Physics Pipeline

All physics jobs (initializing simulation data, stepping, and exporting data to ECS) are executed inside PhysicsSystemGroup. It is a ComponentSystemGroup, and is a subgroup of FixedStepSimulationSystemGroup. Therefore, multiple physics steps can occur during one frame.

PhysicsSystemGroup consists of two other subgroups, each responsible for a single phase in physics step, and ExportPhysicsWorld system, which schedules jobs that convert physics simulation data to ECS data (LocalTransform and PhysicsVelocity). Subgroups are:

System group	Description
PhysicsInitializeGroup	Schedules the jobs that create physics simulation data from ECS data for the current simulation step.
PhysicsSimulationGroup	Schedules the jobs that execute physics simulation pipeline.

PhysicsSimulationGroup is further divided into four other subgroups that are responsible for different stages of simulation, and between which it is possible to modify physics simulation data. Those are:

System group	Description
PhysicsCreateBodyPairsGroup	Schedules the jobs that find pairs of bodies whose AABB's overlap.
PhysicsCreateContactsGroup	Schedules the jobs that create contacts based on overlapping pairs.
PhysicsCreateJacobiansGroup	Schedules the jobs that create jacobians based on created contacts.
PhysicsSolveAndIntegrateGroup	Schedules the jobs that solve jacobians.

The running order is illustrated in the image below: