angular.module('positionerDirective', [])
  .directive('positioner', function() {
    return {
      restrict: 'A',
      link: function(scope, element){
        var top = element[0].offsetTop;
        var left = element[0].offsetLeft;
        //do whatever math you need here
        angular.element(element).addClass(class you need);
      }
    };
  });

angular.module('positionerDirective', []).
  directive('positioner', function() {
    return {
      restrict: 'A',
      scope: true, // <- create isolated scope
      link: function(scope, element) {
        var el = element[0];
        scope.$watch(function() {
          return (el.offsetTop - scope.scrollTop)+':'+(el.offsetLeft - scope.scrollLeft); // <- check element class is to be updated
        }, function() {
          el.className = 'top-'+(el.offsetTop - scope.scrollTop)+' left-'+(el.offsetLeft - scope.scrollLeft); // <- apply new element class
        });
      },
      controller: ['$scope', '$window', function($scope, $window) {
        $scope.updatePosition = function() {
          $scope.scrollTop = $window.document.body.scrollTop,
          $scope.scrollLeft = $window.document.body.scrollLeft;
          if ($scope.$root.$$phase != '$apply' && $scope.$root.$$phase != '$digest') { // <- Avoid call of $apply while digest is already running
            $scope.$apply();
          }
        }
        angular.element($window).on('resize scroll', function() { // <- subscribe to DOM events and update scope accordingly
          $scope.updatePosition();
        });
        $scope.updatePosition(); // <- set initial values of $scope.scrollTop and $scope.scrollLeft
      }]
    };
  });