VIX Question – Extended Hours Calculation

If I understand correctly that the VIX value is derived from option activity of the SPX, and options don't trade outside of regular market hours…what drives it's movement in the off-hours?

Is it getting calculated from call/put orders as they get added to the book, rather than what actually gets executed and printed to the tape? More specifically, if heavy put orders are coming in during premarket, does the VIX rise in response…and does high call activity tend to cause the opposite?

Thanks in advance for your responses.