jQuery_jqueryを使用したドラッグアンドドロップエフェクトプラグインの実装方法

/**
* jQuery Drag and Scroll
*
* Copyright (c) 2012 Ryan Naddy (ryannaddy.com)
* Dual licensed under the MIT and GPL licenses:
* http://www.opensource.org/licenses/mit-license.php
* http://www.gnu.org/licenses/gpl.html
*/
(function($){
  var down = false;
  var prevX = 0;
  var prevY = 0;
  var x = 0;
  var y = 0;
  var px = 0;
  var py = 0;
  var lastPX = -1;
  var lastPY = -1;
  var $target = null;
  var $me = null;
  var $selector = "";
  var settings = {
    mouseButton: 3,
    context: false,
    selectText: false
  };
  $.fn.dragScroll = function(options){
    settings = $.extend(settings, options);
    $selector = $(this).selector;
    $(this).contextmenu(function(){
      return false;
    }).bind("mousedown touchstart", function(e){
      $me = $(this);
      e = event.touches ? event.touches[0] : e;
      $target = $(e.target);
      $target = $target.closest($selector);
      if(settings.viewPort){
        if(!settings.context){
          $me.contextmenu(function(){
            return false;
          });
        }
      }
      if(!settings.selectText){
        $me.attr('unselectable', 'on').css('user-select', 'none').on('selectstart', false);
      }
      $me = $me.closest($selector);
      if($target && $me.attr("id") != $target.attr("id")){
        return false;
      }
      if(e.which == settings.mouseButton || event.touches){
        $me.css("cursor", "move");
        down = true;
      }
      px = $me.scrollLeft();
      py = $me.scrollTop();
      x = px + e.pageX;
      y = py + e.pageY;
      prevX = x;
      prevY = y;
      return true;
    }).bind("mouseup touchend", function(e){
      $me = $(this);
      e = event.touches ? event.touches[0] : e;
      $me.css("cursor", "auto");
      down = false;
    }).bind("mousemove touchmove", function(e){
      $me = $(this);
      $me = $me.closest($selector);
      e = event.touches ? event.touches[0] : e;
      if((e.which == settings.mouseButton || event.touches) && down){
        if(event.touches){
          event.preventDefault();
        }
        if($target && $me.attr("id") != $target.attr("id")){
          return false;
        }
        $me.css("cursor", "move");
        px = $me.scrollLeft();
        py = $me.scrollTop();
        x = px + e.pageX;
        y = py + e.pageY;
        $me.scrollLeft(px + (-(x - prevX)));
        $me.scrollTop(py + (-(y - prevY)));
        prevX = x - (x - prevX);
        prevY = y - (y - prevY);
        if(lastPX == px)
          prevX = x;
        if(lastPY == py)
          prevY = y;
        lastPX = px;
        lastPY = py;
      }
      return true;
    });
    return this;
  }
})(jQuery);