IDragger

/**                                                                                                                                                                  
 * @constructor                                                                                                                                                      
 */
chartbeat.widgets.IDragger = function(target, handle, limits) {
  goog.fx.Dragger.call(this, target, handle, limits);
  if (goog.userAgent.MOBILE) {
    target.addEventListener('touchstart', goog.bind(this.startDragTouch, this));
  }
};
goog.inherits(chartbeat.widgets.IDragger, goog.fx.Dragger);

chartbeat.widgets.IDragger.prototype.startDragTouch = function(e) {
  // Start tracking when the first finger comes down in this element                                                                                                 
  if (e.targetTouches.length != 1)
    return false;

  this.startX = e.targetTouches[0].clientX;
  this.startY = e.targetTouches[0].clientY;

  this.screenX = this.startX;
  this.screenY = this.startY;
  this.deltaX = this.target.offsetLeft;
  this.deltaY = this.target.offsetTop;
  this.pageScroll = goog.dom.getDomHelper(this.document_).getDocumentScroll();

  this.mouseDownTime_ = goog.now();

  var self = this;
  this.handle.addEventListener('touchmove', function(e) { return self.onTouchMove(e) }, false);
  this.handle.addEventListener('touchend', function(e) { return self.onTouchEnd(e) }, false);
  return false;
};

chartbeat.widgets.IDragger.prototype.onTouchMove = function(e) {
  // Prevent the browser from doing its default thing (scroll, zoom)                                                                                                 
  e.preventDefault();

  // Don't track motion when multiple touches are down in this element (that's a gesture)                                                                            
  if (e.targetTouches.length != 1)
    return false;

  var dx = e.targetTouches[0].clientX - this.screenX;
  var dy = e.targetTouches[0].clientY - this.screenY;
  this.screenX = e.targetTouches[0].clientX;
  this.screenY = e.targetTouches[0].clientY;

  if (!this.dragging_) {
    var diffX = this.startX - this.screenX;
    var diffY = this.startY - this.screenY;
    var distance = diffX * diffX + diffY * diffY;
    if (distance > this.hysteresisDistanceSquared_) {
      this.initializeDrag_(e);
      if (!this.dragging_) {
        // If the start drag is cancelled, stop trying to drag.                                                                                                      
        this.endDrag(e);
        return;
      }
    }
  }

  var pos = this.calculatePosition_(dx, dy);
  var x = pos.x;
  var y = pos.y;

  if (this.dragging_) {

    var rv = this.dispatchEvent(new goog.fx.DragEvent(
                                                      goog.fx.Dragger.EventType.BEFOREDRAG, this, e.clientX, e.clientY,
                                                      e, x, y));

    // Only do the defaultAction and dispatch drag event if predrag didn't                                                                                           
    // prevent default                                                                                                                                               
    if (rv !== false) {
      this.doDrag(e, x, y, false);
      e.preventDefault();
    }
  }
};

chartbeat.widgets.IDragger.prototype.onTouchEnd = function(e) {
  // Prevent the browser from doing its default thing (scroll, zoom)                                                                                                 
  e.preventDefault();

  // Stop tracking when the last finger is removed from this element                                                                                                 
  if (e.targetTouches.length > 0)
    return false;


  this.handle.removeEventListener('touchmove', function(e) { return self.onTouchMove(e) }, false);
  this.handle.removeEventListener('touchend', function(e) { return self.onTouchEnd(e) }, false);
  this.endDrag(e);
  return false;
};