AngularJS 1.3.x Inter Controller-communication through nested scope.

var app = angular.module('plunker', []);

//For siplicity I put the 3 controllers in this same file.

app.controller('MainCtrl', function($scope) {
  $scope.name = 'Main Controller';
  $scope.commonData = {};
});


app.controller('buttonCtrl', function($scope) {
  $scope.name = 'Button Controller';
  $scope.handleShowLoadingCoverClick = handleShowLoadingCoverClick;
  var isLoading = false;

  ///////////////////

  function handleShowLoadingCoverClick() {
    isLoading = !isLoading;
    $scope.commonData.isLoading = isLoading;  //Note JS will create these properties (commonData on $scope and isLoading on commonData) at this point, now how cool is that? (I come from C#).
  }
});


app.controller('loadingCoverCtrl', function($scope) {
  $scope.name = 'LoadingCover Controller';
  //$scope.showCover = $scope.$parent.commonData.isLoading; //Note this will NOT work!
  $scope.parentScopeData = $scope.$parent.commonData; 
});

<!DOCTYPE html>
<html ng-app="plunker">

<head>
  <meta charset="utf-8" />
  <title>AngularJS Plunker</title>
  <script>
    document.write('<base href="' + document.location + '" />');
  </script>
  <link rel="stylesheet" href="style.css" />
  <script data-require="angular.js@1.3.x" src="https://code.angularjs.org/1.3.13/angular.js" data-semver="1.3.13"></script>
  <script src="app.js"></script>

  <style>
    .content-container {
      position: absolute;
    }
  </style>

</head>

<body ng-controller="MainCtrl">
  <p>{{name}}</p>
  
  <div ng-controller="buttonCtrl">
    <button ng-click="handleShowLoadingCoverClick()">Toggle Loading Cover (nesting)</button>
  </div>
  
  <hr/>

  <div class="content-container">
    <div ng-include="'loadingCover.html'"></div>
    <pre>
      This is some more text to be covered by
      the loading cover.
      The cover will land on top using position:absolute 
      and putting the two in the same div.
      It will have transparent background and making what 
      it covers un-reachable. It stacks on-top using z-index. 
    </pre>
  </div>
</body>

</html>

/* Put your css in here */

<style>
  .loading-cover {
    display: block;
    position: absolute;
    background-color: rgba(99, 99, 99, 0.6);
    z-index: 1;
    width: 100%;
    height: 100%;
  }
  .center-middle {
    position: absolute;
    left: 0;
    top: 0;
    right: 0;
    bottom: 0;
    margin: auto;
  }
</style>

<div ng-controller="loadingCoverCtrl">

  <div ng-show="showCover || parentScopeData.isLoading" class="loading-cover">
    <strong>Loading...</strong>
    <!-- I don't know how to include gif to Plunker and used http://websemantics.co.uk/online_tools/image_to_data_uri_convertor/ to convert mine to base64 data and include this stuff here -->
    <img class="center-middle" width="66" height="66" title="" alt="" src="data:image/gif;base64,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">
  </div>

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