only run a single iteratePings so we cross the interval barrier gracefully
only run a single iteratePings so we cross the interval barrier gracefully

With multiple iteratePings running one would clearRect over the other's
paint. Now there's a single global array of pings and any animations still
running get carried over when a new interval starts.

potch/glow,potch/glow,potch/glow,potch/glow