Has all the structure of the classes needed for extension to arrows/markers/whatever.
However, this is just the minimal subset of those base classes required to implement the line drawing functionality
with the asynchronous resampling, and fully compatible with 'current track' which is NOT resampled in any way.
These files are a branch from the prior pull request, and hopefully will make everyone more comfortable about including
the code. The altitude and speed displays, all the bells and whistles - that can come later if needed.
In the drawing loop, culling was performed on pixel boundaries based on x/y positions compared to the tileBox x/y position,
however calculating these from lat/lon was quite a slow process involving calls to getPixXFromLatLon and getPixYFromLatLon
which in turn had a horrendous amount of calculations happening. But since the tileBox has lat/lon and the pixel/lines being
drawn also have lat/lon it seems reasonable - despite potential spherical issues on lat/lon coordinates (?) to just use the
lat/lon as a visibility cull. So, that's what I've done and it does seem to work OK. Heaps faster; aside from the actual
line draw we're talking a couple orders of magnitude improvement in speed. Getting really zippy now, even when drawing
groups super big tracks, and I mean big - hundredsof thousands of points big.
The video at https://youtu.be/J1ppW3_hWds shows well over a thousand kilometers of tracks, 230 thousand points.
By enabling on-zoom resampling of arrows, speed, altitude and conveyor data it is possible to more effectively
tailor the visuals of these renderers. For example, the altitude and speed are point-reduced based on zoom, and now
look much cleaner at low zoom values. Likewise, the arrows are now rendered at consistent size regardless of
zoom. Also, the conveyor segments are similar length onscreen regardless of zoom. During a zoom change, the
prevoiusly resampled track is killed, so there is a brief flash while the appropriate track is resampled. This
appeared visually better than drawing the old track with incorrect spacing/scaling.
