1. Reorder unlock and notify_all calls to avoid notifying when not all worker
threads are waiting.
2. Make sure main thread does not attempt to exclusively lock mSimulationMutex
while not all workers are done with previous frame.
3. Replace mNewFrame flag by counter to avoid modification from multiple
threads.
simulation
The purpose of weak_ptr is to avoid performing the simulation on deleted
Actor by promoting it to a shared_ptr via a lock() call. This clutter
the code with a lot of branches, whereas the overwhelmingly common case is for the call to succeed.
Since the simulation is decoupled from the engine state, we can use a shared_ptr instead of a weak_ptr.
This allow us to ignore (ie not handle) the rarer case where the actor is delete from the scene. This means that the simulation
will run for one frame more than before for each actor, whereas the rest of the engine
will be ignorant of this.
MWWorld::Ptr:
- they are equivalent
- btCollisionObject* is readily available from the simulation, it saves
a call to a mutex
- btCollisionObject* is smaller
- inline PhysicsSystem::applyQueuedMovements() into PhysicsSystem::stepSimulation()
- rename PhysicsTaskScheduler::moveActors() to PhysicsTaskScheduler::applyQueuedMovements()
- move the actor movement code from World::doPhysics() to
PhysicsSystem::moveActors() (analogically to the projectile manager)
- default to 1 thread
- default to always use defered aabb update, remove option
- always keep a cache of LOS request for at least the current frame.
This decreases number of raycast, especially when a lot of actors are
involved and "NPCs avoid collisions" is on
This gives finer control over reseting positions (switch off tcl is no
longer glitchy) and solve most of the erroneous usage of stale World::Ptr
indicated by:
"Error in frame: moveTo: object is not in this cell"
position being used under heavy load, I introduced a regression that
prevented the position to be updated in case of teleport.
Move the logic in its own function and decide in PhysicsSystem whether a
reset is needed.
Before this change, if an actor position was changed while the physics
simulation was running, the simulation result would be discarded. It is
fine in case of one off event such as teleport, but in the case of
scripts making use of this functionality to make lifts or conveyor (such
as Sotha Sil Expanded mod) it broke actor movement.
To alleviate this issue, at the end of the simulation, the position of the Actor
in the world is compared to the position it had at the beginning of the
simulation. A difference indicate a force move occured. In this case,
the Actor mPosition and mPreviousPosition are translated by the difference of position.
Since the Actor position will be really set while the next simulation runs, we
save it in the mNextPosition field.
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.
