/*
  dragObj:  拖拽对象
  parent: 指定区域
*/
function dragFn (dragObj,parent) {
  $(dragObj).mousedown(function (e) {
    var _this = $(this)
    var parent_h = $(parent)[0].offsetHeight
    var parent_w = $(parent)[0].offsetWidth
    var drag_h = $(this)[0].offsetHeight
    var drag_w = $(this)[0].offsetWidth
    var dragX = e.clientX - $(this)[0].offsetLeft
    var dragY = e.clientY - $(this)[0].offsetTop

    // 当前拖拽对象层级优先
    $(this).css('z-index','9').siblings().css('z-index','1')

    $(document).mousemove(function (e) {
      var l = e.clientX - dragX
      var t = e.clientY - dragY
      if (l < 0) {
        l = 0
      } else if (l > parent_w - drag_w) {
        l = parent_w - drag_w
      }
      if (t < 0) {
        t = 0
      } else if (t > parent_h - drag_h) {
        t = parent_h - drag_h
      }
      _this.css({
        left: l + 'px',
        top: t + 'px',
      })
    })
  })

  $(document).mouseup(function () {
    $(this).off('mousemove')
  })
}