message: Copy when device was changed
diff: @@ -2542,10 +2542,35 @@ void renderer::on_key_press(key_event const& event)
  if (rt.mode() == host_device_rt::CPU)
  {
  rt.mode() = host_device_rt::GPU;
  +
  + if (device_bvhs.empty())
  + {
  + // TODO: that'll currently not happen, but would be
  + // helpful to defer the copy to not run oom although
  + // the device is not even used
  + copy_bvhs(
  + device_bvhs,
  + device_top_level_bvh,
  + host_bvhs,
  + host_top_level_bvh,
  + HostToDevice
  + );
  + }
  }
  else
  {
  rt.mode() = host_device_rt::CPU;
  +
  + /*if (host_bvhs.empty())
  + {
  + copy_bvhs(
  + host_bvhs,
  + host_top_level_bvh,
  + device_bvhs,
  + device_top_level_bvh,
  + DeviceToHost
  + );
  + }*/
  }
  counter.reset();
  clear_frame();
  