d3.behavior.drag = function() {

  var event = d3.dispatch("drag", "dragstart", "dragend");

  function drag() {

    this

        .on("mousedown.drag", mousedown)

        .on("touchstart.drag", mousedown);

    d3.select(window)

        .on("mousemove.drag", d3_behavior_dragMove)

        .on("touchmove.drag", d3_behavior_dragMove)

        .on("mouseup.drag", d3_behavior_dragUp, true)

        .on("touchend.drag", d3_behavior_dragUp, true)

        .on("click.drag", d3_behavior_dragClick, true);

  }

  // snapshot the local context for subsequent dispatch

  function start() {

    d3_behavior_dragEvent = event;

    d3_behavior_dragEventTarget = d3.event.target;

    d3_behavior_dragOffset = d3_behavior_dragPoint((d3_behavior_dragTarget = this).parentNode);

    d3_behavior_dragMoved = 0;

    d3_behavior_dragArguments = arguments;

  }

  function mousedown() {

    start.apply(this, arguments);

    d3_behavior_dragDispatch("dragstart");

  }

  drag.on = function(type, listener) {

    event.on(type, listener);

    return drag;

  };

  return drag;

};

var d3_behavior_dragEvent,

    d3_behavior_dragEventTarget,

    d3_behavior_dragTarget,

    d3_behavior_dragArguments,

    d3_behavior_dragOffset,

    d3_behavior_dragMoved,

    d3_behavior_dragStopClick;

function d3_behavior_dragDispatch(type) {

  var o = d3.event, p = d3_behavior_dragTarget.parentNode, dx = 0, dy = 0;

  if (p) {

    p = d3_behavior_dragPoint(p);

    dx = p[0] - d3_behavior_dragOffset[0];

    dy = p[1] - d3_behavior_dragOffset[1];

    d3_behavior_dragOffset = p;

    d3_behavior_dragMoved |= dx | dy;

  }

  try {

    d3.event = {dx: dx, dy: dy};

    d3_behavior_dragEvent[type].apply(d3_behavior_dragTarget, d3_behavior_dragArguments);

  } finally {

    d3.event = o;

  }

  o.preventDefault();

}

function d3_behavior_dragPoint(container, type) {

  // TODO Track touch points by identifier.

  var t = d3.event.changedTouches;

  return t ? d3.svg.touches(container, t)[0] : d3.svg.mouse(container);

}

function d3_behavior_dragMove() {

  if (!d3_behavior_dragTarget) return;

  var parent = d3_behavior_dragTarget.parentNode;

  // O NOES! The drag element was removed from the DOM.

  if (!parent) return d3_behavior_dragUp();

  d3_behavior_dragDispatch("drag");

  d3_eventCancel();

}

function d3_behavior_dragUp() {

  if (!d3_behavior_dragTarget) return;

  d3_behavior_dragDispatch("dragend");

  d3_behavior_dragTarget = null;

  // If the node was moved, prevent the mouseup from propagating.

  // Also prevent the subsequent click from propagating (e.g., for anchors).

  if (d3_behavior_dragMoved && d3_behavior_dragEventTarget === d3.event.target) {

    d3_behavior_dragStopClick = true;

    d3_eventCancel();

  }

}

function d3_behavior_dragClick() {

  if (d3_behavior_dragStopClick && d3_behavior_dragEventTarget === d3.event.target) {

    d3_eventCancel();

    d3_behavior_dragStopClick = false;

    d3_behavior_dragEventTarget = null;

  }

}