Last fixes

src/Body.java

@@ -4,7 +4,7 @@ import codedraw.CodeDraw;
  * This class represents celestial bodies like stars, planets, asteroids, etc...
  */
 public class Body {
-    private final double mass;
+    private double mass;
     private Vector massCenter; // position of the mass center.
     private Vector currentMovement;
 
@@ -83,6 +83,12 @@ public class Body {
         return massCenter;
     }
 
+    public void update(Body b) {
+        double combinedMass = this.mass + b.mass;
+        this.massCenter = this.massCenter.times(this.mass / combinedMass).plus(b.massCenter.times(b.mass / combinedMass));
+        this.mass = combinedMass;
+    }
+
     public boolean collidesWith(Body body) {
         return this.distanceTo(body) < this.radius() + body.radius();
     }

src/Octree.java

@@ -38,7 +38,6 @@ public class Octree {
 
     public void applyForces(Body[] bodies, double t) {
         if (root == null) return;
-        root.preCalc();
         Vector[] forces = new Vector[bodies.length];
         for (int i = 0; i < bodies.length; i++) {
             forces[i] = root.getForcesOnBody(bodies[i], t);
@@ -55,8 +54,8 @@ public class Octree {
 }
 
 abstract class OctreeItem {
-    protected Vector center;
+    protected final Vector center;
-    protected double size;
+    protected final double size;
 
     protected Body pseudoBody;
 
@@ -67,8 +66,6 @@ abstract class OctreeItem {
 
     abstract protected OctreeNode add(Body body);
 
-    abstract protected void preCalc();
-
     abstract protected Vector getForcesOnBody(Body body, double t);
 
     abstract protected void draw(CodeDraw cd);
@@ -76,16 +73,25 @@ abstract class OctreeItem {
 
 class OctreeNode extends OctreeItem {
     private final OctreeItem[] children;
+    private final Vector p1;
+    private final Vector p2 ;
 
     protected OctreeNode(Vector center, double size) {
         super(center, size);
         children = new OctreeItem[8];
+        p1 = center.plus(new Vector(size / 2));
+        p2 = center.minus(new Vector(size / 2));
     }
 
     @Override
     protected OctreeNode add(Body body) {
         int num = getOctantNum(body.massCenter());
         if (num < 0) return this;
+        if (this.pseudoBody == null) {
+            this.pseudoBody = new Body(body);
+        } else {
+            this.pseudoBody.update(body);
+        }
         OctreeItem oct = children[num];
         if (oct == null) {
             children[num] = new OctreeLeaf(getOctantCenter(num), size / 2, body);
@@ -95,22 +101,6 @@ class OctreeNode extends OctreeItem {
         return this;
     }
 
-    @Override
-    protected void preCalc() {
-        double mass = 0;
-        for (OctreeItem oct : children) {
-            if (oct == null) continue;
-            oct.preCalc();
-            mass += oct.pseudoBody.mass();
-        }
-        Vector massCenter = new Vector();
-        for (OctreeItem oct : children) {
-            if (oct == null) continue;
-            massCenter = massCenter.plus(oct.pseudoBody.massCenter().times(oct.pseudoBody.mass() / mass));
-        }
-        this.pseudoBody = new Body(mass, massCenter);
-    }
-
     @Override
     protected Vector getForcesOnBody(Body body, double t) {
         double r = pseudoBody.massCenter().distanceTo(body.massCenter());
@@ -122,7 +112,7 @@ class OctreeNode extends OctreeItem {
         Vector force = new Vector();
         for (OctreeItem child : children) {
             if (child == null) continue;
-            force = force.plus(child.getForcesOnBody(body, t));
+            force.add(child.getForcesOnBody(body, t));
         }
         return force;
     }
@@ -133,10 +123,12 @@ class OctreeNode extends OctreeItem {
             if (child == null) continue;
             child.draw(cd);
         }
+        /*
         Vector p1 = center.minus(new Vector(size / 2));
         Vector p2 = new Vector(size).minus(new Vector(Simulation.SECTION_SIZE / 2));
         cd.setColor(Color.CYAN);
         cd.drawRectangle(p1.getScreenX(cd), p1.getScreenY(cd), p2.getScreenX(cd), p2.getScreenY(cd));
+        */
     }
 
     private int getOctantNum(Vector bodyPos) {
@@ -146,8 +138,6 @@ class OctreeNode extends OctreeItem {
     }
 
     private boolean isInOctant(Vector pos) {
-        Vector p1 = center.plus(new Vector(size / 2));
-        Vector p2 = center.minus(new Vector(size / 2));
         return  pos.getX() <= p1.getX() && pos.getY() <= p1.getY() && pos.getZ() <= p1.getZ() &&
                 pos.getX() >= p2.getX() && pos.getY() >= p2.getY() && pos.getZ() >= p2.getZ();
     }
@@ -167,6 +157,7 @@ class OctreeLeaf extends OctreeItem {
     public OctreeLeaf(Vector center, double size, Body body) {
         super(center, size);
         this.body = body;
+        this.pseudoBody = new Body(this.body);
     }
 
     @Override
@@ -174,11 +165,6 @@ class OctreeLeaf extends OctreeItem {
         return new OctreeNode(this.center, this.size).add(this.body).add(body);
     }
 
-    @Override
-    protected void preCalc() {
-        this.pseudoBody = new Body(this.body);
-    }
-
     @Override
     protected Vector getForcesOnBody(Body body, double t) {
         return body.gravitationalForce(pseudoBody);

src/Simulation.java

@@ -22,8 +22,8 @@ public class Simulation {
 
     // set some system parameters
     public static final double SECTION_SIZE = 2 * AU; // the size of the square region in space
-    public static final int NUMBER_OF_BODIES = 22;
+    public static final int NUMBER_OF_BODIES = 10000;
-    public static final double OVERALL_SYSTEM_MASS = 20 * SUN_MASS; // kilograms
+    public static final double OVERALL_SYSTEM_MASS = 2000 * SUN_MASS; // kilograms
 
     public static void main(String[] args) {
         CodeDraw cd = new CodeDraw();
@@ -51,24 +51,13 @@ public class Simulation {
         while (true) {
             seconds++;
 
-            /*
-            BodyLinkedList mergedBodies = new BodyLinkedList();
-            for (Body b1 : bodies) {
-                BodyLinkedList colliding = bodies.removeCollidingWith(b1);
-                for (Body b2 : colliding) {
-                    b1 = b1.merge(b2);
-                }
-                mergedBodies.addLast(b1);
-            }
-            bodies = mergedBodies;
-            */
             Octree octree = new Octree(new Vector(0, 0, 0), SECTION_SIZE);
             for (Body body : bodies) {
                 octree.add(body);
             }
-            octree.applyForces(bodies, 1);
+            octree.applyForces(bodies, 100);
 
-            if ((seconds % 3600) == 0) {
+            if ((seconds % 60) == 0) {
                 cd.clear(Color.BLACK);
                 for (Body body : bodies) {
                     body.draw(cd);

src/Vector.java

@@ -45,6 +45,12 @@ public class Vector {
         return new Vector(x + v.x, y + v.y, z + v.z);
     }
 
+    public void add(Vector v) {
+        this.x += v.x;
+        this.y += v.y;
+        this.z += v.z;
+    }
+
     /**
      * Returns the product of this vector and 'd'.
      */