锤拖中心

我正在使用锤子库为我的应用程序。我怎么能拖动我的元素从任何点，我触摸，而不是中心?谢谢!

var hammertime = Hammer(document.getElementById('contentTab'), {
    transform_always_block:true,
    transform_min_scale: 1,
   drag_block_horizontal: true,
    drag_block_vertical: true,
    drag_min_distance: 0,
    drag_max_touches: 2,
    release: false
});
var rect = document.getElementById('tabella');
var posX=0, posY=0,
    scale=1, last_scale,
    rotation= 1, last_rotation,
    dt =0;
hammertime.on('touch  doubletap drag transform', function(ev) {
    switch(ev.type) {
    case 'doubletap':
        if (dt == 0){
            dt=1;
            scale = 2;
        }else if (dt ==1){
            dt = 0;
            scale = 1;
            posX=0;
            posY=0;
        }
      last_rotation = rotation;
        break;
        case 'touch':
            last_scale = scale;
          last_rotation = rotation;
            break;

     case 'drag':

          posX = ev.gesture.deltaX;
            posY = ev.gesture.deltaY;
            break;
        case 'transform':
   //         rotation = last_rotation + ev.gesture.rotation;
            scale = Math.max(1, Math.min(last_scale * ev.gesture.scale, 10));
            break;
    }
    // transform!
    var transform =
            "translate3d("+posX+"px,"+posY+"px, 0) " +
            "scale3d("+scale+","+scale+", 0) " ;
            "rotate("+rotation+"deg) ";
    rect.style.transform = transform;
    rect.style.oTransform = transform;
    rect.style.msTransform = transform;
    rect.style.mozTransform = transform;
    rect.style.webkitTransform = transform;
});