working on fpp locomotion, camera spring

Assets/jelycho/Code/Player/CameraSpring.cs

@@ -0,0 +1,59 @@
+using UnityEngine;
+
+namespace RealityReboot.jelycho.Player {
+    public class CameraSpring : MonoBehaviour {
+        [Min(0.01f), SerializeField] float m_HalfLife = 0.075f;
+        [SerializeField] float m_Frequency = 10.0f;
+        [SerializeField] float m_ForwardAngularDisplacement = 1.0f;
+        [SerializeField] float m_SidewaysAngularDisplacement = 1.0f;
+        [SerializeField] float m_HeightAngularDisplacement = 2.0f;
+        [SerializeField] float m_LinearDisplacement = 0.05f;
+        
+        Vector3 m_SpringPosition;
+        Vector3 m_SpringVelocity;
+
+        public void Initialize() {
+            m_SpringPosition = transform.position;
+            m_SpringVelocity = Vector3.zero;
+        }
+
+        public void UpdateSpring(float deltaTime, Vector3 up, Vector3 right, Vector3 forward) {
+            Spring(ref m_SpringPosition,
+                   ref m_SpringVelocity,
+                   transform.position,
+                   m_HalfLife,
+                   m_Frequency,
+                   deltaTime);
+
+            Vector3 localSpringPosition = m_SpringPosition - transform.position;
+            float springHeight = Vector3.Dot(localSpringPosition, up);
+            float springForward = Vector3.Dot(localSpringPosition, forward);
+            float springSideways = Vector3.Dot(localSpringPosition, right);
+
+            float pitch = -springHeight * m_HeightAngularDisplacement + -springForward * m_ForwardAngularDisplacement;
+            transform.localEulerAngles = new Vector3(pitch,
+                                                     0.0f,
+                                                     springSideways * m_SidewaysAngularDisplacement);
+        }
+
+        // Source: https://allenchou.net/2015/04/game-math-precise-control-over-numeric-springing/
+        static void Spring(ref Vector3 current,
+                           ref Vector3 velocity,
+                           Vector3 target,
+                           float halfLife,
+                           float frequency,
+                           float timeStep) {
+
+            float dampingRatio = -Mathf.Log(0.5f) / (frequency * halfLife);
+            float f = 1.0f + 2.0f * timeStep * dampingRatio * frequency;
+            float oo = frequency * frequency;
+            float hoo = timeStep * oo;
+            float hhoo = timeStep * hoo;
+            float detInv = 1.0f / (f + hhoo);
+            Vector3 detX = f * current + timeStep * velocity + hhoo * target;
+            Vector3 detV = velocity + hoo * (target - current);
+            current = detX * detInv;
+            velocity = detV * detInv;
+        }
+    }
+}