Comment 11 for bug 1675179

Circular revealing is easy to do:

function concentric_reveal(plr, center, amount, delay)
   if not delay then delay = 50 end
   local steps = 1
   while steps < amount do
      plr:reveal_fields(center:region(steps))
      steps = steps + 1
      sleep(delay)
   end
end

But for a 'concentric hide' i have no idea so far.