in the beginning

arbor_src/physics/atoms.js

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+//
+// atoms.js
+//
+// particle system- or physics-related datatypes
+//
+
+var Node = function(data){
+	this._id = _nextNodeId++; // simple ints to allow the Kernel & ParticleSystem to chat
+	this.data = data || {};  // the user-serviceable parts
+	this._mass = (data.mass!==undefined) ? data.mass : 1
+	this._fixed = (data.fixed===true) ? true : false
+	this._p = new Point((typeof(data.x)=='number') ? data.x : null, 
+                     (typeof(data.y)=='number') ? data.y : null)
+  delete this.data.x
+  delete this.data.y
+  delete this.data.mass
+  delete this.data.fixed
+};
+var _nextNodeId = 1
+
+var Edge = function(source, target, data){
+	this._id = _nextEdgeId--;
+	this.source = source;
+	this.target = target;
+	this.length = (data.length!==undefined) ? data.length : 1
+	this.data = (data!==undefined) ? data : {};
+	delete this.data.length
+};
+var _nextEdgeId = -1
+
+var Particle = function(position, mass){
+  this.p = position;
+  this.m = mass;
+	this.v = new Point(0, 0); // velocity
+	this.f = new Point(0, 0); // force
+};
+Particle.prototype.applyForce = function(force){
+	this.f = this.f.add(force.divide(this.m));
+};
+
+var Spring = function(point1, point2, length, k)
+{
+	this.point1 = point1; // a particle
+	this.point2 = point2; // another particle
+	this.length = length; // spring length at rest
+	this.k = k;           // stiffness
+};
+Spring.prototype.distanceToParticle = function(point)
+{
+  // see http://stackoverflow.com/questions/849211/shortest-distance-between-a-point-and-a-line-segment/865080#865080
+  var n = that.point2.p.subtract(that.point1.p).normalize().normal();
+  var ac = point.p.subtract(that.point1.p);
+  return Math.abs(ac.x * n.x + ac.y * n.y);
+};
+
+var Point = function(x, y){
+  if (x && x.hasOwnProperty('y')){
+    y = x.y; x=x.x;
+  }
+  this.x = x;
+  this.y = y;  
+}
+
+Point.random = function(radius){
+  radius = (radius!==undefined) ? radius : 5
+	return new Point(2*radius * (Math.random() - 0.5), 2*radius* (Math.random() - 0.5));
+}
+
+Point.prototype = {
+  exploded:function(){
+    return ( isNaN(this.x) || isNaN(this.y) )
+  },
+  add:function(v2){
+  	return new Point(this.x + v2.x, this.y + v2.y);
+  },
+  subtract:function(v2){
+  	return new Point(this.x - v2.x, this.y - v2.y);
+  },
+  multiply:function(n){
+  	return new Point(this.x * n, this.y * n);
+  },
+  divide:function(n){
+  	return new Point(this.x / n, this.y / n);
+  },
+  magnitude:function(){
+  	return Math.sqrt(this.x*this.x + this.y*this.y);
+  },
+  normal:function(){
+  	return new Point(-this.y, this.x);
+  },
+  normalize:function(){
+  	return this.divide(this.magnitude());
+  }
+}
+