In threaded OSG drawing, MapWidget::draw runs in the render
thread context, but touches lots of main thread state. Move most of the
work to an update() helper run on the main thread instead, so draw()
mostly makes pure GL calls.
(This is a fix for 3.0, the real solution is to migrate to a
Canvas-based map and GUI)
Adding a spherical projection mode which will work at the poles and
+180/-180 line correctly. Not yet enabled since it has other issues to
be addressed.
Record the historical flight-path (by default, since last takeoff). Optionally display the flight-path in the map; other visualisations (e.g., an 'in-world' view) could also be created. Nasal API to follow so Canvas-map or FMS can show the same data.
Altitude and attitude (Euler angles) are currently recorded but not used anywhere.
Panning feature looked broken to some users since auto-center is enabled
by default which blocks panning. center-on-aircraft is now disabled
automatically when view is panned.
