: document.getElementById('multitarget-reference-4')
            }
          ]
        }
      ];

      function setupDemoUI() {
        var next = document.getElementsByClassName('next')[0];
        var prev = document.getElementsByClassName('prev')[0];
        next.addEventListener('click', scene.nextTarget);
        prev.addEventListener('click', scene.prevTarget);
        document.body.addEventListener('keydown', onKeydown);
      }

      function onKeydown(e) {
        switch(e.keyCode) {
          c