// WebGL setup.
      var webglCanvas = document.getElementById("webgl-canvas");
      var glAttribs = {
        alpha: false,
      };
      var gl = webglCanvas.getContext("webgl", glAttribs);
      if (!gl) {
        gl = webglCanvas.getContext("experimental-webgl", glAttribs);
        if (!gl) {
          VRSamplesUtil.addError("Your browser does not support WebGL.");
          return;
        }
      }
      gl.clearColor(0.1, 0.2, 0.3, 1.0);
      gl.enable(gl.DEPTH_TEST);
      gl.enable(gl.CULL_FACE);
      var textureLoader = new WGLUTextureLoader(gl);
      var texture = textureLoader.loadTexture("media/textures/cube-sea.png");
      var cubeSea = new VRCubeSea(gl, texture);
      var enablePerformanceMonitoring = WGLUUrl.getBool(
          'enablePerformanceMonitoring', false);
      var stats = new WGLUStats(gl, enablePerformanceMonitoring);
      var presentingMessage = document.getElementById("presenting-message");
      // ================================
      // WebVR-specific code begins here.
      // ================================
      function onVRRequestPresent () {
        // This can only be called in response to a user gesture.
        vrDisplay.requestPresent([{ source: webglCanvas }]).then(function () {
          // Nothing to do because we're handling things in onVRPresentChange.
        }, function (err) {
          var errMsg = "requestPresent failed.";
          if (err && err.message) {
            errMsg += "<br/>" + err.message
          }
          VRSamplesUtil.addError(errMsg, 2000);
        });
      }
      function onVRExitPresent () {
        // No sense in exiting presentation if we're not actually presenting.
        // (This may happen if we get an event like vrdisplaydeactivate when
        // we weren't presenting.)
        if (!vrDisplay.isPresenting)
          return;