UpgradingFromV1.md

Upgrading from v1

v2 is a complete rewrite and is about as different from v1 as any unrelated physics engine. Reading the Getting Started documentation to get an overview is recommended. The following maps concepts and features in v1 to their equivalents in v2.

Some of this might look way more complicated, and it might seem like features were removed for no reason, but trust me it's great! For some definitions of great! The API just avoids hiding performance-related things and punts responsibility for application-specific convenience features to the user. Stuff that looks the same as the v1 version can be created pretty easily, it's just not in the core library.

Concept	v1	v2
Top level type containing all execution stages and all existing objects	Space	Simulation
Mobile dynamic and kinematic objects	Entity	Body, but there is no Body type- see Simulation.Bodies to allocate, access, and delete bodies. Creating a body using Simulation.Bodies.Add returns a handle that uniquely identifies the body for the duration of its existence, and Simulation.Bodies.HandleToLocation finds the current memory location of a body. BodyReference can be used to handle lookups for you.
Mobile object properties	Entity properties, like Position and LinearVelocity	Create a BodyReference from the body handle, then access properties like Pose and Velocity. Can also manually perform the lookup into the Simulation.Bodies sets and their raw property buffers.
Collision events	entity.CollisionInformation.Events	No out of the box events; ContactEventsDemo shows how to use narrow phase callbacks to create events.
Enumerating existing collisions	entity.CollisionInformation.Pairs	Collision data is not explicitly cached anywhere. Narrow phase callbacks can be used to collect collision information. Collision-created contact constraints (and all other connected constraints) can be enumerated using the Constraints body property. See the SolverContactEnumerationDemo for an example of enumerating contact constraints.
Collision filtering	e.CollisionInformation.CollisionRules and CollisionRules static functions	INarrowPhaseCallbacks has AllowContactGeneration and ConfigureContactManifold which return a boolean that controls whether narrow phase testing and constraint generation should proceed. See RagdollDemo for an example of collision filtering.
Custom gravity	entity.Gravity	IPoseIntegratorCallbacks can be used to implement any form of gravity or other per-body velocity influence. See PlanetDemo for an example.
Object velocity damping	entity.LinearDamping and entity.AngularDamping	IPoseIntegratorCallbacks again- damping is just a velocity influence. See DemoCallbacks for an example.
Scene-wide ray casts	Space.RayCast or s.BroadPhase.QueryAccelerator.RayCast for AABB-only testing	Simulation.RayCast or Simulation.BroadPhase.RayCast for AABB-only testing
Scene-wide sweep tests	Space.ConvexCast	Simulation.Sweep, which supports angular motion in the sweep as well, or Simulation.BroadPhase.Sweep for AABB-only testing
Bounding box queries	s.BroadPhase.QueryAccelerator.GetEntries	Simulation.BroadPhase.GetOverlaps
Collidable composed of a bunch of triangles	StaticMesh or InstancedMesh	Mesh
Triangulated heightmap collidable	Terrain	There is no dedicated heightmap type at the moment, so just Mesh
Sphere collision shape	SphereShape	Sphere
Capsule collision shape	CapsuleShape	Capsule
Box collision shape	BoxShape	Box
Triangle collision shape	TriangleShape	You can probably guess, Triangle
Cylinder collision shape	CylinderShape	Cylinder
Convex hull collision shape	ConvexHullShape	ConvexHull
Cone collision shape	ConeShape	N/A- consider a ConvexHull approximation
Weird combination shape in minkowski space that no one ever used	MinkowskiSumShape	N/A- I'd say "consider a ConvexHull approximation," but I'm pretty sure no one will ever want to do this
Combination shape that acts like a convex hull around arbitrary subshapes	WrappedShape	N/A- consider a ConvexHull approximation. Not sure if anyone ever used this one either.
Affinely transformable wrapper around any other convex shape	TransformableShape	N/A- consider a ConvexHull approximation
Multiple convex shapes bundled into one shape supporting concavity	CompoundShape	Compound for shapes with only a few pieces; BigCompound for ones that have enough children to benefit from an acceleration structure
Static-only optimization for a bunch of other convex shapes	StaticGroup	Doesn't exist because it's not necessary; just use Simulation.Statics.Add to toss them directly into the simulation. The broad phase can handle it just fine.
Should you use really detailed concave triangle soup meshes for mobile objects?	No	Still no! v2 might be way faster than v1, but that doesn't mean you should just throw all those spare cycles right into the garbage can!
Constraints	Oof there's a lot of them	Here's another bunch; main differences are the addition of a couple of simultaneously solved combos like Hinge and SwivelHinge which will be more stable than their old SolverGroup v1 versions, a couple of new cloth/deformable-helpful constraints, and the removal of questionable constraints like the EllipseSwingLimit.
Constraint springiness (for those with position goals)	constraint.SpringSettings.Stiffness and constraint.SpringSettings.Damping	SpringSettings set in the constraint description, which contains Frequency and DampingRatio properties. Frequency is the undamped frequency of oscillation of the constraint, and DampingRatio is the ratio of the damping to critical damping, 0 being undamped, 1 being critically damped, and higher values being overdamped. Try to avoid using Frequency values higher than around half the update rate. That is, if you're updating at 60hz, 30 is a generally stable upper bound for Frequency. Higher frequencies in complex constraint configurations may require faster update rates or using the SubsteppingTimestepper. Note that, given a mass, frequency, and damping ratio, an equivalent stiffness constant and damping constant can be computed (and vice versa). I should probably add a helper for that at some point.
Buoyancy zone	FluidVolume	N/A, may show up later in a less bad form
Mesh-based collision detector with containment testing	DetectorVolume	No support for out of the box containment events, but a Mesh and narrow phase callbacks can perform a pretty similar job.