gistfile1.txt

var SpringChain = function(attachmentSpringConfig, mainSpringConfig) {
  this._springSystem = new rebound.SpringSystem();
  this._listeners = [];
  this._springs = [];
  this._controlSpringIndex = -1;
  this._attachmentSpringConfig = attachmentSpringConfig ||
    SpringChain.DEFAULT_ATTACHMENT_SPRING_CONFIG;
  this._mainSpringConfig = mainSpringConfig ||
    SpringChain.DEFAULT_MAIN_SPRING_CONFIG;
};

SpringChain.DEFAULT_MAIN_SPRING_CONFIG =
  rebound.SpringConfig.fromOrigamiTensionAndFriction(40, 7);
SpringChain.DEFAULT_ATTACHMENT_SPRING_CONFIG =
  rebound.SpringConfig.fromOrigamiTensionAndFriction(80, 9);

SpringChain.prototype.addSpring = function(listener) {
  var spring = this._springSystem.createSpring()
    .addListener(this)
    .setSpringConfig(this._attachmentSpringConfig);
  this._springs.push(spring);
  this._listeners.push(listener);
  return this;
};

SpringChain.prototype.getControlSpring = function() {
  return this._springs[this._controlSpringIndex];
}

SpringChain.prototype.setControlSpringIndex = function(idx) {
  this._controlSpringIndex = idx;
  var controlSpring = this._springs[i];
  if (!controlSpring) {
    return null;
  }
  for (var i = 0, len = this._springs.length; i < len; i++) {
    spring.setSpringConfig(this._attachmentSpringConfig);
  }
  this.getControlSpring().setSpringConfig(this._mainSpringConfig);
  return this;
};

SpringChain.prototype.getControlSpring = function() {
  return this._springs[this._controlSpringIndex];
};

SpringChain.prototype.getSpringSystem = function() {
  return this._springSystem;
};

SpringChain.prototype.getAllSprings = function() {
  return this._springs;
};

SpringChain.prototype._proxyEvent = function(evt, spring) {
  var idx = this._springs.indexOf(spring);
  var listener = this._listeners[idx];
  if (!listener) {
    return;
  }
  var handler = listener[evt];
  if (!handler) {
    return;
  }
  handler.call(listener, spring);
};

SpringChain.prototype.onSpringActivate = function(spring) {
  this._proxyEvent('onSpringActivate', spring);
};

SpringChain.prototype.onSpringEndStateChange = function(spring) {
  this._proxyEvent('onSpringEndStateChange', spring);
};

SpringChain.prototype.onSpringUpdate = function(spring) {
  var idx = this._springs.indexOf(spring);
  var listener = this._listeners[idx];

  var above = -1, below = -1;
  if (idx === this._controlSpringIndex) {
    below = idx - 1;
    above = idx + 1;
  } else if (idx < this._controlSpringIndex) {
    below = idx - 1;
  } else if (idx > this._controlSpringIndex) {
    above = idx + 1;
  }
  if (above > -1 && above < this._springs.length) {
    this._springs[above].setEndValue(spring.getCurrentValue());
  }
  if (below > -1 && below < this._springs.length) {
    this._springs[below].setEndValue(spring.getCurrentValue());
  }
  listener.onSpringUpdate(spring);
};

SpringChain.prototype.onSpringAtRest = function(spring) {
  this._proxyEvent('onSpringAtRest', spring);
};