Evented (cool) collision system update

gistfile1.js

function CoolCollisionSystem() {
  this.currentTime = 0;
  this.pq = new PriorityQueue(eventComparator);

  //warmup happens only at startup (duh), to predict collisions between every particle
  //this is the only n^2 loop
  this.warmUp = function() {
    for(var i = 0, length = this.circles.length; i < length; i++) {
      this.predict(this.circles[i]);
    }
    this.redraw();
  };

  //predict future collisions and insert then inside the priority queue
  this.predict = function(circle) {
    if(!circle) return;

    for(var i = 0, length = this.circles.length; i < length; i++) {
      var circleToHit = this.circles[i];
      var dt = circle.timeToHit(circleToHit);
      //the if below is an optimization to avoid distant predictions that will probably never happen
      if(dt > 0 && dt < this.circles.length/2) 
        this.pq.enqueue(new Event(this.currentTime + dt, circle, circleToHit));
    }

    var dtX = circle.timeToHitVerticalWall(this.canvas.width);
    var dtY = circle.timeToHitHorizontalWall(this.canvas.height);

    this.pq.enqueue(new Event(this.currentTime + dtX, circle, null));
    this.pq.enqueue(new Event(this.currentTime + dtY, null, circle));
  };

  //"hack" to keep the drawing away of the main loop
  //this is necessary because drawing is also an event like a collision
  this.oldDraw = this.draw;
  this.draw = function(){};
  this.redraw = function() {
    this.oldDraw();
    this.pq.enqueue(new Event(this.currentTime + .1, null, null));
  };

  this.update = function() {
    //first we must find a valid event
    var e = this.pq.dequeue();

    while(!e.isValid())
      e = this.pq.dequeue();

    var a = e.circleA;
    var b = e.circleB;
    
    //"move" every particle to the moment of the selected event
    for(var i = 0, length = this.circles.length; i < length; i++) {
      this.circles[i].move(e.time - this.currentTime, this.canvas.width, this.canvas.height);
    }
    this.currentTime = e.time;

    //do the collision or just redraw
    if(a && b) a.bounceOff(b);
    else if(a && !b) a.bounceOffVerticalWall();
    else if(!a && b) b.bounceOffHorizontalWall();
    else { this.redraw(); }

    //predict new collisions with the event particles (if any)
    this.predict(a);
    this.predict(b);
  };
}