code: static GVRPerspectiveCamera makePerspShadowCamera(GVRPerspectiveCamera centerCam, float coneAngle)
      {
          GVRPerspectiveCamera camera = new GVRPerspectiveCamera(centerCam.getGVRContext());
          float near = centerCam.getNearClippingDistance();
          float far = centerCam.getFarClippingDistance();
  
          camera.setNearClippingDistance(near);
          camera.setFarClippingDistance(far);
          camera.setFovY((float) Math.toDegrees(coneAngle));
          camera.setAspectRatio(1.0f);
          return camera;
      }
docs: Adds a perspective camera constructed from the designated
  perspective camera to describe the shadow projection.
  This type of camera is used for shadows generated by spot lights.
  @param centerCam GVRPerspectiveCamera to derive shadow projection from
  @param coneAngle spot light cone angle
  @return Perspective camera to use for shadow casting
  @see GVRSpotLight