currentPosition = Entity.Transform.Position;
        var currentRotation = Entity.Transform.Rotation;

        var lerpSpeed = 1f - MathF.Exp(-Speed * deltaTime);

        EntityToFollow.Transform.GetWorldTransformation(out var otherPosition, out var otherRotation, out var _);

        var newPosition = Vector3.Lerp(currentPosition, otherPosition, lerpSpeed);
        Entity.Transform.Position = newPosition;

        Quaternion.Slerp(ref currentRotation, ref otherRotation, lerpSpeed, out var newRotation);
        Entity.Transform.Rotation = newRotation;
    }
}

Example Usage

This example demonstrates modifications to the First Person Shooter template to integrate smooth camera movement.

  1. Detach the camera from the physics entity.
  2. Remove the FPS camera script from the camera.
  3. Create a new entity as a child of the character body.
  4. Add the FPS script to the new entity.
  5. Adjust any code that directly references the CameraComponent to reflect these changes.

PlayerInput.cs

Change

public CameraComponent Camera { get; set; }

to

public Entity Camera { get; set; }

Utils.cs

Change

CameraComponent camera

to

Entity camera,

and change

camera.Update();
var inverseView = Matrix.Invert(camera.ViewMatrix);

to

var inverseView = camera.Transform.WorldMatrix;

FpsCamera.cs

Remove

/// <summary>
/// Gets the camera component used to visualized the scene.
/// </summary>
private Entity Component;

and change

private void UpdateViewMatrix()
{
    var camera = Component;
    if (camera == null) return;
    var rotation = Quaternion.RotationYawPitchRoll(Yaw, Pitch0);

    Entity.Transform.Rotation = rotation;
}

to

private void UpdateViewMatrix()
{
    var rotation = Quaternion.RotationYawPitchRoll(Yaw, Pitch, 0);

    Entity.Transform.Rotation = rotation;
}

That should be all that is needed to see the smoothing in action as a before and after. You can see the original issue in the Stride GitHub here if you need to find more info on the problem.

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