Ticker

Ticker class

Hooks into the scheduler’s scheduleFrameCallback() mechanism to invoke a callback every tick.

• Can be started and stopped.
  When started, it returns a Future that will resolve when it is stopped.
• Each tick, the Ticker provides the callback with the duration since the first tick after it was started.
• Because tickers always give their elapsed time relative to the first tick after they were started, tickers are all synchronised.

  Note:

  If you start three ticks at different times between two frames, they will all nonetheless be synchronised with the same starting time, and will subsequently tick in lockstep.