"Curtis L. Olson" said:

> Update of /var/cvs/FlightGear-0.9/source/src/Scenery
> In directory baron:/tmp/cvs-serv20966/Scenery
> Modified Files:
>       newcache.cxx tileentry.cxx tileentry.hxx tilemgr.cxx 
> Log Message:
> Make a subtle change to tile loading/unloading policy in order to make the tile
> paging system much more robust when position change is very rapid and sporadic.
> Recall that we must load 3d models in the main render thread because model
> loading can trigger opengl calls (i.e. with texture loading) and all opengl
> calls *must* happen in the main render thread.
> To accomplish this we load the base tile in the pager thread and build a work
> queue of external models that need to be loaded.  We never allow a tile to be
> paged out of the tile cache until all it's pending model loads are complete.
> However, when changing position very rapidly, we can quickly create a huge
> backlog of pending model loads because we are changing positions faster than we
> can load the associated models for the existing tiles.  The end result is
> that tiles that are long out of range can't be removed because there is still
> a huge backlog of pending model load requests and memory blows up.
> This change being committed allows the tile paging system to remove tiles
> if they are out of range, even when there are pending models to load.  The
> model loading code in the render thread can now check to see if the tile
> exists and discard any model load request for tiles that no longer exist.
> This situation should never occur in normal operation, but could occur in
> "contrived" situations where an external script was rapidly changing
> the simulator position to then be able to query FG terrain height, and doing
> this for a large number of points that are distributed across a large area.

Is it possible for a "legit" model load to be lost because the model queue
gets ahead of the tiles?  I know, it's a dumb question, but I won't have a
chance to look myself for a few days anyway.



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