Since actors can be active in 3x3 grid around the player, we need to
first load all objects in a 5x5 grid around the player.
Split load and unloading in 2 phases. Add an mInactiveCells set into the
scene, which contains all cells inside the aforementioned 5x5 grid.
These cells contains only heightfields and non-animated physics objects.
Animated objects are tied to the scene graph, which doesn't exists yet
in these cells, so we skip them.
A prerequisite to create physics objects for statics was to remove the
dependency on base node (since it doesn't yet exists) for object
position. It is still necessary for animation though.
Restore the basenode (and the associated FIXME) so that animated objects works properly.
Before movement calculation, the main thread prepare a
vector of ActorFrameData, which contains all data necessary to perform
the simulation, and feed it to the solver. At the same time it fetches
the result from the previous background simulation, which in turn is
used by the game mechanics.
Other functions of the physics system (weapon hit for instance)
interrupt the background simulation, with some exceptions described
below.
The number of threads is controlled by the numeric setting
[Physics]
async num threads
In case 'async num threads' > 1 and Bullet doesn't support multiple threads,
1 async thread will be used. 0 means synchronous solver.
Additional settings (will be silently switched off if async num threads = 0)
[Physics]
defer aabb update
Update AABBs of actors and objects in the background thread(s). It is not an especially
costly operation, but it needs exclusive access to the collision world, which blocks
other operations. Since AABB needs to be updated for collision detection, one can queue
them to defer update before start of the movement solver. Extensive tests on as much
as one installation (mine) show no drawback having that switched on.
[Physics]
lineofsight keep inactive cache
Control for how long (how many frames) the line of sight (LOS) request will be kept updated.
When a request for LOS is made for the first time, the background threads are stopped to
service it. From now on, the LOS will be refreshed preemptively as part of the background
routine until it is not required for lineofsight keep inactive cache frames. This mean
that subsequent request will not interrupt the background computation.
