text: function GUIManager() {
      var vm = this, noSleep = new NoSleep();
  
      function callOneIfExists(element, methods) {
          methods.some(function (method) {
              if (element[method]) {
                  element[method]();
                  return true;
              }
          });
      }
  
      function goFullScreen() {
          callOneIfExists(document.documentElement, ['requestFullscreen', 'webkitRequestFullscreen', 'mozRequestFullScreen', 'msRequestFullscreen']);
          noSleep.enable();
      }
  
      function goWindowedScreen() {
          callOneIfExists(document, ['exitFullscreen', 'webkitExitFullscreen', 'mozCancelFullScreen', 'msExitFullscreen']);
          noSleep.disable();
      }
  
      vm.isVRCameraSelected = false;
  
      var images = {
          normalCamera: 'img/phone.png',
          vrCamera: 'img/cardboard.png',
          fullScreen: 'img/fullscreen.png',
          windowedScreen: 'img/screen.png'
      };
  
      vm.selectVRCamera = function () {
          vm.isVRCameraSelected = true;
          cameraButton.onclick = vm.selectNormalCamera;
          cameraButton.src = images.normalCamera;
          window.redrawScene();
          vm.selectFullScreen();
      };
      vm.selectNormalCamera = function () {
          vm.isVRCameraSelected = false;
          cameraButton.onclick = vm.selectVRCamera;
          cameraButton.src = images.vrCamera;
          window.redrawScene();
      };
  
      vm.selectFullScreen = function () {
          screenButton.onclick = vm.selectWindowedScreen;
          screenButton.src = images.windowedScreen;
          goFullScreen();
      };
  
      vm.selectWindowedScreen = function () {
          screenButton.onclick = vm.selectFullScreen;
          screenButton.src = images.fullScreen;
          goWindowedScreen();
      };
  
      var cameraButton = document.getElementById('cameraButton');
      cameraButton.src = images.vrCamera;
      cameraButton.onclick = vm.selectVRCamera;
  
      var screenButton = document.getElementById('screenButton');
      screenButton.src = images.fullScreen;
      screenButton.onclick = vm.selectFullScreen;
  
  }
  