limit.js

(function ($) {

  $.Drag.prototype

  .limit = function (container, center) {

    var styles = container.styles('borderTopWidth', 'paddingTop', 'borderLeftWidth', 'paddingLeft'),
      paddingBorder = new $.Vector(
      parseInt(styles.borderLeftWidth, 10) + parseInt(styles.paddingLeft, 10) || 0, parseInt(styles.borderTopWidth, 10) + parseInt(styles.paddingTop, 10) || 0);

    this._limit = {
      offset: container.offsetv().plus(paddingBorder),
      size: container.dimensionsv(),
      center: center === true ? 'both' : center
    };
    return this;
  };

  var oldPosition = $.Drag.prototype.position;
  $.Drag.prototype.position = function (offsetPositionv) {

    if (this._limit) {
      var limit = this._limit,
        center = limit.center && limit.center.toLowerCase(),
        movingSize = this.movingElement.dimensionsv('outer'),
        halfHeight = center && center != 'x' ? movingSize.height() / 2 : 0,
        halfWidth = center && center != 'y' ? movingSize.width() / 2 : 0,
        lot = limit.offset.top(),
        lof = limit.offset.left(),
        height = limit.size.height(),
        width = limit.size.width();

      if (offsetPositionv.top() + halfHeight < lot) {
        offsetPositionv.top(lot - halfHeight);
      }

      if (offsetPositionv.top() + movingSize.height() - halfHeight > lot + height) {
        offsetPositionv.top(lot + height - movingSize.height() + halfHeight);
      }

      if (offsetPositionv.left() + halfWidth < lof) {
        offsetPositionv.left(lof - halfWidth);
      }

      if (offsetPositionv.left() + movingSize.width() - halfWidth > lof + width) {
        offsetPositionv.left(lof + width - movingSize.left() + halfWidth);
      }
    }

    oldPosition.call(this, offsetPositionv);
  };

  return $;
})(jQuery);