replaced "friction" with "velocityHalfLife"

tom-mohr · Feb 3, 2023 · 31bbd77 · 31bbd77
1 parent 3739013
commit 31bbd77
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Showing 2 changed files with 17 additions and 5 deletions.
diff --git a/src/main/java/com/particle_life/Physics.java b/src/main/java/com/particle_life/Physics.java
@@ -382,11 +382,18 @@ private int wrapContainerY(int cy) {
         }
     }
 
+    private double computeFrictionFactor(double halfLife, double dt) {
+        if (halfLife == 0) return 0.0;  // avoid division by zero
+        if (halfLife == Double.POSITIVE_INFINITY) return 1.0;
+
+        return Math.pow(0.5, dt / halfLife);
+    }
+
     private void updateVelocity(int i) {
         Particle p = particles[i];
 
         // apply friction before adding new velocity
-        p.velocity.mul(Math.pow(settings.friction, settings.dt));
+        p.velocity.mul(computeFrictionFactor(settings.velocityHalfLife, settings.dt));
 
         int cx0 = (int) Math.floor((p.position.x + 1) / containerSize);
         int cy0 = (int) Math.floor((p.position.y + 1) / containerSize);

diff --git a/src/main/java/com/particle_life/PhysicsSettings.java b/src/main/java/com/particle_life/PhysicsSettings.java
@@ -13,9 +13,14 @@ public class PhysicsSettings {
     public double rmax = 0.04;
 
     /**
-     * velocity will be multiplied with this factor every second
+     * The time in seconds after which half the velocity of a particle
+     * should be lost due to friction.
+     * The actual friction factor <code>f</code> that the velocity is
+     * multiplied with in every time step is calculated on the basis of
+     * this value according to the following formula:
+     * <code>f = Math.pow(0.5, dt / frictionHalfLife)</code>
      */
-    public double friction = 0.0000001f;
+    public double velocityHalfLife = 0.043;
 
     /**
      * Scaled force by an arbitrary factor.
@@ -36,7 +41,7 @@ public PhysicsSettings deepCopy() {
 
         p.wrap = wrap;
         p.rmax = rmax;
-        p.friction = friction;
+        p.velocityHalfLife = velocityHalfLife;
         p.force = force;
         p.dt = dt;
         p.matrix = matrix.deepCopy();
@@ -50,7 +55,7 @@ public boolean equals(Object o) {
 
             if (s.wrap != wrap) return false;
             if (s.rmax != rmax) return false;
-            if (s.friction != friction) return false;
+            if (s.velocityHalfLife != velocityHalfLife) return false;
             if (s.force != force) return false;
             if (s.dt != dt) return false;
             if (!s.matrix.equals(matrix)) return false;