[Opensim-dev] BulletSim upgrade and fixes

[Mister Blue]

It sounds like it is not noticing the changes in the prim parameters to
recalculate the prim mesh. I'll look into that.

On Tue, Aug 15, 2017 at 11:20 AM, Mike Lorrey <bntholdings at gmail.com> wrote:

> I have found an interesting bug in Kitely with Bullet: when you torture a
> prim, or scale a prim, that has hollow spaces, even a mesh with hollow
> spaces, the object defaults to its non-hollow/non-cut collision mesh, UNTIL
> region restart, whereupon the simulator seems to recalculate the collision
> mesh accounting for any hollows/cuts/empty spaces in mesh.
> There is also some difficulty in making doors/passages easy to go through
> in mesh with Bullet, it often requires adding a number of rows of faces
> inside the edge of the opening to make the physics engine recognise that
> there is an opening there that avatars and other objects can pass through
> without collisions.
>
> On Tue, Aug 15, 2017 at 1:37 PM, Mister Blue <misterblue at misterblue.com>
> wrote:
>
> > An update to BulletSim has been checked into the OpenSimulator that
> > upgrades BulletSim with version 2.86 of the Bullet physics engine
> > <http://bulletphysics.org/> as well as fixing some known problems.
> >
> > Mantis 8010 <http://opensimulator.org/mantis/view.php?id=8010>
> (“BulletSim
> > does not always call collision events on collisions”) was caused by
> > BulletSim not doing collision detection on all of the physics engine
> > sub-steps. This meant that fast moving objects (like bullets) could
> bounce
> > off of a target without reporting any collisions. For those into details,
> > any OpenSimulator <http://opensimulator.org/> physics engine is called
> > every tenth of a second to simulate the next tenth of a second of time.
> > BulletSim internally steps 10 times within that tenth of a second to do a
> > higher resolution physics simulation – a tenth of a second is a long
> > simulation step but that’s the way OpenSimulator
> > <http://opensimulator.org/> does
> > it.
> >
> > Mantis 8011 <http://opensimulator.org/mantis/view.php?id=8011>
> (“BulletSim
> > fails to send land_collision messages on some terrain”) was caused by
> > BulletSim computing terrain height differently than the mesh in the
> physics
> > engine. So, an object on steep terrain could compute as underground to
> some
> > code while appearing above ground in other code. BulletSim prevents
> > physical objects from going underground by pushing them up when the do.
> > This check would sometimes cause a falling object to float over terrain
> > rather than colliding with the terrain.
> >
> > The problem in Mantis 7132
> > <http://opensimulator.org/mantis/view.php?id=7132> (“Collisions stop for
> > no
> > apparent reason on BulletSim”) hasn’t been explicitly fixed. Still
> looking
> > for that problem.
> >
> > I found an additional problem that collision_end events don’t happen if
> the
> > colliding object does an llDie() on its collision. For instance, a target
> > object wouldn’t get a collision_end event for a bullet object that hits
> the
> > target and does an llDie() on its collision. It looks like the ODE and
> > ubODE physics engines don’t exhibit this problem because of the order
> that
> > collisions are reported to the simulator. The fix is some code
> > re-organization in SceneObjectPart.cs.
> >
> > Still in the pipeline is the proper implementation of PhysicsShapeType
> and
> > then physics engine implementation of raycast.
> > _______________________________________________
> > Opensim-dev mailing list
> > Opensim-dev at opensimulator.org
> > http://opensimulator.org/cgi-bin/mailman/listinfo/opensim-dev
> >
>
>
>
> --
> Mike Lorrey
> CEO Galactic Systems, Inc
> VP Stokens Venture Capital
> bntholdings at gmail.com <mike at tokens.vc>
> mike at stokens.co
> International Spaceflight Museum
> mike at ismuseum.org
> Skype: michael.lorrey
> LinkedIn: https://www.linkedin.com/in/mikelorrey
> _______________________________________________
> Opensim-dev mailing list
> Opensim-dev at opensimulator.org
> http://opensimulator.org/cgi-bin/mailman/listinfo/opensim-dev
>