Merge pull request #265 from Doprez/add-jitter-fix-tutorial

Taking care of this..

en/manual/physics/fix-physics-jitter.md

@@ -0,0 +1,115 @@
+# Fix Physics Jitter
+
+<span class="badge text-bg-primary">Beginner</span>
+<span class="badge text-bg-success">Programmer</span>
+
+In Stride there is no default smoothing applied to Entities that are attached to physics entities. This can cause a noticable jitter especially if you have the camera attached to a character component.
+In this tutorial we will look at whats needed to add smoothing to an entity through a SyncScript.
+
+>[!Note]
+>You can also decrease the `Fixed Time Step` in the physics configuration, for example change it from `0.016667` to `0.008` for more accurate physics but this will be more expensive on the CPU.
+
+## Code to handle smoothing between 2 entities
+This should be all thats needed to attach 2 entities together. Make sure that you unparent the entity you are trying to smooth or else the transofrm processor will override this script.
+```cs
+[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
+For this example we will modify the First Person Shooter Template.
+
+Step 1: Detach the camera from the Physics entity
+
+Step 2: Remove the FPS camera script from the camera
+
+Step 3: create a new entity as a child to the character body
+
+Step 4: Add the FPS script to the new entity
+
+Step 5: change the following code since they reference the CameraComponent directly
+
+### PlayerInput.cs
+change
+```cs
+public CameraComponent Camera { get; set; }
+```
+to
+```cs
+public Entity Camera { get; set; }
+```
+
+---
+
+### Utils.cs
+change
+```cs
+CameraComponent camera
+```
+to
+```cs
+Entity camera,
+```
+and change
+```cs
+camera.Update();
+var inverseView = Matrix.Invert(camera.ViewMatrix);
+```
+to
+`var inverseView = camera.Transform.WorldMatrix;`
+
+---
+
+### FpsCamera.cs
+Remove
+```cs
+
+        /// <summary>
+        /// Gets the camera component used to visualized the scene.
+        /// </summary>
+        private Entity Component;
+```
+and change
+```cs
+        private void UpdateViewMatrix()
+        {
+            var camera = Component;
+            if (camera == null) return;
+            var rotation = Quaternion.RotationYawPitchRoll(Yaw, Pitch, 0);
+
+            Entity.Transform.Rotation = rotation;
+        }
+```
+to 
+```cs
+private void UpdateViewMatrix()
+{
+    var rotation = Quaternion.RotationYawPitchRoll(Yaw, Pitch, 0);
+
+    Entity.Transform.Rotation = rotation;
+}
+```
+
+That should be all thats needed to see the smoothing in action as a before and after. You can see the original issue in the Stride Github [here](https://github.com/stride3d/stride/issues/2216) if you need to find more info on the problem.