There is an initial experimental integration of Box2D 2.3.1 and various associated changes to enable 2D physics in the
engine. This is a totally unsupported and undocumented prototype, exercise great caution and do not use in production.
The current build only includes precompiled libraries of Box2D for Win32 and Win64, so 2D collision will not work on
other platforms. Collision detection and response is automatic when the 2D domain is selected in a sprite, but queries
like point traces must be separately enabled in the Physics project settings (bEnable2DPhysics option).
The integration supports collision detection and response (including Unreal collision channels/filtering), rigid body
simulation, and ray casts. Non-zero extent queries, sweep tests, and overlap tests are not implemented yet. Things like
CharacterMovementComponent and MoveComponent with bSweep=true rely on these sorts of queries and do not work correctly yet.
The long term integration strategy is to make it a first class citizen, where the same techniques and knowledge used in
3D scenes will directly apply to 2D scenes; for example, there'll only be one Overlap event, not a separate 2D and 3D
one. 3D raycasts are already implemented for Box2D and you can both trace 'in-plane' (gameplay traces within the 2D 'world')
or 'perpendicular to plane' (things like the Touch input trace to determine the object under your finger / mouse cursor),
providing a proper hit result location and normal as well.