Currently, we use an `UnrefQueue` which supposedly aims to transfer destruction costs to another thread. The implications of this unusual pattern can not be well understood because some allocators might free resources more efficiently if they are freed by the same thread that allocated them. In addition, `UnrefQueue` complicates the validation of thread safety in our engine. Lastly, our current usage of `UnrefQueue` triggers `ref()`, `unref()` atomic operations as objects are passed into the queue. These operations could be more expensive than the actual destruction.
With this PR we thus remove `UnrefQueue`. We can expect these changes to have a minor impact at most because we free most resources elsewhere in `ResourceSystem::updateCache`.
Since commit e8662bea3133ba9dbb09b86c3abb1af39425e90d, we're using OSG functionality that contains an unfixed crash bug in version 3.2. The bug is fixed in version 3.4 (OSG commit 6351e5020371b0b72b300088a5c6772f58379b84)
This fixes initWorldSpaceParticles not taking object scale into account. Still not taking into account object rotation or node animations. Ideally the initWorldSpaceParticles needs to run in an updateCallback.
OSG 3.4 adds the ability to place Drawables directly in the scene graph, without a Geode decorating them. Leveraging this should give a small performance boost, because the redundant Geodes increase culling overhead.
There is still an oustanding issue with the RemoveDrawableVisitor no longer working correctly, because Drawables can have multiple parents.
For now, not much difference, but should result in a sizable speed up once MyGUI no longer needs the DYNAMIC flag (i.e. the loading screen truly renders in the background).
