Abstracted from the SvgVerlet.js class

Verlet.js

// Generated by CoffeeScript 1.6.3
var RubberPoint, VerletPoint, VerletStick,
  __hasProp = {}.hasOwnProperty,
  __extends = function(child, parent) { for (var key in parent) { if (__hasProp.call(parent, key)) child[key] = parent[key]; } function ctor() { this.constructor = child; } ctor.prototype = parent.prototype; child.prototype = new ctor(); child.__super__ = parent.prototype; return child; };

VerletPoint = (function() {
  VerletPoint.prototype.down = false;

  VerletPoint.prototype.oldX = null;

  VerletPoint.prototype.oldY = null;

  VerletPoint.prototype.originalX = 0;

  VerletPoint.prototype.originalY = 0;

  VerletPoint.prototype.x = 0;

  VerletPoint.prototype.y = 0;

  VerletPoint.prototype.forceX = 0;

  VerletPoint.prototype.forceY = 0;

  VerletPoint.scene = null;

  function VerletPoint(x, y, locked) {
    this.x = x;
    this.y = y;
    this.locked = locked != null ? locked : false;
    this.originalX = this.oldX = this.x;
    this.originalY = this.oldY = this.y;
  }

  VerletPoint.prototype.setPos = function(x, y) {
    this.x = this.oldX = x;
    return this.y = this.oldY = y;
  };

  VerletPoint.prototype.force = function(x, y) {
    this.forceX += x;
    return this.forceY += y;
  };

  VerletPoint.prototype.update = function() {
    var tempX, tempY;
    if (this.dead || this.down || this.locked) {
      return null;
    }
    tempX = this.x;
    tempY = this.y;
    this.x += this.x - this.oldX + this.forceX;
    this.y += this.y - this.oldY + this.forceY;
    this.oldX = tempX;
    this.oldY = tempY;
    this.forceX = 0;
    this.forceY = 0;
    return null;
  };

  return VerletPoint;

})();

RubberPoint = (function(_super) {
  __extends(RubberPoint, _super);

  RubberPoint.prototype.rubberAmplitude = 0.1;

  RubberPoint.prototype.rubberDamping = 0.1;

  RubberPoint.prototype.rubberForceX = 0;

  RubberPoint.prototype.rubberForceY = 0;

  RubberPoint.maxAmp = 0.02;

  RubberPoint.minAmp = 0.005;

  function RubberPoint(x, y, locked) {
    this.x = x;
    this.y = y;
    this.locked = locked != null ? locked : false;
    RubberPoint.__super__.constructor.call(this, this.x, this.y, this.locked);
    this.rubberAmplitude = RubberPoint.minAmp + (RubberPoint.maxAmp - RubberPoint.minAmp);
  }

  RubberPoint.prototype.update = function() {
    if (this.dead || this.down || this.locked) {
      return null;
    }
    this.rubberForceX = (this.originalX - this.x) * this.rubberAmplitude;
    this.rubberForceY = (this.originalY - this.y) * this.rubberAmplitude;
    this.x += this.rubberForceX;
    this.y += this.rubberForceY;
    return RubberPoint.__super__.update.call(this);
  };

  RubberPoint.resetDefaults = function() {
    RubberPoint.minAmp = 0.02;
    return RubberPoint.maxAmp = 0.005;
  };

  return RubberPoint;

})(VerletPoint);

VerletStick = (function() {
  function VerletStick(a, b) {
    var dx, dy,
      _this = this;
    this.pointa = a;
    this.pointb = b;
    this.torn = false;
    this.tearResist = 9999;
    dx = a.x - b.x;
    dy = a.y - b.y;
    this.hypotenuse = Math.sqrt(dx * dx + dy * dy);
    if (this.pointa.locked && this.pointb.locked) {
      this.contract(function() {
        return null;
      });
    } else if (this.pointa.locked) {
      this.contract = function() {
        var diff, h, offx, offy;
        dx = _this.pointb.x - _this.pointa.x;
        dy = _this.pointb.y - _this.pointa.y;
        h = Math.sqrt(dx * dx + dy * dy);
        if (h > _this.tearResist) {
          _this.torn = true;
        }
        diff = _this.hypotenuse - h;
        offx = diff * dx / h;
        offy = diff * dy / h;
        _this.pointb.x += offx;
        _this.pointb.y += offy;
        return null;
      };
    } else if (this.pointb.locked) {
      this.contract = function() {
        var diff, h, offx, offy;
        dx = _this.pointb.x - _this.pointa.x;
        dy = _this.pointb.y - _this.pointa.y;
        h = Math.sqrt(dx * dx + dy * dy);
        if (h > _this.tearResist) {
          _this.torn = true;
        }
        diff = _this.hypotenuse - h;
        offx = diff * dx / h;
        offy = diff * dy / h;
        _this.pointa.x -= offx;
        _this.pointa.y -= offy;
        return null;
      };
    } else {
      this.contract = function() {
        var diff, h, offx, offy;
        dx = _this.pointb.x - _this.pointa.x;
        dy = _this.pointb.y - _this.pointa.y;
        h = Math.sqrt(dx * dx + dy * dy);
        if (h > _this.tearResist) {
          _this.torn = true;
        }
        diff = _this.hypotenuse - h;
        offx = (diff * dx / h) * .5;
        offy = (diff * dy / h) * .5;
        _this.pointa.x -= offx;
        _this.pointa.y -= offy;
        _this.pointb.x += offx;
        _this.pointb.y += offy;
        return null;
      };
    }
  }

  return VerletStick;

})();