Merge pull request #3 from sandalconsumer/spring-damping

Spring damping

Author: sandalconsumer

Assets/Scenes/SampleScene.unity

@@ -231,22 +231,31 @@ MonoBehaviour:
   recordData: 1
   masses:
   - position: {x: 5, y: 0, z: 0}
+    acceleration: {x: 0, y: 0, z: 0}
+    velocity: {x: 0, y: 0, z: 0}
     mass: 1
     leadForce: {x: 0, y: 0, z: 0}
   - position: {x: 10, y: 0, z: 0}
+    acceleration: {x: 0, y: 0, z: 0}
+    velocity: {x: 0, y: 0, z: 0}
     mass: 1
     leadForce: {x: 0, y: 0, z: 0}
   springs:
   - springConstant: 1
     restLength: 6
     rootLinkedIndex: 0
     endLinkedIndex: 1
+    dampingCoefficient: 0
     rootLinked:
       position: {x: 0, y: 0, z: 0}
+      acceleration: {x: 0, y: 0, z: 0}
+      velocity: {x: 0, y: 0, z: 0}
       mass: 0
       leadForce: {x: 0, y: 0, z: 0}
     endLinked:
       position: {x: 0, y: 0, z: 0}
+      acceleration: {x: 0, y: 0, z: 0}
+      velocity: {x: 0, y: 0, z: 0}
       mass: 0
       leadForce: {x: 0, y: 0, z: 0}
     restorativeForce: {x: 0, y: 0, z: 0}

Assets/Scripts/Physics/PhysicsController.cs

@@ -57,6 +57,13 @@ void FixedUpdate()
 
             spring.rootLinked.leadForce -= spring.restorativeForce;
             spring.endLinked.leadForce += spring.restorativeForce;
+
+            Vector3 relativeVelocity = spring.rootLinked.velocity - spring.endLinked.velocity;
+            float velocityOnSpringDirection = Vector3.Dot(relativeVelocity, springDirection);
+            Vector3 dampingForce = -spring.dampingCoefficient * velocityOnSpringDirection * springDirection;
+            
+            spring.rootLinked.leadForce += dampingForce;
+            spring.endLinked.leadForce -= dampingForce;
 
             if(visualizeSprings) {Debug.DrawLine(spring.rootLinked.position, spring.endLinked.position, Color.yellow);}
             if(recordData) {simulationEndData.stretches.Add(extension);}

Assets/Scripts/Physics/PhysicsObjects.cs

@@ -12,6 +12,8 @@ public class Spring
     public int rootLinkedIndex;
     public int endLinkedIndex;
 
+    public float dampingCoefficient;
+
     [HideInInspector]public Pointmass rootLinked;
     [HideInInspector]public Pointmass endLinked;
 
@@ -22,8 +24,8 @@ public class Spring
 public class Pointmass
 {
     public Vector3 position;
-    Vector3 acceleration;
-    Vector3 velocity;
+    [HideInInspector] public Vector3 acceleration;
+    [HideInInspector] public Vector3 velocity;
 
     public float mass = 100;
     [HideInInspector]public Vector3 leadForce;

README.md

@@ -5,7 +5,6 @@ Harmonic Motion in Unity.
 - This project is still in its **very** early phase. I plan to make this project into a cloth engine to be used in games and for industrial purposes.
 
 ## Planned Features
-- Spring Damping
 - Higher-Order ODE Integrator (RK4) For more accurate Velocity, Position, and Acceleration calculations with more computation
 - Lower-Order ODE Integrator (Euler) for less computation but less accuracy
 - Collisions with geometric meshes
@@ -55,6 +54,7 @@ Every element in springs is an individual instance of class **Spring**:
 - Rest Length is the length of the spring `x` in Hooke's law `Fs = -kx` where if x = 0 there is no restorative force `Fs = 0`.
 - Root linked index is the pointmass that is linked to the spring from its root.
 - End linked index is the pointmass that is linked to the spring from its end.
+- Damping Coefficient determines the amount of damping on the spring. 0 means no damping (perfect oscillation).
 
 Note: If either of the "linked indices" do not exist, the spring is considered to come from the origin.