We do this by using the GImpact shapes. These work, but are resource
intensive. So make sure you don't use too many of these in free mode.
This isn't thouroughly researched though. It might be worth looking into
btCollisionHull, or to alter some of the parameters to fine tune the
simulation.
In some cases you want to store property data for each instance. Often
you'll use member data on the entities themselves for this. But in some
cases you don't want to bloat the entity class with data for seldomly
used properties.
In these cases you can instead use the PropertyInstanceState class, and
keep a static instance of this per property.
