The entry point to the physics system; an engine represents the manager of all physics resources and structures. An engine is tied to a specific physics backend, and allows creating native objects to interface with the physics backend.

The units used throughout the engine are metric: meters, radians, seconds, kilograms.

Thread safety

Physics structures used by the engine are not thread-safe, so must be treated carefully when interacting with them from multiple threads. Typically, the user of e.g. a PhysicsSpace or RigidBody would wrap accesses to that object in a lock. To enforce this, you can specify a java.util.concurrent.locks.ReentrantLock on some structures. Before any read or write access, this lock will be checked to make sure the current thread holds an exclusive lock. If it does not, an exception will be thrown.