[Opensim-dev] BulletSim updates

[Adams, Robert]

Here is a short update on changes made to BulletSim[1] and related code in the last few weeks:

Mesh Asset Hulls: Dahlia updated Meshmerizer with experimental hull unpacking code. Not only does OpenSimulator now unpack mesh asset hull specifications but it now falls back to the display mesh if a physical mesh is not available (should mean fewer "no physical mesh available" errors).  BulletSim has been updated to use the mesh hull if present. This feature is enabled by default but, if you notice problems with physical mesh objects, try disabling this feature by adding to your INI file "[BulletSim]ShouldUseAssetHull=false".

Vehicles: The SL Vehicle Model implemented by BulletSim has received some work in the last weeks and is working well for many vehicle types (cars, planes, balloons, ...). The implementation is not exact and tuning is ongoing (especially for cars) with the goal of BulletSim simulating close to the "reference implementation" (i.e., SL). Tuning analysis and notes are being recorded at http://opensimulator.org/wiki/BulletSim/VehicleTuning . If you have vehicle problems or needs, please Mantis them.

Avatar Height: Avatar height has been tuned (again) so feet don't sink into the ground. INI parameters are available for tuning and are explained at http://opensimulator.org/wiki/BulletSim#Adjusting_Avatar_Height .

Stairs: Avatar stair walking has been improved and problems with stair orientation (stairs oriented north working differently than stairs oriented westward) have been fixed. If you are into stair tuning, INI parameters are explained at http://opensimulator.org/wiki/BulletSim#Avatar_Walking_Up_Stairs .

Multi-Threading: An experimental removal of physics simulation from the simulator's heartbeat thread has been added. Setting "[BulletSim]UseSeparatePhysicsThread=true" causes BulletSim to simulate physics steps on its own thread and, even if physics is overloaded, avatar movement will not be effected. This is not yet "multi-threaded physics" but a move in the right direction. This feature is not enabled by default but people using this feature have not reported any problems. If you try this feature out, please Mantis any problems.

Bullet on 0.7.5-pf: BulletSim has been back-ported to OpenSimulator 0.7.5-postfixes and is available at http://github.com/radams1/opensim in branch "bs-backport-075pf". This is for anyone who hasn't moved up to OpenSimulator 'master'. I will be cherry picking BulletSim updates to this repository over time.

Just Use It: As always, BulletSim is easy to enable and adds better physics performance and better vehicle simulation than the other brands. In the INI file:
               [Startup]
               physics = BulletSim

-- radams1

[1] A physics engine for OpenSimulator which uses Bullet (http://bulletphysics.org).


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