title: Get Visible Markers in google_maps_flutter
body: <p>Using <a href="https://github.com/flutter/plugins/tree/master/packages/google_maps_flutter" rel="nofollow noreferrer">Google Maps for Flutter</a> I've placed some markers on different places on the map. I have a separate RaisedButton on my Flutter app which I need to only be visible when one or more of those markers are currently visible on the map.</p>
  
  <p>How can this be achieved? I've found a somewhat <a href="https://stackoverflow.com/questions/2906427/how-to-get-all-visible-markers-on-current-zoom-level">similar solution</a> for Google Maps API but I need this for google_maps_flutter on Flutter.</p>