Android Question function IsPointInView for b4xmap

[NilsBe]

B4XMap (Open Street Map viewer)

Just came across this and thinking about moving to this from OSMDroid. Trying to figure out how to download a map area based on min and max latitude and longitude and can't figure out how to get from latitude and longitude to the Open Street Map x and y tile numbers, so I can do something like...

www.b4x.com

I use the nice OSM Viewer b4xmap and I have just one single question.

How do I find out if a specific position (lat/lon) is already visible on the map or not.
If Not I would like to show that position If it is already visible then no repositioning required.

Thanks for your kind support

Nils